A Modeling Investigation of Combustion Control Variables During DI-Diesel HCCI Engine Transients

A comprehensive system level modeling approach is used to understand the effects of the various physical actuators during diesel HCCI transients. Control concepts during transient operations are simulated using a set of actuators suitable for combustion control in diesel HCCI engines (intake valve actuation, injection timing, cooled EGR, intake boost pressure and droplet size). The impact of these actuating techniques on the overall engine performance is quantified by investigating the amount of actuation required, timing of actuation and the use of a combination of actuators. Combined actuation improved actuation space that can be used to phase combustion timing better and in extending the operating range. The results from transient simulations indicate that diesel HCCI operation would benefit from the combined actuation of intake valve closure, injection timing, boost and cooled EGR. While IVC actuation and cooled EGR provide ways to improve combustion phasing, variations in intake boost pressure and injection timing help to reduce wall wetting, improve fuel economy, increase homogeneity and maintain combustion stability. An example of a mode transition between conventional diesel and HCCI combustion regimes is also demonstrated by altering the charge preparation (spray characteristics) and using a combination of control variables. The study shows that diesel-HCCI-diesel mode transitions can be achieved with minimal effects from cycle-to-cycle coupling by trapping the least amount of hot residuals from previous engine cycles.