Abstract
Unthrottled, direct injection ignition assisted (DI–IA) engines have demonstrated DI diesel efficiencies and multi-fuel capabilities. However, high hydrocarbon (HC) emissions have been a problem with this concept. Torch ignition, provided by a separately fuelled small volume prechamber with spark ignition, was applied as a research tool to define the benefits of large volume ignition for controlling HC emissions. Torch ignition was found to be beneficial for HC control relative to the use of single point spark ignition; however, HC levels were higher than those observed from a DI diesel using low emissions technology. To assist in investigating the cause of the higher HC emissions, tracer experiments were conducted to verify that prechamber combustion characteristics did not contribute significantly to the total exhaust HC emissions. Separate, but similar, fuels were used for the main chamber and prechamber. Through gas chromatographic analysis of the major exhaust HC species, prechamber combustion was found to contribute substantially less than 20 per cent to the overall HC emissions for the engine conditions studied.
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