Petroleum supply and environmental issues have increased interest in renewable low polluting alternative fuels. Published test results generally indicate decreased pollution with similar power output from internal combustion engines burning alternative fuels. More specifically, diesel engines burning biodiesel derived from plant oils and animal fats, not only reduce harmful exhaust emissions, but are renewable and environmentally friendly.

A literature review found little previous research with biodiesel in small commercial diesel engines. This paper presents the research that was conducted to study the effect of biodiesel/diesel fuel blends on engine performance and emissions for a Yanmar L100 EE (7.1 kW) engine. This is a standard commercial grade diesel engine used for small equipment such as generators.

Independent engine dynamometer and emissions testing were performed to validate the lower emission claims and assess the feasibility of alternative fuels. A testing apparatus capable of making relevant measurements was designed, built and used to perform this study.

Fuel blends used included B2, B20, B40, B60, B80, and B100 where the biodiesel component of the blend was a commercial product. An analysis of the fuel showed large percentages of linoleic acid, palmitic acid and stearic acid which is typical for a blend of soybean oil and beef tallow.

Test were performed at a constant torque (95 % of the continuously rated value) and variable engine speeds. Test results included calculated values of BMEP, BSFC, thermal efficiency, air mass flow rate, air fuel ratio, corrected NOx, energy lost to exhaust, and heat rejection, and measured values of unburned hydrocarbons, carbon monoxide, and carbon dioxide.

Results indicate an increase in thermal efficiency compared to standard diesel and significant reductions of unburned hydrocarbons and carbon monoxide at all engine speeds. Brake specific fuel consumption increased with increasing percent biodiesel consistent with the decreased energy content of blended fuel. Significantly, there were small but consistent reductions in corrected NOx for all blends at all speeds. We posit possible explanations for these results, which are contrary to the published results for larger engines which show an increase in NOx for biodiesel blends.

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