Location of Peak Pressure for an Axially Stratified-Charge Engine

Characteristics of the cylinder pressure waveform have long been considered for optimizing the operation of automotive engines. In particular, the strategy of maintaining a constant crank angle location of the peak cylinder pressure (LPP) during combustion has been predominant in the reported studies. This technique was therefore evaluated for an existing minimum fuel consumption calibration of an experimental axially stratified-charge (ASC) engine. For the ASC engine the LPP responded to spark advance and exhaust gas recirculation changes in a similar manner to that of a homogeneous-charge engine; LPP decreased with spark advance and increased with exhaust gas recirculation. However, the LPP for the predetermined minimum fuel consumption calibration of the ASC engine varied over a range of 8° to 19° after top dead center (ATDC) under steady state conditions. This is in contrast to the nearly constant 15° ATDC LPP observed by others for most homogeneous-charge engines. In light of the increased compression ratio and charge dilution used on the ASC engine, as well as the stratified-charge nature of the engine, the wide range of LPP experienced is not surprising.

Chassis dynamometer and road test results of a vehicle equipped with the ASC engine were largely in agreement with the steady-state observations. It is concluded that controlling the LPP at a single value is inadequate as a simple calibration or control method for the axially stratified-charge engine.