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This paper aims to evaluate the impact of cetane improvers on the combustion, performance and emission characteristics of a compression ignition engine fueled with a 20% peppermint bio-oil/diesel blend (P20). It is hypothesized that the low viscosity and boiling point of peppermint oil could improve the atomization characteristics of the fuel. However, the usage of peppermint oil is restricted due to its low cetane index. To improve this, Diethyl Ether (DEE) and Di- tertiary Butyl Peroxide (DTBP) are added to the P20 blend. The tests are performed in a single-cylinder naturally aspirated water-cooled diesel engine and results indicate that NOx emission for P20 + DEE and P20 + DTBP is decreased by 10.4% and 9.8%, respectively, when compared to P20 at full load condition. Among these two cetane improvers, DTBP is more effective in reducing the CO, HC and smoke emission and the performance of the engine was reported to be higher for P20 + DTBP blends.

In the search for an alternative energy source with lesser pollution for transportation needs, bio-oil, a denser and viscous fuel that needs a transesterification process, have been widely considered for diesel engines. However, these problems are solved by using low viscous biofuel, but this improvement also significantly leads to increased NOx emission. Hence this present study investigates the usage of a low viscous biofuel in the CRDI engine with measures to reduce NOx emission through water injection technique. The low viscous bio-oil was used in this study along with an ignition enhancer (di-tert-butyl-peroxide), non-metallic nano additive (rice husk). They were tested in a constant speed, single-cylinder, diesel engine for various loads. Considering the brake thermal efficiency (BTE), 2% and 150 ppm were selected as the optimum value after testing five ratios (1%, 1.5%, 2%, 2.5% and 3%) of di tert butyl peroxide (DTBP) and four ratios (50, 100, 150 and 200 ppm) of rice husk (RH). The lemon peel oil (LPO) with the optimum additive ratio produced 30.69% BTE, which was 4.7% lesser than diesel fuel. A considerable decrease in fuel consumption and emissions except for nitrogen oxides (NOx) is recorded. NOx emission increased by 17.3% for the biofuel blend containing RH and DTBP. To control NOx emission, 2% of water was injected into the intake manifold with the fresh intake air. Two percent by vol. was finalised after experimenting four ratios (1%, 2%, 3% and 4%) of water addition. This 2% water reduces 11% of NOx emission and affects the other outputs, denoted with the 8.9% reduced BTE value compared with diesel fuel. Thus, the LPOC combination proved to operate well in the CRDI engine and produces lower NOx emissions than other LPO blends.