Possibilities to Reduce Influence of Compression Ratio on Total Hydrocarbon Emission from a D.I. Diesel Engine 831293
The compression ratio of a direct-injection Diesel engine was decreased by steps. The total hydrocarbon emissions and various component stresses were measured.
HC emissions rise hyperbolically when compression ratio decreases. The curve can be shifted towards lower CR values by increasing load, charge air pressure or charge air temperature. The measured ignition delays are in every respect in significant agreement with the HC emissions, leading to the hypothesis that excessive quantities of the injected fuel are deposited on the wall when the compression ratio decreases. If the calculated paths of the whole jet up to the beginning of combustion are put in relation to the HC emissions there result critical ranges for the jet tips beyond which the emissions increase drastically.
By that the conditions for reducing the influence of compression ratio can be considered for granted. For example any possibility to reduce the ignition delays is suitable for decreasing emissions since by that the range of the injection jets diminishes accordingly. Beside the influence of various engine specific parameters, the influences of higher charge air pressure, exhaust gas recirculation, exhaust back pressure and intake throttling were investigated in this paper.