Comparison of performance of a Greener direct-injection stratified-charge (DISC) engine with a spark-ignition engine using a simplified model

The direct-injection stratified charge (DISC) engine is a hybrid between spark ignition (SI) and compression-ignition engines, it combines many of the best features of both with some unique advantages of its own. This includes multi-fuel capability, high thermal efficiency, low NOx production, and low particulate emissions.This work shows how simple semi-global models can predict the performance of the SI and DISC engines with reasonable accuracy, without going to details of modeling for internal processes such as: swirl, mixing and detailed combustion kinetics.The operating variables studied were inlet manifold pressure pi, exhaust manifold pressure pe, engine speed N, equivalence ratio Φ, and volumetric efficiency ηv at different loads. The corresponding performance parameters were the brake mean effective pressure bmep, brake power Pb, and brake thermal efficiency ηb,th. The main contribution of this work is the production of friendly set of curve-fitting correlations for engine performance. The bmep and the Pb increase with the load for both engines. For spark ignition engines the bmep increases by about 70% when load increases from 50% to 100%. With the DISC engine, this ratio increases to 75%. The percent improvement in ηb,th for the DISC to the SI engine is around 50% which increases with part load, lower compression ratio rc and pi.

► The contribution of this work is the friendly set of curve-fitting correlations, based on experimental and simulation results.
► The other main contribution is showing how semi-global models can predict the performance of SI and DISC, with reasonable accuracy.
► The DISC engine has a higher brake thermal efficiency than the spark ignition engine at different loads, 40–60%.
► The disadvantage of the DISC engine is the low brake power (unless the inlet pressure is boosted).
► The best value of mechanical friction rubbing factor is 0.2.