Abstract
An advanced numerical investigation has been carried out in order to study the effect of multiple injection strategies on Caterpillar heavy-duty diesel engine emissions. Both different injected fuel percentages for each pulse and several dwells between main and post phase were investigated via computational fluid dynamics (CFD) and large eddy simulation (LES). Two sets of simulations were taken into account for 10% and 20% exhaust gas recirculation (EGR) fractions. In the first one, the main injection was split into two identical phases, while in the second one into three pulses. Within each set, three strategies were considered, increasing the amount of fuel injected during the main and concurrently decreasing the post pulse. Overall, 48 simulations were employed, since four different dwells between the last phase of the main and post injection were considered. Results show that the pollutant emissions minimization has been obtained for the Schemes injecting 65% and 70% of fuel for both two and three split strategies, but for different values of dwell. In fact, emissions very close to each other for NOx and particulate matter have been reached for these cases. Reductions of about −30% and −71% were respectively obtained for NOx and soot in comparison with experimental emissions related to the single injection case.
Highlights
Even if diesel engines produce lower partially burned hydrocarbons in comparison with gasoline engines, NOx and particulate matter are significant pollutants that require proper control strategies because of their impact on health and the environment [1]
Research efforts can be focused on both the development of after-treatment devices and the study of in-cylinder combustion phenomena [2]. This latter aspect involves several physical quantities and operative parameters, as well as different combustion strategies: one of the most advances to simultaneously reduce NOx and soot emissions while maintaining fuel consumption and engine performance is multiple injection combustion [3]. Since both particulate matter and NOx are strongly dependent on temperature and equivalence ratio, their emission can be reduced by controlling the flame temperature and the mixture formation through an optimized injection law during the compression and power strokes [4]
The first scheme of the first strategy can be represented as 5(10)5(15)32.5(4)32.5(x)25: the variable dwell between the main and the post pulse is represented by the x letter
Summary
Even if diesel engines produce lower partially burned hydrocarbons in comparison with gasoline engines, NOx and particulate matter are significant pollutants that require proper control strategies because of their impact on health and the environment [1] To reduce this impact, research efforts can be focused on both the development of after-treatment devices and the study of in-cylinder combustion phenomena [2]. Research efforts can be focused on both the development of after-treatment devices and the study of in-cylinder combustion phenomena [2] This latter aspect involves several physical quantities and operative parameters, as well as different combustion strategies: one of the most advances to simultaneously reduce NOx and soot emissions while maintaining fuel consumption and engine performance is multiple injection combustion [3]. About multiple injection strategies will be discussed: the effect on pollutant emissions of the fuel quantity associated to each pulse and the dwell between the main and post phase will be analyzed as well as the impact of the main injection splitting into two and three shorter pulses
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