A Comparative Analysis on Engine Performance of a Conventional Diesel Fuel and 10% Biodiesel Blends Produced from Coconut Oils

摘要

This paper presents engine performance and emissions of coconut oil-derived 10% biodiesel blends in petroleum diesel demonstrating simultaneous reduction of smoke and NO_x emissions and increased brake power. The experiments were performed in a single-cylinder version of a light-duty diesel engine for three different fuels including a conventional diesel fuel and two B10 fuels of chemical-catalyst-based methyl-ester biodiesel (B10_(mc)) and biological-catalyst-based ethyl-ester biodiesel (B10_(eb)). The engine tests were conducted at fixed speed of 2000 rpm and injection pressure of 130 MPa. In addition to the fuel variation, the injection timing and rate of exhaust gas recirculation (EGR) were also varied because they impact the combustion and thus the efficiency and emissions significantly. For each operating condition, the in-cylinder pressure traces were recorded using a piezo-electric pressure transducer, which was used to calculate the indicated mean effective pressure (IMEP), apparent heat release rate (aHRR), burn duration. The brake MEP (BMEP) was calculated from a brake torque reading in the EC dynamometer, which was then used to obtain friction MEP (FMEP) as the difference between IMEP and BMEP. The results show lower IMEP for B10_(mc) and B10_(eb) than that of petroleum diesel, which is expected considering the lower calorific value of B10 fuels. However, the BMEP of B10_(mc) displays a comparable value to that of petroleum diesel. The reason for this unexpected observation is likely enhanced lubrication and thus reduced frictional loss because the addition of coconut-derived biodiesel compensates for the reduced IMEP. This effect is higher when B10_(eb) is used, showing even higher BMEP than the petroleum diesel fuel, particularly at the earliest and latest injection timings. The advantages of B10_(eb) over B10_(mc) as well as petroleum diesel are also evident in the engine-out emissions. The emission results show that the smoke emissions are significantly lower for B10_(eb) than those of B10_(mc) or the petroleum diesel. The NO_x emissions of B10_(eb) are also lowest among the tested fuels. This finding is significant because B10_(mc) show higher NO_x emissions than the diesel fuel and B10_(eb). Another interesting finding from the experiments was the fact that EGR can be more effective in achieving further NO_x reduction when B10_(eb) was used than the petroleum diesel. For tested conditions of this study, the EGR tests demonstrate that B10_(eb) achieves 10% opacity and 4 g/kWh NO_x emission, which are lower than 20% opacity and 5.5 g/kWh NO_x emission of the petroleum diesel. Therefore, B10_(eb) in this study not only demonstrate a benefit in increasing the brake power of a conventional diesel fuel but also in simultaneously reducing smoke and NO_x emissions.