Computational analysis of injection-rate shapes in a small-bore direct-injection diesel engine

Abstract

The purpose of this study is to analyse the differences in the combustion process, and pollutants formation (especially soot) due to top-hat and boot injection-rate shapes at one specific high-load point of a single-cylinder small-bore diesel engine using multidimensional engine simulations. The simulations are performed using a response interactive flamelet model with detailed chemical kinetics. A detailed chemistry-based soot model is used for the prediction of soot emissions. The heights of the first and second stages of the boot shape are varied to observe the effect of the injected fuel mass distribution. In addition, results of boot shapes are compared with a trapezoidal (top-hat) shape. A detailed analysis of soot formation and oxidation is also presented for some selected rate shapes. Through computational analysis it is shown that the boot shapes have the potential to decrease combustion-generated noise and to lower emissions at the investigated load point compared to the top-hat shape. Variations in the temporal distribution of the injected fuel mass show that a lower height of the first stage and a higher height of the second stage of the boot shape result in a relatively slower rise of heat release (lower combustion-generated noise) in the early part of combustion and enhanced soot oxidation as a result of higher spray momentum near the end of injection.