Autoignition of low-heating value gases in a direct-injected diesel engine.

The autoignition of gaseous mixtures representative of coal-derived low-heating-value gaseous fuels in a direct injected diesel engine was investigated theoretically over pressure and temperature ranges of 10 to 50 atm and 800 to 1000 K respectively. A computer model was validated with experimental engine data operated on direct injected synthetic coal gas by Caterpillar, Inc. The computed results demonstrated the importance of the characteristic time associated with the chemical kinetics when compared to fluid dynamics mixing. High gas temperatures resulting from high compression ratios, high boost, high inlet air temperature or other ignition aids are needed to ignite these gases in a compression-ignition engine in the required time. The predicted sensitivity of the autoignition delay time to changes in the engine operating conditions was significant for temperature, but almost negligible for pressure in excess of the 30 atm. Investigation of the chemical kinetics process indicated that the autoignition delay time, which reflects the extent of reaction progress, is primarily a measure of the time required to build up the radical species. Of all the combustible species used to model these low-heating-value fuel gases (hydrogen, carbon monoxide, propane, and methane) the chemistry of methane and propane is most important during the pre-ignition period. The model was also used to determine a correlation between the ignition delay and the cylinder temperature and fuel composition at determined engine parameters. A constant volume combustion bomb system was designed as a vehicle to rate these low quality fuels under typical diesel engine conditions. The development of a scale that depends on the fuel composition and engine operating parameters would be valuable for the diesel engine industry