Common Rail Multi-Jet Diesel Engine Combustion Model Development for Control Purposes

Multi-jet injection strategies open significant opportunities for the combustion management of the modern diesel engine. Splitting up the injection process into 5 steps facilitates the proper design of the combustion phase in order to obtain the desired torque level, whilst attempting a reduction in emissions, particularly in terms of NOx. Complex 3-D models are needed in the design stage, where components such as the injector or combustion chamber shape have to be determined. Alternatively, zero-dimensional approaches are more useful when fast interpretation of experimental data is needed and an optimization of the combustion process should be obtained based on actual data. For example, zero-dimensional models allow a quick choice of optimum control settings for each engine operating condition, avoiding the need to test all the possible combinations of engine control parameters. In this paper a zero-dimensional model suitable for multi-jet engines with up to 4 injections is proposed, in order to synthesize the experimental results that have been obtained running a 1.3 liters multi-jet diesel engine in a test cell. The effects of Pilot injection rate on the heat release after the following injections in the same pattern are particularly emphasized: tests with different injection patterns have been run, focusing the attention on the very first part of the combustion process, where the fuel injected in the Pilot and Pre injections is burned. The model is finally employed to perform the optimization of the injection and intake control parameters for a single engine operating condition as an example of what has been done throughout the entire engine operating range. The optimization has been performed on the basis of the torque, noise and emission outputs obtained.