The influence of intake charge conditions on pre-ignition reactions for gasoline-fueled HCCI engines

This study investigates the influence of intake charge conditions on pre-ignition reactions, specifically intermediate temperature heat release (ITHR), in gasoline-fueled HCCI engines. The influence of changes in intake pressure, intake temperature, and equivalence ratio are investigated for their influence on the relative amount of ITHR as a fraction of total heat release. The study of ITHR in gasoline HCCI is critical as the ITHR enables delayed combustion timing which allows high power output while avoiding excessive ringing. The ITHR behavior of gasoline fuel is studied on a 1.9 L Volkswagen TDI engine modified for HCCI operation. 91-Octane E10 commercial grade gasoline is port-injected to produce a relatively homogeneous in-cylinder fuel-air mixture. Experimental tests are conducted for intake pressures from 1.4 bar to 2.0 bar boosted. Intake temperatures are varied in a range that enabled combustion timing (CA50) from TDC to misfire. The equivalence ratio is varied from 0.20 to 0.55. Using the rate of heat release computed from the in-cylinder pressure data, the trends of change of the ITHR magnitude with the change of the intake charge conditions are indentified.