Evaluation of the effects of injection timing and rate-shape on diesel low temperature combustion using advanced CFD modeling

It is well known that injection strategies including the injection timing and the injection rate-shape play an important role in determining engine performance, especially pollutant emissions. But how the injection timing and the injection rate-shape quantitatively affect the performance of diesel low temperature combustion (LTC) is still not well understood. In this paper, the KIVA–CHEMKIN computational fluid dynamics (CFD) code with an improved spray model is used to simulate the spray and combustion processes of diesel LTC with early and late injection timings and seven different injection rate-shapes. The validation of the models is based on comparisons with laser diagnostic and in-cylinder pressure data under a low load operating condition. It is concluded that the use of early injection provides lower soot, HC and CO emissions but higher NOx emissions than the late injection. A rectangular-type (case1) and boot-type (case 4) injection rate-shape displays the potential to reduce the soot, HC and CO emissions compared the other generic rate-shapes considered.