Analysis of Supercharged HCCI Combustion Using a Blended Fuel 2011-32-0521

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted much interest as a combustion system that can achieve both low emissions and high efficiency. But the operating region of HCCI combustion is narrow, and it is difficult to control the auto-ignition timing.

This study focused on the use of a two-component fuel blend and supercharging. The blended fuel consisted of dimethyl ether (DME), which has attracted interest as alternative fuel for compression-ignition engines, and methane, the main component of natural gas. A spectroscopic technique was used to measure the light emission of the combustion flame in the combustion chamber in order to ascertain the combustion characteristics. HCCI combustion characteristics were analyzed in detail in the present study by measuring this light emission spectrum. The effects of the combustion process on the engine operating characteristics were also investigated under the conditions of the two-component fuel blend and supercharging.

A spectroscopic measurement technique was used to obtain the light emission spectra of the combustion flame. The results showed that the application of supercharging moderated the recombination reaction of CO and O. Notably, it was observed that post-ignition heat release occurred in two stages with the blended fuel of DME and methane when supercharging was applied, depending on the quantity of methane injected. That is attributed to the occurrence of the combustion reactions of the two fuels at different times. As a result, the rate of the cylinder pressure rise was controlled, enabling stable high-load operation. Because the quantity of DME injected determines the ignition timing, the engine load level can be adjusted by means of the quantity of methane injected and supercharging to achieve ignition near top dead center. This suggests the possibility of obtaining stable operation at even higher loads.