Document
LIGHTWEIGHT DIESEL AIRCRAFT ENGINES FOR GENERAL AVIATION
Steven C . Berenyi and Alex P. Brouwers
General Products Division Teledyne Contimtal Motors This design study reintroduces the d i e s e l engine as an a i r c r a f t powerplant.
A methodical design study was conducted t o a r r i v e a t new d i e s e l engine con- figurations and applicable advanced technologies.
ILo engines a r e discussed and t h e description of each engine includes concept dravings. A performance analysis, stress and weight prediction, and a c o s t study were a l s o conducted.
This information w a s then applied t o two airplane concepts, a six-place M a and a four-place s i n g l e engine a i r c r a f t . The a i r c r a f t study consisted of in- s t a l l a t i o n drawings, computer generated performance data, a i r c r a f t operating costs and drawings of the r e s u l t i n g airplanes.
The performance d a t a s h w s a vast improvement over current gasoline-pwered a i r c r a f t . A t the ctnnpletion of t h i s basic study, the program was expanded t o evaluate a t h i r d engine configu- ration. This third engine i ~ c o r p o r a t e s the b e s t features of the o r i g i n a l two, Preliminary information on t h i s engine and its design is currently i n progress.
is presented.
INTRODUCTION Encrgy conservation, uncertainties of f u e l supply and limited a v a i l a b i l i t y of high octane gasoline, have renewed the i n t e r e s t i n the d i e s e l a i r c r a f t engine, since its f u e l economy is b e t t e r than any type of a i r c r a f t engine currently i n product ion.
Aircraft d i e s e l engines have been developed before, notably the Junkers "JUMO", O f these, only t h e the Napier "NOMAD" and the McCulloch TRAD 4180.
Junkers opposed piston, 2-stroke cycle engine ever reached the production stage.
Its complexity The Napier Nomad was a 2-stroke cycle, turbocompounded design.
and the f a c t t h a t it invaded the t e r r i t o r y of turbine engines probably accounted for its demise. The McCulloch engine came close t o f l y i n g when the program was terminated for non-technical reasons.
New technologies, now under a c t i v e development, w i l l r e s u l t i n even b e t t e r f u e l economies than can be obtained with current state-of-the-art d i e s e l engines.
These technologies a l s o make it possible t o develop a powerplant which is more compact and l i g h t e r than current gasoline a i r c r a f t engines.
Tuo engines were investigated i n the study, a 298 kW (400 HP) d i e s e l f o r a twin engined airplane and a 149 kW (200 HP) d i e s e l f o r a s i n g l e engined a i r c r a f t .
\ C The study consisted of three major phases: 1 . Technology Analysis.
A survey of available aviation and automotive sources was conducted to identify new developments which offer potential benefits to an aircraft engine. These technologies were ranked and then evaluated on the basis of performance and adaptability.
2 . Engine Concept Design.
The technologies which were chosen as a result of the evaluation and ranking process were applied to the design of the 149 and 298 kW engines. Performance, stress, weight, and cost calculations were made concurrently.
3 . EnginefAircraf t Integration Study .
The results of Step 2 were then used in an engine-aircraft integration study to determine the performance improvement of an airplane equipped with these diesel engines.
Some of the technologies which were applied in these engine designs are anticipated to be available in the late 1980's.
These technologies result in high level of performance and, although advanced, are not untried. The adiabatic engine, the catalytic combustor, and the high speed alternator envisioned are currently under development under various contracts. It should be noted here that, although the concept engine proposes the use of ceramic combustion system components, the use of such materials for "man-rated" aircraft may be 20 years These concepts were included primarily to shov what may be ultimately away.
possiblz. However, alternate less advanced solutions are also given which will result in a small reduction of performance when compared to the ultimate; but nevertheless will result in a powerplant which far outperforms the current gasoline aircraft .
RESULTS AND DISCUSSION Advantages of the Diesel Engine The diesel engine has always been burdened with the stigma of being heavy, thus offsetting its advantage of low fuel consumption for aircraft applications.
If it is possible to build an engine that combines low fuel consumption and low weight, then that engine becomes a very attractive aircraft powerplant. Old and once discarded concepts can become attractive by applying new technologies.
A conventional diesel er~gine requires high compression ratios for starting This results in high firing pressures at full load when and low load operation.
in fact the engine could run adequately at a much lower compression ratios.
New technologies make i t possible t o combine good s t a - r t a b i l i t y with lov f i r i n g pressures at f u l l load. This study shows t h a t the weight of t h e d i e s e l can be reduced below t h a t of current gasoline a i r c r a f t engines.
The d i e s e l engine o f f e r s other advantages i n addition t o low f u e l consumption, i.e. : 1. Lower operating cost.
- Lover c o s t of f u e l
- Reduced maintenance
- Extended TBO
2. Greatly reduced f i r e and explosion hazard.
3. Better in-flight r e l i a b i l i t y . N o i g n i t i o n and mixture control problems.
4. Multi-fuel capability.
5. N o carburetor icing problems.
6. Improved a l t i t u d e performance.
7. Safe cabin heating from exhaust s t a c k s ( l e s s danger of carbon monoxide) .
8. Exact f u e l metering indicator. The rack position determines t h e f u e l flow.
9. N o e l e c t r i c a l interference from i g n i t i o n system Previous A i r c r a f t Diesel Engines Table I shows a l i s t i n g and design data of past a i r c r a f t d i e s e l engines.
N o c l e a r trends follow from t h i s tabulation. Seven of the t h i r t e e n engines have a r a d i a l configuration, seven w e r e aircooled, eight were 2-stroke cycle.
The tabulation becomes more meaningful i f specific. r a t i o s a r e used. See Table 11.
Some observations can be made from these tables. Average s p e c i f i c weight values are: 4-Stroke cycle engines .710 kW/Kg 2-Stroke cycle engines .926 kW/Kg Aircooled engines .783 kW/Kg Liquid-cooled engines .923 kW/Kg 'fie numbers i n d i c a t e t h a t a 2-stroke cycle engine can be expected t o be l i g h t e r than a 4-stroke cycle engine. A comparison of aircooled and l i q u i d cooled engines would seem t o favor t h e liquid-cooled engine. However, t h e engine weights of liquid-cooled engines tabulated do not include t h e weight of the cooling package. With t h i s modification, the corrected values then becose: Aircooled engines .78 3 kW/Kg Liquid-cooled engines ,805 kW/Kg New Engine Design Study
- 298 kW Engine -
In addition to considering the historical background of aircraft diesel engines, a literature search was made and a technology base was established to evalute any concepts that may be considered for an all new engine design.
The follwing criteria were observed in considering any new ideas: The engine must be a pistonfcrankshaft type powerplant.
Be compatible with conventionally designed aircraft (size and arag).
nilow manufacture of an experimental model in five years.
Be ready for production in the late 1980's.
M ?P+ 1979 EPA Emission Standards (guide-ref erence only) .
Have multi-fuel capability.
Have engine performance comparable to current aircraft engine.
Have lower BSFC than present engines.
Maximum specific weights of .852 KgIkW for the 298 kW and 1.095 Kg/kW for the 149 kW engine.
Life cycle costs equal or less than present aircraft engines.
Avoid problem areas encountered in current aircraft engine designs.
Design attributes that had to be considered included: Performance, weight, size, C. G . , fuel economy, reliability, multi-fuel capability, noise, life cycle cost, component costs, and technology required.
Figure 1 is a flow chart that shows the different possible combinations of design features that were considered and evaluated within the frame work outlined above.
A detailed description of each of these features is beyond the scope of this paper, but was included in the original basic study. The evaluation then result- ed in the technologies that follow from Figure 1 by taking the high score items along the "common to all versions" and "radial 2-stroke cycle" lines.
Common to All Radial 2-S troke Versions Line Cycle Line Open Chamber Individual Cylinders Ceramic Pistons Low Compression Ratio Insulated Exhaust Manifolds Geared Prop Drive No Cylinder Cooling !.oop Scavenge Tool Steel Piston Rings Independent Turbo Loop Composite Connecting Rods Catalytic Combustor Synthetic Lube Oil High Pressure Fuel Injection Electronic Controls Conventional Oil Filter Conventional Fuel F i l t e r Pendulum Damper The engine concept was then l a i d out around these features.
Figure 2 s h w s an a r t i s t rendering of the proposed 298 k W 6-cylinder engine.
Figure 3 shows t h e schematic of t h i s engine. The design incorporates t h e technologies which were defined before.
The chosen system uses the C u r t i s loop scavenging. The i n t a k e p o r t s and intake manifold a r e located at t h e propeller s i d e of the engine, exhaust p o r t s and exhaust manifold a t the back end.
The cylinder l i n e r and piston top are ceramics and, therefore, cylinder cooling w i l l not be required. Tool steel p i s t o n r i n g s w i l l be required. Cool- ing air w i l l be used only f o r t h e a f t e r c o o l e r , o i l cooler, and t h e f u e l i n j e c t o r s .
The exhaust p o r t s w i l l be o i l cooled.
Each cylinder receives f u e l from a separate i n j e c t i o n pump located i n f r o n t of t h e cylinder (cool s i d e of t h e engine). F a i l u r e of one pump still leaves 516 of engine paver available. A high i n j e c t i o n l i n e pressure w i l l be required t o limit i n j e c t i o n duration a t high engine speeds.
The turbocharger can run independent of t h e engine. For t h a t pilrpose a high speed s t a r t e r / a l t e r n a t o r and an o i l pump a r e mounted on t h e turbocharger. A two-way valve is placed i n t h e intake manifold. To s t a r t t h e engine, t h i s valve is i n t h e v e r t i c a l position of t h e schematic, which r e s u l t s i n a turbocharger loop independent of t h e engine. Combustor f u e l is ignited by t h e heater. This heater can be turned off a s soon a s the c a t a l y s t becomes s u f f i c i e n t l y hot. The cycle w i l l become self-sustaining a t approximately 1 / 3 of t h e maximum turbo speed, and t h e s t a r t e r now runs a s an a l t e r n a t o r . Hot, high pressure a i r w i l l flow t o t h e engine when t h e two-way valve is partia1l.y opened. The cylinder intake p o r t s a r e opened during approximately 120 craxrk-degrees, so hot a i r can flaw through two cylinders f o r preheating on cold days. The high pressure a i r w i l l next be admitted t o the engine mounted bleed a i r s t a r t e r t o crank t h e engine. The whole sequence would be automatic.
This system o f f e r s many advantages: 1. The a v a i l a b i l i t y of hot induction a i r a t s t a r t reduces the need f o r a high compression r a t i o . The engine w i l l s t a r t and i d l e a t a 10:l compression r a t i o provided t h i s hot, high pressure a i r is a v a i l a b l e t o i t during cranking. Thus, with t h i s low compression r a t i o , the f i r i n g pressures a r e held down t o 9650 kPa (1400 psig) a t f u l l load r e s u l t i n g i n low engine weight.
2. The engine w i l l s t a r t e a s i l y under cold conditions, a problem with current engines.
3. Hot s t a r t problems a r e eliminated.
4.
The engine can be -hut-off and t h e turbocharger kept running when t h e a i r c r a f t i s on the ground f o r some period. Meanwhile, e l e c t r i c p w e r , cabin heat o r a i r conditioning remain available.
This i n e f f e c t converts t h e turbocharger i n t o an APU.
5 . The b a t t e r y requirement is g r e a t l y reduced s i n c e engine cranking is accomplished by a i r pressure.
The use of synthetic o i l is required i n t h i s engine design due t o the hot cylinders. The synthetic o i l can take higher temperatures and requires fever changes than conventional petroleum bases o i l s .
Over t h e long term perhaps a method can be found t o generate an a i r f i l m between pistons and cylinder walls, i n e f f e c t , using a i r bearing technology. This would a l s o reduce the expected r e l a t i v e l y high o i l consumption which is inherent t o 2-stroke cycle engines.
The engine design concept is shown i n Figures 4 through 8. The cylinders a r e arranged i n two o f f s e t banks of three cylinders each, a c t i n g on a s i n g l e crankpin.
The r o t a t i n g and reciprocating i n e r t i a s are 100% balanced by coumer- weights on the crank cheeks.
The pendulum dampers a r e mounted t o the counter- weights and w i l l be tuned f o r t h e 4-1/2 and 6th orders. The cylinders a r e un- cooled and provided with ceramic l i n e r s .
The intake ports and the intake mi- fold a r e located a t t h e f r o n t s i d e - the cool s i d e of t h e engine. The exhaust p o r t s and exhaust manifolds a r e located a t t h e backside - t h e hot s i d e of the engine. Two exhaust manifolds a r e required t o prevent the exhaust pulse of one -vlinder t o i n t e r f e r e with t h e scavenging of the previous cylinder i n t h e f i r i n g s tlence. The piston tops a r e ceramic.
The s n a l l end of t h e connecting rods is designed t o allow f r e e r o t a t i o n of the piston. This should reduce t h e wear r a t e of the piston rings. The b i g end of t h e connecting rods is designed a s a s l i p p e r , i.e., each rod contacts only 113 of the circumference of t h e crankpin. This is possible f o r 2-stroke cycle engines because the combined load of gas pressure and i n e r t i a s is always d i r e c t - ed toward the crankpin. The bearing material w i l l i n i t i a l l y be conventional, but a study could be conducted l a t e r of s e l f - l u b r i c a t i n g and gas bearings t o eliminate the need f o ~ o i l i n t h e crankcase.
Immediately i n f r o n t of t h e f i r s t main bearing a r e 6 individual i n j e c t i o n Individual pumps were chosen t o pumps, operated by a s i n g l e lobed cam ring.
improve engine r e a l i a b i l i t y - f a i l u r e of one pump still leave 5 cylinders
operable. Also, a l l f u e l l i n e s can have the same length r e s u l t i n g i n t h e same i n j e c t i o n timing f o r a l l cylinders.
A bevel gear i n f r o n t of t h e cam ring drives the prop governor and t h e f u e l priming pump.
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A gesr reduction reduces t h e cranksh=ft speed of 3500 rpm a t take-off down
t o 2300 rpm propeller speed.
A t the back of the crankcase i s an accessory housing which contains t h e gearing f o r t h e engine o i l pump, t h e vacuum pump, and the bleed a i r s t a r t e r .
The a i r s t c r t e r drive is provided with a s l i p clutch t c ?revent engine damage i n the case of a h y d r o s t ~ t i c lock i n one of the cylinders (accumulation of f u e l Four engine mounting points a r e provid- due t o t h e leakage of a f u e l i n j e c t o r ) .
Above t h e accessory case is t h e c a t a l y t i c combustor ed on the accessory housing.
Leading t o it a r e t h e two exhaust manifolds and the a i r bypass f o r assembly.
operation i n t h e APU mode.
Figure 8 shows The turbocharger is located behind t h e accessory housing.
To the r i g h t is a t h e turbine t o the l e f t and the compressor i n t h e center.
gear housing with the high speed a l t e r n a t o r and turbo o i l pump drives.
The a f t e r c o o l e r and o i l cooler a r e located below t h e engine accessories.
The engine w i l l operate with a dry sump.
The operating parameters f o r t h e 298 kW engine a r e shown i n Table 111 and t h e sea l e v e l performance curve is included a s Figure 9.
In addition t o t h e performance projections, d e t a i l e d calculations were made of weights, t o r s i o n a l vibrations, power component stresses, turbomachinery sizing, cooling requirements, and projected c o s t s t o manufacture.
Results of each of these s t u d i e s are very favorable f o r the d i e s e l engine, however, these d e t a i l s a r e beyond t h e scope of t h i s presentation.
Emissions were not q u a n t i t a t i v e l y addressed, however, the following q u a l i t a t i v e statements a r e valid: 1. Hydrocarbons and carbon monoxide w i l l be oxidized by the use of a c a t a l y t i c converter.
2. NOx concentration w i l l be minimized due t o the r e l a t i v e l y low peak pressures (9650 kPa) and lower peak temperatures.
3. Smoke l e v e l s should be r e l a t i v e l y low s i n c e the minimum trapped A/F r a t i o w i l l always be on the order of a t l e a s t 24:l.
A s with emissions, only q u a l i t a t i v e evaluations were made of the anticipated engine noise a s l i s t e d below: 1. The c a t a l y t i c combustor and insulated exhaust stacks i n s e r i e s with the turbocharger should minimize d i r e c t combustion noise.
2. The absence of cylinder cooling f i n s should reduce externally generated vibratory noise.
3. The absence of valves, rocker arms, push rods, and camshaft should minimize i n t e r n a l l y generated mechanical noise.
4. The geared drive w i l l allow a r e l a t i v e l y low propeller speed, thereby, reducing prop generated noise.
5. Two-stroke cycle operation, however, tends t o o f f s e t some of the gains noted above.
A s was described e a r l i e r , t h i s engine's f e a s i b i l i t y relies heavily on nev technology. Following are t h e areas where e x i s t i n g technologies need t o be advanced t o make such an engine feasible: 1, Piston rings - operating i n uncooled cylinders.
2. Cylinders - ceramic components and t h e i r I n t e r f a c e with m e t a l l i c
hardware.
3. Turbo s t a r t e r / a l t e r n a t o r operating a t high speeds.
4. C a t a l y t i c combustor and its associated controls.
5. Cooling of the cylinder exhaust ports.
6. Piston lubrication.
7. Spherical connecting rod end.
8. E f f i c i e n t f u e l i n j e c t i o n systems.
A comparison of t h e 298 kW engine was made with t h e 4-stroke cycle GTSIO-520-H gasoline engine.
Table I V shows t h i s comparison i n a tabular form.
Figure 10 is a s i z e comparison.
The f r o n t a l area of t h e d i e s e l ensbl 78% of t h a t of a comparable gasoline engine.
- 149 k W Engine Design -
The technologies epplied t o t h e 149 kV engine a r e not a s f a r advanced a s i n the case of the 298 kW engine.
The 149 kW engine w i l l primarily serve t h e p r i v a t e owner market where i n i t i a l cost and e a s t of maintenance carry more weight than i n the case of the corporate a i r c r a f t .
The engine w i l l be e a s i e r t o develop and manufacture.
Figure 11 shows an a r t i s t rendering of t h e p.:oposed engine.
Figure 12 shows t h e schematic of the engine.
The following f e a t u r e s a r e incor,orated i n t h e 149 ! 7 design concept: 1. Radial configuration.
2. Two-stroke cycle C u r t i s luop scavenging.
3. Minimum cylinder cooling - reduced f i n area.
4. Variable compression r a t i o pistons (VCR) .
5. Mechanically driven c e n t r i f u g a l blower, declutched when not needed.
6. G ' o w plug s t a r t i n g a i d i n cylinders.
7. Conventional s t a r t e r and a l t e r n a t o r .
8. Conventional exhaust system (no combustor) .
9. Direct propeller drive.
Calculations of t h e heat t r a n s f e r through cylinder walls, as well a s s i n g l e cylinder engine t e s t s have conf!nned t h a t the heat f l u x is highest through the cylinder walls surrounding the comkustion chamber (when the piston is i n top The maximin gas temperature t o vhich t h e cylinder v a l l is l o c a l l y dead center).
exposed drops off f a s t a s the p i s t o n t r a v e l s dounrard, r e s u l t i n g i n a lower l o c a l average cycle gas temperature and, therefore, r reduced heat flwt. It can be safeiy predicted t h a t most cooling f i n s below t h e p i s t o n r i n g b o l t (piston i n TDC) can be eliminated vithout an appreciable e f f e c t on cylinder w a l l , piston and piston r i n g temperatures. Using t h i s approach r e s u l t s i n an increase of cooling drag vhen compared t o uncooled cylinders; but elidnates t h e need for ceramic :orponents, thus making the engine a n u & . more v i a b l e a l t e r n a t i v e f o r nearer cem applications.
S i w e t k i s smaller engine does not havz t h e independent turbocharger loop, Other means must be found t o low coapression r a t i o pistons cannot be u t i l i z e d .
It becomes necessary t o reduce the keep f i r i n g pressures d m t o 9,650 kPa.
compression r a t i o under load t o 10:l.
However, t h e engine cannot be s t a r t e d o r run i d l e a t such a low compression r a t i o . I n t h e case of t h e larger 298 kW engine, t h i s was solved by m a n s of the inaependent turbocharger loop which provides intake a i r of s u f f i c i e n t pressure and temperature t o start the engine and the c a t a l y t i c combustor vhich keeps t h e turbocharger a t a high speed during sugine i d l e operation. This is not t h e case here, therefore f o r t h i s case a variable compression r a t i o piston is rc:ommended.
The VCR piston, Figure 1 3 v a r i e s t h e compression r a t t o from 17:l at start and lw load t o 10:l a t f u l l load. This high C . R . is s u f f i c i e n t under normal ambient conditions t o s t a r t t h e engine. Even t h e 17:l compression r a t i o , h w - ev-i, does not provide a s u f f i c i e n t l y high compression temperature t o i g n i re t h e f u e l a t very low ambient temperatures.
Operation of t h e glow plug may be re- quired t o assure good s t a r t a b i l i t y . It is a l s o intended t h a t g l w plug oper- a t i o n would automatically be i n e f f e c t a t lw t h r o t t l e s e t t i n g s . This would be an added safety feature t o assure absolutely no misfiring during descent mode operation.
Scavenging of a 2-stroke cycle cylinder requires t h a t t h e intake manifold pressure exceeds the exhaust manifold pressure at any load and engine speed.
The turbocharger, however, produces a negative a P a t l c r w load. This is no
problem for 4-stroke cycle engines where t h e piston does t h e scavenging. The 2-stroke cycle engine without a combustor requires an engine drxven blower t o
produce a p o s i t i v e A P across t h e cylinders a t low loads. The blower w i l l be
disconnected a t the load point where the turbocharger provides a p o s i t i v e n P .
It a l s o 3ecame obvious e a r l y i n the design phase of t h e 149 kW engine t h a t a d i r e c t drive would r e s u l t i n a smaller engine paclcage and a weight reduction.
The e ~ g i n e r e l i a b i l i t y is somewhat improved by t h i s appru.-.ch due t o fewer p a r t s required.
The chosen BWEP of approximately 1200 Wa 2s 100 kPa higher than t h e BMEP of t h e larger 298 kU engine.
The much lower crankshaft speed d i c t a t e d by t h e d i r e c t propeller drive w i l l r e s u l t in b e t t e r scavenging and, hence, a l a r g e r
amount of a i r trapped i n the cylinde .. It should, therefore, be possible t o
obtain :.iis higher BMEP without a- i n c e a s e of cylinder temperatures. The detailed cycle calculation^ bear t h i s out.
'fie 143 kU engic;e concept design then is shown i n t h e Figures 14 thrcugh 18.
The cylinders a r e arrangdd i n one bank of four cylinders. The r o t a t i n g and reciprocating i n e r t i a s a r e 100% balanced. 'Ihe cylinders have a liptited number of cooling f i n s t o cool t h e c o d u s t i o n chamber. The necessity f o r a gear driven blower a t the back s i d e of t h e engine made it more p r a c t i c a l t o have t h e cylinder intake port a t t h e back s i d e and the exhaust manif@lds a t t h e front. The exhaust manifolds w i l i be insulated t o avoid radiation t o the i n j e c t i o n pupps.
TWO exhaust manifolds a r e required t o avoid pulse interference between cylinders.
The connecting rods a r e t h e s l i p p e r type. The b i g weds are wider than i n t h e case of the 298 %!r' engine t o coapensate f o r t h e reduced circmaferential coatact length.
The use of synthetic o i l is not e s s e n t i a l i n t h i s engine because of lower cylinder temperatures (compared t o the ceramic), but may be advantageous t o extend the periods betveen o i l changes.
Four individual i n j e c t i o n pumps a r e provided driven off a single fabe cam ring, The c e n t r i f u g a l blower is driven off t h e propeller shaft through a lay s h a f t which is located above t h e crankcase betveen t h e cylinders d l and 14.
This arrangwent was chosen r a t h e r than a d r i v e f r a m tile rear end t o avoid torsional problems. The nodal point lies c l o s e t o t h e l a r g e s t i n e r t i a member of the crankshaft system, t h a t is the propeller. Putting t h e blower d r i v e gear nepr t h i s point reduces t h e input of torsional amplitudes i n t o the blower drive.
The lay s h a f t , which is a q u i l l s h a f t , further i s o l a t e s che blower from t h e crank- s h a f t vibrations. Houever, t h i s feature forced t h e use of a d i r e c t propaller drive. Ta put a propeller reduction gearing i n f r o n t of the blower d r i v e vould have led t o an unacceptable length of the engine. A weight a n a l y s i s f o r t h i s particular engine shoved t h a t the d i r e c t d r i v e with the inherent larger p i s t o n displacement still r e s u l t s i n a l i g h t e r engine than the geared drive.
The blower d r i v e is provided with two clutches. One, t h e magnetic clutch, disengages the blover d r i v e once t h e t u r t o c b r g e r has c o w up t o speed, The location of t h e magnetic clutch is such t h a t =s much of blower d r i v e a s possible is disengaged t o prevent unnecessary drag on tile engine. A d i s c type s l i p clutch is provided t o prevent large t o r s i o n a l amplitudes a s they occur a t lw engine speeds due t o c y c l i c i r r e g u l a r i t y from reaching t h e blower.
The turbocharger is mounted behind the engine, a s a r e t h e o i l cooler and the aftercooler. ZLo versions of t h e engine w e r e drawtr. One, a s shown, f c r a n a i r c r a f t v i t h fixed landing gear. A second versiim of t h e engine was d r a m which accommodates a r e t r a c t a b l e nose gear. The coolers a r e moved outboard and the turbocharger raised t o provide space between cylinders #2 and 83 f o r t h e nose gear s t r u t .
Table V presents the operatinp parameters of the 149 kV engine concept and Figure 19 shows th:. pro2ected f u e l consrrmption curve for t h i s engine.
A s with the 298 kW engine, calculations were made t o define power component s t r e s s e s , turbocharger and cooler s i z i n g , t o r s i o n a l vibration d e f i n i t i o n , as well a s c o s t and t light projections.
Table V I and Figure 20 aze presented t o show comparisons v i t h today's state- of-the-art gasoline engines.
a11 comparisons favor t h e d i e s e l Again, a s v t t h t h e l a r g e r engine, ewine.
EngineIAirframe I n t e g r a t i o n This study was conducted as a subcontract by Beech A i r c r a f t Corp. t o e v a l u s t e t h e i n t e g r a t i o n of the proposed d i e s e l a i r c r a f t engines I n t o f u t u r e airframes and t o detenaine t h e e f z e c t of t h e engiae on a i r c r a f t perforaaace m d operating c o s t s . The r e s u l t s were then compared with corresponding d a t a f o r c u r r e n t p r d u c t i o n type gasoline engine powered a i r c r a f t .
Engine I n s t a l l a t i o n I n s t a l l a t i o n design layouts were made which show t h e 298 kk' d i e s e l mounted on a w i n engine a i r p l a n e and the 169 kg engine i n s t a l l e d i n a s i n g l e engin* a i r c r a f t with r e t r a c t a b l e landfng gear. The Figures 21 through 23 show t h e twin engine i n s t a l l a t i o n ; t h e Figures 2 1 through 26 show t h e s i n g l e engine install- a t i o n . Figure 27 and 28, t h e t h r e e view drawings, are based on t h e wing a r e a s indicated by t h e performarace s y n t h e s i s program, t h e engine drawings and standard a i r p l a n e proportions. Some p e r t i n e n t f e a t u r e s about t h e i n s t a l l a t i o n a r e as follous:
1. Engine m u n t s a r e of two b a s i c types - c a n t i l e v e r and bed mount. A
e a n f i l e v e r mount from the f i r e v a l l was used i n t h e twin and a bed mount incorporating the nose gear support s t r u c t u r e was used i n the single. "Dynafocal" type Eocnts woull be used with the c a n t i l e v e r method t o minimize v i b r a t i o n transmission t o the airframe.
1. The induction system i n both cases would be a SACA f l u s h i n l e t , duct- ing and an a i r f i l t e r . Alternate a i r would be a v a i l a b l e t o t h e engine through a door operated by d i f f e r e n t i a l pressure.
3.
Both engi.nes have a dry o i l sump and require e x t e r n a l o i l tanks mounted i n the engine cmpartments.
I. Both engines would have cooling a i r i n l e t s p-oviding a i r t o a plenum chamber. Ducts from the plenure would d i r e c t a i r t o individual c y l i n d e r s , o i l coolers. a f t e r c o o l e r s and f u e l i n j e c t o r s a s needed.
On the s i n g l e .
c o d i n g s i r e x i t s a r e outboard of the nose gear on the lower s i d e of the cowling. Exits from the twin n a c e l l e would be a t t h e laver a f t end.
5. The i n s t a l l a t i o n drawings were done i n enough d e t a i l t o i n d i c a t e t h e f e a t - , e s noted above and t o provide reasonable assurance t h a t no major i n s t a l l a t i o n problems would be encountered with t h e proposed d i e s e l engine concepts.
A i r c r a f t Configurations Three v i e w sketches of the airplane are shown i n t h e Figures 27 and 28.
Following a r c some c h a r a c t e r i s t i c s of both planes: 1. Propeller Data.
Prop. diameter 2.057 n Prop. speed a t take-of f 2,345 rpm Tip speed a t take-off 253 mr'sec = .74a a = Velocity of sound = 20.06 m m / s e c (T i n OK) A t standard aPlbient temp. 15.50C a = 20.06 v m 5 . 5 = 341 d s e c Prop. speed a t economy c r u i s e 1,790 r p m Tip speed a t ecommy c r u i s e 193 d s e c
Prc? . ground clearance 330 nr
2. Sight Angles.
The p i l o t ' s s i g h t angles f o r t h e tvia are indicated by A and B (Figure 27).
The c e n t e r l i n e angle over t h e nose, A, as i3dicated is about 120. If t h e a i r p l a n e were l o f t e d , t h e angle from t h e p i l o t ' s a c t u a l eye p o s i t i o n vould be about 1 8 O which is considered more than zdequate. The srallest l a t e r a l angle E is 100.
This is a l s o more than adequate e s p e c i a l l y c o q a r e d t o sorae current pis-on engine twins with l a r g e r nacelles.
3. A i r c r a f t Data.
Twin Engine Twin Engine Diesel Gasoline Airfraae minus engine (a) kg 1,860 1,860 Engines (2)
Empty weight (a) + (b)
Payload Fuel load
Useful load (d) + (e)
Max. tzke-of f weight ( c ) Wing span Length T a i l height T a i l span Wing area Figure 28 shows the s i n g l e engine a i r c r a f t . C h a r a c t e r i s t i c s are: 1. Propeller Data.
Prop. diameter 2.134 m Prop. speed a t take-off 2,400 r p m Tip speed a t take-off 268 m/sec = .79a prop speed a t economy c r u i s e 1,800 rpm Tip speed at ecaooly cruise Prop ground clearawe 2 . The c e n t e r l i n e angle over t h e nose f o r t h e s i n g l e engine a i r p l a n e C, is This should correspond t o z c t u a l p i l o t ' s viewing angle of about 12O.
go.
This is probably adequate, e s p s c i a l l y vhen compared t o some of today's long nose s i n g l e engine a i r c r a f t .
3. A i r c r a f t Data.
Single mine Single E a g h D i e s e l Gasoline Airframe minus engine 667 (a) ke. 667
Engine -
4 t y weight (a) + (b)
Payload Fuel load Useful load (d) + (e) Max. take-of f veight ( c ) Wing span Leagth T a i l height T a i l span Wing area A i r c r a f t Performance Evaluation The m j o r t o o l used i n t h e a i r p l a n e design synthesis was a sa-t modified version of t h e synthesis method o r i g i n a l l y developed f o r t h e NASA =TE (General Aviation Turbine Engine) Study. The process - w a s simplified f o r t h i s purpose s i n c e taks-off and c r u i s e pover could be specified a s program inputs. The program is not accurate enough nor does i t account f o r enough v a r i a b l e s t o a c t u a l l y design airplanes, but it is considered adequate t o i n d i c a t e trends i n r e l a t i v e s i z e and performance f o r airplanes t h e o r e t i c a l l y equipped with s u f f i c i e n t engines. The w i n point t o bear i n mind when looking at t h e r e s u l t s of the program is t h a t t h e objective is t o provide an indication of t h e differences i n perforaance and c o s t b e t w e n d i e s e l and gasoline powered airplanes. The methods used i n estimating throughout are no b e t t e r than 5 t o 1CZ accurate, but the uniform assumptions and metilods used i n a l l cases vould make the r e s u l t i n g differences good indications of t h e trends t o be expected.
This is t h e proper objective f o r a conceptual investigation.
Hypothetical gasoline and d i e s e l powered a i r p l a n e s were synthesized and compared i n two ways. I n one case, t h e airframe was held constant and t h e mission p r o f i l e was allowed t o change when t h e powerplant type changed. I n the o t h e r case, the mission requirements w e r e held constant and the a i r p l a n e needed t o perform t h a t mission changed s i z e a s necessary t o meet the mission requirements.
These comparisons were made f o r both the s i n g l e 149 kW 3nd t h e twin 298 kU engine air?lanes.
The r e s u l t s of t h e a i r c r a f t performance simlatioa program are shaun in the Tables F f I and VIII.
Table VII shovs t h e differences in a i r c r a f t p e r f o m e f o r a fixed airplrrw site.
The fixed parameters are:
- b i . take-off weight
- Max. land- veight
- Take-off distance
- Landing distance
- S t a l l speed
- Wing area
The advantages of the d i e s e l s with t h e i r high c r u i s e power output sad lw fuel ccmsu~prioas can be r e a d i l y seen in the basic parareters of range, speed, and payload.
The advantages of t h e d i e s e l s with t h e i r high c r u i s e power output and l w f u e l c o n s ~ t i o n s can be reatilly seen i n t h e basic p a r a r e t e r s of range, speed, and payload.
Table VIII shows t h e dizferences i n a i r p l a n e s i z e f o r a fixed performance.
The fixed parameters are:
- Paylead
- Xax. c r u i s e speed
- Range
The gasoline pwered a i r p l a n e s a r e bigger and considerably less e f f i c i e n t .
Operating Cost Csi'mates Production c o s t s were estimated by assuming t h a t nev a i r p l a n e s would be designed and equipped with the d i e s e l engines and, a l t e r n a t i v e l y , coapatible gasoline engines. Development, material, ad labor c o s t s w e r e chosen t o be of roughly the correct magnitude, but a r e intended primarily t o i l l u s t r a t e c o s t differences due t o using d i e s e l rnstead of gasoline engines. Operating c o s t estimates were made using figures obtained from current estimates of average operating costs.
The acquisitton cost estimates were based on information from the a i r p l a n e synthesis process. The a i r p l a n e empty weights vere t h e main parameters used v i t h FY79 r a t e s f o r labor, material costs, and OPI engine costs. The estimating methods used a r e based on h i s t o r i c a l data and "learning curve" theory. An a i r - frame weight was estimated from the operating empty weight. This w a s used with estimating d a t a t o get material weights t o which material c o s t could be applied.
Manhnur per pound data were used t o get labor content t o which labor rates were applied. A productten run of 600 units was used.to amortize a s s 4 development costs and to locate facrors on the learning curves. When a basic factory cost was swmned up, assumed ~anufacturer's and dealer's mark-ups vere applied.
Costs were included for currently typical optional equipment a d avionics selections.
The final total represented a dealer's price tag figure for a typically equipped airplane. Both the single and the twin were considered to be all neu designs.
The same sets of reasonably realistic assumptions vere used throughout so the results are quite adequate for looking at differences between gasoline and diesel airplane prices within the overall accuracy of this study. Acquisition price percentage changes from the diesel to the gasoline engine pavered airplanes is shown on the cost srpaaries. See Tables IX and X for the twin and single engine airplanes, respectively.
The columns headed "gasoline" refer to the airplanes for equivalent size to the diesels but with the iaission capability as indicated in the performance estimates. The "equal plane performance gasoline" column refers to the airplanes that will do the same missions as the diesels but are bigger and less efficient.
The cost suaary tables s h w the considerable overall cost advantages of the diesel powered airplanes.
Gasoline airplanes of equivalent size cost less initially but this advantage is not sufficient in view of the reduced mission capability and higher overall costs. The biggest factors in raising the gasoline airplanes operating costs are fuel and overhaul expense, as indicated.
Propeller Noise Estimates Propeller performance estimates were made to get some idea of the propeller sizes needed to realize a cruise propulsive efficiency of -85 for both the twin and single engine airplanes. These calculations indicated that a two-blade, 84 inch diameter, constant speed propeller will vurk for the single engine airplane.
The propellers indicated for the twin are 81 inch three-blade. Estimates of 1000 ft. flyover noise predict valstes of 72 dB(A) for the single and 74 OB(A) for the twin. These compare favorably to the limits of 77.5 dB(A), respectively.
Limits are based on airplane weight as set out in FAR 36, Appendix F. A favorable carrection factor can reasonably be expected, creating a greater margin relative to the limits.
The correcticn factor is based on detailed take-off performance estimates that are beyond the scope of this st-ady. Even without correction factors, the noise regulations appezr to present no problem for the conceptual diesel airplanes.
186 kW (250 HP) Engine Configuration -9 third engine configuration is currently under evaluation and design definition. This engins is rated at 186 kW (250 UP) net shaft power at 25.000 ft. cruise altitude. Table XI outlines the pertinent features of this engine configuration. Engine specifications are summarized in Table XII.
As shown in t h i s table, a cruise fuel consumptioa value of .36 lb/hp-ht i.
projected f o r t h i s engine. Some pertinent data comparing t h i s projected fuel consmption with other engines is shown in Table X I I I . Mote tbat the projected v a : -. is relatively conservative compared t o actual n u m h g engines, c m f S ~ the tact that an engine such as proposed is within reach.
A study indicates that the diesel engine praises to be a superior pouer- plant for general aviation a i r c r a f t for the follaving reasons: 1. ?he diesel engine offers high cruise power a t a l t i t u d e and l o w fuel scmsumption. This w i l l result in improved range, high cruialng speed and more payload for a diesel englned a i r c r a f t .
2. The diesel powered airplane has a considerable overall cost advantage.
Gasoline airplanes of equivalent s i z e cost less initiaLly, but t h i s advantage is offset by reduced mission capability and higber operatlag costs.
3. The diesel engine presents no installation p r o b l w . Altbough tbe radial configuration is different than current gasollne engines, the mounting t o the airframe is essentially tbe sare and requires no major a i r f rare modifications.
5 . The independent turbo loop provides:
- Easy cold and hot s t a r t s
- Can crank engine indefinitely
- Electric power available independent of engine operation (APU wde)
- Reduced battery capacity
- Cabin cooling or heating available while a i r c r a f t is on the ground
6. The r a d i a l cylinder configuration results Ln:
- Low engine weight
- Reduced engine f r i c t i o n
- Absence of piston i n e r t i a forcaa
- Compactness of the power package
7. The two-stroke cycle feature results in:
- Weight reduction
- Improved r e l i a b i l i t y due to fewer parts
- Reduced frontal area
8 . The following key technologies will be required to demonstrate the feasibility of the engines proposed in this study:
- Coaabustionlscavenging in 2-cycle loop scavenged system
- High pressure ratio, high efficiency turbocharger
- High pressure fuel injection system
- High speed starter/alternator .
1985-2000 (400 HP Engine)
- All of the above
- Ceramic components
- Advanced labricants (solids, air bearings, etc .)
- Catalytic combustor
TABLE I Pnrkus Aircmft D h d s N o . k n s l r o L . D l r O L ~ .
Ylb ro61 Conlig.CldrCodlngCIL- - -
Rdw *
1. PwLVd 8ir 2. Guiblrson R.dw liquid 30.A S(kschmpQ Radii1 4. efistd pho.nix air 5. LbmlovLI LOD ma .h 6. H i m CNWt l4F2 Rldial air 7. Ynr#w, SH18 Rdw 8il OF2 60- v IiQuid 8. MOWOOOS leuid 9. Junksn 204 oRw=d rquid 10. Judms 205 mw=d liquid 11. Junkers (1)' 207 Turbo opposed liquid 12. N.pier 0 . Nomd Flat 13. McCulbch (3)' TRAMlaO Radial air 'Nurnbsrr in parentheses refer to list of references at the end of this rapwt.
TABLE 11 Specific Data of Previous Aircraft Diesels Pman PWonHw( w e Pactcard Guibewn Deschamps Bnstol Zbropvka Hlspano Salmson Merccdcs Junkers 204 Junkers 205 hnkers 207 Nap~er McCulloch TABLE Ill
Operating Panmeters - 2911 kW E n g h
Altitude 0 6.096 meters 6.096 Power 298 298 194 kW RPM 3 . 5 0 0 3,500 2,675 Displacement 4 . 7 1 4 . 7 1 4 . 7 1 liters Bore x Stroke 100 x 100 100 x 100 100 x 100 mm BMEP 1,085 1,085 923 kPa Compressor Pressure Ratio 4 . 0 6 : 1 8.30: 1 6 . 2 5 : l Nominal Compression Ratio 1 3 . 1 8 5 : l 1 3 . 1 8 5 : 1 1 3 . 1 8 5 : 1 Effective Compression Ratio 1 0 . 0 : 1 1 0 . 0 : 1 1 O . O : l Barometric Pressure 1 0 1 . 4 46.4 6 6 . 4 kPa Ambient Temperature 1 5 . 5 -25 -25 'C lntake Manifcld Pressure 402.4 370.2 277.6 kPa lntake Mnifold temperature 116 116 116 'C Exhaust Manifold Pressure 309.5 284.8 245.5 kPa Scavenge System Curtis Loop Curtis Loop Curtis Loop Sca~enge Ratio 1 . 5 1 . 3 1 . 3 Ratio BoosUBack Pressure 1 . 3 1 . 3 1 . 1 3 1 He~ght lntake Ports 20.65 20.65 2 0 . 6 5 mm Height Exhaust Ports 26.14 26.14 mm 26.14 61' 4 7 ' lntake Ports OpenlClose 6 1 ' 4 7 ' 6 1 ' 4 7 ' BBDCIABDC Exhaust Ports OpenlClose 6 9 ' 3 9 ' 69-39' 6 9 ' 3 9 ' BBDCIABDC BSFCsngine 212.9 1 9 4 . 6 gkW-hr.
206.8 BSFCcombustor 1 8 . 2 6 . 1 0 glkW-hr.
BSFC-powerpack 225.0 219.0 194.6 glkW-hr.
Fuel Flow Powerpack 6 7 . 1 65.3 37.8 kglhr Air Density .00279 .00256 ,00205 kg/f AirIFuel Ratio 27.50 24.59 25.47 TABLE I'J Comparison of GTSIO-520-H Gasoline and GTDR-290 Aircraft Diesel Engine 2.slmk* C* &stroll* c m GTSK)-SZDH 0TDRJ)O
- Engicr
-- * - --E!
6 cyl. opposed 6 cyl. radial Configuration 4.71 Displacement .! 8.52 Take-off RPM 3400 3500 Rated max. take-off power kW 280 298 Rated max. for cruising kW 210 298 Prop speed at take-off RPM 2278 2345 BSFC glkW-hr: Take-off 100?/0 power cruise 65% power cruise Dimensions: Length mm V1:dth mm Keight mn, Er,gtne weight dry, kg TABLE V E n g h Opofoting Pwrmohn r o o v r k r r 1 - clr*.
Altitude 0 3,048 Power 149 119 RPM 2100 2400 Displacement 3.14 3 . 1 4 Bore x Stroke 100x 100 ' 0 0 x 100 BMEP 1,187 1 . 1 8 7 4 . 1 6 : l 6 . 1 0 : l Compressor Pressure Ratio Compression h t i o variable Variable Max. C.R. 173 (effective) 1&1 (eftective) Min. C.R.
Barometric Pressure 1 0 1 A 69.6 69.6 kPa
Ambient Temperature 1 5 . 5 - 5 -5 'C
411.8 411.8 lntake Manifold Pressure 200.9 kPa lntake Manifold temperature 116 r 16 1 1 6 ' C Exhaust Manifold Pressure 316.8 316.8 255.4 kPa Scavenge System Curtis Loop Curtis Loop Curtis Loop Scab~~rge Ratio 1 . 3 1 . 3 1 . 3 1 . 3 1 . 3 1 . 1 Ratio BoosUBackpressure 2 0 . 1 3 mm Height Intake Ports 2 0 . 1 3 2 0 . 1 3 Height Exhaust Ports 27.15 27.15 2 7 . 1 5 mm
* 6 1 ' *6l0 a 6 1 BBDClABOC
lntake Ports OpenlClose Exhaust Ports OpenlClose t 7 1 ' a 7 1 ' 7 BBDClABDC 222.0 2 2 8 . 1 209.8 glkW-hr.
BSFC Fuel Flow 20.3 kglhr.
3 3 . 1 34.0 AirIFuel Ratio 26.6 26.0 2 4 . 0 TABLE VI Comprrlron d TSIO-3o.E Gasoline and TOR-192 Aircnft D M Engine 2afeka C* -cFI.
tSKIJ(M TDIEln2 -EnOln -Engh.
Configuration 6 cyl. opposed 4 cyl. radial Displacement 1 5 . 9 1 3.14 Takeoff RPM 2800 Rated m u . takeoff power kW 149 149 Rated max. for cruising kW 112 149 Prop drive direct direct BSFC glkW-hr: Takeoff 3 7 7 . 1
100% power cruise -
65% power cruise 267.6 Dimensions: Length mm 1188 Width mm 795 Height mm 672 Engine weight dry, kg 174.6 TABLE VII Comparison Gasoline and Diesel Aircraft Engines Airplane Size Fixed, Variable Performance Twin-Englm Twin E n d n Gasolirw' - -:- ---- - -. - - - -.
Rated power kWlRPM 14912400 29812300 (ea) 29812267 (ea) Max. take-off weight (gross) kg 1349 3654 Max. landing weight kg 1349 3654 3654 Standard empty weight kg 829 2275 2385 Useful load kg 520 1378 1269 Usable fuel 2511180 9081653 8321598 Payload (with full fuel) kg 340 726 671 Altitude -ml".b power 30481 100 ',o 304e175% 7620181.5% 7620175% Ma,. crurse speed kmlhr 324 291 474 448 Range km 1481 1468 2592 1726 Altttude - rnl0,~ power 304817540 30481 75 % 7620/81.5% 7620175% Speed kmlhr 289 291 474 448 Range km 1 968 1468 2592 1 726 Take-off dtstance (normal. OV. 15 m) n 579 579 70 1 701 Landlng dis:ance (normal. OV 15 m) m 369 369 677 677 Stall speed (land~ng) kmlhr 85 85 135 135 m : Wlng area 17.7 17 7 22.6 22.4 'All englnes are turbocharged w- krtglma Gaalm-
- - --
+ l l ' r ine Configuration Features