Heat Release Analysis and Modeling for a Common-Rail Diesel Engine

The main purpose of this study was to perform a heat release analysis in order to formulate a heat-release model for a common-rail diesel engine. The fundamental idea of the model is to describe the observed physical processes with empirical formulas based on the experimental data.

A Fiat 2.4Liter common rail engine was used in the tests. A rotary incremental encoder with 0.1° resolution was coupled to the crankshaft pulley with a special adapter. The engine was operated at a number of different speeds and load conditions. Cylinder pressure data was recorded using a high-speed data acquisition system. The data acquisition was done at variable sampling speeds; encoder signal at every 0.1° dictated the sampling speed for data-acquisition. Cylinder pressure data was logged for 100 cycles at each operating condition. This raw data was averaged and used for further analysis. The actual rate of heat-release/crank angle was evaluated using the first law of thermodynamics. The heat release data was modeled using Weibe functions. Two such functions were used: one to describe the pilot burning and the other to describe the main burning stage of the combustion process. The coefficients and parameters in the model were adjusted to match the observed heat release diagram. Actual cylinder pressure versus crank angle traces were compared with predicted cylinder pressure versus crank angle traces for verification of the technique.