In recent years, emission regulations have been getting increasingly strict. In the development of engines that comply with these regulations, in-cylinder pressure plays a fundamental role, as it is necessary to analyze combustion characteristics and control combustion-related parameters. The analysis of in-cylinder pressure data enables the modelling of exhaust emissions in which characteristic temperature can be derived from the in-cylinder pressure, and the pressure can be used for other investigations, such as optimizing efficiency and emissions through controlling combustion.
Therefore, a piezoelectric pressure sensor to measure in-cylinder pressure is an essential element in the engine research field. However, it is difficult to practice the installation of this pressure sensor on all engines and on-road vehicles owing to cost issues. Therefore, there have been several studies aiming to estimate the in-cylinder pressure using only the data available from the Engine Control Unit (ECU) without an additional pressure sensor.
An in-cylinder pressure prediction model for conventional light-duty diesel engines had been established by authors and described in this paper. First, the pressure during the compression stroke was estimated using a variable polytropic index. Next, the Wiebe function was applied to describe pressure during pilot and main combustion. This prediction of the in-cylinder pressure was established for real-time estimation.
The complete pressure prediction model consists of subordinate models, where physical phenomena are simplified for the real-time application of the model. The accuracy of the submodels has a direct influence on the error in the parent model the pressure prediction. Therefore, sensitivity analysis was conducted in this study to verify the effect of the submodels, including the polytropic index model, ignition delay model, heat loss model and combustion duration model, on the entire pressure prediction model. This study will contribute to establishing a more accurate pressure prediction through sensitivity analysis and will be useful to many studies that require in-cylinder pressure information.