The overall objective of this study is to assess the benefits and limitations of the diesel fuel blended with oxygenated compounds, (oxygenates), on combustion and performance in diesel engines. In the wide variety of oxygenates, it is very essential to identify the suitable oxygenates to blend with diesel and to be used as diesel formulations based on their physical and chemical properties. The impact and the limitations of oxygenates on the diesel combustion process have been defined only to a limited extent, because the data available in the literature are confounded by different engine types and operating conditions. However in this paper, three selected oxygenates were tested in the same engine, under identical operating conditions.
The experimental investigation was carried out in three phases. Firstly, initial screening of oxygenates were carried out by studying their physical and chemical characteristics after an extensive literature survey and review. Based on this, dibutyl maleate, diethyl malonate and diethyl maleate were selected and blended with diesel in different proportions by volume for engine testing and investigation. In the second phase, experimental investigations were carried out to evaluate the effects of these oxygenates on combustion and performance. The tests were carried out on a single cylinder, naturally aspirated, direct injection diesel engine.
Finally, the evaluated experimental values were compared with the values obtained with the standard commercial diesel fuel and the results were found to be satisfactory in the acceptable level.
The study showed that the premixed combustion is prolonged and the duration of the diffusive combustion is shortened with the increase in oxygenates addition. The cylinder gas pressure, the rate of pressure rise, the heat release and the rate of heat release also increased with the addition of oxygenates whereas the maximum gas temperature decreases with the increase in oxygenate addition. The ignition delay increases while the rapid combustion duration and the total combustion duration shows less variation with the addition. The brake specific energy consumption and the thermal efficiency increases with the increase in addition of oxygenate. The CO, smoke and PM emissions decrease with the increase in oxygenates addition and there is no increase of NOx.
