Jacek Misztal

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine Philip Price , Richard Stone Jacek Misztal, Hongming Xu, Miroslaw Wyszynski, Trevor Wilson and Jun Qiao Department of Engineering Science, University of Oxford, OX1 3PJ, UK Department of Mechanical Engineering, University of Birmingham, B15 2TT, UK Jaguar Research, Whitley Engineering Centre, CV3 4LF, UK philip.price@eng.ox.ac.uk

An autoignition combustion model for homogeneous charge compression ignition engine cycle simulations

Abstract This paper presents an autoignition combustion model, which can be used in conjunction with a one-dimensional gas dynamics and zero-dimensional thermodynamics engine simulation code for homogeneous charge compression ignition (HCCI) engine cycle simulations. The model consists of two parts: the first predicts autoignition timing, based on the integral of the knock delay time, and the second predicts the heat release rate, based on the Watson correlation for diesel engines. The equations for the model were fitted with empirical coefficients derived from experimental results. The experimental data were measured under a number of engine operating conditions for different loads, speeds, and equivalence ratios. The experiments were performed on a Jaguar V6 HCCI engine employing internal exhaust gas residual trapping through cam profile switching and variable valve timing control. It was found that the location of 50 per cent mass fraction burned (MFB) and the peak rate of pressure rise can be chosen as the key parameters charactering the HCCI combustion in engine simulations. The fitted combustion model was then implemented into the V6 engine Ricardo WAVETM model and validation of its predictive calculations was obtained using a different set of experimental data. The results show that the predicted 50 per cent MFB position is within an average error of 1.84° crank angle (CA) and the predicted peak rate of pressure rise is within an average error of 0.53bar/deg CA (7.2 per cent).

Cylinder-to-Cylinder Variations in a V6 Gasoline Direct Injection HCCI Engine

Despite the fact that homogeneous charge compression ignition (HCCI) has been demonstrated as a combustion technology feasible for implementation with different fuels in various types of engines, cylinder-to-cylinder variations (CTCVs) in multicylinder HCCI engines remain one of the technical obstacles to overcome. A reduction in CTCV requires further developments in control technology. This study has been carried out with regard to the overall engine parameters, involving geometric differences between individual cylinders, coolant paths through the engine, combustion chamber deposits, and also the differences in the inlet temperature distributions between the cylinders. Experimental investigations on the Jaguar V6 HCCI research engine with negative valve overlapping and cam profile switching show that the differences in the rate of pressure rise between the cylinders can be larger than 1 bar/CA deg and that the load differences can be as high as 5―10%. It has been found that some individual cylinders will approach the misfiring limit far earlier than the others. The complex interaction between a number of parameters makes the control of the multicylinder engine a serious challenge. In order to avoid these differences, an active cylinder balancing strategy will be required. It has been observed that spark assistance and split injection strategy deliver the best control for the cylinder balance. However, spark assistance is restricted to low loads and low engine speeds, while split injection requires a considerable effort to optimize its possible settings. This paper defines the most important parameters influencing cylinder-to-cylinder variations in the HCCI engine and aims to put forward suggestions that can help to minimize the effect of cylinder-to-cylinder variations on the overall engine performance.