Study On The Development Of A High Thermal Efficiency China Stage Ⅵ Heavy-Duty Diesel Engine Combustion System

With the decrease of traditional source of energy and increasingly severe environmental problems,it is necessary that the energy-saving technology and the internal purification level of diesel engines should be further improved.In order to satisfy the requirements of the increasingly stringent regulations on fuel consumption and emissions,designing diesel engines with high thermal efficiency and low emission has become the common aim of all relevant researchers.Based on the study on diesel engine combustion system,this paper developed a kind of heavy-duty diesel engine of 3.5L which meets National VI Heavy Vehicle Emission Regulations,studying the influences of intake port structure,combustion chamber shape,and fuel injection system on the performance of diesel engines through CFD simulation calculation and experiment.Taking into consideration of the economy,power,and emission of diesel engines,this paper developed the combustion system of diesel engine which accorded with the requirements of engineering design.Firstly,designing the intake port.The layout of the intake port of the original engine was changed,and the intake port was optimized through the method of combining CFD steady-state calculation with steady flow test for intake port.According to the experimental data,the optimized intake port meets the design requirements of maintaining appropriate swirl ratio and improving flow capacity.Then,designing the combustion-chamber structure of the diesel engine,and matching the fuel injection system.On the basis of the original combustion chamber,a double oblique combustion chamber was designed.Six cases were formed by the combination of the schemes of combustion chamber and those of the fuel injection beam angle.This paper studied how the matching between the combustion chamber shape and the injection beam angle influences the performance of heavy-duty diesel engine by the instantaneous simulation calculation of the working process of diesel engine at the rated working condition point.Next,considering synthetically the economy,power,and emission of diesel engines and selecting the best combustion system scheme through analytic hierarchy process,and studying the advantages of double oblique combustion chamber.According to the simulation results,it was reasonable for the original combustion chamber(combustion chamber 1)to match 140° injection beam angle,and the newly-designed double oblique combustion chamber to match 145° injection beam angle.At this point,the drop point of injection beam could reach the corner of the combustion chamber,so that the fuel flows up and down,the fuel and air were mixed appropriately,combustion duration was shortened,and rapid combustion was realized.The indicated mean effective pressure of combustion chamber 2 was 3.1% higher than that of the combustion chamber 1,but the indicated specific fuel consumption ofthe former was 3.0% lower than that of the later;the combustion chamber 2 was 3.0%less than the combustion chamber 1 in soot emission,but 12.1% more in NOx.Overall,the double oblique combustion chamber has a better comprehensive performance than original combustion chamber.Finally,based on the optimized intake port,the prototype 1 and the bench 2 were tested for the combustion chamber 1 matching the angle of the 140° oil beam and the combustion chamber 2 matching the angle of the 145° oil beam.The test results were consistent with the simulation results.