Trend and Origins of Particulate and Hydrocarbon Emission from a Direct-Injection Diesel Engine 831290

A systematic study on particulate mass emission from a high-speed direct-injection diesel engine was conducted using a mini-dilution sampling method. Effects of fuel-air equivalence ratio, engine speed, injection timing, and swirl intensity are presented and discussed with special regard to soluble organic fraction (SOF) and hydrocarbons. Results show that these concentrations are greatly affected by ignition delay or by temperature level in the engine cylinder. As the sources of SOF and hydrocarbons, local and bulk quenching of the charge, interaction of the fuel spray with the combustion chamber walls, and slow thermal decomposition of fuel are considered and discussed. Among them, the significance of the fuel decomposition is pointed out, by separate experiments on a simulated engine by using an in-cylinder gas-sampling technique. The proposed mechanism is that at low air temperature, thermal cracking is too slow for the injected fuel to be fully decomposed, resulting in the accumulation of raw and partially cracked fuel.


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