A Simulation Study On Influence Of Variable Intake Swirl System To The Performance Of High Speed Diesel Engine

As the most efficient prime motor which be used widely, diesel engine has been worked for us over 100 years. With the source and environment problems increasingly standing out, people request more and more on the economical and exhale performance of diesel engine. So the study on fluid field in cylinder become especially important. The swirl in cylinder is a very important airflow form, which directly affect the atomization and combustion of fuel, give a essential effect on the economical and exhale performance. In order to make diesel engine work properly in a wide speed range, normally the advanced diesel engines in modern days adjust swirl intensity by the variable swirl system to work properly on different speed. The normal method to measure the swirl intensity is measuring swirl rate on the constant pressure test bench, this method has high instability and low accuracy, can not meet the requirement of modern diesel engine design. Hence we need a more accurate method to study the fluid field in cylinder.In this paper, a simulation method was introduced, which work on the operating process of a high speed diesel engine, to simulate the fluid flow in cylinder, in intake ports and in exhaust port, and to simulate the process of combustion in cylinder and of harmful exhaustion generation. Use the moment of momentum of the airflow in cylinder to evaluate the swirl intensity, and study on the effect of the variable swirl system. An accurate three-dimensional simulation model of cylinder, intake ports and exhaust ports was built firstly, then simulate the operating process in different speed using the knowledge of computational fluid dynamics, computational thermal transmission and computational combustion chemistry, and demarcate this model with experiment data. Based on the demarcated model, simulate the whole cycle in six individual speed. In the simulation, one intake branch was closed partly or completely to generate variable swirl in cylinder,5 scheme of intake branch opening was calculated in each speed, and the effect on engine performance was analyzed.The calculation results show, when the simulation of full cycle of engine was used, comparatively accurate transient fluid field data of whole cylinder can be received, which contribute to studying gas exchange process and swirl emerging; for the 4 valves diesel engine which with two individual intake ports, partly or completely closed one intake branch can change swirl intensity within a certain range. At low speed, swirl intensity would be enhanced while one intake branch was completely closed, and volumetric efficiency would be barely affected; at high speed, swirl intensity would be changed while one intake branch be partly closed, volumetric efficiency would be evidently reduced only when the sectional area less than 25%. With swirl intensity increased, the value of Soot generation will be reduced, but NOx generation will be increased; at high speed, the effect of swirl vary on pollutant generation is smaller than it at low speed, and the effect of swirl vary on Soot generation is large than it on NOx generation.