The rapidly increasing petroleum prices, uncertainties concerning its availability and growing concern of the environment revived research interests on the usage of alternative fuels in internal combustion engines. Biodiesel is a methyl or ethyl ester of fatty acids made from vegetable oils and animal fat. It can be used in diesel engines with very little or no engine modifications. In this present work the experimental investigations are carried out on the test engine operated with methyl esters of sesame oil and diesel blends. Comparative measures of performance parameters, smoke opacity, unburned hydrocarbons (HC), carbon monoxide (CO), Oxides of nitrogen (NOx), Carbon dioxide (CO2) and unused oxygen (O2) emissions are calculated. In the initial stage the tests are conducted on the four stroke single cylinder water cooled direct injection diesel engine by using diesel and base line data is generated. In the second stage, tests are carried out using Methyl esters of sesame oil with diesel blends at various loads and compared with the base line data obtained earlier. Engine performance in terms of higher brake thermal efficiency and lower brake specific fuel consumption and lower emissions (HC, CO, NOx) has observed for 20% Sesame oil and 80% diesel.__ampersandsignnbsp;the burning. This causes lower temperatures inside the cylinder and low NOx emissions in the exhaust gases. Exhaust gas temperatures of the blend are lower than those of the diesel fuel due to the lower heating value of the blend. It is proved that the lower temperature causes low NOx emissions when compared with diesel fuel. The variation of NOx emissions for D100 and SME blends with B.P is shown in Figure 4. NOx content is drastically reduced for S10 and S20 blends compared with D100 which is 1236ppm to 1061ppm and 1040ppm respectively, means it is reduced by 14% and 15% for the blends S10 and S20 compared to Diesel. Smoke The variation of smoke density with brake power of the engine for D100, S10, S20 and S30 by volume of concentrations is shown in Figure 5. It was observed that the smoke density of all the blends is lower than that of diesel at maximum load. The maximum smoke density recorded using diesel was 79.6 HSU and 58.8 HSU for S10 and 60 HSU for S20 at maximum brake power. Because of the oxygen enrichment contained by S10 and S20, it improves fuel evaporation during diffusion combustion which subsequently reduces the smoke density. The decrease in smoke density by percentage compared to D100 for S10 and S20 is 26% and 24.6% respectively. But for the S30 blend Smoke density slightly increased because of increased viscosity and incomplete combustion. Carbon Monoxide CO emission depending on many parameters such as air__ampersandsignndash;fuel ratio and the engine temperature are the causes of exhaust gas emissions in the internal combustion engine. It is one of the toxic products of combustion due to the improper burning of hydrocarbon (HC). Figure 6 shows the variation of CO emissions for D100 with other blends. From the plot it is observed that the CO emissions at full load for D100, S10, S20 and S30 are 0.07%, 0.06%, 0.07% and 0.06% respectively. It is clear from the plot that CO emissions decreases with S10, S30 blends, produced significantly lower CO emissions than that of diesel fuel because of Oxygen availability from this blend for complete combustion. Unburned Hydrocarbons The variation of HC with brake power of the engine for D100 and S10, S20, S30 blends are shown in Figure 7. Because of the oxygen enrichment contained by S10 and S20 improves fuel evaporation during diffusion combustion which slightly reduced the unburned Hydrocarbons. For D100, HC content is 58ppm but for S10, S20 it is reduced to 56ppm. These reductions indicate a more complete combustion of the fuel. The presence of oxygen in the fuel was thought to promote complete combustion. Unburned hydrocarbons are reduced by 3.4% using the blends S10 and S20 as compared with diesel. Carbon Dioxide The variation of CO2 with brake power of the engine for D100 and S10, S20, S30 blends are shown in Figure 8. From the plot it is observed that the CO2 content for D100, S10, S20, S30 blends at full load conditions are 8.5%, 8.4%, 8.3% and 8.5% respectively. But there is no considerable change in CO2 only slight decrease in CO2 occurred for S20 blend compared to D100. Since enough amount of oxygen is available for complete combustion. The CO2 emissions from a diesel engine indicate how efficiently the fuel is burnt inside the combustion chamber. The esterbased fuel burns more efficiently than diesel. CONCLUSIONS From the above discussions it was proved that exhaust emissions of the sesame oil__ampersandsignndash;diesel mixture were lower than that of using diesel and it can be used as an alternative fuel in view of reduced environmental pollution by reduction in HC, NOx, CO emissions and also in increased performance parameters like brake thermal efficiency and decreased brake specific fuel consumption. Properties of S20 are nearer to diesel and it is. __ampersandsignnbsp; ACKNOWLEDGEMENT The authors acknowledge the immense help received from the scholars whose articles are cited and included in references of this manuscript. The authors are also grateful to authors / editors / publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.