A Combustion Heat Release Correlation for CAI Combustion Simulation in 4-Stroke Gasoline Engines

One-dimensional engine simulation programmes are often used in the engine design and optimization studies. One of the key requirements of such a simulation programme is its ability to predict the heat release process during combustion. Such simulation software has built in it the heat release models for spark ignited premixed flame and compression ignited diesel combustion. The recent emergence of Controlled Auto Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has generated the need for a third type of heat release models for this new combustion process. In this paper, a heat release correlation for CAI combustion has been derived from extensive in-cylinder pressure data obtained from a Ricardo E6 single cylinder research engine and a multi-cylinder Port Fuel Injection (PFI) gasoline engine running with CAI combustion. The experimental data covered a wide range of air/fuel ratios, speed and percentage of residual gas. The heat release correlation includes two parts: one for the first slower part of the heat release process at low temperature, and the other for the second faster part of the heat release process at high temperature. The heat release correlation was then evaluated on a single cylinder PFI gasoline engine running with CAI/HCCI combustion by comparing the experimental data with the 1-D engine simulation results obtained using the GT-Power simulation programme.