The Use of Dimethyl Ether as a Starting Aid for Methanol-Fueled SI Engines at Low Temperatures 881677
Methanol-fueled SI engines have proven to be difficult to start at ambient temperatures below approximately 10°C. The use of dimethyl ether (DME) is proposed to improve the cold starting performance of methanol-fueled SI engines. Tests to evaluate this idea were carried out with a modified single-cylinder CFR research engine having a compression ratio of 12:1. The engine was fueled with combinations of gaseous dimethyl ether and liquid methanol having DME mass fractions of 30%, 40%, 60% and 70%. For comparison, tests were also carried out with 100% methanol and with winter grade premium unleaded gasoline. Overall stoichiometric mixtures were used in all tests.
All DME/methanol combinations provided good cold starting behavior down to -15°C, the lowest temperature attainable by the refrigeration system. The engine required approximately 50% fewer cranking cycles to produce the first fired cycle when fueled by the DME/methanol combinations compared to fueling with gasoline. Over the range tested, the DME mass fraction had no discernable effect on the number of cranking cycles required to produce the first fired cycle.
Emissions of NOx from the engine fueled by DME/methanol combinations were comparable to those resulting from the use of methanol and lower than those emitted during operation on gasoline. Specific hydrocarbon emissions from the engine fueled by DME/methanol combinations were lower at any of the starting temperatures tested than those emitted during operation on neat methanol at its minimum starting temperature of 10°C. The amount of methanol found in the exhaust condensate from the engine fueled by DME/methanol combinations was substantially less than that found in the condensate of a neat methanol fueled engine.