The Effect of Ethanol Fuels on the Power and Emissions of a Small Mass-Produced Utility Engine 2019-32-0607

The effect of low level ethanol fuel on the power and emissions characteristics was studied in a small, mass produced, carbureted, spark-ignited, Briggs and Stratton Vanguard 19L2 engine. Ethanol has been shown to be an attractive renewable fuel by the automotive industry; having anti-knock properties, potential power benefits, and emissions reduction benefits. With increasing availability and the possible mandates of higher ethanol content in pump gasoline, there is interest in exploring the effect of using higher content ethanol fuels in the small utility engine market. The fuels in this study were prepared by gravimetrically mixing 98.7% ethanol with a balance of 87 octane no-ethanol gasoline in approximately 5% increments from pure gasoline to 25% ethanol. Alcor Petrolab performed fuel analysis on the blended fuels and determined the actual volumetric ethanol content was within 2%.

The purpose of this study is to evaluate the performance and emissions of a small utility engine across several load points. Compared to previous works, this study concentrated on engine operation at wide open throttle as any decrease in engine power output due to a fuel's ethanol content would negatively impact an engine's sales potential; small engines developed for this market sector are engineered to meet a certain horsepower rating. For this study, the engine governor was set at 3800 rpm. After the engine governor was adjusted to its maximum position (i.e. 3800 rpm), the engine was loaded by a hydraulic dynamometer. As the load was increased, the engine speed slowly decreased as the dynamometer's torque was increased. Full load engine operation down to an engine speed of approximately 2800 rpm, just higher than the engine's torque peak, was investigated. In addition to engine out emissions and shaft power, exhaust temperatures and cylinder pressure were recorded.

Overall, the experimental results showed increasing ethanol content results in a small gain in power output even though the energy content of the fuel was decreasing. It was found that nitrogen oxides plus hydrocarbons emissions slightly decreased or stayed equivalent while the carbon monoxide emissions were reduced by 10% for the E10 blend and by 20% for the E15 blend. Finally, cylinder pressure and heat release analysis showed that the addition of ethanol increased peak cylinder pressure and advanced the main heat release closer towards top dead center.