Study on the combustion and emission characteristics of a diesel engine with multi-injection modes based on experimental investigation and computational fluid dynamics modelling

Abstract

In this paper, experiments were carried out on a direct-injection diesel engine using a common-rail system, in order to study the effects of multi-injection modes on the combustion characteristics and pollutant emissions. A soot model was proposed for the post-injection mode, namely the Hiroyasu—Kodota averaged-reaction-rate soot model, which took into account both the chemical kinetics reaction and the turbulent mixing motion of the spray jet. Through integrating the revised soot model into a computational fluid dynamics (CFD) code, the combustion process and pollutants formation of the tested engine were simulated. The in-cylinder gas pressure and combustion heat release rate showed satisfactory agreement with measurements. The experimental data demonstrated that the pilot-injection mode was one of the most effective measures for reducing combustion noise. Meanwhile an optimum split-injection mode consisting of an appropriate pilot-injection fuel quantity combined with an optimal pilot-injection—main-injection interval could be achieved to decrease the nitrogen oxide (NO x) emission while not causing the particulate matter (PM) emission to deteriorate very much. Two innovative concepts of an active thermo-atmosphere and a passive inert atmosphere were presented from numerical simulation to discuss the effect of the pilot-injection mode on the combustion behaviour of the main injection. Regarding the post-injection mode, its prominent advantage was to decrease significantly the PM emission without an NO x emission penalty. Furthermore, by CFD modelling of the soot formation process, it can be observed that the turbulent mixing motion caused by the post-injection spray played a vital role in the soot oxidization process.

Combustion noise radiation during the acceleration of a turbocharged diesel engine operating with biodiesel or n-butanol diesel fuel blends

“…Electronically controlled common-rail injection systems that split the injection event into one pilot injection and one main injection can prove beneficial by facilitating the physical preparation of the air-fuel mixture, thus reducing premixed combustion and limiting (combustion) noise radiation. 7,8 On the other hand, the emergence of new promising diesel combustion technologies, such as low-temperature combustion and premixed charge compression ignition, are based on lower cycle temperatures, e.g. using very high exhaust gas recirculation (EGR) rates, in order to limit soot and nitrogen oxide (NO x ) emissions simultaneously; 9,10 these technologies are expected to have a detrimental effect on combustion noise owing to the higher portion of premixed combustion that the lower cycle temperatures induce.…”

Fast NOx emission prediction methodology via one-dimensional engine performance tools in heavy-duty engines

“…Shi et al 4 worked on a 3D CFD simulation of direct-injection (DI) diesel engine and used Hiroyasu-Kadota averaged-reaction-rate soot model for soot calculation. Via model calculations, they have shown that the significant effect of introducing fuel post-injection is to reduce soot production.…”

Multi-zone phenomenological model of combustion and emission characteristics and parametric investigations for split injections and multiple injections in common-rail direct-injection diesel engines

“…[15][16][17] It is reported that a post injection increased the turbulence level, which enhanced the soot oxidation process and also has a strong potential to meet the stringent emission norms. 18 Benajes at al. 19 reported that a post injection is an efficient way to reduce the soot emissions, with no change in the NO x emissions and a small increase in the BSFC.…”