Search Results

In transportation sector, higher engine thermal efficiency is currently required to solve the energy crisis and environmental problems. In spark ignition (SI) engine, lean-burn strategy is the promising approach to improve thermal efficiency and lower emissions. Olefins are the attractive component for gasoline additives, because they are more reactive and have advantage in lean limit extension. However, owing to lower research octane number (RON), it is expected to exhibit the drawback to reducing the anti-knock performance. The experiments were performed using a single-cylinder engine for 6 fuel types including gasoline blends which have difference in RON varying between 90.4 and 100.2. The results showed that adding olefin content to the premium gasoline provided unfavorable effect on auto-ignition as the auto-ignition happened at unburned gas temperature of 808 K which was 52 K lower at excess air of 2.0. Thus, it reduced anti-knock performance.

Homogeneous charge compression ignition (HCCI) combustion of methane was performed using dimethyl ether (DME) as an ignition improver. The ignition mechanisms of the methane/DME/air HCCI process were investigated on the basis of the chemical kinetics. The engine test was also conducted to verify the calculation results, and to determine the operation range. Analysis of the results showed that DME was an excellent ignition improver for methane, having two functions of temperature rise and OH radical supply. It was also shown that the operation range was extended to an overall equivalence ratio of 0.54 without knocking, by controlling DME quantity.