Prediction of Peak Cylinder Pressure Variations Over Varying Inlet Air Condition of Compression-Ignition Engine

Peak cylinder pressure $(pmax)$ of a compression-ignition engine can be affected by the engine inlet air condition, such as its inlet air temperature $(Ti)$ and pressure $(pi)$⁠. The variation of peak cylinder pressure due to varying inlet air temperature or pressure is analytically studied. A model is developed and simplified, and thus the variations of $pmax$ can be predicted along with varying inlet air temperature or pressure. The analysis and prediction indicate that cylinder active compression ratio (CR) and intake air boost ratio $(pm0∕pi0)$ play relatively significant roles in affecting the variation of $pmax$ over inlet air temperature and pressure, and the pressure variation is proportional to $CRk$ and ratio $pm0∕pi0$⁠. Comparison between the predicted results using the simplified model and those from engine experiments shows a close agreement in both the trend and magnitude. The investigation and prediction also include modeling the variation in $pmax$ due to varying the cylinder TDC clearance volume $(Vc)$⁠. The simplified model is presented and shows that the change in $pmax$ versus varying $Vc$ also depends on the cylinder compression ratio. It is indicated that for a certain change in the clearance volume, a higher compression-ratio configuration would produce a greater change in $pmax$ than a lower one does, especially as the rest of the engine design and operating parameters remain unchanged.