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Natural Gas (NG) is currently a cost effective substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. Dual-Fuel engines substitute NG in place of diesel for decreased NOx and soot emissions, but suffer from high engine-out methane (CH4) emissions. Premixed Dual-Fuel Combustion (PDFC) is one method of decreasing methane emissions and simultaneously improving engine efficiency while maintaining low NOx and soot levels. PDFC utilizes an early diesel injection to adjust the flammability of the premixed charge, promoting more uniform burning of methane. Engine experiments were carried out using a NG and diesel HD single cylinder research engine. Key speeds and loads were explored in order to determine where PDFC is effective at reducing engine-out methane emissions over Conventional Dual-Fuel which uses a single diesel injection for ignition.

Vegetable oils have been seen as promising surrogates to petroleum diesel in compression ignition internal combustion engines, showing similar performance and combustion characteristics of the fossil fuel. Nevertheless, the use of straight (crude) vegetable oil (SVO) is unfavorable due to its high viscosity, which affects the Sauter Mean Diameter of fuel spray and, consequently, fuel-air mixing process, resulting in incomplete combustion. The SVO heating, as well as transesterification and blending with diesel or additives, are some of the techniques to reduce its viscosity and enable its use. Of these the most simple and direct is the heating and was used in this paper to evaluate the performance and emissions of a diesel engine fueled with preheated soybean oil (PSO) by electrical resistances. The experiments were carried out in a single cylinder four-stroke compression ignition engine with mechanical fuel injection.

Using Exhaust Gas Recycling (EGR) on internal combustion engines enables the reduction of emissions with a low or even no cost to the engine efficiency at part-load operation. The charge dilution with EGR can even increase the engine efficiency due to de-throttling and reduction of part load pumping losses. This experimental study proposed the use of late exhaust valve closure (LEVC) to achieve internal EGR (increased residual gas trapping). A naturally aspirated single cylinder direct injection spark ignition engine equipped with four electro-hydraulic actuated valves that enabled full valve timing and lift variation. Eight levels of positive valve overlap (PVO) with LEVC were used at the constant load of 6.0 bar IMEP and the speed of 1500 rpm. The results have shown that later exhaust valve closure (EVC) required greater intake pressures to maintain the engine load due to the higher burned gases content. Hence, lower pumping losses and thus higher indicated efficiency were obtained.