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Experimental data on the concentration of hydrocarbons (HC) emitted in the exhaust are presented for both direct injection (DI) and indirect injection (IDI) engines and cover the effect of a wide range of engine operating parameters. The analysis shows that there are two main sources of HC in DI engines. One is due to the volume of fuel in the sac and holes of the injection nozzle and the other is from fuel premixed to leaner than lean limit conditions. Reduction of sac volume and reduction of ignition delay are effective in reducing the HC from the sac volume and lean limit sources respectively. Developments in fuel injection equipment and engine design to reduce HC emissions are outlined.
Greeves et al. (Tue,) studied this question.