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To counteract the harmful effects of vehicle emissions on humans and the environment, such as global warming due to greenhouse gases, there is a focus on gaseous fuels as an alternative energy source of transportation. Heavy-duty natural gas vehicles are widely used to improve the air quality of urban areas in Korea because natural gas has the advantage of low greenhouse gas emission levels. However, more in-depth study is required in order for clean fuel vehicles to hold a dominant position over well-developed diesel vehicles. It is difficult to meet reinforced emission standards with only a lean combustion strategy without an aftertreatment system in a lean-burn natural gas engine. Hydrogen-natural gas (HCNG) blends have been proposed as an alternative to improve fuel economy and emissions of lean-burn natural gas engines, since they have a wider flammability range and faster burning speed. HCNG blends could also play a role as a technical bridge for the hydrogen era.

The combustion and exhaust emission characteristics of a DME fueled HCCI engine were investigated. Different fuel injection strategies were tested under various injection quantities and timings with exhaust gas recirculation (EGR). The combustion phase in HCCI was changed by an in-cylinder direct injection and EGR, due to changes in the in-cylinder temperature and mixture homogeneity. The gross indicated mean effective pressure (IMEPgross) increased and the hydrocarbon (HC) and carbon monoxide (CO) emissions decreased as the equivalence ratio was augmented. The IMEPgross with direct injection was greater than with the port injection due to retarded ignition timing resulting from latent heat of direct injected DME fuel. It was because that most of burn duration was completed before top dead center owing to higher ignitability for DME with high cetane number. However, HC and CO emissions were similar for both injection locations.