The stratification of in-cylinder mixtures appears to be an effective method for managing\nthe combustion process in controlled auto-ignition (CAI) engines. Stratification can be achieved and\ncontrolled using various injection strategies such as split fuel injection and the introduction of a\nportion of fuel directly before the start of combustion. This study investigates the effect of injection\ntiming and the amount of fuel injected for stratification on the combustion and emissions in CAI\nengine. The experimental research was performed on a single cylinder engine with direct gasoline\ninjection. CAI combustion was achieved using negative valve overlap and exhaust gas trapping.\nThe experiments were performed at constant engine fueling. Intake boost was applied to control the\nexcess air ratio. The results show that the application of the late injection strategy has a significant\neffect on the heat release process. In general, the later the injection is and the more fuel is injected for\nstratification, the earlier the auto-ignition occurs. However, the experimental findings reveal that the\neffect of stratification on combustion duration is much more complex. Changes in combustion are\nreflected in NOX emissions. The attainable level of stratification is limited by the excessive emission\nof unburned hydrocarbons, CO and soot.
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