Aircraft Piston Engine Exhaust Emission Symposium

APPENDIX A REVIEW OF MEASUREMENT AND TESTING PROBLEMS* Avco Lycodng Williamsport, Pennsylvania PROBLEMS EXPERIENCED

I. Instrumentation - Good instrumentation i s required t o o b t a i n r e l i a b l e

and r e p e a t a b l e b a s e l i n e data. Problems have been encountered i n developing such a t o t a l system.

A. Accurate a i r f l o w measurement at a l l modes i s e s s e n t i a l . Leanout curve trends have s u b s t a n t i a l dependence on t h i s q u a n t i t y .

B. Precise f u e l flow measurement i s required t o maintain good f u e l / small flows t y p i c a l of t h e i d l e / t a x i a i r r a t i o agreements. The modes demand extreme accuracy.

C. The instrumentation used f o r p o l l u t a n t measurement has proven t o be s u s c e p t i b l e t o frequent malfunctions and has required c e r t a i n modifications.

1. Changes t o console pumps, f i l t e r s , and gas ‘Sample p a t h have been made i n an attempt t o comply with the 2 second response t i m e .

2. Modifications t o t h e NO/NOx analyzer have been recommended t o e l i m i n a t e p o s s i b l e water condensation i n t h e r e a c t i o n chambe r .

FID w a s replaced with a l a r g e r 3. The instrument pump i n the u n i t t o improve response t i m e .

4 . An oxygen analyzer has been added t o t h e sample a n a l y s i s in- s t r u m n t a t i o n t o permit computation of t h e carbon balance s There is no requirement o r s p e c i f i c a t i o n f o r t h i s instrument by t h e EPA, P a r t 87. \ 5. Frequent instrument and component f a i l u r e s , some r e q u i r i n g lengthy t r o u b l e shooting and r e p a i r periods have been en- countered throughout t h e test program. A partial list of t h e f a i l u r e s follows :

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Material d i s t r i b u t e d b u t n o t presented at t h e Symposium.

Instrument Problem

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HC FID Pressure r e g u l a t o r f a i l e d HC FID Pressure gage f a i l e d HC FID Thermistor f a i l e d HC FID Heater f a i l e d HC FID Meter readout miswired NO/NOx chem. Thermistor switch f a i l e d , r e s u l t i n g i n h e a t e r f a i l u r e ~ NO/NOx chem. Photomultiplier tube cracked NO/NO, chem. Meter readout f a i l e d

co Detector f a i l e d

Heated sample l i n e Thermistor f a i l e d 6 . During low power operation ( i d l e / t a x i ) t h e r e is considerable f l u c t u a t i o n i n i n d i c a t e d p o l l u t a n t concentrations, as re- corded by t h e p l o t t e r . N o determination has y e t been made as t o whether t h i s v a r i a t i o n is i n h e r e n t i n t h e instrumenta- t i o n o r r e f l e c t s pulses i n t h e exhaust sample, A t present Avco Lycoming approximates t h e mean of t h e recorded p l o t t e r output as t h e measured p o l l u t a n t concentration. Of course, each s i g n a l could be e l e c t r i c a l l y dampened o r averaged; how- ever, some determination must be made t o e v a l u a t e t h e t r u e average and i s o l a t e t h e cause of t h e f l u c t u a t i o n s

Span Gases - Span gas q u a l i t y has a s i g n i f i c a n t e f f e c t on emissions

test r e s u l t s .

A. The r e j e c t i o n rate of incoming span gases based on a +2 percent t o l e r a n c e is approximately 15 percent.

B. U n t i l s u f f i c i e n t test experience w a s accumulated, it w a s o f t e n d i f f i c u l t t o i d e n t i f y span gas discrepancies and divorce them completely from instrumentation problems.

C. The S c o t t Reference Service is performed only four t i m e s a year.

Such v a r i a b l e s as span gas replacement and instrumentation changes must be considered. I n a d d i t i o n , t h i s service publishes an aver- age value from t h e reported results of t h e p a r t i c i p a n t s . N o allowance is made f o r an abnormal p a t t e r n i n r e s u l t s f o r a given test period. The S c o t t Service provides an i n d i c a t i o n o f major span gas discrepancies and should be used i n t h a t manner.

D. NAFEC has e s t a b l i s h e d its own c r o s s reference service. Sample periods have been increased t o one a month; however, t h i s service has been l i m i t e d t o only four sample periods. I n a d d i t i o n , t h e b a s e l i n e engine test program w a s completed p r i o r t o r e c e i p t of t h e f i r s t sample. It w i l l be extremely d i f f j c u l t t o use t h e s e r e s u l t s t o improve c o r r e l a t i o n of p a s t t e s t i n g .

111. Engine Condition - It has been shown t h a t t h e mechanical condition

t h e test engine can a f f e c t the test r e s u l t s s u b s t a n t i a l l y .

of Prolonged low power operation i n t h e i d l e / t a x i modes without A.

i n t e r c e d i n g e x t e n s i v e higher power o p e r a t i o n is n o t considered t o be normal of in-service engine o p e r a t i n g conditions.

1 . Such extended operation at i d l e / t a x i r e s u l t s i n fouled spark plugs and glazed c y l i n d e r b a r r e l s .

I f t h e b a r r e l glazing condition is severe, o i l w i l l move 2.

p a s t t h e r i n g s i n t o t h e combustion chamber, r e s u l t i n g i n o i l fouled plugs o r plugged f u e l nozzles.

3. An engine i n t h i s condition may e x h i b i t high o i l consumption, moderate t o extreme roughness o r a l o s s of i g n i t i o n i n one o r more cylinders.

B . The engine condition should be c l o s e l y monitored f o r any p o s s i b l e mechanical malfunctions throughout a l l modes of operation.

Emissions d a t a taken on an engine experiencing mechanical d i f f i - C.

cannot be used t o p r e d i c t b a s e l i n e c h a r a c t e r i s t i c s .

c u l t i e s 1. Emissions d a t a r e f l e c t i n g extremely poor combustion charac- teristics f o r t h e i d l e / t a x i modes is n o t r e p r e s e n t a t i v e of a c t u a l in-service engine operation.

2. Constant e f f o r t should be made t o ensure t h a t t h e test engine is maintained i n s a t i s f a c t o r y condition.

- T e s t procedures have been shown t o have considerable

IV. T e s t Procedure e f f e c t on emissions test r e s u l t s .

A. The required test procedures as s p e c i f i e d by t h e EPA, P a r t 8 7 , are incomplete and do not promote the adoption of one u n i f i e d test procedure by a l l test facilities.

Additional d e s c r i p t i o n on t h e following should be provided : 1. An acceptable method of performing t h e precycle warmup . should be noted.

2. S p e c i f i c d e s c r i p t i o n of t h e required exhaust c o l l e c t i o n system should be made. is no system r e p r e s e n t a t i v e There of a l l a i r c r a f t models i n t h e general a v i a t i o n f l e e t .

3. The sample t r a n s p o r t and response t i m e should be changed a t i m e r e p r e s e n t a t i v e of t h e test system and s t a t e - o f - t o the-art instrumentation, 4. An instrument s p e c i f i c a t i o n f o r t h e oxygen analyzer should be included i f i t is t o be an o p t i o n a l piece of equipment.

5. I f t h e cycle is t o be run consecutively with no i n t e r v e n i n g o p e r a t i n g p o i n t s , t h e allowable l e n g t h o f t i m e f o r operation at t h e i n i t i a l i d l e / t a x i modes should be s p e c i f i e d t o pre- vent p o s s i b l e d e t e r i o r a t i o n i n engine condition.

6. The s p e c i f i e d c y c l i c power s e t t i n g s are at b e s t unrepre- s e n t a t i v e of t y p i c a l in-service engine operation. The per- cent power f o r t h e climb mode should be s p e c i f i e d , n o t 75 t o 100 percent.

7. There is no s p e c i f i c a t i o n regarding standard i n l e t condi- t i o n s at t h e entrance t o the i n j e c t o r o r c a r b u r e t o r o r f o r cooling a i r supplied t o the engine.

8. Some minimum requirement should be noted f o r t h e exhaust gas a t t h e probe i n l e t t o prevent loss temperature of t h e sample of hydrocarbon sample.

B. If t h e EPA is unable o r unwilling t o make t h e s e s p e c i f i c a t i o n s , i n d u s t r y and o t h e r f a c i l i t i e s involved with t h i s t e s t i n g should formulate and approve a well-defined procedure.

C. Avco Lycoming has experienced problems with a i r leakages i n both t h e induction and exhaust s y s t e m s .

1. Since t h e induction air system is pressurized above ambient p r e s s u r e , leakages between t h e a i r flow measuring system and engine r e s u l t i n t h e observed a i r flow readings being higher than the q u a n t i t y of flow being used by t h e engine.

2. Cracks forming i n t h e exhaust system u s u a l l y permit a i r leak- age i n t o t h e exhaust sample. The r e s u l t a n t p o l l u t a n t con- c e n t r a t i o n s show s i g n s of d i l u t i o n o r higher than normal oxygen values.

3. Avco Lycoming has found t h a t t h e d a t a a f f e c t e d by t h e s e sys- t e m discrepancies can be minimized by c a r e f u l a t t e n t i o n t o q u a n t i t i e s and trends of t h e f u e l / a i r r a t i o agreement ( u t i - l i z i n g t h e Spindt Method f o r carbon balance). However, t h i s r e q u i r e s t h a t a l l d a t a be reduced d a i l y and reviewed com- p l e t e l y .

D. The t o t a l emissions d a t a system is f a i r l y complex and Avco Lycoming has experienced s u b s t a n t i a l "down" t i m e f o r system main- tenance and r e p a i r .

V. Calculation Procedure - The required c a l c u l a t i o n procedure, as speci-

f i e d by t h e EPA, P a r t 8 7 , f o r reducing r a w emissions d a t a leaves s e v e r a l intermediate s t e p s t o "good engineering p r a c t i c e . " A. It is p o s s i b l e that some d i f f e r e n c e s i n reported emissions values between test f a c i l i t i e s can be a t t r i b u t e d t o d i f f e r e n c e s i n cal- A well-defined procedure f o r determining c u l a t i o n procedures.

EPA: t h e following v a r i a b l e s should be s p e c i f i e d by t h e 1. Some method f o r determining the c o r r e c t i o n f a c t o r f o r ambient and combustion formed w a t e r vapor should b e s p e c i f i e d .

2. The c a l c u l a t i o n procedure f o r t h e exhaust molecular weight should be defined.

3. Acceptable methods t o perform t h e required carbon balance should be s p e c i f i e d . The 5 percent agreement, as s p e c i f i e d , is considered excessively i n t o l e r a n t when dealing w i t h t h e low a i r and f u e l flows of t h e i d l e / t a x i modes.

B. Again, i f t h e EPA cannot o r w i l l not make well-defined require- ments i n these areas, i n d u s t r y together with o t h e r f a c i l i t i e s i n - volved with t h e a c t u a l t e s t i n g should s p e c i f y acceptable proce- dures.

C. Correction f a c t o r s f o r t h e e f f e c t t h a t nonstandard conditions have on c y c l i c emissions t o t a l s should be developed between f a c i l i t i e s and approved.

1. Avco Lycoming has developed in-house c o r r e c t i o n f a c t o r s f o r t h e e f f e c t of temperature and v a r i a t i o n s i n power output on emissions when reduced t o a pound/mode b a s i s .

2. However, c o r r e c t i o n f a c t o r s f o r t h e e f f e c t t h a t humidity o r temperature v a r i a t i o n s have on p o l l u t a n t formation (ppm o r percent by volume) are needed.

RECOMMENDATIONS I. Engine T e s t Procedures A. The engine m u s t be maintained i n good condition f o r t h e e n t i r e test program t o ensure t h a t r e p r e s e n t a t i v e d a t a is obtained.

1. A performance c a l i b r a t i o n should be made t o ensure t h a t t h e engine i s w i t h i n production limits and t y p i c a l of t h a t par- t i c u l a r model. The c a l i b r a t i o n should c o n s i s t of t h e follow- i n g types of runs: f u l l t h r o t t l e performance., mixture d i s - t r i b u t i o n a t r a t e d speed, v a r i a b l e manifold p r e s s u r e a t r a t e d speed, f u e l metering response with varying p r o p e l l e r load, o i l consumption. Additional t e s t i n g may be included, i f necessary.

2. Daily i n s p e c t i o n s of the engine and sampling system should be made t o i n s p e c t f o r p o s s i b l e discrepancies. The inspec- t i o n procedure c u r r e n t l y used by Avco Lycoming is described i n attachment I.

3. During operation, frequent magneto checks should be made t o ensure t h a t the i g n i t i o n system is functioning properly, 4 . Cylinder head temperatures should be monitored c l o s e l y f o r s i g n s of engine problems. For i d l e and t a x i modes, a com- p a r a t i v e l y low head temperature could be i n d i c a t i v e of i g n i t i o n o r f u e l nozzle problems. Comparing c y l i n d e r head temperature trends f o r t h e takeoff, climb, and approach mode leanout runs can a l s o be used i n t h e same manner, 5. The engine m u s t be constantly monitored f o r abnormally rough o r uneven operation, p a r t i c u l a r l y i n t h e i d l e / t a x i modes.

Prolonged running at low power conditions causes d e t e r i o r a - t i o n i n engine condition such as fouled spark plugs and glazed cylinder b a r r e l s which are not r e p r e s e n t a t i v e of an engine i n good condition.

a. A p o s s i b l e i n d i c a t o r of glazed cylinder b a r r e l s is higher than normal engine o i l consumption.

b. Frequent magneto checks w i l l show a high rpm drop be- tween magnetos o r highly uneven c y l i n d e r head tempera- t u r e s when on s i n g l e i g n i t i o n as i n d i c a t i v e of p o s s i b l e fouled spark plugs.

c. Corrective a c t i o n s are prolonged periods of operation a t high power conditions. Badly fouled spark plugs may r e q u i r e removal and cleaning.

d. A period (10-20 min) of continuous operation at take- o f f power should precede a b a s e l i n e run t o improve spark plug and cylinder b a r r e l conditions.

Avco Lycoming has found t h a t t h i s procedure tends t o mini- mize d a t a scatter i n the i d l e / t a x i modes f o r t h e base- l i n e cycle.

e. Once the b a s e l i n e cycle has been i n i t i a t e d , t h e modes must be run i n sequence w i t h no "clearing" between modes.

f . The only t i m e a b r i e f period (2-5 sec) of engine clear- i n g is permitted between consecutive i d l e o r t a x i runs i s during a leanout test when engine d e t e r i o r a t i o n is suspected due t o prolonged low power operation. The engine should be b r i e f l y c l e a r e d a f t e r each run.

B. Two types of tests are c u r r e n t l y employed t o determine t h e emis- s i o n s c h a r a c t e r i s t i c s of an engine model: 1. The b a s e l i n e cycle c o n s i s t s of a seven-mode test program run a t each mode.

consecutively with s t a b i l i z e d engine conditions The following are t h e engine speeds and power s e t t i n g s f o r each mode : Power, Engine speed

I p e r cent

I

--

Taxi Takeoff Rated Full t h r o t t l e Climb 90% r a t e d 80 Approach 87% r a t e d 40

1:: Taxi 1200

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The leanout run shows t h e e f f e c t s of mixture v a r i a t i o n s on 2.

emissions output and v i t a l engine parameters f o r each mode.

The r e s u l t s of t h e leanout run when p l o t t e d on a pounds/mode o r percent p o l l u t a n t concentration versus f u e l / a i r r a t i o b a s i s can be used t o i d e n t i f y emissions t r e n d s , formulate p o s s i b l e temperature o r humidity c o r r e c t i o n f a c t o r s o r con- s t r u c t improved o r optimumbaseline cycles based on l e a n e r f u e l schedules.

11. Emissions Instrumentation It is required by t h e EPA, i n P a r t 8 7 , t h a t t h e following exhaust A.

emissions concentrations be measured:

co (Carbon monoxide)

co (Carbon dioxide)

NO?NOx (Oxides of nitrogen) HC (Hydrocarbons) I n a d d i t i o n t o t h e above q u a n t i t i e s , measurement o f t h e 02 con- c e n t r a t i o n i n t h e exhaust sample is necessary t o complete t h e carbon balance c a l c u l a t i o n procedure (Spindt Method) c u r r e n t l y i n use.

1. Avco Lycoming has experienced several instrumentation d i f f i - c u l t i e s s i n c e t h e i n i t i a t i o n of t e s t i n g .

a. The instrumentation employed is b a s i c a l l y s e n s i t i v e l a b o r a t o r y test equipment. Usage f o r extended periods frequent adjustment o r o f t i m e r e s u l t s i n the need f o r i n equipment malfunctions.

b. Careful d a i l y monitoring of instrument response charac- teristics provides a i d in determining t h e onset of . instrumentation d i f f i c u l t i e s .

2. Avco Lycoming e s s e n t i a l l y follows t h e procedures o u t l i n e d i n t h e EPA, i n P a r t 8 7 ; however, r e v i s i o n s are necessary t o update and improve t h e required test procedures.

a. Revisions f o r improving and updating instrument C a l i - b r a t i o n procedures and s p e c i f i c a t i o n s are necessary.

b. It has been s t a t e d by t h e EPA t h a t changes w i l l be made t o t h e 2 second sample response t i m e . Such a r e v i s i o n i s necessary and should a l s o include a w e l l defined procedure f o r determining t h i s response t i m e .

B. The exhaust c o l l e c t o r and sample probe should b e designed and f a b r i c a t e d i n accordance with t h e requirements by t h e EPA i n P a r t 87.

1. The exhaust system should be made of a s u i t a b l e material and designed t o permit no exhaust gas d i l u t i o n b u t minimize engine power l o s s . Carefully f i t t e d s l i p j o i n t s are per- mitted b u t may r e q u i r e a d d i t i o n a l s e a l i n g t o guard a g a i n s t d i l u t i o n .

2. The sample probe is f a b r i c a t e d from 1 / 4 inch diameter s t a i n - less steel tube with 5 i n l e t h o l e s approximately 1 / 1 6 inch diameter l o c a t e d evenly across t h e t a i l p i p e . The sample probe i n l e t holes are positioned i n t o t h e exhaust flow, although t e s t i n g has shown no d i f f e r e n c e i n measured con- c e n t r a t i o n s f o r o t h e r r o t a t e d p o s i t i o n s .

3. The sample probe should be l o c a t e d f a r enough downstream t o allow f o r good mixing i n t h e t a i l p i p e . However, t h e EPA i n P a r t 87 s p e c i f i e s that t h e sample p a t h t o and through t h e Hydrocarbon Analyzer m u s t be maintained a t 3 0 2 ' F (150O C) t o prevent t h e l o s s of heavy hydrocarbons i n t h e sample l i n e , Therefore, t h e minimum allowable EGT a t t h e i n l e t o f t h e is 3 0 2 ' F.

sample p a t h Avco Lycoming has noted t h a t f a i l u r e - t o maintain s u f f i c i e n t exhaust gas temperature a t t h e sample probe i n l e t results i n s i m i l a r l o s s e s . I n a d d i t i o n , low EGT's are o f t e n i n d i c a t i v e of exhaust sample d i l u t i o n .

111. Span Gases A. Maintaining a set of good q u a l i t y working span gases is important i n o b t a i n i n g a c c u r a t e and repeatable emissions d a t a , 1. Comparative services such as t h e S c o t t Reference Service and t h e NAE'EC Cross Reference Service can be used as i n d i c a t o r s of p o s s i b l e span gas discrepancies a. Due t o t h e 3 month period between samples w i t h t h e S c o t t Service o t h e r f a c t o r s such as changes i n i n s t r u - ments and d e p l e t i o n and replacement of span gases m u s t be considered.

b. The S c o t t Service uses t h e average of t h e reported values as a b a s i s f o r comparison. This average could be influenced i n a s p e c i f i e d test p e r i o d by an abnormal r e p o r t i n g p a t t e r n from t h e p a r t i c i p a n t s . It is i n v a l i d t o use t h i s average as t h e a b s o l u t e value of t h e sample gas i n an attempt t o revise span gas values.

c. A review of t h e Scott Service r e s u l t s between f a c i l i - ties shows no d e f i n i t e r e l a t i v e trends. It is d i f f i - c u l t t o j u s t i f y t h e use of e i t h e r service t o formulate c o r r e l a t i o n c o r r e c t i o n f a c t o r s e i t h e r f o r p a s t o r present t e s t i n g .

2. Avco Lycoming has e s t a b l i s h e d an in-house q u a l i t y c o n t r o l procedure f o r t e s t i n g working span gas accuracy. A set of master grade span gases have been purchased t o be used as comparative standards. P e r i o d i c a l l y , a l l in-house working span gases w i l l be checked a g a i n s t two o r more of t h e master standards. A t p r e s e n t , d e t a i l s as t o frequency of t e s t i n g , acceptable t o l e r a n c e s , e t c . , are being formulated.

I V . Computational Procedure A. The b a s i c computational procedure employed by Avco Lycoming is as s p e c i f i e d by t h e EPA i n P a r t 8 7 , Federal Register.

Figure A-1 shows a flow diagram summarizing t h e d a t a reduction process.

Shown i n attachment I1 is a complete d e t a i l e d d e s c r i p t i o n o f t h e procedure c u r r e n t l y used, 1. The EPA, i n P a r t 87, does not r e q u i r e t h a t the i n l e t a i r pressure, temperature, o r humidity be c o n t r o l l e d t o a speci- f i e d range. Differences i n mass of induction a i r flow be- tween varying ambient conditions can be s u b s t a n t i a l , As t h e air flow q u a n t i t y is involved d i r e c t l y i n t h e c a l c u l a t i o n f o r p o l l u t a n t pound/mode, some e f f o r t should be made t o c o r r e c t f o r varying ambient conditions. A t p r e s e n t , Avco Lycoming is i n v e s t i g a t i n g p o s s i b l e c o r r e c t i o n f a c t o r s which w i l l improve d a t a agreement.

2. I n a d d i t i o n t o a f f e c t i n g a i r flow MSS, temperature and humidity d i f f e r e n c e s can a f f e c t p o l l u t a n t concentration output. Avco Lycoming has made l i m i t e d e f f o r t at d e f i n i n g c o r r e c t i o n f a c t o r s f o r t h e s e e f f e c t s . Other f a c i l i t i e s such as NASA L e w i s , which have t h e a b i l i t y t o f u l l y c o n t r o l ambient test conditions, should provide b e t t e r c o n t r o l l e d d a t a trends f o r a complete a n a l y s i s .

B. Although t h e b a s i c c a l c u l a t i o n procedure f o r reduction of r a w emissions d a t a is s p e c i f i e d by t h e EPA i n P a r t 87, some of t h e intermediate s t e p s are n o t defined adequately.

1. The method f o r determining exhaust molecular weight should b e s p e c i f i e d .

2. The procedure f o r c a l c u l a t i n g w a t e r c o r r e c t i o n f a c t o r s f o r both combustion formed water and ambient water vapor should be o u t l i n e d .

3. A method f o r performing t h e required carbon balance should be included.

V . Data Analysis C r i t e r i a A. I n emissions t e s t i n g , t h e review and a n a l y s i s o f d a t a trends and q u a l i t y becomes a complex procedure because of t h e l a r g e number of values recorded as input parameters.

1. Some method of carbon balance must be used t o i d e n t i f y p o s s i b l e d a t a discrepancies. A t p r e s e n t t h e Spindt Method is used by a l l f a c i l i t i e s involved i n t h e p i s t o n a i r c r a f t emissions program.

a. The Spindt Method provides a comparative computational procedure f o r f u e l / a i r r a t i o based on measured emis- s i o n s concentrations.

b. The f u e l / a i r r a t i o agreement is obtained by comparing t h e measured and c a l c u l a t e d f u e l / a i r r a t i o s .

The EPA, i n P a r t 87,requires t h a t t h i s agreement be w i t h i n +5 percent f o r a l l modes.

Although t h i s requirement is realistic f o r the higher power and t a x i modes, compli- ance f o r t h e i d l e mode is d i f f i c u l t where low a i r and f u e l flow values as w e l l as small changes i n engine speed n e c e s s i t a t e s extremely p r e c i s e measurements.

34 7 2 . Avco Lycoming has found t h a t emissions d a t a with consider- a b l e scatter i n f u e l / a i r r a t i o agreements fisually produces t h e same scatter when p l o t t e d on a pound/mode versus fuellair r a t i o b a s i s . In a d d i t i o n , t h e b e s t d a t a c o r r e l a t i o n s be- tween f a c i l i t i e s , o r even in-house t e s t i n g , are obtained when t h e f u e l / a i r r a t i o agreements are w e l l w i t h i n t h e t o l - erance.

3. Experience has shown t h a t t h e f u e l / a i r r a t i o agreement be- tween measured and c a l c u l a t e d f u e l / a i r r a t i o s is p o s s i b l y t h e most valuable i n d i c a t o r i n recognizing and l o c a t i n g d i s - crepancies i n t h e emissions system. Recognizing t h e s e t r e n d s o r v a r i a t i o n s i n trends i n t h e f u e l / a i r r a t i o agree- ment is most important.

ATTACHMENT I EXPERIMENTAL BULLETIN NO. 129

c1. 11

April 22, 1975

CHECK LIST TO PERFORM BEFORE BEGINNING EMISSIONS TESTING - (Daily)

1. Sample System: Please remove heated sample l i n e from probe. Remove covering from t e f l o n s e c t i o n of l i n e and i n s p e c t f o r any heat damage. I f t e f l o n has become discolored, replace s e c t i o n . Check a l l f i t t i n g s f o r t i g h t n e s s . Cap o f f end of sample l i n e and t u r n on console- pump t o l e a k check.

Remove s t a i n l e s s steel probe and i n s p e c t f o r cracks. Check exhaust system from exhaust p o r t s t o probe l o c a t i o n f o r cracks. Reconnect a l l p a r t s of l i n e and r e i n s t a l l probe.

2. Induction Air: Please i n s p e c t induction a i r hose f o r l e a k s . Check clamp a t a i r b o x f o r t i g h t n e s s .

3 . Magneto Timing Device ( i f i n s t a l l e d ) : Please check connecting a r m f o r t i g h t n e s s . Inspect around magneto base f o r o i l leakage o r gasket slippage. Tighten s l i g h t l y i f necessary. Check p o s i t i o n i n d i c a t o r cable connector f o r t i g h t n e s s .

4 . To rqueme te r : Please check f o r o i l leakage around any p o r t i o n of the torquemeter, adapter p l a t e s o r p r o p e l l e r , Inspect r e s t r a i n i n g w i r e s t o torque- meter t o make s u r e they are i n good condition.

R. Moffett ATTACHMENT I1 DATA REDUCTION TECHNIQUES EMPLOYED BY AVCO LYCOMING The following d a t a reduction techniques are c u r r e n t l y employed by Avco Lycoming :

1. Water Correction Factors - t o account f o r t h e water vapor con-

densed from t h e analyzed exhaust samples

2. Exhaust Molecular Weight - t o convert the volumetric percentages

read from t h e exhaust analyze,rs t o a gravimetric percentage

3. Exhaust Volume Technique - t o calculate t h e t o t a l mass exhausted

from t h e engine based on t h e mass percentage of t h e i n d i v i d u a l p o l l u t a n t s and t h e t o t a l gas flow through t h e engine 4. Carbon Balance - t o v e r i f y t h a t those p o l l u t a n t s d e t e c t e d by t h e exhaust gas analyzers are i n d i c a t i v e of t h e f u e l - a i r mixture supplied t o t h e engine WATER VAPOR CORRECTION Water vapor i n t h e exhaust sample o r i g i n a t e s from two sources: (1) combustion formed w a t e r vapor, (2) water vapor contained i n ambient induction air. Avco Lycoming has developed independent c o r r e c t i o n fac- t o r s f o r each source.

Correction Factor f o r Combustion Formed Water Vapor Considering a general equation €or t h e combustion process a t equi- l i b r i u m i n t h e form where e a = .

a carbon balance y i e l d s

a2 + a3 + a5

a = 0 C and a hydrogen balance y i e l d s

2a4 + l.85a5 + 2a6

a = (3) h 0 Combining (2) and (3) and s o l v i n g f o r a4 gives

a2 + a + a5 2 a + 1.85a5 + 2a6

h 3

- - - -

9 - a h C C

a ( a 2 + a3 + as) = 2a4 + 1.85a5 + 2a6

0.51 a3 = a6 o r 0.51 CO = H2: A t t h i s p o i n t t h e r e l a t i o n s h i p reference: "Relation of Exhaust G a s Composition t o A/F Ratio ," B A.

D'Alleva and W . G. Lovell, SAE Journal (Trans.), Vol. 38, No. 3 The re f o re (4) is still i n terms of mol f r a c t i o n s A t t h i s p o i n t because equation w e can s u b s t i t u t e t h e chemical terms f o r a2, a 3 . . . t o s i m p l i f y t h e equation. O f course, t h e CO and C02 q u a n t i t i e s are measured dry and rep- r e s e n t such i n t h e equation, so they must be converted t o w e t concentra- (1 - H20).

t i o n

H20 = a (1 - H20)C02 + C O ( 1 - H20) (4 - 0.51) + 2 (4 - y)

= (1 - H20) [ ; C02 + (4 - 0.51)Ca) + 3 (F - T) 1.85

= [ ; C02 + (g - 0.51)Cd - H 2 0 [ : C02 + (g - 0.5,) CO]

1 ; C02 + (t - 0.51)C.J + HC 2 ( ; - T) 1.85

H20 = a 4-

C 0 2 + ( : - 0.51)Cd

B y d e f i n i t i o n

Cw = 1 - H20

F i n a l l y , (7) equals t h e water c o r r e c t i o n f a c t o r (& f o r t h a t c o n t r i b u t i o n a r i s i n g from t h e combustion process.

Correction Factor Ambient Water Vapor Development Previously i t w a s assumed t h a t the f u e l w a s represented by a s p e c i f i c f u e l molecule. However, t h i s approach, w h i l e allowing c a l c u l a t i o n of t h e water contained i n t h e a i r , f i x e d the d e f i n i t i o n too r i g i d l y . With l i t t l e o r no d i f f e r e n c e i n t h e f i n a l r e s u l t a mre general approach w a s adopted t h a t i s based on t h e assumption t h a t t h e w a t e r contained i n t h e i n t a k e and simply passes d i - mixture does n o t e n t e r i n t o any combustion r e a c t i o n r e c t l y through t h e engine. Expressing t h i s i n a word equation

(Water i n exhaust - l b / h r ) = (Air flow i n t o engine - l b / h r ) ( % humidity)

(1) Dividing each s i d e of t h e equation by t h e t o t a l flow through t h e engine, air p l u s f u e l , y i e l d s t h e percentage of water i n the exhaust due t o humidity .

I n a f i n a l form t h e humidity c o r r e c t i o n becomes Vapor p r e s s .

(Air flow)(% humidity) - - Mair (0.622 Patm - Vapor p r e s s .

Fraction w a t e r =

(Air flow + Fuel flow)

cMair + Mfuel) o r

Water c o r r e c t i o n factorIHuddity = 1 - Fraction water

(3) The t o t a l w a t e r c o r r e c t i o n f a c t o r , t h e r e f o r e becomes a multiplica- t i v e combination of t h e two i n d i v i d u a l contributions.

The exhaust molecular weight computation is based on "Procedure and Charts f o r Estimating Exhaust G a s Quantities and Compositions" - GMR 372, Figure A-2 shows t h e v a r i a t i o n of exhaust B. A. D'Alleva, May 15, 1960.

molecular weight with f u e l / a i r r a t i o , as determined by t h i s method.

Exhaust Volume Calculation Procedure The method s p e c i f i e d by t h e EPA f o r t r e a t i n g t h e emissions measure- ments is s p e c i f i e d i n t h e Federal R e g i s t e r , P a r t 87.99, Vol. 38, 7-17-73.

A s s t a t e d i n t h i s s e c t i o n , par. 3, ""he engine exhaust volume s h a l l be c a l c u l a t e d i n accordance with good engineering p r a c t i c e from a c t u a l a i r and f u e l flow measurements . .

The exhaust volume can be equated as - ' a + ' f

' e - D

where Wa airflow, l b / h r Wf f u e l flow, l b / h r D density of exhaust The exhaust d e n s i t y can be expressed as 0.075 E m D = 28.96 where 0.075 density of air 28.96 molecular weight of a i r exhaust molecular weight Em A t t h i s p o i n t it i s necessary t o provide t h e exhaust molecular weight.

Figure A-2 shows t h e r e l a t i o n s h i p between exhaust plecular weight and A/F r a t i o as derived according t o "Procedure and Charts f o r Estimating t h e Exhaust Gas Quantities and Compositions," GMR 372, by B. A. D'Alleva.

S u b s t i t u t i n g the value f o r and working according t o t h e calcu- Em l a t i o n procedure i n t h e Federal Register, t h e mass emission rate of any exhaust component is

P o l l u t a n t = 0 v P

'100 e p where t h e p o l l u t a n t concentration i n percent (P) P t h e p o l l u t a n t d e n s i t y a t standard conditions and i s s p e c i f i e d i n P the Federal R e g i s t e r This y i e l d s t h e emission rate i n pounds/hr. To convert t o lblmode it is necessary t o multiply by one of t h e corresponding mode t i m e s : I d l e 0.0167 h r T a x i .1833 h r ,005 h r Takeoff Climb .083 h r Approach .lo0 h r Taxi .05 h r I d l e .016 7 h r Summing t h e emissions f o r each mode f o r t h e t h r e e p o l l u t a n t s and dividing by t h e r a t e d horsepower of the engine gives t h e d e s i r e d end r e s u l t i n p o l l u t a n t lb/hp-hr, which corresponds t o t h e l i m i t s set by t h e EPA.

Carbon Balance The i n t e n t of t h e carbon balance technique is t o v e r i f y t h a t those concentrations i n d i c a t e d by t h e exhaust a n a l y s i s equipment are represen- tative of t h e a c t u a l p o l l u t a n t levels present. This is accomplished by c a l c u l a t i n g an o p e r a t i n g f u e l / a i r r a t i o i n g e s t e d i n t o t h e engine on t h e b a s i s of t h e measured exhaust gas components. A measured f u e l / a i r r a t i o obtained from a c t u a l a i r and f u e l flows serves as t h e standard f o r com- p a r is on.

To p r e d i c t t h e f u e l / a i r r a t i o from t h e concentrations of t h e exhaust gas components t h e procedure of Spindt ( S A E Paper 650507) w a s chosen.

T h i s method assumes t h a t a f r a c t i o n (Fb) of t h e f u e l supplied t o t h e engine is involved i n a combustion process t h a t proceeds t o completion and t h e remaining f u e l (F,) passes through t h e engine e s s e n t i a l l y un- changed. That is t o s a y , f o r t h e t o t a l mixture introduced i n t o t h e engine, F + F b = l U o r

(CO) + (C02)

(HC) = 1

(CO) + (C02) + (HC) (CO) + (C02) + (HC)

where t h e measured exhaust concentration of each s p e c i e is i n d i c a t e d by t h e parentheses.

02, and HC, t h e a i r / f u e l r a t i o is expressed by In terms of CO, 60 2’ 120 Fn 1 + R / 2 + 9 )

+ ( 3.5 + R )]

where f r a c t i o n of carbon i n f u e l Fc f r a c t i o n of hydrogen i n f u e l Fn R (CO>/(CO,> Q ( 0 2 ) / ( C 0 2 ) ENG t NE r EXHAUST GAS ANALY t E R S I r POLLUTAXT CONCENTRAT 1 ON

L (DRY)

VATE R CORRECTION F A C T OR S CARBON E XHAU S T BALANCE VOLUME I POLLUTAHT CA L C U L A T E EXHAUST GAS

KOLECULAR , COllCENTRATIOII . A I R/FUEL

(WET 1 c E X H A U S T GAS DE I! S I T Y E X H A U S T

1 VOLUi4E I

FLOW RATE POLLUTA f IT PRODUCT I Of1 AVCO-LYCOXING EXHAUST EM1 SSI ON DATA RE DUCT I O N SC!!CliAT I C Figure A-1 . - .... .

9 11 13 15 17 Air-fuel ratio AVCO-LY COMING EXHAUST MOLECULAR WEIGHT VERSUS AIR/FUEL RATIO FROM GMR 372 Figure A-2

APPENDIX B REVIEW OF MEASUREMENT AND TESTING PROBLEMS* Teledyne Continental Motors Mobile, Alabama APPARATUS AND RELATED PROCEDURE Background ex- Teledyne Continental Motors experience with t h e measurement of haust emissions from a i r c r a f t p i s t o n engines goes back t o t h e latter p a r t of 1971 when f i v e engines of each of four d i f f e r e n t models were t e s t e d under c o n t r a c t t o t h e Environmental Protection Agency. Additional test- i n g w a s accomplished i n late 1971 and e a r l y 1972 on an inhouse program t o e v a l u a t e t h e emissions of an exhaust-air-injected, turbocharged engine.

Subsequently, a c o n t r a c t w a s awarded on June 28, 1974, which w a s j o i n t l y funded by both t h e F A A and N A S A (DOT FA74NA-1091).

This r e v i e w of measurement and t e s t i n g problems p r e s e n t s an overview of work i n t h l s area from t h e beginning of che FAA c o n t r a c t .

Exhaust Emissions Measurement Equipment Attachment I p r e s e n t s a concise list and d e s c r i p t i o n of problems en- countered with t h e exhaust emissions measurement analyzers and t h e attend- a n t sample handling systems.

The problems have been a t t r i b u t a b l e mainly t o emission analyzer dur- a b i l i t y and design. Some problems e a r l y i n the c o n t r a c t were t h e r e s u l t of t h e l e a r n i n g process. I n e f f e c t a l l of t h e p a r t i c i p a n t s i n t h e NAFEC Contract w e r e required t o custom make a t o t a l system package which would comply with t h e requirements of t h e Federal R e g i s t e r , Volume 38, Number 136, P a r t 87.93.

While equipment development continues and d u r a b i l i t y problems have not e n t i r e l y been overcome, w e b e l i e v e t h a t our p r e s e n t system is capable of being maintained i n accordance with P a r t 87.

Testing Problems Throughout t h e c o n t r a c t , t e s t i n g problems have been encountered

*

Material d i s t r i b u t e d b u t n o t presented a t t h e Symposium.

which r e s u l t e d i n lack of d a t a r e p e a t a b i l i t y , both inhouse and between TCM and NAFEC. These r e p e a t a b i l i t y problems s t e m b a s i c a l l y from t h e f a c t t h a t t e s t i n g conditions were n o t and could not be held constant with c u r r e n t test cell equipment.

It w a s agreed t h a t , f o r each o p e r a t i n g mode, t h e c o n t r o l l e d v a r i - ables f u e l flow, engine speed, manifold p r e s s u r e , induction a i r i n l e t pressure, and engine cooling a i r pressure would be held t o s p e c i f i e d values. The v a r i a b l e s l e a d i n g t o poor d a t a r e p e a t a b i l i t y which w e r e re- corded but n o t c o n t r o l l e d w e r e induction a i r and cooling a i r tempera- t u r e s , induction a i r humidity,and exhaust back-pressure. These l e a d t o v a r i a t i o n s i n engine power, c y l i n d e r head temperature, induction air flow and, most importantly, emissions.

I n a d d i t i o n , t h e s p e c i f i c a t i o n of t h e amount of cooling a i r pressure t o be supplied being f i x e d a t a constant v a l u e does not lend i t s e l f t o sound judgmental values of c y l i n d e r head overtemperature s a f e t y l i m i t s .

The question c o n t i n u a l l y arose as t o t h e expected v a r i a b i l i t y of t h e s e s a f e t y limits i n a v a r i e t y of a c t u a l airframe i n s t a l l a t i o n s . The matter w a s considered important enough t o be i n v e s t i g a t e d under a supplement t o t h e Phase I c o n t r a c t i n t h e form of a f l i g h t test program, It i s clear at t h i s p o i n t i n t i m e t h a t more s a t i s f a c t o r y , repeat- a b l e r e s u l t s would have been obtained had t h e uncontrolled v a r i a b l e s been controlled. Since, t o d a t e , no u n i v e r s a l c o r r e c t i o n f a c t o r s are a v a i l - a b l e t o account f o r v a r i a t i o n s i n emissions due t o humidity, temperature, and pressure of induction a i r , it is apparent t h a t f u t u r e t e s t i n g of t h i s s o r t should include requirements aimed a t maintaining t h e induction air i n l e t conditions t o a set of some, y e t unspecified, standard atmospheric conditions.

Engine-Related Problems During t h e course of t h e NAFEC c o n t r a c t , TCM has t e s t e d f i v e engines ranging i n horsepower from 100 t o 4 3 5 . These engines vary i n complexity from t h e simple 0-200-A, a carbureted engine with a f i x e d p i t c h p r o p e l l e r , GTSIO-520-K, which is geared, turbocharged, f u e l t o t h e highly complex i n j e c t e d , i n t e r c o o l e d , and has s o n i c v e n t u r i bleed a i r provisions f o r cabin p r e s s u r i z a t i o n .

The b a s i c problem t o which t h e c o n t r a c t terms addressed themselves w a s a matter of how t o measure emissions f o r a11 these engines on a com- mon b a s i s so t h a t t h e r e s u l t s would be comparable. This involved select- i n g various parameters f o r each i n d i v i d u a l engine which would comply with both the intended airframe requirements on t h e one hand consistency and w i t h c o n t r a c t goals on the o t h e r . A s a r e s u l t , the c o n t r a c t s p e c i f i c a - t i o n s had t o b e reevaluated and changed t o accommodate t h e v a r i a t i o n s among t h e f i v e engines as experience w a s gained on t h e emissions t e s t stand. S t i l l , i t cannot be s a i d t h a t every engine w a s t r e a t e d on an equal b a s i s with t h e o t h e r s .

As an example, t h e 0-200-A engine w a s operated a t t h e same condi- t i o n s f o r takeoff and climb modes as is normal f o r t h a t engine. The GTSIO-520-K, however, which has a 5-minute takeoff r a t i n g a t f u l l power w a s operated a t 80 percent power, 90 percent speed i n t h e climb mode.

The 0-200-A,which w a s equipped w i t h a t y p i c a l fixed-pitch f l i g h t prop, could not develop f u l l power ( f u l l rpm) i n the s t a t i c test s t a n d condi- t i o n , whereas t h e remaining f o u r engines w e r e equipped w i t h constant speed p r o p e l l e r s allowing prop governor adjustments so t h a t f u l l rpm could be a t t a i n e d .

All TCM engines are designed t o operate most e f f i c i e n t l y a t t h e higher power modes. While t h e engines would i d l e s a t i s f a c t o r i l y f o r long periods of t i m e , t h e inappropriate valve and spark timing and -in\duc- t i o n system c h a r a c t e r i s t i c s caused widely v a r i a b l e exhaust emissions values t o be measured i n t h i s mode of operation. As a consequence a l a r g e degree of d a t a scatter w a s observed and poor r e p e a t a b i l i t y r e s u l t e d .

Air Flow Measurement emissions measurement equipment problems I n a d d i t i o n t o t h e exhaust discussed previously, t h e r e w a s l i t t l e reason t o suspect any d i f f i c u l t i e s with our engine o p e r a t i n g parameter measurements. I n i t i a l l y i n t h e pro- gram when t e s t i n g t h e 0-200-A engine, an a i r f l o w measurement device w a s used t h a t later w a s suspected t o b e inaccurate due t o d a t a reduction re- s u l t crosschecks. The valve device w a s replaced with a modern laminar flowmeter which is compensated f o r pressure and temperature. Subsequent cross-calibration with o t h e r devices including a gas flowmeter, a sharp- edged o r i f i c e , a c a l i b r a t e d laminar flow standard, and two turbine-type flowmeters have shown t h e laminar flowmeter t o be t h e most a c c u r a t e s i n g l e device covering t h e widest range of engine a i r f l o w requirements.

R e t e s t of t h e 0-200-A has been accomplished using t h e laminar flow- meter.

While t h e phase I c o n t r a c t completion d a t e has been extended by additions t o t h e work plan t o gather more d a t a , t h e p r i n c i p a l reason f o r delays beyond t h e i n i t i a l phase I completion d a t e of September 1, 1975, has been a t t r i b u t a b l e t o long periods of i n a c t i v i t y because of exhaust emissions measurement equipment d u r a b i l i t y problems and delays due t o t h e a d d i t i o n a l e f f o r t involved i n s o r t i n g o u t t h e s e and o t h e r problems w i t h t h e measurement system.

Systematic checks and c a l i b r a t i o n s of t h e instrumentation have re- duced t h e above measurement and t e s t i n g problems t o a minimum.

The d a t a presented i n t h i s r e p o r t are considered r e p r e s e n t a t i v e of t h e engines t e s t e d . Absolute values may d i f f e r from f a c i l i t y t o f a c i l i t y , but i n no i n s t a n c e has t h i s d i f f e r e n c e changed t h e trends o r conclusions presented herein.

il EXHAUST EMISSIONS CALCULATION PROCEDURE Background The Federal R e g i s t e r , Volume 38, Number 136, P a r t 11, dated J u l y 1 7 , 1973, sets f o r t h t h e requirements f o r t h e c o n t r o l of a i r p o l l u t i o n from all a i r c r a f t and a i r c r a f t engines. Subparts E and I and appendix B d e a l with t h e requirements f o r compliance with t h e l a w regarding exhaust emissions from a i r c r a f t p i s t o n engines.

The exhaust emission test is designed t o measure hydrocarbons (HC), carbon monoxide (CO), and oxides of n i t r o g e n ( N S ) concentrations (per- cent o r p a r t s ~~ by volume) and determine mass emissions through c a l c u l a t i o n s during a simulated a i r c r a f t landing-takeoff (LTO) cycle.

The c a l c u l a t i o n s required t o convert exhaust emission concentrations ( r a w emissions measurements) i n t o mass emissions- ttre sf &&s- discussion.

Combustion Equation The chemical equation f o r t h e combustion of a hydrocarbon f u e l i n air can be represented symbolically by

Fuel + Air + Products of combustion

To be a b l e t o d e a l mathematically with t h e combustion equation it m u s t be w r i t t e n i n a form such t h a t t h e c o e f f i c i e n t s , representing t h e q u a n t i t i e s of each c o n s t i t u e n t , are known by v i r t u e of measurement o r are c a l c u l a b l e using t h e p r i n c i p l e s of mass conservation o r ch'emical equilibrium.

The combustion equation used as t h e b a s i s f o r t h e emissions calcula- t i o n s is Atmospheric Fuel Air humidity

(Mf) *m+ (Ma)\02 + (3.72744)N2 + (0.04451)Arf + (Mw) - +

X Y H2°

+ ( M 1 ) * H20 + (3) C02 + (M3) CO + (M4) NO + (M5) O2

where number of lbm-moles of ith c o n s t i t u e n t ; 1 lbm-mole (lb-mass mole) Mi a substance is q u a n t i t y of t h a t substance i n pounds-mass (nu- of merically equal t o t h e molecul'ar weight of substance i n atomic MSS u n i t s ) : 1 lbm-mole of water (H20), t h e r e f o r e , would have

mass of (2)(1.008) + 16 = 18.016 lbm

pure hydrocarbon f u e l containing x atoms of carbon and y atoms cx Hy of hydrogen i n each molecule O2 n i t r o g e n N2 Ar argon water (vapor) H20 carbon dioxide co2

co carbon monoxide

NO n i t r i c oxide n i t r o g e n dioxide NO2 unburned hydrocarbon exhaust product containing p atoms of car- cP Hq bon and q atoms of hydrogen i n each molecule hydrogen H2 C s o l i d carbon Examining each c o n s t i t u e n t of t h e equation, it is necessary t o de- termine what can be measured, what can be c a l c u l a t e d , and what assump- t i o n s must be made i n o r d e r t o c a l c u l a t e mass emissions values of HC, CO, and NO,.

Fuel and Air W e have represented t h e f u e l Cx tly as a pure hydrocarbon molecule.

In r e a l i t y , gasoline is a blend of many hydrocarbon products of r e f i n e d crude o i l and contains, i n a d d i t i o n , antiknock agents such as t e t r a e t h y l lead, d e p o s i t modifiers, a n t i o x i d a n t s , d e t e r g e n t s , a n t i r u s t agents, dyes, and a n t i - i c i n g agents which contain elements o t h e r than hydrogen and carbon.

These o t h e r elements are ignored i n t h e combustion equation as they are deemed n e g l i g i b l e . then is representa- The f u e l molecule Cx H

Y

tive of a nominal o r average hydrocarbon molecule with a r a t i o of hydro- gen t o carbon atoms of y/x. Although t h e actual values of y and x f o r t h e gasoline varies considerably and no s p e c i f i c values can be as- signed t o them i n our s i m p l i f i e d f u e l molecule, t h e r a t i o of hydrogen t o carbon atoms i n 100/130 octane a v i a t i o n gasoline can be measured and re- mains r e l a t i v e l y constant a t a value of about 2.125.

Likewise, t h e unburned hydrocarbon c o n s t i t u e n t i n t h e exhaust may of 1.85 contain s e v e r a l s p e c i e s of hydrocarbons, b u t a r a t i o of q/p has been suggested t o r e p r e s e n t t h e average r a t i o of hydrogen t o carbon This value, however, f o r t h e pur- i n t h e exhaust hydrocarbon p o l l u t a n t .

pose of t h i s a n a l y s i s w i l l be considered unknown.

The f u e l flow is measured using a Cox Vortex Flowmeter, Model #4271.

A t TCM, a i r f l o w is measured by a M e r r i a m laminar flowmeter which gives a l i n e a r r e l a t i o n s h i p between mass flow and p r e s s u r e drop and compensates f o r temperature and pressure. The t o t a l mass flow measured includes t h e atmospheric humidity.

Humidity is c a l c u l a t e d from measured values of w e t and dry bulb t e m - peratures and is given i n terms of pounds-mass of water vapor per pound- mass of dry air.

Products of Combustion The products o f combustion as shown i n t h e combustion equation are again s i m p l i f i e d i n t h a t t h e nonhydrocarbon f u e l a d d i t i v e s are ignored.

The exhaust c o n s t i t u e n t s which are measured include C02, 60, NO, The c o n s t i t u e n t s which are known, a p r i o r i , are A r N02, 02 and C H q l p .

Those c o n s t i t u e n t s which are not measured are C, E2 and H20. and N2.

The formation of s o l i d carbon C i s t h e r e s u l t of r i c h combustion of f u e l ( f u e l burned i n t h e presence of i n s u f f i c i e n t a i r ) and t o a varying e x t e n t , depending on engine age and condition, the burning of t h e o i l l u b r i c a n t e n t e r i n g t h e combustion chamber along t h e p i s t o n r i n g s o r valve guides. Chemical equilibrium c a l c u l a t i o n s have shown t h a t below f u e l - a i r equivalence r a t i o s of about 3.0 ( f u e l - a i r r a t i o of 0.20), s o l i d carbon as a product of combustion is n e g l i g i b l e compared t o t h e remainder of t h e gaseous products. A i r c r a f t p i s t o n engines do n o t normally run a t o v e r a l l equivalence r a t i o s over 2.0 ( f u e l - a i r r a t i o of 0.13). The chemi- cal equilibrium c a l c u l a t i o n s , however, assume homogeneity of t h e f u e l - a i r mixture. The l a c k of p e r f e c t mixture uniformity i n a real engine would l e a d t o some production of s o l i d carbon due t o l o c a l i z e d r i c h mixtures w i t h i n t h e combustion chamber.

A t t h e present t i m e s o l i d carbon is n o t measured and i s assumed f o r c a l c u l a t i o n purposes t o be n e g l i g i b l e . There is c u r r e n t l y no equipment a v a i l a b l e t o measure s o l i d carbon production on a real-time b a s i s .

Free hydrogen (Hz), which is present i n t h e exhaust products i n s m a l l b u t s i g n i f i c a n t q u a n t i t i e s , is a l s o not measured. R e a l - t i m e meas- urement equipment f o r H2 i s a v a i l a b l e .

While t h e r e are systems on t h e market which w i l l measure water (H20) vapor content i n t h e exhaust, they are expensive. Calculative procedures are a v a i l a b l e t o estimate t h e q u a n t i t y of w a t e r vapor i n t h e exhaust.

Table B-1 o u t l i n e s t h e equipment c u r r e n t l y used by TCM t o determine those exhaust products which are measured.

TABLE B-1 Exhaust Measuring Method used by measuring instrument product instrument Beckman eo Measurement of d i f f e r e n t i a l absorption of Model 864 (NDIR) i n f r a r e d l i g h t B e ckman Measurement of d i f f e r e n t i a l absorption of (332 Model 864 (NDIR) i n f r a r e d l i g h t

NO, N O 2 Beckman NO + 03 -t N O 2 + Light; measurement of

Model 951 H(CL) l i g h t i n t e n s i t y due t o r e a c t i o n S c o t t Model 150 Measures e f f e c t of paramagnetic oxygen i n gas sample on magnetic f i e l d S c o t t Measures e f f e c t on e l e c t r o s t a t i c f i e l d of cP Hq Model 215 (FID) ionized hydrogen and carbon from gas sample Balancing Combustion Equation By t h e p r i n c i p l e of conservation of mass w e know t h a t t h e atomic q u a n t i t i e s introduced i n t o t h e engine induction system must a l s o b e present i n t h e exhaust even though they are rearranged i n t o d i f f e r e n t molecules by t h e combustion chemical reaction. Hence, a l l t h e carbon atoms e n t e r i n g t h e engine i n t h e form of hydrocarbon f u e l molecules must be p r e s e n t i n t h e exhaust i n t h e form of CO, C02, and Cp Hq. This atom- balancing technique provides us with a system of equations by which w e may s o l v e f o r unknown q u a n t i t i e s .

Going back t o t h e o r i g i n a l combustion equation, w e e l i m i n a t e s o l i d

carbon (9 and n i t r o g e n dioxide (302) ( i t has been found t h a t NO2 does n o t

e x i s t i n any s i g n i f i c a n t q u a n t i t y f o r our engines). W e then d i v i d e each molar value on both s i d e s of the equation by t h e sum of t h e molar values on t h e - r i g h t side. The equation then becomes H

+ (ma)[02 + (3.72744)N2 + (0.04451)Arl + (mw) H 2 0

(m,) C X Y

CO + (m4) - NO + (m,) - O2

H20 + (m,) * C02 + ,(m3)

H + (m,) W2 + (m,) N2 + (mg) A r

+ ( m , ) * C

P 4 where m = i c o e f f i c i e n t on t h e r i g h t s i d e of t h e e q u a t i o n is now Thus, every molar expressed i n mole f r a c t i o n s such t h a t + m + m + m 4 + m 5 + m 6 + m 7 + m 8 + m g = 1 . 0 ml 2 3 This is done f o r convenience and t h e reason f o r i t w i l l b e demonstrated later.

The n i n e p r o d u c t s of combustion r e p r e s e n t an e s t i m a t e d 99.998 per- cent o f t h e chemical composition of an e q u i l i b r i u m mixture at exhaust R.

gas temperatures below 3000' An oxygen b a l a n c e r e s u l t s i n

2ma + mw = "1 + 2m2 + m3 + m4 + 2m5

o r

"1 = 2 m + mw - 2 9 - m3 - m4 - 2m5

a A carbon b a l a n c e g i v e s

x mf = 9 + m3 + p

' " 6 o r

m2 + m3 + p m6

-

mf - X

Since o u r measurement of C li is i n ppm carbon equivalent,we can r e p r e - p . 9 s e n t Cp Hq as CH Equation (2) then becomes 4IP' m 2 + m + m

- 3 6

"f - X

The remaining atomic balances are as follows: y mf + 2mw = Hydrogen balance:

2 m + - m + 2m7

(3) 1 P 6

Nitrogen balance: (3.72744)(2)m a = m4 + 2m8 (4)

Argon balance: (0 .04451)ma = 3 (5 1

Water Correction F a c t o r Since CO, C02, and 02 are measured on a dry volumetric b a s i s (water and HC vapor b e i n g removed from the exhaust sample b e f o r e measurement) and NO are measured on a w e t volumetric b a s i s , w e must determine the dry sample i n o r d e r t o c o r r e c t a l l amount o f water vapor removed from t h e f o r c a l c u l a t i v e measured values t o e i t h e r a dry o r a w e t volumetric b a s i s

I n doing t h i s w e are s o l v i n g f o r one of t h e unknowns -

purposes.

m i (H20).

W e can d e f i n e t h e f u e l t o dry air mass r a t i o as

mf(12.011x + 1 . 0 0 8 ~ )

f

- -

-

A ma(138. 2689) where

( 1 2 . 0 1 1 ~ + 1 . 0 0 8 ~ ) = f u e l molecular weight

and 138.2689 = pounds-mass o f a i r p e r lbm-mole of oxygen The s p e c i f i c humidity, o r water vapor t o dry a i r mass r a t i o , is mw(18. 016) W

_ -

-

(7) A ma(138. 2689) S u b s t i t u t i n g equations ( 2 ) , ( 6 ) , and (7) i n t o equation (1) and rearrang- i n g the terms g i v e s

(m2 + m3 + m6)(12.011 + 1.008 $)

138.2689(:)

- 2m2 - "3 - "4 - 2"5

(8) For c l a r i t y , equation (8) may be r e w r i t t e n using chemical symbols t o rep- r e s e n t t h e mole f r a c t i o n f o r each c o n s t i t u e n t :

(C02 + CO + HC) 12.011 + 1.008

= [z + 7.67478 :][ ‘

H2°

138.2689 (f )

- 2C02 - CO - NO - 202

(9) Equation (9) then r e p r e s e n t s t h e t o t a l w a t e r vapor (humidity p l u s w a t e r meas- of combustion) contained i n t h e exhaust gas with each c o n s t i t u e n t ured on a w e t b a s i s .

Defining t h e water c o r r e c t i o n f a c t o r as w e can convert t h e e n t i r e equation (9) t o dry b a s i s measurements by d i v i d i n g by (1.0 - H2O):

4 - ‘‘dry + 1 H C w e t - H 2 0 (12.011 + 1.008

1 - H 2 0 138.2689( i)

Nowet - 2o

- c o - - 2co

(11)

2 dry dry 1 - H20

2 dry where “2 w e t etc.

- -

co 2 dry 1 - H20

(11) may be obtained i t e r a t i v e l y by assum- The s o l u t i o n t o equation i n g a value f o r H20 on t h e r i g h t s i d e of t h e equation, s o l v i n g f o r H20 on the l e f t s i d e , using t h i s new value f o r H20 on t h e r i g h t s i d e and repeat- i n g t h e process u n t i l s a t i s f a c t o r y agxeement has been obtained between the assumed and c a l c u l a t e d values. Using t h i s scheme, convergence is ob- t a i n e d usually w i t h i n f o u r i t e r a t i o n s , A more expansive chemical. equilibrium c a l c u l a t i o n w a s made over t h e normal range of f u e l - a i r r a t i o s , considering t h e products of combustion t o include C, A r , CO, C02, H2, H20, N 2 , 02, 0, OH, H, NO, N , NH3, and CH4.

The maximum e r r o r determined i n t h e c a l c u l a t i o n of water vapor using our w a s less than one-half of one abbreviated product of combustion equation percent.

The s o l u t i o n t o t h e w e t c o r r e c t i o n f a c t o r then w a s obtained by using f i v e equations ( ( l ) , (2), (6), ( 7 ) , and (10)) involving f i v e unknowns (%, The assumptions made i n order t o e f f e c t a s o l u t i o n s, m l , mf, and %).

t o t h e water c o r r e c t i o n f a c t o r are (1) The combustion equation r e p r e s e n t s a l l of t h e elemental c o n s t i t u - e n t s involved i n t h e a c t u a l combustion process.

/ f o r a l l 100/130 octane (2) The r a t i o of hydrogen t o carbon atoms a v i a t i o n gasolines remains constant at (y/x) .

While t h e r e are similar methods which can be used t o c a l c u l a t e t h e water c o r r e c t i o n f a c t o r , it is b e l i e v e d t h a t this method involves t h e use of t h e least number of assumptions l e a d i n g t o t h e most accurate estimate of C, based on t h e q u a n t i t i e s c u r r e n t l y being measured.

Calculation of Mass Emission Values A s mentioned previously, t h e raw emissions are measured on a volu- metric b a s i s i n percent o r ppm. I n order t o determine t h e emissions based on t h e requirements of the EPA Standards, t h e s e volumetric values must b e converted t o volumetric flow rate and then t o mass flow values i n accordance with P o l l u t a n t Exhaust P o l l u t a n t P o l l u t a n t mass volumetric

- -

X X volumetric (12) emission flow dens i t y concentration rate rate For t h i s equation, t h e p o l l u t a n t d e n s i t i e s are s p e c i f i e d i n t h e Federal Register at a standard pressure and temperature of 760 mm H and 6 8 ' F.

The values of p o l l u t a n t volumetric concentrations (CO, HC, 8%) are

measured, and i n o r d e r t o c a l c u l a t e t h e mass emission rates t h e exhaust volumetric flow rate m u s t be known.

The EPA Standards state t h a t t h e exhaust volumetric flow rate " s h a l l be c a l c u l a t e d i n accordance with good engineering p r a c t i c e s . I ' 73.~0 methods are used by TCM t o c a l c u l a t e t h e exhaust volumetric flow

rate - one is c a l l e d t h e Exhaust Volume Method and t h e o t h e r , t h e Carbon

Balance Method.

The b a s i s f o r t h e Exhaust Volume Method is i n the c a l c u l a t i o n of t h e exhaust volunaetric flow rate at t h e standard p r e s s u r e and temperature of 760 mm Hg and 68' F using t h e assumption t h a t t h e exhaust gas follows t h e i d e a l gas equation of state: where exhaust v o l u m e t r i c flow rate, f t / h r VEXH R u n i v e r s a l gas c o n s t a n t , 1545.33 f t-lbf/lbm-mole-oR t o t a l exhaust gas m a s s flow ( a l s o e q u a l t o t o t a l i n d u c t i o n m a s s m flow of f u e l and a i r by p r i n c i p l e o f mass c o n s e r v a t i o n ) , lbm/hr T a b s o l u t e temperature, 528' R (68' F) exhaust gas molecular weight

M E m

P exhaust p r e s s u r e , 2116 l b f / f t (760 mm Hg) f f u e l mass flow, lbm/hr A' humid air mass flow, lbm/hr I n e q u a t i o n ( 1 3 ) , R, T, and P are given v a l u e s and & is measured.

The v a l u e of t h e exhaust gas molecular weight can b e c a l c u l a t e d from ex- h a u s t products where MEXH i s t h e "apparent molecular weight" of t h e exhaust g a s , M i is t h e molecular weight of each c o n s t i t u e n t and is t h e mole f r a c t i o n m i o f each c o n s t i t u e n t which can b e determined from measured c o n c e n t r a t i o n s and s o l u t i o n o f e q u a t i o n s (2) t o ( 7 ) . S o l u t i o n of e q u a t i o n ( 1 4 ) f u r t h e r r e q u i r e s an assumption of e x h a u s t hydrocarbon hydrogen t o carbon r a t i o q/p. S t u d i e s have i n d i c a t e d , however, t h a t extremely unreasonable v a l u e s of c a l c u l a t e d f u e l - a i r r a t i o are o b t a i n e d when t h e sum o f t h e exhaust gas mole f r a c t i o n s are c o n s t r a i n e d t o u n i t y .

Therefore, t h e method used by TCM f o r e s t i m a t i n g t h e exhaust gas molecular weight is based OR chemical e q u i l i b r i u m c a l c u l a t i o n s and as- sumes t h a t chemical e q u i l i b r i u m e x i s t s among the exhaust products f o r a given measured f u e l - a i r equivalence r a t i o . This assumption i s reasonable since t h e major c o n s t i t u e n t s which c o n t r i b u t e t o the exhaust molecular weight (e.g., N2, C02, H20, CO) do not v a r y s i g n i f i c a n t l y from e q u i l i b - rium p r e d i c t i o n s . The c a l c u l a t i o n of mass emissions of carbon monoxide as an example would b e as f o l l o w s by s u b s t i t u t i n g e q u a t i o n (13) i n t o e q u a t i o n (12) : Since, by t h e i d e a l gas assumption, S u b s t i t u t i n g e q u a t i o n (16) i n t o (15) y i e l d s o r

lh co = re) ( f + A ' ) ( C O )

where Iil m a s s emission rate of CO, lbm/hr co M molecular weight of C O Y 28.011 lbm/lbm-mole co exhaust gas molecular weight lbm/lbm-mole

%m

( f + A') t o t a l i n d u c t i o n mass flow rate, lbm/hr

co w e t volume f r a c t i o n of CO i n exhaust

The Carbon Balance Method of c a l c u l a t i n g exhaust volumetric flow rate is a l s o used by TCM. This method provides a cross-check on the Exhaust Volume Method and is t h e s a m e method used i n t h e c a l c u l a t i o n of t u r b i n e engine emissions.

The Carbon Balance Method is b e l i e v e d t o b e t h e more a c c u r a t e as measurement of a i r f l o w A and e s t i m a t i o n of exhaust gas molecular weight MEXH are n o t r e q u i r e d . The Carbon Balance Method accounts f o r a l l t h e carbon atoms i n t h e combustion e q u a t i o n , and by c o n s e r v a t i o n of mass, t h e carbon i n t r o d u c e d i n t o t h e engine i n t h e molecular form of f u e l must be accounted f o r i n t h e carbon-containing exhaust product molecules CO, 0 2 9 c p Hq" A s w i t h t h e Exhaust Volume Method, t h e assumption is made t h a t t h e i d e a l gas e q u a t i o n o f state a p p l i e s .

The d e r i v a t i o n o f the Carbon Balance Method is as follows. From e q u a t i o n (2) t h e carbon b a l a n c e e q u a t i o n ,

mZ + m3 + m6

- moles of f u e l

-

-

mf - X moles of w e t exhaust

The volumetric flow rate of t h e exhaust can then be c a l c u l a t e d as f o l - lows : where molar flow rate of exhaust, lbm-moles/hr

kXH

molecular weight of exhaust, lbm/lbm-mole

MEXH

exhaust gas density , lbm/ f t

PEXEi W e d e f i n e f

% X H = i q q

where f mass f a e l flow, lbm/hr Mf molecular weight of f u e l m from carbon balance eq. (2), moles of fuel/moles of w e t exhaust f From t h e i d e a l gas equation of state %XI RT

-- - -

P PEXH S u b s t i t u t i n g equations (19) and (20) i n t o (18) gives f S u b s t i t u t i n g t h i s r e s u l t i n t o equation (12) and using carbon monoxide as an example gives c The density of CO (pco) by i d e a l gas consideration i s and t h e molecular weight of t h e f u e l is

Mf = ~ ( 1 2 . 0 1 1 + 1.008

"1

W e can s u b s t i t u t e equations (23), (24), and (2) i n t o equation (22) t o o b t a i n

fM co

co

;n' =

co

(12.011 + 1.008 z, (HC + CO + C02)

X Note t h a t t h e value x i n equation (24) cancels with t h e x i n equa- (2) s o t h a t it i s not necessary t o know t h e molecular form of t h e t i o n f u e l b u t only t h e H / C r a t i o y/x.

This method is a t t r i b u t a b l e t o Stivender (see SAE Paper 710604) and has t h e advantage of producing an exhaust volumetric flow rate c a l c u l a t i o n independent of measured air flow which is a source of some probable e r r o r i n t h e Exhaust Volume Method. It is i n s t r u c t i v e t o look at t h e d i f f e r - ence between t h e s e two methods. I n order t o do this w e can take t h e r a t i o of Carbon Balance t o Exhaust Volume m a s s flow values f o r CO using equations (25) and (17):

i i ' ( f / N (MExH)

co - = (26 1

(12.011 + 1.008 f ) ( H C + CO + C02) (1.0 + : + i)

' co

This i n d i c a t e s t h a t any d i f f e r e n c e s between t h e two methods (hLo/hco f 1.0) are a function of f u e l - a i r r a t i o and measured values of as used by TCM is a function of HC, C O Y and C02 ( t h e value of f/A MEXH only). Therefore, t h e r a t i o of these two values is a good i n d i c a t o r of t h e measurements of f u e l flow, airflow, and HC, 60, and C02. TCM experi- ence has shown t h a t while t h i s r a t i o is not equal t o u n i t y f o r most engines, a general range of values can be e s t a b l i s h e d f o r a p a r t i c u l a r engine model and o p e r a t i n g mode.

As an example, when t e s t i n g t h e Tiara 6-285-B engine, t h e r a t i o of w a s near 0.97 f o r t h e takeoff modes. A p o i n t w a s observed t o

Go/&co

have a value of this r a t i o of 1.33.

Upon rechecking t h e recorded emis- s i o n s d a t a i t w a s found t h a t an e r r o r had been made i n reading t h e value of c02.

These two methods of c a l c u l a t i n g exhaust m a s s emissions provide a good check on t h e accuracy of measured values. I n a d d i t i o n , t h e Carbon Balance Method provides a convenient means f o r t h e measurement of exhaust 372.

emissions i n a f i e l d survey o r f l i g h t test s i t u a t i o n , as measured a i r f l o w is not required.

Calculation of Fuel-Air Ratio The Exhaust Emissions Standards r e q u i r e a check on accuracy of meas- ured d a t a which involves t h e c a l c u l a t i o n of f u e l - a i r r a t i o from exhaust gas c o n s t i t u e n t s . This c a l c u l a t e d f u e l - a i r r a t i o must b e w i t h i n k5.0 per- cent of the measured f u e l - a i r r a t i o i n o r d e r f o r t h e test t o b e v a l i d .

(See P a r t 87.96, subparagraph (b) of the Regulation.)

A n example of t h i s method is given i n t h e t e x t " I n t e r n a l Combustion

Engines and Air Pollution" by E. F. Obert , page 353. The method is

simple and r e l i a b l e i f t h e molecular form of t h e f u e l and exhaust hydro- carbons i s known, t h a t is i f w e know t h e values x , y, p, and q i n Cx Hy and Cp Hq.

To t h i s point i n t h e a n a l y s i s w e have scrupulously avoided assump- t i o n of these values by using equations i n t h e form such t h a t only t h e value of y/x must be known. This value has been measured and thus e l i m i n a t e s a p o s s i b l e source of e r r o r .

An a l t e r n a t i v e method f o r c a l c u l a t i n g f u e l - a i r r a t i o has been de- veloped by R. S. Spindt i n S A E Paper 650507 which r e q u i r e s t h e use of r a t i o s including y/x, e l i m i n a t i n g t h e assumption of f u e l molecular form, and avoiding t h e e r r o r s encountered by previous i n v e s t i g a t o r s .

A subsequent S A E Paper (660118) e n t i t l e d "An Evaluation of Techniques f o r Measuring Air-Fuel Ratio" by L. C. Broering, Jr., shows t h a t t h e Spindt Method is a c c u r a t e t o w i t h i n k5.0 percent a t a f u e l - a i r r a t i o of 0.067. This conclusion, however, w a s based on a l i m i t e d d a t a base using an automotive engine.

The d e r i v a t i o n of t h e Spindt Method w i l l not be covered h e r e except t o say t h a t t h e required input values are 02, CO, C02, HC, y / x , and t h e assumption of t h e water-gas equilibrium parameter, K Equation (27) is P' t h e Spindt equation: € 1-0 -

- - -

'= FBk11.492)FC 1.0 + E/2 + D +

+ E where f /A calculated. f u e l - a i r r a t i o

FB (CO + C02)/ (CO + C02 + HC)

FC (12,011)/(12.011 + 1.008 y / x ) , f r a c t i o n of carbon i n f u e l , Cx Hy

E co/co2

D 02/ CO2 K ( H p ) (CO) / ( 3 ) (C02) P The water-gas equilibrium parameter comes from t h e chemical equation

H2 + C02 2 H 2 0 + CO

where B a s i c a l l y , chemical equilibrium d i c t a t e s through t h e "mass a c t i o n law" t h a t when a chemical system is i n equilibrium a t a constant temperature t h e mole f r a c t i o n s of t h e r e a c t a n t s (H2 and C02) and products (H70 and CO) take on values such t h a t t h e value i n equation (29) remgins Kp constant.

Another way t o look a t t h i s phenomenon is t h a t i n equation (28)

t h e rate of change of H2 + C02 i n t o H20 + CO i s equal t o t h e rate of

change of H 2 0 + CO i n t o H2 and C02.

The b a s i s f o r t h i s assumption i n t h e combustion process is t h a t as t h e exhaust gases expand and cool in the expansion and exhaust s t r o k e s , rates of r e a c t i o n decrease t o a very s m a l l value due t o t h e sudden t h e decrease i n temperature and t h e water-gas equilibrium r e a c t i o n is essen- t i a l l y "frozen" a t t h e higher temperature values. This assumption is i n v a l i d i n t h a t the temperatures of the exhaust gases a t t h e start of t h e expansion s t r o k e vary considerably with engine o p e r a t i n g mode and fuel- a i r r a t i o . For tihe most p a r t , a t least a t t h e higher power modes of t h e a i r c r a f t emissions c y c l e ( t a k e o f f , clinib, approach), TCM h a s found t h a t measured values of f u e l - a i r r a t i o agree t o w i t h i n t h e required 55.0 per- cent of those c a l c u l a t e d by t h e Spindt Method.

Having taken a l l reasonable s t e p s necessary t o assure t h e accuracy of t h e d a t a c o l l e c t e d from t h e f i v e d i f f e r e n t engines i n v e s t i g a t e d t o date, t h e conclusion has been reached t h a t t h e Spindt Method is n o t ac- c u r a t e t o w i t h i n 55.0 percent a t low power modes ( t a x i / i d l e ) . I n addi- t i o n , i t has been determined t h a t t h e requirement t h a t measured and cal- c u l a t e d f u e l - a i r r a t i o s be w i t h i n k5.0 percent is not s u f f i c i e n t t o prove t h a t t h e measured emissions d a t a i s accurate. A case i n p o i n t is t h e takeoff mode d a t a p o i n t mentioned previously where a reading e r r o r w a s discovered i n t h e value of C02 on t h e Tiara 6-285-B engine. The e r r o r w a s made evident by n o t i n g an unusual value of Carbon Balance a g a i n s t Exhaust Volume mass emissions data. The c a l c u l a t e d f u e l - a i r r a t i o f o r t h a t d a t a p o i n t w a s w e l l within k5.0 percent o f t h e measured value.

3 74 A thorough i n v e s t i g a t i o n of the source of e r r o r i n t h e Spindt Method l e d t o t h e discovery t h a t t h e assumption of a constant value of t h e water-gas e q u i l i b r i u m parameter is i n e r r o r . Spindt used a value of 3.5 as i t b e s t f i t h i s data. Indications from TCM d a t a show t h a t t h e value of Kp may vary from 2.1 t o 4 . 4 . A s p e c i f i c value of t h e water-gas equilibrium constant may be a p p l i c a b l e i n comparing s i m i l a r engine operat- i n g conditions, but i n general it would not b e v a l i d t o assume it as a constant f o r a l l modes of operation.

When using t h e Spindt Method f o r c a l c u l a t i n g f u e l - a i r r a t i o with a constant value f o r Kp, it seems inappropriate t o eliminate a lower power d a t a p o i n t where c a l c u l a t e d and measured f u e l - a i r r a t i o s are n o t w i t h i n t h e prescribed k5.0 percent tolerance.

Unless another c a l c u l a t i v e procedure is developed with t h e proinise of g r e a t e r accuracy i n p r e d i c t i n g f u e l - a i r r a t i o s at lower power modes, it seems unlikely t h a t t h e requirements of d a t a v a l i d i t y can be m e t , Exhaust Emissions Standards Once t h e mass emission values of CO, HC, and NO have been d e t e r - mined, t h e c a l c u l a t i o n of exhaust emissions relative t o t h e EPA standards ( t a b l e B-2) i s straightforward.

TABLE B-2. - EPA EMISSIONS REGULATIONS REQUIREMENTS

Mode Mode name T i m e i n Power, Engine rpm, mode, percent percent min 1 Taxi / 12.0 ( a) (a> idle-out 2 Takeoff .3 100 (100) 3 Climb 5.0 75-100 (a> 4 Approach 6.0 40 (a) 5 Taxi / 4.0 (a) (a) i d l e - i n

--- ---

Total cycle 27.3 This t a b l e shows t h e required five-mode LTO cycle. In each mode, run consecutively, t h e mass emissions are c a l c u l a t e d i n lbm/mode. The sum of these values, lbm/cycle, is then divided by t h e engine r a t e d brake horsepower s o t h a t t h e f i n a l emissions values are given i n lbm/bhp/cycle. The Standards s p e c i f y as maximum allowable values: CO, 0.042 lbm/bhp/cycle; HC, 0.0019 lbm/bhp/cycle; NO,, 0.0015 lbm/bhp/ cycle.

ATTACHMENT I TCM Emissions Measurement System Modifications - Date: 9/3/74 t o 10125174.

Problem: Loss of sample flow due t o i n t e r a c t i o n of 3 analyzer pumps being connected t o common s u c t i o n l i n e .

Correction: Balancing valves and surge chambers f i t t e d t o improve t h i s condition.

Problem: S t r i p c h a r t recorders out of c a l i b r a t i o n w i t h no means of c a l i b r a t i n g .

Correction: Instrumentation designed and constructed f o r 6 channels incorporating a standard cell f o r c a l i b r a t i n g 0 - 1 mV scale.

Problem: No means of measuring sample flow response and residence times.

Correction: Event markers and c h a r t speed switching i n s t a l l e d on each s t r i p c h a r t recorder.

- Date: 12/2/74 t o 2110175.

Problem: Exhaust sample residence t i m e excessively slow.

Correction: Two 20-foot heated l i n e s from exhaust sampling pipe t o analyzers provided by Scott. One of t h e s e removed t o a g r e e w i t h the EPA Federal R e g i s t e r ( i s s u e July 1 7 , 1973, p. 19099, Sec. 87.93).

Rewiring and plumbing e f f e c t e d t o maintain a temperature i n t h i s l i n e of 310' F .

Problem: Standby sampling of cell a i r i n cold weather caused t h e line t o drop.

temperature of t h e 20-foot heated Correction: Heater i n s t a l l e d i n t h e standby a i r i n l e t with c o n t r o l hardware t o maintain i n l e t air a t 3 1 0 ' F.

-- Problem: D i f f i c u l t y i n c a l i b r a t i n g analyzers when only one span gas

per analyzer a v a i l a b l e .

Correction: Fourteen a d d i t i o n a l gases purchased and connected i n t o t h e system w i t h appropriate changeover valves f o r c a l i b r a t i n g 25, 50, 75, and 100 percent of instrument scales.

Problem: No means of measuring sample a i r on input t o induction air t e m .

s y s Correction: Sample l i n e and f i l t e r i n s t a l l e d with necessary change- over valves and f i t t i n g s as requested by NAFEC.

Date: 5/6/75 t o 6/26/75.

Problem: Sample l i n e s t o NOx analyzer and d r y e r u n i t i n main con- s o l e n o t h e a t e d causing moisture problems.

Correction: Heating a p p a r a t u s i n s t a l l e d t o maintain sample l i n e s a t 180° F.

Problem: Sample flow n o t b e i n g maintained when sampling exhaust gas. I n s u f f i c i e n t c a p a c i t y of pumps t o overcome r e s t r i c t i o n of line h e a t e d f i l t e r due t o exhaust contaminants.

Correction: Higher c a p a c i t y pump i n s t a l l e d i n t h e downstream end of t h e 20-foot h e a t e d l i n e . This gave o n l y a p a r t i a l c o r r e c t i o n t o problem.

Date: 10/20/75 t o 11/26/75 Problem: Sample flow s t i l l unstable.

Correction: A l l pumps r e p l a c e d by one master pump s i t u a t e d n e a r exhaust sampling p i p e a t upstream end o f 20-foot h e a t e d l i n e . Ex- cess sample gas r e l i e f valve i n s t a l l e d downstream o f 20-foot h e a t e d l i n e w i t h flow gage. This has e f f e c t i v e l y s t a b i l i z e d flow rates, Problem: CO and 602 flow gages h a r d t o r e a d a t r e q u i r e d flow rate o f 3.0 CFH.

Correction: 24 CFH gages r e p l a c e d w i t h 5 CFH gages.

TCM 215 HC Analyzer Modifications Date: 10/14/74 t o 10/21/74.

_I_ Problem: D e t e c t o r bench temperature e x h i b i t s lack of c o n t r o l (i.e., kfjV F) .

C o n t r o l updated by S c o t t t o c o n t r o l w i t h i n k Z 0 F.

Correction: Date: 12/2/74 t o 12120174.

Problem: HC sample pump (MEi21) gave i n s u f f i c i e n t sample flow (i.e., 3 CE'H max.).

Correction: Higher c a p a c i t y pump (MB115) f i t t e d t o g i v e 10.5 CFH.

Date: 5/6/75 t o 6/26/75.

analyzer c a l i b r a t i o n nonlinear on 50 K and 100 K Problem: HC ranges.

Correction: Fine w i r e i n s e r t e d i n t o d e t e c t o r c a p i l l a r y tube t o reduce flow rate.

Problem: R e s t r i c t i o n t o flow caused by vapor condensing i n HC sampling tubes and flowmeter downstream o f detector.

Correction: I n t e r i o r temperature of HC analyzer r a i s e d from 80 t o 120" F by disconnecting f a n , c l o s i n g a l l vents, and i n s u l a t i n g flowmeter from f r o n t panel.

Problem: Particles g e t t i n g i n t o system and p a r t i a l l y blocking de- t e c t o r c a p i l l a r y tube.

Correction: Heated f i l t e r (310' F) i n s t a l l e d i n input t o HC analyzer.

TCM NO, Analyzer Modifications Date: 9/3/74 t o 10/25/74.

Problem: Cannot maintain S c o t t 325 analyzer sample flow rates.

Correction: Changed sample pump from MB21 t o Model MB41.

All N4, measurements measured dry as per design of equip- Problem: ment.

Correction: S c o t t 325 w a s replaced with a Beckman 951 (unheated analyzer). Sample l i n e s t o t h e 951 heated and pipe work rerouted t o bypass dryer.

Date: 12/2/74 t o 2/15/75.

-

Problem: Beckman 951 (unheated version) giving low readings of NO,.

Correction: Replaced 951 with Model 951H.

Date: 5/6/75 t o 6/26/75.

Problem: 951H e x h i b i t i n g a progressively reduced readout due t o moisture e n t e r i n g t h e r e a c t i o n chamber.

Correction: Temperature of r e a c t i o n chamber r a i s e d from approximately 80° t o 1 1 0 ' F by disconnecting h e a t c o n t r o l fan and i n s u l a t i n g reac- t i o n chamber. Thermocouple w a s i n s t a l l e d t o record temperature.

3 78 Problem: N O 2 could not be measured because of pressure d i f f e r e n c e a t input of r e a c t i o n chamber when switching from converter t o bypass of converter.

Correction: Balance valve which c o n s i s t e d of c r u d e clamp pinching the tube gave unstable results and w a s replaced w i t h needle valve and pressure gage connected t o t h e c a p i l l a r y tube.

- Date: 12/18/75 t o 1/12/76.

Problem: Instrument could n o t b e c a l i b r a t e d , Reaction chamber w a s s t a r v e d of ozone. Ozonator Teflon lamphousing w a s cracked and c a p i l l a r y tube t o ozonator w a s p a r t i a l l y blocked due t o d i s t o r t i o n of Teflon tubing.

Correction: Lamphousing w a s replaced and c a p i l l a r y tubing w a s re- Beckman has advised replacing Teflon placed with needle valve.

housing every 6 months.

is normally always present Ozone, which reacts with impure Teflon, even when t h e analyzer is n o t i n use as t h e r e i s no provision i n t h e instrument f o r purging.

nitrogen has been i n s t a l l e d Capability of purging t h e ozonator w i t h and is now a r o u t i n e procedure.

Instrument c a l i b r a t i o n w a s nonlinear at high values of Problem: span gas. Reaction chamber flow rates had changed from 693 cc/min t o 500 cc/min, due t o t h e c a p i l l a r y tube becoming p a r t i a l l y re- s t r i c t e d .

Correction: Reaction chamber c a p i l l a r y tubing was replaced w i t h a 1/8-inch tube and a needle valve.

Problem: There w a s a zeroing problem - t h e 951H u n l i k e t h e 951. had

no provision f o r feeding i n zero gas, Zero p o i n t adjusted when t h e oxygen i s turned o f f . This gives a zero p o i n t somewhat lower than when using a zero gas.

Correction: Solenoid valve with tubing and switching w a s i n s t a l l e d t o allow zero gas t o be introduced i n t o t h e analyzer..

Date: 6/22/76 t o 7/26/76.

Problem: Sent instrument t o Beckman t o b e modified f r e e of charge with promised r e t u r n of 1 w e e k . A f t e r modification, Beckman found problem with n o i s e s i g n a l on output due t o f a u l t y photomultiplier tube. Tube w a s replaced a t TCM expense. Upon r e t u r n t h e u n i t w a s

found t o have water vapor condensation i n t e r n a l l y - a problem which

had not e x i s t e d before sending t h e u n i t .

ATTENDEES Federal Aviation Administration AiResearch Manufacturing Company Washington, D . C .

Phoenix, Arizona Joan Barriage Wolf Schlegel George Bates Montgomerie C . Steele Eric E . Becker George Brewer Avco Lyooming Steven Imbrogno Williamsport, Pennsylvania Eugene Klueg Larry C. Duke Nick Krull Stanley Jedrziewski Ernest Manzi Richard Moffett Donald Page Frank W . Riddell Clark Price C . Tex Ritter Beech Aircraft Corporation Robert F . Salmon Wichita, Kansas William T . Westfield William Wiseman Chester A . Rembleske Harold Riesen General Aviation Manufacturers Association Bendix Corporation Washington, D.C.

South Bend, Indiana Stanley Green Elmer Haase James Kirwin Grumann American Aviation Corporation Cessna Aircraft Company Cleveland, Ohio Wichita, Kansas George W . Westphal Bruce Barrett Cesar Gonzalez Gulf Research and Development Frank Monts Company Harvey 0 . Nay Pittsburgh, Pennsylvania Environmental Protection Agency Bruce Bricklemyer Washington, D . C .

Jet Propulsion Laboratory Thomas Cackette Pasadena, California William Houtman George D. Kittredge Jose Chirivella David Tripp Pennsylvania State University Marvel Schebler University Park, Pennsylvania Decatur, Illinois Thomas Ryan William Smith National Aeronautics and Space Piper Aircraft Corporation Lock Haven, Pennsylvania Administration Washington, D.C.

J. Lynn Helms Elliot Nichols Gordon Banerian Gary Hicks Scott Environmental Technology, Inc .

NASA Lewis Research Center Plumsteadville, Pennsylvania Cleveland, Ohio Thorvald W . Brink Anthony Souza Charles S . Corcoran Donald V . Cosgrove Stanford University Larry Diehl Stanford, California Peggy E . Evanich J. David Powell Harold Gold Jack Grobman Teledyne Continental Motors Glen Hennings Mobile, Alabama Maureen Hollander Jay E . Meyer Robert Jones Bernard J. Rezy Erwin E . Kempke Kenneth Stuckas Morton H. Krasner Ronald Tucker Stacey Lumannick Leslie Waters Phillip R . Meng Mark Olek Michael Skorobatckyi University of Michigan Adolph C. Spagnuolo Ann Arbor, Michigan Robert Summers William A. Tomazic William Mirsky Alfred S. Valerino J. Art Nicholls George F. Wildschrey William T . Wintucky Consultant Dennis Zimpfer Carl F . Bachle NASA Wallops Flight Center Wallops Island, Virginia Roger Navarro f? U. S. GOVERNMENT PRlNTlNG OFFICE: 1977 - 757-070/6302