A Comparison of Burn Characteristics and Exhaust Emissions from Off-Highway Engines Fueled by E0 and E85

Ethanol fuel has received renewed attention in recent years because of its oxygenate content and its potential to reduce greenhouse gas emissions from spark ignition engines. The economic impact on farm industry has been one of the drivers for its use in engines in the U.S. Although ethanol, in various blends, has been used in automotive engines for almost a decade the fuel has seldom been utilized in off-highway engines where the fuel systems are not well controlled. This investigation was conducted to evaluate exhaust emissions and combustion characteristics of E85 fuel in an off-highway engine used in farm equipment. A single-cylinder, four-stroke, spark ignition engine equipped with a carburetor was used to investigate combustion and exhaust emissions produced by gasoline and blends of gasoline and ethanol fuels. The engine fuel system was modified to handle flow rates required by the engine. A variable size-metering orifice was used to control air-to-fuel ratios. The ignition system was modified to allow the operator to change ignition timing.

Ethanol blends improved specific energy consumption relative to E0. At stoichiometric air-to-fuel ratio the alcohol blends improved exhaust CO emissions marginally. However, there were consistent reductions in NOx levels with blends at the OEM ignition settings. Combustion of E85 in the engine resulted in higher levels of hydrocarbons relative to E0 over most of the engine operating conditions. The E85 engine exhaust contained aldehydes at concentrations much higher than those measured with the E0 and E10 fuels.

An examination of the engine revealed increased combustion chamber deposits after the engine was run on E-85 fuel for a prolonged period of time of over 150 hours. Analysis of cylinder pressure data showed that E85 had slightly faster main burn rate than the E0 fuel. Not much differences were noticed when E10 was used in the engine. Relative to E-0 the specific HC emissions increased when the engine was run on E-85 at the OEM spark timing while a smaller increase in HC was measured with the E10 fuel.