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Semi-premixed diesel combustion with a twin peak shaped heat release with the two-stage fuel injection (twin combustion) has the potential to establish efficient, low emission, and low noise operation. However, with twin combustion at low loads the indicated thermal efficiencies are poorer than at medium loads due to the lower combustion efficiencies. In this report, to increase the combustion efficiencies at low loads, the thermal efficiency related parameters were investigated in a 0.55 L single cylinder diesel engine. The results show that the indicated thermal efficiency improves with increases in the intake gas temperatures at low loads. However, at the higher loads where the combustion efficiencies are somewhat higher the indicated thermal efficiencies decrease with increases in the intake gas temperatures due to increases in the cooling losses.

Nowadays, due to stringent emission regulations, it is imperative to incorporate modeling efforts with experiments. This paper presents the development of a phenomenological model to investigate the effects of various in-cylinder strategies on combustion and emission characteristics of a common-rail direct-injection (CRDI) diesel engine. Experiments were conducted on a single-cylinder, supercharged engine with displacement volume of 0.55 l at different operating conditions with various combinations of injection pressure, number of injections involving single injection and multiple injections with two injection pulses, and EGR. Data obtained from experiments was also used for model validation. The model incorporated detailed phenomenological aspects of spray growth, air entrainment, droplet evaporation, wall impingement, ignition delay, premixed and mixing-controlled combustion rates, and emissions of nitrogen oxides (NOx) and diesel soot.

The influence of fuel volatility on the thermal efficiency of premixed diesel combustion was evaluated with three ordinary diesel fuels with different distillation temperature distributions and also with a primary reference fuel with an octane number of 20 (PRF20) as a high volatility fuel. The experiments were conducted on a single-cylinder DI diesel engine for the premixed diesel combustion with a single injection at 11% intake oxygen concentration and conventional diesel combustion with a pilot fuel injection at 21% intake oxygen concentration. With the premixed diesel combustion, the indicated thermal efficiencies with the ordinary diesel fuels were lower than with PRF20 although the shapes of the rate of heat release and the combustion efficiencies calculated from the exhaust gas components were almost unchanged. With the conventional diesel combustion, the indicated thermal efficiencies with the ordinary diesel fuels and PRF20 were similar.