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NASA TECHNICAL NASA TM X-71670 MEMORANDUM C:) I-I (NASA-TM-X-71670) TECHNOLOGY FOR REDUCING N75-1823' (A AIRCRAFT ENGINE POLLUTION (NASA) 38 p HC <$3 Z CSCL 21A Unclas G3/07 12449 o
TECHNOLOGY FOR REDUCING AIRCRAFT ENGINE
POLLUTION
by Richard A. Rudey and Erwin E. Kempke, Jr.
Lewis Research Center Cleveland, Ohio 44135 TECHNICAL PAPER to be presented at 1975 Business Aircraft Meeting and Engineering Displ of sponsored by the Society of Automotive Engineers Wichita, Kansas, April 9-11, 1975 TECHNOLOGY FOR REDUCING AIRCRAFT ENGINE POLLUTION by Richard A. Rudey and Erwin E. Kempke, Jr.
National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio ABSTRACT Programs have been initiated by NASA to develop and demonstrate advanced technology for reducing aircraft gas turbine and piston engine pollutant emissions. These programs encompass engines currently in use for a wide variety of aircraft from widebody-jets to general aviation.
Emission goals for these programs are consistent with the established EPA standards.
Full-scale engine demonstrations of the most promising pollutant reduction techniques are planned within the next three years.
Preliminary tests of advanced technology gas turbine engine combustors indicate that significant reductions in all major pollutant emissions should be attainable in present generation aircraft engines without ad- verse effects on fuel consumption. Fundamental-type programs are yielding results which indicate that future generation gas turbine aircraft engines may be able to utilize extremely low pollutant emission combus- tion systems.
INTRODUCTION This paper describes some of the techniques that are being developed and employed to reduce aircraft engine pollutant emissions. The entire spectrum of engines covered by the 1979 EPA Standards will be impacted by the advanced technology development programs now underway. Future engine designs may be affected by fundamental studies also in progress.
Results from these advanced technology programs are needed to establish realizable levels for emission pollutant regulations without sacrificing fuel economy.
The Clean Air Act of 1970 charged the EPA with the responsibility to establish acceptable exhaust emission levels of carbon monoxide (CO), total unburned hydrocarbons (THC), oxides of nitrogen (NOx), and smoke for all types of aircraft engines. In response to this charge, the EPA promulgated the standards described in detail in reference [1]* and sum- marized in table I. The standards were issued in 1973 and have pro- vided a significant incentive for the timely development of advanced technology to reduce aircraft engine exhaust emission pollutants. Prior to this time, both the industry and the government were involved in re- search and development of low emission gas turbine engine combustors.
This research provided some input to the proposed levels. Considerable success has already been achieved in reducing the smoke of current jet aircraft engines. The principal technique used was to "lean-out" the combustor primary zone thus eliminating the fuel-rich combustion that produces carbon particle formation [2]. Most of the current JT8D engines, which are used in the 727, 737 and DC-9 aircraft, now have been retro- fitted with the low smoke combustors. The newer high pressure ratio gas turbine engines, e.g., JT9D and CF6, employ lean primary zone combus- tors and are very low in smoke emissions. Because of the progress in smoke reduction, this paper will not describe techniques specifically de- signed to reduce smoke. However, some of the approaches used to reduce gaseous emissions are also effective for reducing smoke.
Numbers in brackets designate References at end of paper.
broadly divided into Aircraft engine exhaust emissions can be II (values five principal categories of constituents as shown in table we are for a gas turbine engine). The constituents that shown are combus- with are those resulting from inefficient principally concerned tion (CO & THC), heating the air in the combustion process (NO, NO NO ) and impurities contained in the fuel or more commonly called x SOx). The SO emissions can be reduced to negligible (SO , SO or x 2 3 quantities by reducing the sulphur content in the fuel. The CO, THC, inefficient combustion and heating and NO emissions that are caused by x be controlled by engine and/or combustor design.
of the air can developed to reduce gaseous Some of the advanced technology being gas turbine and piston aircraft engines emissions for current and future considerable work is described and discussed in this paper. Although is being supported by other government agencies (DOD, FAA, & EPA), paper is information used in the preparation of this the main source of at or under the sponsorship of the from the programs being conducted The paper is divided into two main NASA Lewis Research Center.
and piston aircraft engines.
categories: gas turbine aircraft engines will be more thoroughly de- The effort on gas turbine aircraft engines of the on-going low emission advanced tech- scribed since the majority these engines.
nology development has been for GAS TURBINE ENGINE TECHNOLOGY pollutants varies with engine operating The level of gaseous emission as illustrated in figure 1.
conditions, for most conventional combustors, fuel burned) levels of CO and THC The emission index (g pollutant/kg of such as idle, where are highest at the off-design operating conditions, condition combustion efficiency is lower than at the design operating (near takeoff). Conversely, the NOx (normal practice is to express NOx levels in terms of NO ) is the highest at the takeoff condition primarily The rate of because the combustion gas temperatures are their highest.
NOx production is known to be a function of the gas temperature and the to the high tem- time that free nitrogen and oxygen are exposed residence condition to the com- The relationship of engine operating perature [3].
bustion process is shown in figure 2. This figure relates the causes, at the two ex- and cures for the pollutant emissions effects, results, power takeoff.
i. e., low power idle and high treme operating conditions, Tin, and combustor inlet temperature, During low power idle operation, effects which ratio, F/A, are low causing the pressure, Pin, and fuel-air and thus the production of CO and contribute to combustion inefficiency THC. At high power takeoff, combustor inlet temperature and pressure, results in high combustion flame and fuel-air ratio are all high which all of which contribute to the plus the other effects shown, temperature, engines must operate of NO Since aircraft gas turbine production x .
takeoff) and many conditions between effectively at both extremes (idle and to all operating con- them, low emission combustors that are compatible in ditions must be developed. If we observe the list of "cures" shown that a dilemma exists at the two operating figure 2, we can recognize extremes. Those "cures" which can reduce CO and THC are directly improved of those required to reduce NOx with one exception; the opposite challenge then is to develop advanced combustor fuel distribution. Our of the needed "cures" at a particular technology that can take advantage effecting the pollutant engine operating condition without adversely conditions.
production at the other operating CONTROL TECHNIQUES - Some of the techniques which POLLUTION schematically can be used to reduce low power emissions are illustrated in figure 3. The "tulip" spray pattern shown is indicative of poor fuel from low fuel flow and pressure in pressure- atomization resulting shown can improve atomizing type fuel nozzles. All three techniques fuel nozzles use high pres- fuel atomization. The air-assist and air-blast the fuel. The fuel scheduling sure and high velocity air to aid in atomizing with fuel.
approach reduces the number of fuel nozzles that are supplied Thus, for a given F/A the fuel flow through each nozzle is increased and atomization is improved. In addition, fuel scheduling increases local fuel-air ratio and can improve fuel distribution. Applying any or all of these techniques improves combustion efficiency.
which can be used to reduce high power Some of the techniques in figure 4. In a conventional emissions are illustrated schematically combustor, near stoichiometric fuel-air ratios (the fuel-air ratio present in the flame zone needed to completely burn all of the fuel) are promote the formation of thus producing high gas temperatures which the flame zone is rather large resulting in long residence NO [4]. Also, x the leaner mixture and premixing techniques times in the hot gas. Both in the flame zone to reduce are aimed at controlling the gas temperature at fuel-air ratios much less the NO formation by allowing combustion x swirl-can technique (many (lean combustion). The than stoichiometric provides some modules arranged in an annular array) small combustion time be- combustion and also reduces the residence capability for lean down into many small zones instead of cause the flame zone is broken one large one.
control techniques, which are accomplished In addition to the above by combustor design, other approaches such as water injection for NO x bleed for improving idle efficiency reduction and increasing compressor of emissions. Manipulation are also effective for reducing pollutant such as reference velocity, VREF, is combustor operating variables technique [5].
another effective - The effectiveness of EVALUATION OF CONTROL TECHNIQUES are continuing to be evalu- control techniques have been and the various programs. Funda- in-house and contract research ated by NASA through are being full scale experimental combustor studies mental as well as utilized.
approach to achieving Studies - One very simplified Fundamental is to use the in CO and THC emissions at idle substantial reductions One method of fuel nozzle to improve fuel atomization.
air-assist type High pressure schematically in figure 5.
using this approach is shown through a valve combi~stor inlet pressure) air is supplied (higher than the secondary fuel supply line of a duplex fuel and tee arrangement into nozzle since fuel is supplied only to the nozzle. This is possible at idle air For high power operation, the compressed primary fuel passage.
secondary both the primary and fuel supplied to would be shut off and would in an engine use this approach To in the nozzle.
fuel passages shown as or supercharger compressor sort of external some require air high pressure of supplying resultant effect The on the schematic.
the 6, where is shown in figure combustor a can-type the nozzle of to a function of plotted as and NOx are of CO, THC, emissions exhaust were reduced by THC emissions pressure.
air-assist differential the negligible increase of three. A a factor eight and CO by a factor of about conducted using the Similar studies production was observed.
in NO re- significant also produced approaches scheduling and fuel air-blast [7].
in CO and THC.[6] and ductions air on the fuel and and premixing prevaporizing The effect of rig shown a flame tube at Lewis using under study of NOx is formation Jet-A is or atomized Propane 7. Gaseous in figure schematically with sufficient distance holder flame of a perforated injected upstream to the mixture fuel-air prevaporized/premixed a completely to provide can be gas samples Exhaust test section.
(flame zone) zone primary to insure flame holder of the downstream at varying distances extracted position.
measurement at the sample is completed that combustion figure 8 where presented in to date are obtained Some of the results a as two inlet temperatures is:.plotted for index of NOx the emission ratio to the of local fuel-air ratio, P (ratio equivalence function of g/kg) of NO (<1 low values Extremely x fuel-air ratio).
stoichiometric 5) for the two ratios (<0. 6 - 0.
lean equivalence at the very were obtained well-stirred agreement with The good tested.
inlet temperatures premixing was indicates that good model predictions reactor (WSR) of the combustion at the edge were obtained lowest values obtained. The combustion in flow caused slight perturbation limits and any flammability con- these results are stability sensitivity, Because of this blowout.
emissions for limit of NOx lower be near the fundamental sidered to is It used in this investigation.
of experimental hardware the type experiment for this conditions the operating note that to important con- duplicate do not necessarily and very carefully controlled were and of inlet pressure for the levels engine except ditions in an actual a typical supersonic cruise condition.
temperature which simulate More details of this experiment are given in [8].
that the premix Fundamental test results such as these, indicate in gas candidate for achieving low values of NOx approach is a prime A similar experiment with similar turbine combustion systems.
under contract with Advanced Technology results, [9] is being conducted Laboratories.
is being conducted Another evaluation of the premix technique Harvestor using under contract to the Solar Division of International hardware, figure 9. Concepts A "quasi-combustor" type tubular test very lean com- two different approaches to achieve and B represent Concept A uses jets of premixed bustion using premixed fuel-air.
of hot gases into the flame fuel-air to create a large recirculation stability at very low zone which aids in maintaining combustion flow field to create ratios. Concept B uses a rotating equivalence C provides premixed fuel-air to a catalytic a similar effect. Concept catalytic bed, the in which the H, C, O reactions occur. In the bed at levels below which NOx formation gas temperature can be controlled is expected to be negligible (<1800 K). Testing of these concepts is completed in mid 1975.
on the evalu- Combustors - The majority of effort Experimental conducted in-house by ation of low pollutant emission combustors shown in fig- has been with the swirl-can-modular combustor NASA array of 120 10(a) is a photograph of a full-annular ure 10. Figure arranged in three radial rows. A cross-sectional swirl can modules 10(b) and the components view of this combustor is shown in figure 10(c). Each module of the swirl can module are illustrated in figure flame stabilizer. Fuel composed of a carburetor cup, swirler, and is cup where it premixes with air flowing is injected into the carburetor created cup and then passes through a swirler into the wake through the which acts as a quasi-bluff body in the air flowing by the flame stabilizer fuel-air mixture provides for a small around the module. The swirling stable flame zone in the stabilizer wake.
zone and premixed fuel-air The combination of a small flame of gas tempera- provides for low residence times and some degree ob- in the flame zone. Typical NO emission results ture control x combus- this type of combustor, compared to conventional tained with in figure 11. Thirty to fifty percent reductions in tors, is shown at operating conditions representative NO emissions are indicated x This of narrow and wide body commercial jet aircraft engines.
only one row combustor can also use the fuel scheduling (fueling emissions.
of modules) technique for reducing CO and THC have also been Other types of NASA experimental combustors for reducing pollutant emissions.
evaluated in terms of their potential has been used to further study the A double-annular combustor [10] THC at idle. A NASA effects of fuel scheduling for reducing CO and small (5-10 lbs/sec) reverse and axial in-house program to study will be performance and emission characteristics flow combustor initiated in 1975.
of ASSESSMENT OF CONTROL TECHNIQUES - The degree in applying the various control techniques discussed difficulty involved hardware must be assessed in relation to to actual engine acceptable an for reducing pollutant emissions. Only through such the potential between pollutant assessment can we arrive at sensible trade-offs goals and the time and cost to implement control techniques.
emission III. As one In a qualitative way, this assessment is given in table techniques that have the best potential for reducing might expect, those in terms of all pollutant emissions also require major modifications the most difficult develop- current combustor technology and present a demonstrated ment risk. Risk is defined as the ability to convert into a workable engine combustor. Good re- experimental technique or ductions in CO and THC emissions may be achievable with minor moderate modifications and with a low development risk.
However, modification and appreciable reduction in NOx will require major any moderate to high development risk. It should be understood that techniques can be combined in a staged type combustor several of these control of emission may require combinations and that the optimum and variable geometry.
that quantitative discussion it is obvious From the preceding in making satis- needed if we are to be successful information is infor- obtainment of quantitative sensible trade-offs. The factory and series of advanced tech- has been initiated by NASA through a mation programs aimed at demonstrating nology combustor development The of existing engines.
in a wide variety emission performance discussed in the next of these programs will be scope and goals this paper.
section of of TECHNIQUES - The application APPLICATION OF CONTROL two is being implemented in pollutant emission control techniques large NASA/Industry programs.
Program - The first of these Clean Combustor Experimental programs, the NASA Experimental Clean Combustor Program (ECCP), objective is to in December of 1972. The program was initiated advanced tech- in full-scale engine tests, develop and demonstrate, emissions in that are capable of reducing pollutant nology combustors over 8000 ratio engines (EPA Class T2, thrust the large high by-pass level goals are con- the wide body jets. The emission lbs) that power two contractors that the published EPA standards. The sistent with are Pratt & Whitney and are currently under contract, were selected, and the General Electric Company (CF6 engine).
Aircraft (JT9D engine) engine effort scheduled to culminate in The program is a three-phased of a tests in 1976. Phase I of the program (screening demonstration and the two of low emission concepts) has been completed multitude chosen for phase II most promising combustor concepts have been underway. A complete for engine adapation) which is now (refinement given in reference 11.
description of this program is combustor configurations The two advanced technology CF6 engine along with the standard CF6- that will be evaluated in Phase II are shown utilize the concept of fuel 50 combustor in figure 12(a). Both designs idle pollutant emissions. The pilot stages of scheduling for reducing both the radial/axial staged and the double annular are optimized for emissions) at engine idle fuel-air high efficiency (low CO & THC ratios. The main stages are optimized for lean combustion (low NO x ) combinations of fuel scheduling at full-power fuel-air ratios. Various such as approach and climb out can be used for off-design operation power settings. The radial/axial staged configuration utilizes a pre- stage whereas the double annular mixed fuel-air approach in the main lean combustion configuration uses an air-blast type nozzle to obtain in the main stage. These two configurations employ four of the pre- vious discussed control techniques: (1) fuel scheduling, (2) air blast fuel nozzles, (3) lean mixture combustion, and (4) premixing.
JT9D engine combustor configurations The two advanced technology in Phase II are shown along with the standard that will be evaluated the CF6 configurations both JT9D combustor in figure 12(b). As with as the principal approach to controlling designs use fuel scheduling Optimization of the individual stages at idle pollutant emissions.
is used for overall emission control.
idle and full power conditions The hybrid configuration utilizes a parallel (radial) fuel staging premix technique in the pilot stage and a variation approach with a of the swirl can concept in the main stage. This configuration is an attempt to mate the lowest CO & THC emission design (premix pilot stage) and the lowest NOx emission design (swirl-can-module stage) that was tested in Phase I. The vorbix configuration utilizes a series- type (axial) fuel staging approach with standard type pressure atomizing fuel nozzles in the pilot and main stages. The main stage has high intensity swirlers immediately downstream of the fuel injection point to promote very intense, rapid mixing of the fuel and air in the flame zone. The combination of the intense mixing and hot gases exiting from pilot stage allow lean operation in the main stage and also reduce the time due to quick quenching of the hot gases. These configura- residence tions also employ four of the control techniques: (1) fuel scheduling, (2) lean mixture combustion, (3) premixing, and (4) modular combustion.
Results from the Phase I tests will be discussed in a later section.
Program - The second major Pollution Reduction Technology emission to apply low pollutant that is being implemented program Technology Program is the Pollution Reduction control techniques 1974 as an effort to devel- was initiated in mid (PRTP). The PRTP pollutant emissions combustors to reduce technology op advanced in the 1979 EPA standards classes of engines included of the three the The engines selected for are not covered by the ECCP.
that (EPA class T4), the Garrett- the Pratt & Whitney JT8D PRTP are AiResearch TFE731 (EPA class T1, thrust less than 8000 pounds), P2, turboprop).
Allison 501-D22 (EPA class and the Detroit-Diesel will be conducted in a multi- engine combustor evaluations All three engine demonstrations to the ECCP with phase approach similar and fabri- Combustor concept design in 1976 and 1977.
scheduled the bulk of testing is in progress with and some preliminary cation near. mid to be completed I screening tests scheduled the Phase 1979 EPA standards.
are: consistent with published 1975. Program goals the Phase I screening configurations selected for The combustor tests are shown in figure 13(a) through (c) for the JT8D, TFE731, to three advanced technology con- and 501-D22, respectively. Two evaluation were selected for of each engine combustor figurations and development of emission reduction potential based on the degree representing cases the selected configurations risk involved. In all likelihood of achieving risk (A or B) have the least the least development D configurations represent goals. The C or all of the pollutant emission best chance of achieving risk but provide the the highest development emission reduction goals.
or exceeding the pollutant fuel nozzles, air will utilize air-assist The JT8D configurations pre- lean mixture combustion, and blast fuel nozzles, fuel scheduling, use all of The TFE731 configurations will mixing control techniques.
of increased also document the effects the above techniques and will configur- injection. The 501-D22 discharge bleed and water compressor JT8D engine.
use the same techniques described under the ations will also Although all the engine programs use the same type of control techniques, uses the TFE731 configuration applications vary. For example, the C) whereas the 501-D22 parallel or radial fuel scheduling (configuration D). Other differences or axial fuel scheduling (configuration uses series where- that the JT8D and 501-D22 are can-annular combustors of note are is a full annular design and that the TFE731 is a reverse as the TFE731 flow types of the JT8D, 501-D22 and the JT9D flow design versus the axial and CF6 of the ECCP.
the pollutant control techniques The essential point is that although applying these tech- are similar for all combustors, the methods for the individual engine con- niques to actual engines must be varied as The degree of success will be not only dependent figuration dictates.
upon the control techniques used but will to a great degree depend upon these techniques to the ability and ingenuity of the engineer to adapt his engines' specific characteristics.
PROGRESS TO DATE - The results of the ECCP (JT9D & CF6 en- gine combustor configurations) Phase I tests are illustrated in bar chart current engine emission form on figure 14. This figure compares the advanced technology com- index values of CO, THC, and NOx with engine levels needed at the bustor rig test results and the estimated idle and takeoff condition to achieve the EPA 1979 standards. Emission a range of results from levels below (the dashed lines represent various configurations) the required EPA CO and THC values have designs. None of the configurations been obtained with the advanced EPA NOx level tested so far have been able to achieve the required Very low with an acceptable combustion efficiency (>99 percent).
values of NOx are obtainable at reduced efficiencies but this is an unacceptable alternative because of fuel consumption considerations.
All of the results shown were obtained in combustor rig tests and will not be verified in engines until Phase III is conducted.
Substantial reductions in NOx emissions, compared to current combustors, have also been demonstrated in fundamental laboratory tests under carefully controlled conditions simulating high altitude cruise engines. The results of some of these studies are summarized and compared with NOx emissions from current engines (Concorde type) configurations) combustors in advanced technology (ECCP type and and indicate results are extremely encouraging figure 15. The at simulated supersonic reductions of tenfold or greater "potential" It is likely, however, that several more years cruise conditions.
can proceed to the will be needed before we of laboratory studies stage that will be development and demonstration combustor concept the final judgment of what value is realistically necessary to make the ad- NOx emission index of 6 to 8 for achievable. The estimated subsonic (ECCP type configurations) at vanced technology combustors from represents about a two- to three-fold reduction cruise conditions cruise values. To obtain further reductions current JT9D and CF6 prevaporized/pre- likely require more sophisticated (staged and will than have currently been tested mixed fuel-air techniques) concepts geometry in full-scale combustors. The development of variable combustors will likely be required.
PISTON ENGINE TECHNOLOGY are generally operated at Current aircraft piston engines than cruise condition, and as "fuel rich" mixture settings for other that are high in THC and CO.
such, discharge exhaust emissions within the EPA limits. Table II shows the Oxides of nitrogen are emissions that must be accomplished with- reductions in THC and CO NO Unique differences between the automotive and out increasing x .
and design may preclude the appli- aircraft piston engine requirements reduction methods to general cation of the many automotive pollution aviation aircraft engines. Aircraft piston engines are generally and are designed to operate under air-cooled rather than liquid-cooled stringent require- minimal margins of speed and power and with more a low drag geometry ments for safety, while at the same time sustaining and minimum weight. These factors indicate that technological ad- achieve com- vancements specific to aircraft engines may be needed to Standards.
pliance with the EPA Emission - The scope of the EVALUATION OF CONTROL TECHNIQUES measuring base- piston engine technology program includes NASA F/A ratio and ignition line emissions, determining the effects of emissions and performance, analyzing and investigating timing on and as- control techniques, testing prototype engines, alternative engines for future generation light aircraft.
sessing alternative program has three elements.
The Control Effort - The first program element is a FAA/NASA initiated June 1974 with AVCO joint FAA/NASA contractual effort Teledyne Continental. Phase I will provide baseline Lycoming and from 10 representative aircraft characterization of the emissions effects of variable F/A ratios and timing engines and determine the (cooling, mis- on emission level and engine operation modifications etc). Phase II will consist of the analysis and design fire, roughness, which offer promise. toward achieving of minor engine modification s testing of the proposed modifications the emission levels. Limited will be conducted in Phase III.
program element is a NASA NASA Contract Effort - The second effort that would screen and assess more significant contractual and include demonstration tests of those concepts modifications A partial list of candidate emission showing the most promise.
is shown in table IV.
reduction techniques to be used in the evaluation of these techniques The criteria feasibility to reduce emissions and specific will include: technical status of technology; cost; weight; safety; opera- fuel consumption; noise; ease of manufacture; ease of integration tional characteristics; to the various existing engine/aircraft on new engines and adaptability and reliability; cooling; engine/aircraft configurations; maintenance and availability of fuel additives.
performance; Research Effort - The third program element is Lewis In-house of studies a Lewis Research Center in-house research effort consisting and alternative engine and analyses, aircraft engine experiments, experiments.
of aircraft piston and and analyses will be made Detail studies will include feasi- The studies and analyses alternative engines.
to deter- calculations in order system and cycle bility assessments, and technology benefits, operational problems, mine the predicted reduction pollutant emissions imposed by various requirements combustion also be made of rotary An assessment will techniques.
diesel engines for potential cycle engines, and engines, Stirling aviation aircraft.
to future general application two aircraft engines (Lycoming investigation of An experimental baseline performance, 0-320-D and Continental TS10-360-C) to obtain correlation of humidity effects on emission levels and performance, a reduction tech- of various emission to evaluate the effectiveness and emission control tech- conducted. Three is currently being niques are thermal reactors, hydrogen injection, niques being investigated water-alcohol injection.
and "ultra-lean" engines in the of internal combustion Operation in exhaust pollution considerable reduction F/A region can produce good combustion economy. However, potential increase in fuel with a in practice.
been difficult to achieve mixtures using gasoline has of lean of hydrogen relatively small amounts solution is to inject A possible to extend the flam- air mixture in order a lean gasoline and gas into development this technique lie in the limit. Problems with mability system, an increase in complexity a practical hydrogen generator of for larger system, and a requirement to a hydrogen injection due lost due to restore the engine power or supercharging to engines lean operation.
hydro- assess basic feasibility of investigation to An experimental using an automotive is being performed generation and injection gen piston engines. A meth- its evaluation on aircraft test engine prior to generator composed of a vaporizer, catalyst bed, anol fuel hydrogen installed and is being and controls, figure 16, has been intercooler small quantities The system generates relatively tested on the engine.
from a methyl alcohol/water reformation process of hydrogen by a steam exhaust.
catalyst heated from the engine mixture passing over a to be a good technique for reducing Thermal reactors appear assess- hydrocarbons. A better monoxides and unburned the carbon integration, safety, turbo- the practical problems of engine ment.of mechanical integrity, and system versus naturally aspirated, charged manufac- concert with the aircraft being performed in complexity is that this could the assessment indicate turers and the FAA. Should and its reactor would be designed be a viable approach, a thermal evaluated.
performance experimentally and THC piston engine CO in aircraft Significant reductions systems with improved fuel management emissions can be achieved air-fuel mixture.
leaning out of the engine consisting of controlled climb) of current high power (take-off and The air-fuel mixture at rich to prevent overheating engines is excessively high performance of the water-alcohol However, with the injection and detonation.
of the out because the vaporization mixture may be leaned fluid, the supplied can provide the cooling formerly water-alcohol mixture excess fuel.
by the Wankel rotary engine inves- evaluations, along with the The above for the assessment of poten- a large data base tigation, will provide to piston engine for future applications tial engine emission controls aircraft.
powered CONCLUDING REMARKS emission levels of required to control the The major techniques well aircraft engines are smoke for gas turbine CO, THC, NOx, and to define the ultimate capa- Research efforts known and documented.
will con- reduce pollutant emission levels bility of these techniques to and under NASA in NASA in-house facilities tinue to be conducted application universities. The successful with industry and sponsorship hardware will operational engine combustor of these techniques to of the engineer to adapt the upon the ability and ingenuity depend NASA/ of his engine. The to the particular characteristics techniques Reduction Tech- Clean Combustor and Pollution Industry Experimental information needed for Programs will provide quantitative nology re- risk and emission between development evaluating the trade-offs engine and combustor types.
potential for a wide variety of duction EPA emission standards successfully achieve the required The ability to (in terms of levels and implementation time), for selected engines, 1976 and 1977.
demonstration tests during will be resolved by engine altitude cruise of gas turbine engine high The potential impact under heavy debate.
on our environment is currently emissions obtained but more is and data are being Considerable information long periods of time are re- quality measurements over needed. Air imple- these measurements are being quired and programs to obtain studies to evaluate attractive more years of laboratory mented. Several values in combustion formation to minimum to reduce NO approaches x concept develop- to undertaking combustor systems are still needed prior demonstrated be developed and Combustors must ment and demonstration.
we cruise conditions before at simulated high altitude in actual engines future high altitude aircraft achievable levels for can realistically project engine NO emissions.
x the may prohibit and performance considerations Safety, weight, to general reduction methods most automotive pollution application of advancements specific technological piston engines. Therefore, aviation the to achieve compliance with will likely be required to aircraft engines to establish and demonstrate Standards. Research efforts EPA Emission will be conduc- to reduce the exhaust emissions the necessary technology industry.
and under NASA sponsorship with ted in NASA in-house facilities gas turbine engine pollutant emissions, both Reductions in aircraft engine fuel adversely affecting be accomplished without and piston, must programs conducted and overall performance. Experimental consumption and fuel consumption can be that acceptable performance to date indicate is properly implemented.
if the reduced emission technology maintained REFERENCES 1. "Control of Air Pollution for Aircraft Engines-Emission Standards and Test Procedures for Aircraft."
Federal Register, July 17, 1973, pp. 19088-19103.
Vol. 38, and L. C. Papathakos, "Smoke Evaluation of a 2. J. Grobman Aeronautics and Space Modified J-57 Combustor." National Administration TMX-2236, Mar. 1971.
3. I. Glassman, "Combustion Science and Technology."
Princeton University, 1970.
4. D. Thompson, "NO Formation in Combustion." Combus- x pp. 69-79.
tion and Flame, Vol. 19, Aug. 1972, 5. J. Grobman, "Effect of Operating Variables on Pollutant Emissions from Aircraft Turbine Engine Combustors."
National Aeronautics and Space Administration TMX-67887, Sept. 1971.
and C. T. Norgren, "High-Pressure Combustor 6. R. D. Ingebo Exhaust Emissions with Improved Air-Atomizing and Conventional Pressure Atomizing Fuel Nozzles." National Aeronautics and Space Administration TN-D-7154, Feb. 1973.
7. T. R. Clements, "Effects of Fuel Zoning and Fuel Nozzle on Pollution Emissions at Ground Idle Conditions for a Design Ram-Induction Combustor. " Pratt and Whitney Double -Annular Feb. 1973; also National Aeronautics and Aircraft FR-5295, Feb. 1937.
Space Administration CR-121094, Ratio and Dwell Time 8. D. Anderson, "Effects of Equivalence on Emissions from an Experimental Premixing Prevaporizing Burner." Paper to be presented at 20th Annual International Gas Turbine Conf., Houston, Tex., Mar. 2-6, 1975.
and Premixing to 9. G. Roffe and A. Ferri, "Prevaporization Obtain Low Oxides of Nitrogen in Gas Turbine Combustors."
National Aeronautics and Space Administration CR-2495, 1975.
10. D. F. Schultz, "Modifications That Improve Performance of a Double Annular Combustor at Simulated Engine Idle Conditions."
National Aeronautics and Space Administration TMX-3127, Dec. 1974.
11. R. W. Niedzwiecki and R. E. Jones, "The.Experimental Clean Combustor Program - Description and Status. " Paper presented at the Air Transport Meeting, Dallas, Tex., Apr. 30-May 2, 1974.
Figure Captions 1. Typical aircraft gas turbine engine exhaust emission characteristics.
2. Aircraft gas turbine combustor pollution considerations.
3. Emission reduction techniques at idle.
4. Emission reduction techniques at full power.
5. Schematic of an air-assist fuel injection configuration.
6. Effect of improving fuel atomization using air-assist fuel nozzle, can type combustor.
7. NASA premixed primary zone test section.
from premix tests using propane fuel.
8. Nitrogen oxides emissions 9. Ultra-low NO combustor concepts.
x (a) Jet-induced combustor concept.
(b) Vortex airblast combustor concept.
(c) Catalytic combustor concept.
10. NASA experimental swirl-can-modular combustor.
(a) Photo of full annular combustor.
Cross-sectional view of full annular combustor.
(b) (c) Module components.
Comparison of oxides of nitrogen emission levels from conventional 11.
and the NASA swirl-can-modular combustor takeoff combustors conditions.
Experimental clean combustor program, phase 2.
12.
(a) T2 Class, CF6-50 engine.
(b) T2 Class, JT9D engine.
13. Pollution reduction technology program, phase I configurations.
(a) T4 Class, JT-8D engine.
T1 Class, TFE-731 engine.
(b) (c) P2 Class, 501-D22 engine.
20a Figure Captions - Concluded.
status, T2 class engines.
14. Emission level reduction NO reduction status simulated supersonic 15. High altitude cruise x cruise conditions.
reformation hydrogen generator for catalytic steam 16. Research CATALYST of methanol CH + H 0 + HEAT -> 3 2 3H2 + C0 Exhaust Constituents Table I. - Gas Turbine Engine Estimated Source Constituents concentration LD C N Air 77% (Vol) Air 16.6% (Vol) 0.9% (Vol) Air A 2. 7% (Vol) Eff Combustion H 0 (Vol) 2.8% Eff Combustion CO 10 - 50 PPM Combustion INEFF CO Unburned HC 5 - 25 PPMC Partd H THC INEFF Combustion oxidized H Partially 50 PPM 5 - INEFF Combustion H 0.4 - 50 PPM (MASS) INEFF Combustion Smoke (particulates) 50 - 400 PPM Heating of air NO NO, 1 - 10 PPM Fuel SO , SO 5 - 20 PPB Fuel Trace Metals Table II. - Environmental Protection Agency Emission Levels For The LTO Cycle 1979 EPA Standards Engine THC CO NO Smoke x class class Pres Std Pres Std Pres Std Pres Std T1 4-16 1.6 15-60 9.4 2.5-4.5 3.7 ----- <32 T1, T3, T4 2-21 0.8 7-20 4.3 3-10 3.0 20-65 <25 P2 6-12 4.9 20-30 26.8 6-10 12.9 ----- <50 Piston 2.5-4.5 1.9 50-120 42 0.2-1.3 1.5 ----- -- 1981 EPA Standards TI, T3, T4 2-21 0.4 7-20 3.0 3-10 3.0 20-65 <25 T1 - Turbojet/fan engines with less than 8000 pounds thrust.
T2 - Turbojet/fan engines with more than 8000 pounds thrust.
T3 - JT3D engines.
T4 - JT8D engines.
P2 - Turboprop engines.
* - Pounds/1000 pounds thrust - hours/cycle or pounds/1000- horsepower - hours/cycle.
Control Techniques Table III. - Assessment Of Pollution Turbine Combustors For Gas Application difficulty Reduction potential Control technique Minor Good for CO & THC Air-Assist Fuel Atomization Modification Negligible for NO x (Low development risk) Moderate Good for CO & THC Air Blast Fuel Atomization Modification Small for NO x c(Low development risk) co for CO & THC Moderate Excellent Fuel Scheduling Modification * No effect for NO risk) (Moderate development Moderate Poor for CO & THC Leaner Fuel/ Mixtures Modification Moderate for NOx risk) (Moderate development for CO & THC Combustor Major : Poor Modular Modification Excellent for NOx development risk) (Moderate Excellent for CO & THC Premixing Fuel and Air Major Modification Excellent for NOx (High development risk) Poor for CO & THC Major Catalytic Combustor NOx Modification Excellent for high development risk) (Very in conjunction with other techniques.
May be excellent if used risk is defined as the ability to convert a demonstrated experi- Development a workable engine combustor.
mental technique into Reduction Techniques Table IV. - Candidate Emission For Piston Engines 1. Fuel Additives A. Methanol 2. Emission Control Add-On q Reactor ! A. Thermal Catalytic Reactor B.
Injection C. Hydrogen D. Water-Alcohol Injection and Ignition System 3. Fuel Distribution A. Ultrasonic Fuel Atomization B. Thermal Fuel Vaporization Ignition Multiple-Spark C. High-Energy Geometry Modifications 4. Engine Improved Cooling A.
and Supercharge B. Run Lean C. Stratified Charge - 15 / 10 CO 50- 0--- - 5 0 / 0_ THC .
80 90 60 70 (TAKEOFF) ENGINE SPEED, % (IDLE) exhaust Typical aircraft gas turbine engine Figure 1. - characteristics.
emission Co RESULT INEFFICIENCY COMBUSTION MONOXIDE CARBON UNBURNED HYDROCARBONS CURE EFFECTS INCREASE RESIDENCE TIME QUENCHING CAUSES FLOW VELOCITY REDUCE STABILITY COMBUSTION POOR RETARD MIXING & ATOMIZATION POOR FUEL LOW: TO 1 EQUIV RATIO INCREASE DISTRIBUTION Tin IMPROVE FUEL ATOMIZATION LOW POWER IDLE in & DISTRIBUTION IDLE Pin LOW POWER FIA C AR POLLUTANTS TIME REDUCE RESIDENCE INCREASE FLOW VELOCITY TIME ENHANCE MIXING HIG ....... PE EXCESS RESIDENCE REDUCE EQUIV RATIO TO TAKEOFF - HIGH FLAME TEMP Tin FUEL 0.5-0.7 POOR LOCAL FUEL IMPROVE LOCAL DISTRIBUTION Pin OF DISTRIBUTION OXIDES FIA NITROGEN CS-69635 SMOKE combustor pollution considerations.
Figure 2. - Aircraft gas turbine AIR FUEL ATOMIZED SPRAY AIR ASSIST NOZZLE SPRAY TULIP FU L-EL FUEL AAIRR-A NOZZLE AIR BLAST FUEL SCHEDULING reduction techniques at idle.
Figure 3. - Emission EMISSIONS REDUCED BY: FLAME TEMP LOWER AIR- FLAME REDUCED TIME IN COMBUSTORS CONVENTIONAL FUEL FUEL PREMIXING SWIRL CAN LEANER MIXTURES 4. - Emission reduction techniques at full power.
Figure y~~~ 0$~gbp SECONDARY _ [FOR TAKEOFF] FUEL L & CRUISE ] SUPERCHARGER- r--- COMPRESSOR BLEED AIR i PRIMARY FUEL IDLE I L. .FOR CS-60848 Schematic of an air-assist fuel injection configur- Figure 5. - ation.
P z2.5 ATM Tn z580 K FA z 0. 0112-0. 0115 I Iflo a- 30- LC v,20- t- 0-, 200- 10- o z _- CO o NO x 10 20 30 40 50 , PSID AIR-ASSIST DIFFERENTIAL PRESSURE, 6. - Effect of improving fuel atomization using air-assist Figure fuel nozzle, can type combustor.
FUEL 10 CM F 0GAS SAMPLE 210 CM PERFORATED L PREHEATED FLAMEHOLDER AIRFLOW test section.
primary zone premixed Figure 7. - NASA T31 50 - K * o o U- O 1o S6 600 S.5 = P3 5.5 ATM .z o = 25 & 30 M/S VRE F o__0 Ln 0 RESIDENCE TIME = 2 mSEC o L So o 800 K DATA - 600 K DATA - WSR PREDICTION .4 .5 .6 .7 .8 .9 1.0 EQUIVALENCE RATIO, p from premix tests 8. - Nitrogen oxides emissions Figure using propane fuel.
WGINAL PAG$ z.,W 1oR.UAL - EXHAUST - IGNITER ' AIR + FUEL-' FUEL AI 4 FUEL-AIR JETS JET-INDUCED COMBUSTOR CONCEPT.
(a) 2 4 POINTS) r( INJECTION AIR AIR FUEL, E/ XHAUST FUEL-AIR In AIR R ' IGNITER - TORCH L-SWIRLER (24 VANES) COMBUSTOR CONCEPT.
(b) VORTEX AIRBLAST rALUMINA OR r-KANTHAL SILICON I MODULE FLOW SCREEN- I CARBIDE M iAIR FLIEL-)AIR EXHAUST COATED- -PALLADIUM i AIR iFUEL1 II LSWIRLER (24 VANES) -24 INJECTION POINTS (c) CATALYTIC COMBUSTOR CONCEPT.
Figure 9. - Ultra-low NOx combustor concepts.
(a) PHOTO OF FULL ANNULAR COMBUSTOR.
FUEL 1l 20 FUEL INLETS LOCALIZED RECIRCULATION AIRFLOW- ZONES (b) CROSS-SECTIONAL VIEW OF FULL ANNULAR COMBUSTOR.
FUEL STABILIZER S.i SWIRLER CARBURETOR (C) MODULE COMPONENTS.
Combustor.
Figure 10. - NASA Experimental Swirl-Can-Modular T NAL E-8Z57 FUEL PRESENT DAY 40 - COMBUSTORS WIDE BODY JETS A - CF6-50 ENGINE COMBUSTOR (E.G. 747, DC-10)- , 30 - FUEL - , ", NARROW BODY JETS NASA (E.G. DC-8, 727)-\ SWIRL-CAN MAIN "20 S ESTAGE - B -RADIALIAXIAL STAGED COMBUSTOR 0 600 700 800 900 INLET TEMP, K Figure 11. - Comparison of oxides of nitrogen emis- FUEL the PILOT sion levels from conventional combustors and STAGE combustor takeoff NASA swirl-can-modular conditions.
MAIN STAGE C - DOUBLE ANNULAR COMBUSTOR (a) T2 CLASS, CF6-50 ENGINE.
Figure 12. - Experimental clean combustor program, phase 2.
A -JT9D ENGINE COMBUSTOR PILOT STAGE MAIN STAGE FUEL B -HYBRID COMBUSTOR PILOT M I STAGE FUEL-' C -VORBIX COMBUSTOR (b) T2 CLASS, JT9D ENGINE.
Figure 12. - Concluded.
FUEL - A -CONVENTIONAL COMBUSTOR FUEL- PILOT MAIN STAGE STAGE FUEL IGNITOR SECONDARY SWIRLERS B -SWIRL COMBUSTOR PRIMARY PREMIX FUEL PILOT STAGE MAIN STAGE -SECONDARY INLETS C -STAGED PREMIX COMBUSTOR (a) T4 CLASS, JT-8D ENGINE.
Figure 13. - Pollution reduction technology program, phase I configurations.
FUEFUEL , ,BLEED STAGE MAIN A - MODEL 501-D22A STANDARD COMBUSTOR FUEL o A- MODIFICATIONS TO BASELINE COMBUSTOR -FUEL MAIN STAGE FUEL FUEL AND/OR AIR ASSIST B - PILOTED AIRBLAST INJECTION FUEL C - PRECHAMBER COMBUSTOR FUEL MAIN STAGE PILOT -FUELUE t ,,MAIN STAGE P- , STAGE FUEL COMBUSTOR D - STAGED (c) P2 CLASS, 501-D22 ENGINE.
C - PILOTED PREMIXIPREVAPORIZATION FUEL IN- JECTION Concluded.
Figure 13. - (b) TI CLASS, TFE-731 ENGINE.
Figure 13. - Continued.
ENGINES E EXISTING 50- 67 E ADV TECH COMBS.
STANDARDS I I EPA r-i[ RANGE OF RESULTS R40- - 30- -- -JI S10-- CO THC NOx (TAKEOFF) (IDLE) (IDLE) reduction status, T2 class engines.
Figure 14. - Emission level - I 18-20 20 -- CURRENT SST ENGINES S'I TECH EXP COMBUSTORS S 7I ADV TUBE STUDIES 1 PREMIXED FLAME WM 15- CATALYTIC COMBUSTOR ALSO ESTIMATED FOR S6 TO 8 SUBSONIC CRUISE CONDITIONS z, 10- U0.5-1.5 0-?
reduction status simu- altitude cruise NOx 15. - High Figure lated supersonic cruise conditions.
" l TO ENGINE + CH 0H H 0 3 2 TANK CONDENSATION RETURN PUMP TRAP STORAGE FOR COLD-STARTS VAPORIZER -ENGINE EXHAUST CATALYST GAS COMPRESSO BED GAS COOLER 1
t ttt
: COOL AIR for catalytic steam reformation Figure 16. - Research hydrogen generator of methanol CATALYST CH 0 + H 0 + HEAT - 3 H 2 3H + CO 2 2 NASA-Lewis