Fundamentals of Thermodynamic for Pressure-Based Low-Temperature Premixed Diesel Combustion Control

This thesis shows the results of investigations about the combustion mechanisms of low-temperature premixed processes, in particular those in which only a partial homogenization of the fuel mixture is achieved, since they represent a realistic solution for commercial engine applications. Measurements has been carried out on a modern 6-cylinder diesel engine equipped with a rapid-prototyping ECU and in-cylinder pressure sensors. The engine has been operated on a dynamic test bench. On the base of thorough combustion analysis a new closedloop combustion control strategy has been de ned. This has been completed by a procedure for allowing to switch the combustion mode to conventional di usive combustion extending the drivability range up to engine full-load. In a rst step a sensitivity analysis of the system has been carried out in order to identify engine constrains and mayor system limitations. A rst selection between useful actuating and target parameters has been made. The most relevant combustion mechanisms have been also highlighted. Matching these information, targeted measurements has been done under the variation of multiple parameters. In this way a clear target application area in the EGR-injection timing map could be de ned. Optimal combustion phasing has been found for combustion beginning at TDC and large rates of EGR. This has been done for low engine operation mode where charge dilution did not represent a limitation. However, increasing the engine load, because of the larger injection mass by almost constant fresh air quantity, it was necessary to limit the EGR rate for avoiding soot production and a deterioration of the fuel conversion. Therefore, the combustion process has been phased later in the expansion. After the identi cation of the combustion mechanisms and the application target, a new combustion control strategy has been de ned. The goal is the accomplishment of the de ned requirements concerning engine protection, i.e. rate of pressure rise and stability, fuel consumption and emissions. The proposed control strategy foresaw a control of the engine load over the injection duration, a control of the maximum rate of pressure rise over the injection timing (using a block-injection) and a control of the oxygen concentration in the charge over the