A new method to smooth the in-cylinder pressure signal for combustion analysis in diesel engines

摘要

Pressure measurements in diesel engine cylinders provide a valuable way of analysing the combustion process. In this analysis accurate and smooth pressure signals are crucial. At present, mathematic algorithms, such as average filter and local regression, are applied for smoothing the pressure signal directly and up-front. However, with these procedures it is easy to lose information from the signals. In this article, a new smoothing method based on ther-modynamic criteria is introduced. After carrying out a heat release analysis on the unsmoothed pressure signal, a multiple Vibe function is used to fit and smooth the combustion reaction rate which can then be used to recalculate the in-cylinder pressure by a simulation model. The heat release analysis and the simulation model use the same model elements and in fact are each other's reverse. With this new smoothing method, a good description is given of the main combustion process as well as of the start of combustion. More importantly, the method provides a rational breakdown of the heat release in terms of the weighted contributions from the Vibe functions to the heat release. These can be used to characterize combustion, also in part load conditions. The reliability of this method is verified by using measurements from a test diesel engine MAN 4L 20/27.