Abstract
In this study we summarize and analyze experimental observations of cyclic variability in homogeneous charge compression ignition (HCCI) combustion in a single-cylinder gasoline engine. The engine was configured with negative valve overlap (NVO) to trap residual gases from prior cycles and thus enable auto-ignition in successive cycles. Correlations were developed between different fuel injection strategies and cycle average combustion and work output profiles. Hypothesized physical mechanisms based on these correlations were then compared with trends in cycle-by-cycle predictability as revealed by sample entropy. The results of these comparisons help to clarify how fuel injection strategy can interact with prior cycle effects to affect combustion stability and so contribute to design control methods for HCCI engines.
Highlights
Homogeneous charge compression ignition (HCCI) inherits selected features from both spark ignition and compression ignition combustion systems
The effects of fuel injection strategies on cycle-by-cycle variability in a gasoline HCCI engine running in a negative valve overlap (NVO) mode were studied
NVO top dead center (TDC)) and the second injection was applied during exhaust expansion (40 crank angle degrees (CAD) after NVO TDC)
Summary
Homogeneous charge compression ignition (HCCI) inherits selected features from both spark ignition and compression ignition combustion systems. Ignition is not forced via spark discharge but appears spontaneously at multiple sites as an effect of a gas temperature increasing during the compression process. Such a course of combustion process is characterized by the lack of flame propagation and uniform temperature across the cylinder. As combustion is kinetically controlled, heat release process is very quick, resulting in a realization close to the ideal Otto cycle Due to these features, HCCI combustion exhibits uncompromising improvement of working cycle efficiency and reduction of cylinder-out emissions of nitrogen oxides as well as particulates [1,2]
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