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Electrical energy generators often use commercial diesel engines as a source of mechanical power at a fixed rotational speed. While the frequency of the grid cannot be modified, electric generators demand reciprocating engines to operate not always at their best efficiency range. By the use of a generator capable of running on different speeds and an electronic system that controls the output frequency, it is possible to operate the engines at their best efficiency load points. This paper describes the development of a variable speed diesel fueled electric generator with permanent-magnet high-efficiency synchronous generator. It was used a 1-D computational code to build a map through a mean-value model that combines speed and load to achieve the required power with the best engine efficiency. The generator set was instrumented whilebrake and indicated data were obtained in order validate the computational model.

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.