Experimental Investigation on Intake Air Temperature and Air-Fuel Ratio Dependence of Random and Deterministic Cyclic Variability in a Homogeneous Charge Compression Ignition Engine

Due to the increasingly stricter emission legislations and growing demand for lower fuel consumption, there have been significant efforts to improve combustion efficiency, while satisfying the emission requirements. Homogenous Charge Compression Ignition (HCCI) combustion offers significant efficiency improvements compared to conventional gasoline engines. However, due to the nature of HCCI, fully homogeneous charge HCCI combustion can be realized only in a limited operating range. Control of HCCI engines to obtain the desirable operation requires understanding of how different charge variables influence the cyclic variations in HCCI combustion. Under certain operating conditions, HCCI engines exhibit large cyclic variations in ignition timing. Cyclic variability ranging from stochastic to deterministic patterns can be observed. One important design goal for engine development is to minimize cyclic variability. A small amount of cyclic variability can produce undesirable engine vibrations. At the same time, larger cyclic variability leads to increased hydrocarbon emissions. To control HCCI ignition timing, it is often necessary to know the characteristics of HCCI cyclic variations.

This study investigated the cyclic variations in HCCI combustion ignition timing using a range of experimental data with varying intake air temperature and air-fuel ratio at different engine speeds. Temporal dynamics of cyclic variations in HCCI combustion is analyzed using statistical and chaotic theory methods. The analysis of cyclic variation of combustion phasing for a gasoline fuelled HCCI combustion engine is performed. A symbol-sequence statistics method is used to find the occurrence of possible probabilities of the data points under the same operating conditions. The results show that as fuel air mixture becomes richer, the determinism in the ignition timing increases. The quantile return map of the cycle based time series of ignition timing values also confirm that deterministic portion of dynamics occurring in a HCCI engine increases as charge becomes richer or the intake air temperature increases.