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Previous research has shown that the homogeneous charge compression ignition (HCCI) combustion concept holds promise for reducing pollutants (i.e. NOx, soot) while maintaining high thermal efficiency. However, it can be difficult to control the operation of the HCCI engines even under steady state running conditions. Power density may also be limited if high inlet air temperatures are used for achieving ignition. A methodology using a small pilot quantity of diesel fuel injected during the compression stroke to improve the power density and operation control is considered in this paper. Multidimensional computations were carried out for an HCCI engine based on a CAT3401 engine. The computations show that the required initial temperature for ignition is reduced by about 70 K for the cases of the diesel pilot charge and a 25∼35% percent increase in power density was found for those cases without adversely impacting the NOx emissions.

Natural gas is a leading alternative fuel candidate for transportation applications. The fuel offers economic, strategic and potential environmental advantages over conventional fuels. This paper discusses several issues involved with using natural gas a transportation fuel including fuel compostion, on-board fuel storage, and general emission characteristics. Three demonstration projects including marine and land transportion applications in which the University of Alabama participated are presented.

In order to meet stricter diesel engine emissions regulations, several researchers have investigated the feasibility of utilizing natural gas as an alternative engine fuel. This study reports the performance, gas-phase emissions, and particulate emissions of a single-cylinder prechamber type diesel engine modified to run on natural gas/diesel dual fuel. During dual fueling, up to 73 percent of the diesel fuel energy input was replaced with natural gas while the engine power output was maintained at levels similar to those obtained using diesel fuel alone. Thermal efficiency obtained was 38 percent lower for dual-fueling than for straight diesel fueling at one-quarter load. However, at full load the thermal efficiency obtained for dual fueling was similar to that for straight diesel fueling. Similar exhaust NOx concentrations were obtained at one-quarter load, but at higher loads NOx concentrations were higher for dual fueling.