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AIAA-84-1316 A Review of Internal Combustion Engine Combustion Chamber Process Studies at NASA Lewis Research Center Harold J. Schock, NASA Lewis Research Center, Cleveland, OH

Downloaded by Jose Gros-Aymerich on May 30, 2015 | http://arc.aiaa.org | DOI: 10.2514/6.1984-1316

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AIAA/SAE/ASME 20th Joint Propulsion Conference June 11-13, 1984/Cincinnati, Ohio Y

For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 1633 Broadway, New York, NY 10019

NASA Technical Memorandum 83666 AIM-84- 1316


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A Review of Internal Combustion Engine Combustion Chamber Process Studies at NASA Lewis Research Center

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Harold J. Schock Lewis Research Center Cleveland, Ohio

Prepared for the Twentieth Joint Propulsion Conference cosponsored by the AIAA, SAE, and ASME Cincinnati, Ohio, June 11-13, 1984

NASA

A REVIEW OF INTERNAL COMBUSTION ENGINE COMBUSTION CHAMBER PROCESS STUDIES AT NASA LEWIS RESEARCH CENTER H a r o l d J . %hock* N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n Lewis Research Center Cleveland, Ohio 44135

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Abstract

a r e numerical s t u d i e s o r experiments which a r e This type o f study i s not d i s system-related. cussed i n t h i s r e p o r t , b u t i t would i n c l u d e e n g i n e l t u r b o c h a r g e r o r engine s y s t e m l p l a n e l f l i g h t analysis studies.


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T h i s paper d e s c r i b e s work underway a t NASA Lewis Research Center whose o b j e c t i v e i s t o determine t h e i n - c y l i n d e r a i r f l o w c h a r a c t e r i s t i c s o f r o t a r y and p i s t o n engines. Experience has shown t h a t performance of i n t e r n a l combustion s t r a t i f i e d - c h a r g e engines i s h i g h l y dependent on t h e i n - c y l i n d e r f u e l - a i r m i x i n g processes o c c u r r i n g i n these engines. R e s u l t s showing t h e o u t p u t of m u l t i - d i m e n s i o n a l models, l a s e r v e l o c i m e t r y measurements and t h e a p p l i c a t i o n of a u n i q u e h o l o g r a p h i c o p t i c a l element are des c r i b e d . Models which s i m u l a t e t h e f o u r - s t r o k e c y c l e and s e a l dynamics of r o t a r y engines a r e a l s o described.

The macroscopic p r e d i c t i o n s i n c l u d e thermodynamic o r quasi-dimensional models. These models attempt t o s i m u l a t e t h e processes o c c u r r i n g i n t h e combustion chamber o f an engine w i t h o u t modeling t h e a c t u a l p h y s i c a l d e t a i l s of each process. Thermodynamic models can v a r y a g r e a t d e a l i n c o m p l e x i t y . They can be h i g h l y i d e a l i zed process models, which i n c l u d e assumptions such as c o n s t a n t volume heat a d d i t i o n , r e v e r s i b l e compression and expansion, and zero heat l o s s e s o r complex c y c l e analyses which have been r e f i n e d over many years, An e ample of t h e l a t t e r i s g i v e n b y t h e MIT group where i t has used experimental pressure-crank angle h i s t o r i e s t o deduce t h e r a t e a t which f u e l i s burned i n a l i g h t l y loaded s t r a t i f i e d - c h a r g e engine. The o b j e c t o f t h a t p a r t i c u l a r s t u d y was t o analyze t h e causes o f hydrocarbon emission mechanisms i n d i r e c t l y i n j e c t e d s p a r k - i g n i t i o n engines. Every m a j o r c e n t e r of engine r e s e a r c h has codes of t h i s t y p e o p e r a t i o n a l , and most have been r e p o r t e d a t SAE d u r i n g t h e l a s t t h r e e y e a r s .

Introduction

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I n t e r n a l combustion (I.C.) engine o p t i m i z a t i o n has been underway f o r w e l l over 100 years. I t has n o t been u n t i l t h e l a s t 10 y e a r s t h a t t o o l s have been a v a i l a b l e t o p e r f o r m t h e i n - s i t u s t u d i e s necessary t o g a i n a fundamental unders t a n d i n g o f t h e processes o c c u r r i n g i n t h e engines o f i n t e r e s t . Two devices which have reached t h e l e v e l of r e f i n e m e n t necessary t o s t u d y t h e processes which occur d u r i n g combust i o n i n t h e s e engines a r e t h e l a s e r and t h e high-speed d i g i t a l computer. \i

The u s e f u l n e s s o f t h e thermodynamic models j u s t d e s c r i b e d depends h e a v i l y on t h e a v a i l a b i l i t v o f h i a h a u a l i t v Dressure data. v a l v e f l o w

Understanding t h e fundamental d e t a i l s of a i r f l o w and f u e l p y r o l y s i s i n an i n t e r n a l comb u s t i o n engine w i l l l e a d t o t h e development of engines w i t h h i g h e f f i c i e n c y , l o n g l i f e , and good power-to-weight r a t i o c h a r a c t e r i s t i c s . Designs which a r e o p t i m i z e d f o r manufacturing economy can a l s o be considered, once s u i t a b l e p r e d i c t i v e codes have been developed. T h i s paper d e s c r i b e s t h e research e f f o r t underway i n t h e I n t e r m i t t e n t Combustion Engine Branch a t NASA Lewis Research Center f o r understanding t h e corn- b u s t i o n processes o c c u r r i n g i n these engines.

measure i n d i c a t e d mean e f f e c t i v e p r e s s u r e on a T h i s a l l o w s one t o examine r e a l - t i m e basis.2 c y c l e - t o - c y c l e v a r i a b i l i t y , as w e l l as enginedependent i n t a k e and exhaust m a n i f o l d characteristics. M i c r o s c o p i c a n a l y s i s , i n theory, o f f e r s t h e p o t e n t i a l o f understanding t h e d e t a i l s of t h e combustion process i n engines o f i n t e r e s t . The p h y s i c a l processes o f importance are a i r motion, t u r b u l e n c e l e v e l , f u e l m i x i n g and evaporation, combustion, and heat t r a n s f e r . The boundary c o n d i t i o n s a t t h e i n t a k e and exhaust v a l v e s a r e of p a r t i c u l a r importance t o t h e s i m u l a t i o n and a r e p a r t i c u l a r l y d i f f i c u l t t o determine. The engine f l o w s of i n t e r e s t are three-dimensional i n n a t u r e , and a f i n e g r i d system i s r e q u i r e d t o r e s o l v e t h e f l o w d e t a i l s o f importance. A t h r e e dimensional s i m u l a t i o n o f t h e f o u r - s t r o k e c y c l e would i n c l u d e submodels such as a t u r b u l e n c e model, d e t a i l e d f u e l spray and m i x i n g models, m u l t i - s t e p k i n e t i c s , and a g r i d s i z e s m a l l enough t o r e s o l v e t h e i m p o r t a n t f l o w d e t a i l s near t h e surfaces. A coded model of t h i s t y p e would r e q u i r e a computational t i m e on t h e o r d e r of 100 CPU hours, even on t h e f a s t e s t a v a i l a b l e machine today such as a CRAY I.

Background The f o l l o w i n g b r i e f d i s c u s s i o n i s i n t e n d e d t o g i v e those who a r e n o t i n v o l v e d i n t h i s a c t i v i t y a f e e l i n g f o r t h e c u r r e n t s t a t u s of i n c y l i n d e r I . C . engine research. T h i s i s a l s o g i v e n t o s e t t h e stage f o r a d e s c r i p t i o n o f t h e I n t e r m i t t e n t Combustion Engine Branch's b a s i c research e f f o r t and a d e s c r i p t i o n o f t h e p h i l o s ophy upon which t h i s e f f o r t i s based.

I . C . engine i n - c y l i n d e r process s t u d i e s can be c a t e g o r i z e d as experimental o r as a numerical s i m u l a t i o n , and t h e a n a l y s i s can be e i t h e r macroscopic o r microscopic. E q u a l l y i m p o r t a n t but not included i n t h i s type o f c l a s s i f i c a t i o n

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Aerospace Engineer

v Copyright 0 American ln~tilute of Aeronautic8 and Astronautics, Ine.. 1984. Ail righls reicrvtd.

This pap~risdeel.redaworkof the U.S. Government and IherDforeisinthepubliedomain.

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A t t h i s time, n o t enough i n f o r m a t i o n i s known about t h e accuracy o f each submodel t o warrant assembling a code o f t h i s magnitude. The complex i n t e r a c t i o n o f f u e l sprays w i t h s u r r o u n d i n g a i r and t h e mode of v a p o r i z a t i o n and o x i d a t i o n o f m u l t i - d i m e n s i o n a l s p r a y i n a steady environment i s n o t w e l l understood a t t h i s t i m e . The d e t a i l e d modeling o f t h e combustion o f f u e l sprays i n a h i g h l y unsteady engine environment i s even more complicated.

The f u l l - f l o w f i e l d models j u s t d i s c u s s r d o f f e r t h e p o t e n t i a l o f q a i n i n g a fundamental u n d e r s t a n d i n g o f processes which occur i n an i n t e r n a l combustion engine. A t t h i s p o i n t , Iprc-. d i c t i v e codes a r e n o t i n good agreement w i t h measured r e s u l t s . The development o f these cntlrs w i l l deoend on v e r v c a r e f u l exoeriments f o r c o n & ~,~ parison with predicted results. A further d i r c u s s i o n on t h e p r e s e n t s t a t u s o f f l o w f i e l d modeling i s d e f e r r e d u n t i l t h e end o f t h i s S P C t i o n . Experimental techniques used f o r l o c a l i n - c y l i n d e r a n a l y s i s and model v e r i f i c a t i o n a r r now b r i e f l y discussed.


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One of t h e most i m p o r t a n t m i c r o s c o p i c n l e d i urements i n use a t t h e p r e s e n t t i m e i s Laser Doppler V e l o c i m e t r y (LDV). Laser v e l o c i i n e t r y a l l o w s one t o make n o n - i n t r u s i v e v e l o c i t y m r a s urements i n t h e combustion chamber o f an o p r r i t i n q engine. The a b i l i t y t o make c y c l e r e s o l v i v i v e l o c i t y measurements r e q u i r e s c o n f i g u r a t i o n n f LDV systems which w i l l p r o v i d e h i g h d a t a c o u n t i n q r a t e s and a l s o computer systems which would p r o v i d e h i g h d a t a t r a n s f e r r a t e s . Other n o n i n t r u s i v e , and q e n e r a l l y laser-based techniques, a l l o w f o r measurement o f l o c a l temperatures, f u e l l s i r combustion p r o d u 5 t jiomgositions, b u r n i n g r a t e s , and flame speed. 3 3 A f i r s t step f o r u n d e r s t a n d i n g t h e s e processes i s t h e a b i l i t y t.n p e r f o r m f l o w v i s u a l i z a t i o n s . As e a r l y as 1871 N i c h o l a s O t t o b u i l t a g l a s s c y l i n d e r engine' which was hand cranked: however, most f l o w v i c r r a l i z a t i o n s i n p i s t o n engines have r e l i e d on t h c use o f f l a t windows t o s t u d y f l a m e p r o p a g a t i n n and combustion. I n t h e e a r l y 1 9 4 0 ' s . an import a n t f l o w v i s u a l i z a t i o n t u d y o f knock was r e p o r t e d b y C. D. M i l l e r ? , u s i n g a r o t a t i n g p r i s m camera which he designed. T h i s camera was capable o f f r a m i n g r a t e s t o 200,000 frames p r r second. Present day cameras based on t h e M i l l e r p r i n c i p l e a l l o w one t o make photographs a t f r a m i n g r a es g r e a t e r than 2.5 m i l l i o n frames p e r M i l l e r b e l i e v e s t h a t t h i s framing second r a t e would be s u f f i c i e n t t o observe t h e s a l i e n t f e a t u r e s o f knock i n an I . C . engine.9 Geometr i c a l c o n s i d e r a t i o n s have impeded f l o w v i s u a l i r a t i o n s t y d i e s i n f i r i n g p i s t o n engines. R e c e n t l y Richrnanl" r e p o r t e d on t h e development o f a t r a n s p a r e n t c y l i n d e r engine f o r f l u i d mechanics research. He demonstrated t h a t h o l o g r a p h i c o p t i c a l elements can be used as an a b e r r a t i o n c o r r e c t o r i n a piston-cylinder, schlieren flow v i s u a l i z a t i o n system. The s c h l i e r e n t e c h n i q u c produces s p a t i a l averaged d e n s i t y g r a d i e n t i n f o r m a t i o n . For c o m p l i c a t e d f l o w s such as those t h a t o c c u r w i t h i n an engine, t h i s t y p e o f i n f o r m a t i o n i s d i f f i c u l t t o i n t e r p r e t and compare w i t h model p r e d i c t i o n s .

A.

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Most groups working on engine r e s e a r c h havc r e c o g n i z e d t h e importance o f f u l l - f l o w f i e l d models, and numerous r e s e a r c h e r s have publishPC

the- r e s u l t s of t h e i r work. A f a i r l y complete l i s t o f these p u b l i c a t i o n s can be foun I n t h e r p f e r e n c e s e c t i o n o f a r e p o r t b y Shih. ? I ' The m u l t i - d i m e n s i o n a l modeling e f f o r t underw a y a t t h e I m p e r i a l C o l l e g e has been t h e most

e x t i v s i v e one t o date. Recently, t h e y presented t h e r i i s u l t s of a three-dimensional a i r f l o w simul a t i o n u s i n a a K-E t u r b u l e n c e model t o c l o s e t h e ensrmbl e averaged c o n s e r v a t i o n equations. l2 Thc I m p e r i a l C o l l e g e group has a l s o made extensi"