Common Rail Multi-Jet Diesel Engine Combustion Development Investigation for MFB50 On-Board Estimation

摘要

Proper design of the combustion phase has always been crucial for diesel engine control systems. Modern engine control strategies' growing complexity, mainly due to the increasing request to reduce pollutant emissions, requires on-board estimation of a growing number of quantities. In order to feedback a control strategy for optimal combustion positioning, one of the most important parameters to estimate on-board is the angular position where 50% of fuel mass burned over an engine cycle is reached (MFB50), because it provides important information about combustion effectiveness (a key factor, for example, in HCCI combustion control). In modern diesel engines, injection patterns are designed with many degrees of freedom, such as the position and the duration of each injection, rail pressure or EGR rate. In this work a model of the combustion process has been developed in order to evaluate the energy release within the cylinder as a function of the injection parameters. In this case a zero-dimensional approach has been chosen, because it allows obtaining a model accurate enough for the analysis, with a low computational cost. Once the combustion model has been developed, it can be used to evaluate the cumulated heat release and, consequently, MFB50. MFB50 can also be evaluated using in-cylinder pressure sensors, nevertheless they would account for a relevant part of the whole engine control system's cost. On the contrary, if MFB50 is evaluated as a function of the injection parameters, the methodology does not require any additional cost. Therefore, the aim of this work is to develop a zero-dimensional combustion model, and verify if the level of accuracy obtained in MFB50 evaluation is compatible with engine management requirements. Many experimental tests have been performed on a turbocharged common rail multi-jet diesel engine in order to identify the combustion model. The methodology described in this paper is suitable for diesel engines with up to 4 injections within the same engine cycle.