COBEM99

SR11 Máquinas Térmicas, Ciclos Termodinâmicos e Propulsão

Title:

EFFECTS OF CYCLIC PRESSURE VARIATIONS ON COMBUSTION DEVELOPMENT IN A SPARK IGNITION ENGINE

Summary :

AN INVESTIGATION OF THE ENGINE CYLINDER PRESSURE FLUCTUATION HAS BEEN CONDUCTED TO FIND OUT THE MAIN PROBLEMS IT CAUSES ON ENGINE POWER OUT. SEVERAL AIR FUEL RATIO EXPERIMENTS RUNNING THE ENGINE AT 1800 RPM WERE CARRIED OUT TO GET ENOUGH DATA TO COMPLETE THIS STUDY. A GROUP OF 30 CYCLES OF PRESSURE DATA, DOING READINGS EVERY ¼ OF CRANK ANGLE DEGREE WAS USED AS A REFERENCE DATA FOR EACH EXPERIMENT. THE EQUIVALENCE AIR FUEL RATIO WAS VARIED FROM 0.82 TO 1.0, TO INVESTIGATE EFFECTS OF MIXTURE COMPOSITION ON ENGINE CYCLE STABILITY. THE EMPIRICAL WOSCHNI S CORRELATION WAS USED TO COMPUTE THE AMOUNT OF HEAT TRANSFERRED BY CONVECTION INSIDE THE ENGINE COMBUSTION CHAMBER. A COMPUTER PROGRAM WAS SET UP TO USE THE PRESSURE DATA TAKING AT A PARTICULAR AIR FUEL RATIO AND TO WORK WITH EQUATIONS FOR CALCULATING THE HEAT RELEASE PROFILES AS A FUNCTION OF THE CRANK ANGLE DEGREE. THE HEAT RELEASE PROFILES INSIDE THE CYLINDER SHOWED IMPORTANT VARIATIONS, WHICH CORRESPOND, TO BOTH THE CONSUMPTION OF LEAN MIXTURE AND OCCURRENCE OF TOO MUCH PRESSURE FLUCTUATIONS. FOR EACH PARTICULAR CYCLE MAXIMUM PRESSURE DATA AND ITS OCCURRENCE CRANK ANGLE WAS PLOTTED TO SHOW THAT ENGINE CYCLES RUNNING ON MIXTURES WITH AIR FUEL RATIOS CLOSE TO THE STOICHIOMETRIC AIR FUEL RATIO VALUE DEVELOP THE HIGHEST MAXIMUM CYLINDER PRESSURE WITH THE LESS CRANK ANGLE VARIATIONS NEAR TOP DEAD CENTER. A STUDY OF THE COEFFICIENT OF VARIATION OF THE INDICATED MEAN EFFECTIVE PRESSURE WAS PERFORMED TO ANALYZE THE EFFECT OF THE CYCLIC DISPERSION OF COMBUSTION PRESSURE ON THE INDICATED WORK PER CYCLE. KEY WORDS: PRESSURE FLUCTUATIONS, CYCLIC DISPERSION OF COMBUSTION PRESSURE, HEAT RELEASE RATE, INDICATED MEAN EFFECTIVE PRESSURE, FUEL-AIR EQUIVALENCE RATIO.

Author :

Jesus, Araque Omar
Martín, Maria 0
Simon, Fygueroa 0

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