F2008-06-082
Experimental Study of HC Emissions Using Narrow Spray Cone Angles and Different Surrogate Fuels in Low Temperature Diesel Combustion Systems
Diesel engine exhaust contains emissions other than CO2, reductions in such emissions is a high priority issue. PM and NOx 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 center of the spray is overly rich, resulting in smoke, while a stoichiometric mixture is formed in the surrounding area, resulting in a high NOx 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 NOx and smoke formation regions simultaneously. In PCCI approach the combustion temperature is lowered by forming a lean pre-mixture to simultaneously and substantially reduce NOx 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. To avoid this, some method such as suppression of the penetrating force of the spray using a narrow cone angle nozzle must be devised, which in turn requires substantial modification of engines. This paper is focused on reducing the HC and CO emissions with the special nozzles under low loads by optimizing the injection strategy. A fast response technique for measuring the HC in the closed exhaust port will be used to distinguish the effect of various operating conditions on the total engine-out soot emissions and HC concentration. A mixture of n-decane and -methylnaphthalene, denoted as IDEA fuel, was found to be a good surrogate fuel for Diesel for the conventional Diesel combustion mode. IDEA-fuel shows a good agreement when compared with Diesel fuel.
Session: Fuel Efficient Powertrains I