Real-time Heat Release Analysis for Model-based Control of Diesel Combustion

A number of cylinder-pressure derived parameters including the crank angles of maximum pressure, maximum rate of pressure rise, and 50% heat released are considered as among the desired feedback for cycle-by-cycle adaptive control of diesel combustion. For real-time computation of these parameters, the heat release analyses based on the first law of thermodynamics are used. This paper intends to identify the operating regions where the simplified heat release approach provides sufficient accuracy for control applications and also highlights those regions where its use can lead to significant errors in the calculated parameters. The effects of the cylinder charge-to-wall heat transfer and the temperature dependence of the specific heat ratio on the model performance are reported. A new computationally efficient algorithm for estimating the crank angle of 50% heat released with adequate accuracy is proposed for computation in real-time. The improved heat release analyzing algorithms are programmed with a set of field programmable gate array (FPGA) devices that condition the cylinder pressure signal, process/analyze the data and provide the necessary feedback to the fuel-injection model running on subsequent real-time FPGA controllers. The performance of the new algorithms has been demonstrated against various levels of boost, engine load and exhaust gas recirculation with experimental tests on a modern diesel engine.