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HC emissions and ignition delay were investigated in a research single-cylinder DI diesel engine. Correlations were made between the measurements and different air-fuel mixing parameters calculated from a gas-jet spray model and expressions from the literature. The change in ignition delay was caused by varying engine inlet conditions of pressure and temperature and by adding a special cetane improver to No. 2 diesel fuel. In order to be able to interpret the experimental results a zero-heat-transfer heat release model was used in evaluation of the engine pressure data. It was found that the too-lean-mixed fuel could explain a maximum of 20% of the HC emission; the remaining amount is caused by other sources.

Tests were performed on a single-cylinder direct-injection (DI) research diesel engine to investigate the influence of elevated combustion-chamber temperature on combustion performance. The test program examined the low-heat-rejection (LHR) approach by removing the coolant but without employing heat-insulated parts. Heat-release characteristics calculated from pressure-time histories were correlated with measured exhaust emissions. It was found that increasing temperature level decreases the ignition delay and consequently decreases the fraction of total fuel that burns in the premixed-combustion phase. Exhaust hydrocarbon, NOx and particulate emission were found generally to increase with increasing temperature. The premixed-combustion fraction is concluded not to be the main source of the increased emissions.