Influence of the variable valve timing strategy on the control of a homogeneous charge compression (HCCI) engine

Homogeneous Charge Compression Ignition (HCCI) engine concept has the potential to be high efficient and to produce low NOx and particulate matter emissions. However, the problem of controlling the combustion over the entire load/speed range limits its practical application. The HCCI combustion is controlled by chemical kinetics of the charge mixture, with no influence of the flame diffusion or turbulent propagation. Therefore, to achieve a successful control of the HCCI process, the composition, temperature and pressure of the charge mixture at IVC point have to be controlled. The use of the variable valve timing strategy that enables quick changes in the amount of trapped hot exhaust gases shows the potential for the control of the HCCI combustion. The aim of this paper is to analyse influence of the variable valve timing strategy on the gas exchange process, the process between the first valve open event (EVO) and the last valve closing event (IVC), in a HCCI engine fuelled with standard gasoline fuel (95RON). The gas exchange process affects the engine parameters and charge properties and therefore plays a crucial role in determining the control of the HCCI process. Analysis is performed by the experimental and modelling approaches. The single-cylinder research engine equipped with the fully variable valve train (FVVT) system was used for the experimental study. A combined code consisting of a detailed chemical kinetics code and one-dimensional fluid dynamics code was used for the modelling study. The results obtained indicate that the variable valve timing strategy has a strong influence on the gas exchange process, which in turn influences the engine parameters and the cylinder charge properties, hence the control of the HCCI process. The EVC timing has the strongest effect followed by the IVO timing, while the EVO and IVC timings have the minor effects.