Predicting the Effect of Fuel Path Controllable Parameters on the Performance of Combustion Controlled Diesel Engine

Abstract

Research and/or Engineering Questions/Objective: Diesel combustion process control is very important in optimizing diesel engine performance. There are few controllable parameters in engine fuel path which have effects on the combustion process and hence the engine performance. The objective of this study is to develop a control-oriented, low computational cost diesel combustion model and apply it in combustion process control system design. Methodology: The structure of a control-oriented low computational cost combustion model was developed based on sufficient knowledge and comparison of various fuel injection spray and combustion models in literature. The model parameters were identified from a Caterpillar C6.6 diesel engine installed in the Loughborough University laboratory. The model was further validated by the same engine test data both at steady operation points. The model was then used in predicting the effect of fuel path controllable parameters (start of injection and fuel rail pressure) on the engine performance output over all engine operation range. The engine performance output includes NOx and soot emission out and IMEP value for each cycle. This model and the prediction result was finally used in designing a combustion process feedback control system. Results: This combustion model was validated to show that it has high accuracy both for engine steady operation point and transient. The simulation result shows the trade-off among NOx and soot emission for varying start of injection and rail pressure. And this trade-off varies with engine speed and load. The engine test results indicate that the combustion process control system designed based on this combustion model and prediction results is able to improve the engine performance compared to look-up table fuel path control system. Limitations of this study: The combustion model presented in this paper needs to be expanded to include air path and heat transfer dynamics. Model validation needs to cover VGT and EGR control input variation. What does the paper offer that is new in the field in comparison to other works of the author: Developing a control-oriented diesel combustion model; using the model in studying the engine performance space and the controllability of fuel path controllable parameters; and the synthesis of diesel combustion control system are all novel topics. Conclusion: A low computational cost combustion model for combustion process control purpose was developed and validated. The application of this model in control system design was implemented and was experimentally proved to be success in improving the engine performance both emission and fuel consumption. The IMEP feedback control either by main injection duration or by PDW is able to reduce combustion variations at steady state and has strong disturbance rejection performance to other fuel path inputs.

F2012-A02-014