Experimental Investigation of Control Method for SI-HCCI-SI Transition in a Multi-Cylinder Gasoline Engine
Air/Fuel Ratio (AFR) and Residual Gas Fraction (RGF) are difficult to control during the SI-HCCI-SI transition, and this may result in incomplete combustion and/or knocking. As a result, engine load may fluctuate, as indicated by the Net Indicated Mean Effective Pressure (NIMEP). The objectives of this work are to further understand this process and develop control methods to minimize the engine load fluctuation. This paper presents instantaneous AFR and RGF measurements, both taken by novel experimental techniques. The data provides an insight into the cyclic AFR and RGF fluctuations during the switch. The results suggest that the relatively slow change in the intake Manifold Air Pressure (MAP) and actuation time of the Variable Valve Timing (VVT) are the main causes of undesired AFR and RGF fluctuation, and hence unacceptable NIMEP fluctuation. We also found large cylinder-to-cylinder AFR variation in the transition. Therefore, besides throttle opening control and VVT shifting, cyclic and individual cylinder fuel injection control is necessary to achieve a smooth transition. The control method was developed and implemented in the test engine, and resulted in much reduced NIMEP fluctuations during the switch. The instantaneous AFR and RGF measurements could be adopted to develop more sophisticated control methods for SI-HCCI-SI transition.
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Keywords: homogeneous charge compression ignition (HCCI), ignition, modelling, SI engine modelling,
Associated Project: Engines