Abstract
Keywords
Unit-injector System, Injected Fuel Volume, Plunger Chamber Pressure, Duration of Injection,
CAM Rotational Speed, Bulk Modulus, Compressibility Factor
Abstract
Until an emission standard for automotive engines was first introduced in automobile industry in the 1960s, the control of the harmful emissions; HC, CO. Nox, Sox and PM from automotive engines was not an attractive issue for study by engineers. When people came to realize that the main source of the harmful emissions in metropolitan areas is the power generation unit for the city transportation system such as taxies, buses, sedans and trucks, it was decided to embark on serious considerations of these environmental problems to improve the atmospheric conditions in urban areas and awareness of emission control has since spread throughout the world.
The compression ignition (CI) type of engine is preferable to the spark ignition (SI) type for medium and large power outputs in many industrial fields. However, the CI engine is a major source of HC, NOx and particulates. One of the technologies used to reduce the harmful emissions from CI engines is a higher-pressure injection system. There are two kinds of injector systems, which are commonly used in diesel engines; the common-rail injector system and the unit-injector system (5). Even though the former system shows stable and steady characteristics in the injection pressure at the initial stage of injection, the latter can build up a much higher injection pressure, reaching up to 2000bar at the current stage. In this study, a numerical algorithm is developed to analyze the performance of a Unit-injector (UI) System of a diesel engine. The fundamental theory of the algorithm is based on the continuity equation of fluid dynamics. The loss factors that should be seriously regarded on the continuity equation are the compressibility effect of liquid fuel, the wall friction loss in high-pressure fuel lines of the system, the kinetic energy loss of fuel in the system, and the leakage of fuel out of the control volume. For an evaluation of the developed simulation algorithm, the calculation results are compared with the experimental outputs provided by the Technical Research Center of Doowon Precision Industry Co. (DPICO); the maximum pressure in the plunger chamber (Pp) and total amount of fuel injected into a cylinder per cycle (Qf) at each operational condition. The result shows that the average error rate (%) of Pp and Qf are 2.90% and 4.87% respectively in the specified operational conditions. Hence, it can be concluded that the analytical simulation algorithm developed in this study can be reasonably applied to the performance prediction of a newly designed UI system.