1987-11-01

Unassisted Cold Starts to −29°C and Steady-State Tests of a Direct-Injection Stratified-Charge (DISC) Engine Operated on Heat Alcohols 872066

Unassisted cold starts at ambient temperatures down to -29°C were achieved on neat alcohols in a cold room using a 4.8-L direct-injection stratified-charge (DISC) engine with late fuel injection. Starting times for the United Parcel Service (UPS) stratified-charge engine were less than three seconds at -29°C. Cold starts to -29°C also were achieved with gasoline and diesel fuel. Additionally, an SAE OW oil was used as a fuel and started at -18°C.
A key to cold starting was achieving a minimum cranking speed (110 r/min) that ensured injection of fuel. Higher cranking speeds improved cold starting. Increased injection rate enhanced cold starting. For alcohol, the advantage of using a long-duration high-power ignition system was confirmed. The ability to fire and run was relatively independent of the wide range of fuel properties, including heat of vaporization, heat of combustion, and volatility. High fuel viscosity (diesel and OW oil) affected the fuel injection system's ability to inject at low temperatures and promoted shorting of the spark plugs by bridging the plug gaps with liquid fuel. Increased plug gap minimized this latter tendency.
Steady-state operation on an engine-dynamometer at 1000, 2000, and 3000 r/min for a wide range of loads revealed lower brake thermal efficiency (BTE) with methanol and even lower BTE with ethanol compared to BTE with gasoline due to slower combustion and lower combustion efficiency with the alcohols. Accordingly, unburned fuel emissions were higher for alcohol while NOx emissions are substantially lower. Carbon monoxide emissions were about the same magnitude for all fuels. When fueled with alcohol, inadequate fuel-air mixing may explain the characteristics of this particular engine.

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