Abstract
The control of ignition and combustion behavior in a premixed charge compression ignition engine was investigated and ultra low NOx and smokeless combustion was achieved with direct in-cylinder injection of water or methanol as a reaction suppressor. The reaction suppressing effect increased with advancing injection timings of the suppressors, resulting from greater decreases in charge temperature as compression progressed. However, as the in-cylinder temperature is less than the water boiling point before 60° CA BTDC, water vaporization is delayed with too early injection timing and the suppressing effect decreased. Therefore, the optimum timing in terms of the suppressing effect was found at 60° CA BTDC thereabouts when the in-cylinder gas temperature reached the boiling point of water. Methanol showed the ignition suppression effect similar to water, and the water or methanol injection significantly reduced the heat release at cool flame region and also the rapid combustion after the hot flame, resulting from suppression of charge temperature increase.
