31-03-2011, 12:50 PM
anand1-hcci-to-si.pptx (Size: 1.95 MB / Downloads: 87)
EFFECTS OF KEY FACTORS ON THE ENGINE COMBUSTION MODE SWITCHING BETWEEN HCCI AND SI
INTRODUCTION
HCCI IS A PROMISING ENGINE COMBUSTION CONCEPT
ADVANTAGES OF HIGH FUEL ECONOMY AND ULTRA LOW NOx EMISSIONS
LIMITED APPLICATION-DIFFICULTY IN CONTROLLING AUTO-IGNITION
SOLUTION:A HYBRID COMBUSTION SYSTEM IN GASOLINE DIRECT INJECTION ENGINES
HYBRID COMBUSTION SYSTEM
COMBINATION OF SI AND HCCI MODE IN DIFFERENT OPERATING REGIONS
HCCI MODE IN MIDDLE/LOW LOADS
SI MODE IN HIGH SPEED/LOADS
MAJOR CHALLENGE-PERFORM SMOOTH MODE SWITCHING BETWEEN SI-HCCI
VARYING PARAMETERS
TWO STAGE CAM PROFILE-CONVENTIONAL POSITIVE OVERLAP AND NEGATIVE OVERLAP VALVES
THROTTLE POSITIONING
INJECTION STRATEGY
A STEPPED SWITCHING STRATEGY IS PUT FORWARD DUE TO SLOW RESPONSE OF THROTTLE
STEPPED SWITCHING
THROTTLE MOVEMENT IS ISOLATED
DURING TRANSITION THE THROTTLE POSITION REMAINS IN THE INITIAL POSITION
ENSURES SMOOTH SWITCHING
LOOSES THE BENEFIT OF HIGH FUEL ECONOMY
MODE SWITCHING FROM HCCI TO SI
INJECTION SWITCHED TO TWO STAGE
SPLIT INJECTION ENSURES CHARGE STRATIFICATION
DELAY IN ESTABLISHING OIL PRESSURE TO TRIGGER THE CAM SWITCHING MECHANISM LED TO DESYNCHRONISATION
SWITCHING DONE IN THE SAME MANNER BUT THE LAST TWO SI CYCLES FAILED
DELAY IN CAM SWITCH CAUSED DESYNCHRONISATION
NO IGNITABLE CHARGE PRESENT NEAR THE SPARK PLUG
PEAK RISE IN THC EMISSIONS AND SHARP DROP OF IMEP
SYNCHRONISATION CAN BE ACHIEVED BY RETARDING THE INJECTION SWITCHING COMMAND
FIRST HCCI CYCLE-VERY HIGH PEAK PRESSURE AND PRESSURE RISE RATE
THIS ABNORMAL FIRST HCCI CYCLE AFFECTED THE FOLLOWING CYCLES
THEREFORE FIRST CYCLE IS THE KEY STEP FOR THE OPTIMIZATION
OPTIMIZATION OF SWITCHING FROM SI TO HCCI
OPTIMIZATION PARAMETERS INCLUDE INJECTION MASS, INJECTION TIMING AND SPARK TIMING
OPTIMIZING OBJECTIVES ARE RELATIVELY LATE COMBUSTION, LOW PEAK PRESSURE, LOW PRESSURE RISE RATE AND LOW IMEP FLUCTUATIONS
INJECTION MASS
FOR THE FIRST HCCI CYCLE A SINGLE STAGE INJECTION IS ADOPTED
TO ACHIEVE LOWER IMEP FOR FIRST HCCI CYCLE VARIED INJECTION MASSES WERE TESTED
OPTIMAL INJECTION MASS-80% OF NORMAL MASS
THIS CAN ONLY BE ACHIEVED BY SELECTING CORRECT INJECTION MASS AND SYNCHRONIZING THE THROTTLE
INJECTION TIMING
INJECTION TIMING VARIED BETWEEN 260deg BTDC AND 40deg ATDC
PREFERRED FIRST HCCI CYCLE SHOULD HAVE RELATIVELY LATE COMBUSTION,LOWER PEAK PRESSURE
PRESSURE RISE RATE CAN BE DECREASED BY RETARTED INJECTION
MISFIRE OCCURRED WITH INJECTION AT 40deg ATDC
PREFERABLE INJECTION TIMING BETWEEN 80deg BTDC AND 40deg BTDC
SPARK TIMING
OVEREARLY OR OVERLATE SPARK WOULD RESULT IN UNSTABLE COMBUSTION
SPARK TIMINGS VARIED FROM 27deg BTDC TO 10deg ATDC
CONTINOUS PRESSURE TRACE SHOWS STABLE COMBUSTION WHEN OPERATED BETWEEN 27deg-17deg BTDC
CONCLUSIONS
MODE SWITCHING FROM HCCI TO SI IS RELATIVELY STRAIGHT-FORWARD,BUT THE PROCESS IN THE OPPOSITE DIRECTION IS MORE CHALLENGING AND MUST BE OPTIMIZED.
OPTIMIZATION SHOULD BE FOCUSSED ON THE FIRST HCCI CYCLE
THE NVO INJECTION IN THE FIRST HCCI HAS TO BE REDUCED IN QUANTITY IN ORDER TO AVOID AN ADVANCED COMBUSTION
THE INJECTION TIMING IN THE FIRST HCCI CYCLE AFFECTS THE SWITCHING PROCESS.
RETARDING THE INJECTION TIMING TO A CERTAIN EXTENT MAKES SWITCHING SMOOTHER
SPARK TIMING HAS LITTLE INFLUENCE ON THE MODE SWITCHING.