EXPERIMENTAL STUDY OF HC EMISSIONS USING NARROW SPRAY CONE ANGLES AND DIFFERENT SURROGATE FUELS IN LOW TEMPERATURE DIESEL COMBUSTION SYSTEMS

摘要

Diesel engine exhaust contains emissions other than CO_2, reductions in such emissions is a high priority issue. PM and NO_x have been major constituents of the Diesel emissions and the regulations are getting stringent. But these Diesel emissions are difficult to reduce due to the broad range of fuel-air mixtures present during the combustion process. In a conventional Diesel engine, air is gradually drawn into the fuel spray from the surrounding area. The ignition delay period is short, so combustion starts before the fuel has thoroughly mixed with the air. Consequently, the centre of the spray is overly rich, resulting in smoke, while a stoichiometric mixture is formed in the surrounding area, resulting in a high NO_x concentration. In order to develop a low emission engine, research is necessary to come up with a new combustion strategy for Diesel engine. The new combustion strategies such as LTC (low temperature combustion) for Diesel engine have been widely studied as a combustion technology to avoid NO_x and smoke formation regions simultaneously. In PCCI (premixed charged compression ignition) approach the combustion temperature is lowered by forming a lean pre-mixture which simultaneously and substantially reduces NO_x and smoke. A very long mixing period is required to form a lean and uniform mixture, and it is necessary to inject fuel at a fairly early time. At this point, as the temperature and in-cylinder pressure are low, a large amount of the sprayed fuel adheres to the wall, causing problems of oil dilution and a decline in combustion efficiency. This can be avoided by suppressing the penetrating force of the spray using a narrow cone angle nozzle. This paper focuses on reducing the HC and CO emissions with the special nozzles under low loads using conventional piston bowl. Future goals include optimization of injection strategy by varying piston bowl geometry with the selected nozzle. A mixture of n-decane and α-methylnaphthalene known as IDEA fuel was used as the surrogate fuel for Diesel for numerical studies with different spray cone angles. Effect of the choice of surrogate fuel is also studied for conventional spray cone angle.