One of the main factors that cause the earth that we live in is not as clean as it was before is the utilization of fossil fuel. Motorized vehicles still utilize fossil fuel as energy sources, and the number of motorized vehicles is growing every year. Biomass energy are one of the alternative energies currently being developed. Bioethanol are one of the technologies for fuel in motorized vehicles to utilize biomass as an alternative energy. The addition of bioethanol to gasoline will certainly change the fuel properties, the fuel will be more difficult to self-ignite so the pressure generated in the combustion chamber will be more consistent. Coefficient of variation (COV) represent the ratio of the standard deviation to the mean of a set of data, in this study in cylinder pressure data (IMEP) is used. Based on previous research that discussed the analysis of emission gas and fuel consumption on SI engine fueled with low-grade bioethanol and oxygenated additive, the authors examined further to analyze the characteristic of ethanol blend and oxygenated additive to COV_(IMEP) and Heat Release Rate (HRR) of various fuel mixture as well as COV_(IMEP) correlation with HRR at variable engine speed were investigated. The result show that compared with pure gasoline, ethanol blend decreases HRR. When oxygenated additive added to gasoline - ethanol blend, it increases its maximum heat release rate especially on fuel mixture E5 about 6.2% compared to E0. And the Correlation of COV and HRR; as COV value increases, HRR decreases. Whereas, when COV value decreases, HRR increases.
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