Use of a Pressure Reactive Piston to Control Diesel PCCI Operation - A Modeling Study

The heavy-duty diesel engine industry is required to meet stringent emission standards. There is also the demand for more fuel efficient engines by the customer. In a previous study on an engine with variable intake valve closure timing, the authors found that an early single injection and accompanying premixed charge compression ignition (PCCI) combustion provides advantages in emissions and fuel economy; however, unacceptably high peak pressures and rates of pressure-rise impose a severe operating constraint. The use of a Pressure Reactive Piston assembly (PRP) as a means to limit peak pressures is explored in the present work. The concept is applied to a heavy-duty diesel engine and genetic algorithms (GA) are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to provide an optimized set of operating variables. Different sets of PRP parameters (viz. preload, spring constant, damping coefficient and crown mass) were used in an optimization study and the effects of intake valve closure timing, start-of-injection timing, injection duration and exhaust gas recirculation were investigated. The results show that in cases when the combustion is premixed, the inclusion of PRP offers a significant reduction in rate-of-pressure-rise, peak pressure, brake specific fuel consumption and soot and NOx emissions. These benefits are in addition to the advantages offered by variable IVC timing. It is also seen that using PRP could be an effective means to control the timing of the main combustion event and hence the emissions.