Abstract
The aim of this work is to investigate the effect fuel properties on combustion and emission characteristics of the direct injection (DI) diesel engine running with biodiesel (BD) fuel and to compare with those of petroleum diesel (PD) fuel. The rice bran oil was chosen and this oil is transesterified in to methyl ester. The physical, chemical and thermodynamic properties of the fuel such as viscosity, density, bulk modulus, flash and fire points, cloud and pour points, oxygen %, calorific value, C/H ratio, carbon chain length, molecular weight, saturation %, iodine value, and the cetane number of the rice bran oil methyl ester (ROME) was characterized as per ASTM norms and found comparable to PD fuel. Experiments are conducted in a single cylinder, 3.72 kW, constant speed (1500 rpm), water cooled, DI diesel engine equipped with in-line fuel injection system, and fueled with ROME and baseline PD. The engine is also tested with preheated (at 60 ℃) ROME (ROME_H) to maintain the same spray characteristics of PD fuel. It was observed that, the crank angle position of peak cylinder pressures for ROME was shifted towards top dead center, and the peak pressures were increased due to advanced dynamic injection timing, probably caused by its higher bulk modulus. Heat release analysis based on single-zone model has been evaluated from the acquired data. The results shows that, both the fuels exhibited similar combustion stages; however ROME showed earlier start of combustion and higher heat release during premixed combustion phase at all engine loads. The intensity of premixed combustion is decreased and diffused combustion is increased with preheated ROME. The gaseous emissions such as oxides of nitrogen (NO_x), total hydrocarbons (HC), carbon monoxide (CO), and smoke under different load conditions were measured. Dramatically, lower HC emissions were found with the ROME fueled engine and at full load, the HC's are reduced by 28%. The HC emissions are further reduced with preheated ROME. It is also observed that, the NO_x emissions of ROME fueled engine shows higher concentrations, when compared to PD fuel, for the same static injection timing. When the engine is running with preheated ROME, the NO_x emissions are decreased and at full load NO_x levels are lower than PD fuel. At full load, there is a substantial reduction in the smoke emission was observed and the reduction was attributed to its lower 'C/H' ratio, and oxygen present in the ROME. However, when the preheated ester is used, the smoke emission was increased due to prolonged combustion (diffusion) at lower viscosity. There is a significant reduction in CO emissions was observed with the preheated ROME.
