| With the rapid development of the automobile industry and the sharp increase in the demand for petroleum resources,the application of alternative fuel natural gas in engines has attracted the attention of experts and scholars at home and abroad.China’s natural gas resources are abundant,natural gas engines have the characteristics of good ex PISOion resistance,high calorific value,clean and environmental protection,so further improving the thermal efficiency of natural gas engines has important environmental protection and economic value.Current studies have shown that adding a pre-chamber system to the engine combustion chamber can increase the intensity of in-cylinder turbulence and accelerate the combustion of the in-cylinder mixture.The structure and parameters of the pre-combustion chamber not only directly affect the cylinder pressure and heat release rate of the engine,but also indirectly affect the engine performance and thermal efficiency.In order to further improve the thermal efficiency of natural gas engines,this paper intends to explore the influence of passive pre-combustion chambers on the combustion process of natural gas engines.The influence of passive pre-combustion chamber on combustion in the main combustion chamber was analyzed.The influence of the design parameters of the nozzle on the combustion process was explored.Study the influence of its geometry and position on engine performance.The research results can provide theoretical help for improving the thermal efficiency of natural gas engines equipped with pre-combustion chambers.In this study,a numerical simulation platform is built using CFD software CONVERGE.In this study,a variety of passive pre-combustion chambers with different structures were designed as the research objects,such as "4,6,8 holes with different number of nozzle holes","63°,67.5°,70° different nozzle cone angles" and "5.5mm,7.5mm,13 mm,18mm and 22.5mm different arrangement depths".At the same time,environmental parameters are adjusted and boundary conditions are optimized,their influence on engine combustion is studied,its stability is tested and thermal efficiency is calculated.The main research contents and conclusions are as follows:1)The influence of the passive pre-combustion chamber on the combustion of the main combustion chamber was analyzed.This part is based on the simulation results of natural gas engine original engine,and the formation process,turbulence intensity,and mixing state of the mixture before and after the pre-combustion chamber are studied.Studies have shown that adding a pre-combustion chamber to the combustion chamber can accelerate the flow and mixing of fuel-air mixture within the range allowed by combustion conditions on the basis of the original engine.The pre-combustion chamber structure promotes the flow of the mixture in the cylinder.2)The influence of pre-combustion chamber orifice design parameters on the combustion process was explored.This part is based on the research of engines equipped with passive pre-combustion chambers,and analyzes the number of jet holes in the pre-combustion chamber,the angle of the nozzle cone,and environmental parameters.The results show that when the 6-well pre-combustion chamber is used,the main combustion chamber has a high relative pressure peak and the combustion process is moved forward,and the 6-well pre-combustion chamber has better adaptability to the research prototype.Compared with the 67.5° nozzle cone angle,the cylinder pressure peak and the corresponding crankshaft rotation angle at 70° and 63° nozzle cone angle are significantly reduced and delayed,and the adaptability of 67.5° nozzle cone angle is better with the research prototype.When the ignition timing of the pre-combustion chamber is set to-23°CA ATDC,the maximum increase in the indicated work is 3.42%compared with the original engine.Through ignition advance angle control,it is also expected to make the engine obtain greater thermal efficiency improvement effect;Increasing the initial temperature will increase the formation of fire core and combustion reaction rate in the pre-combustion chamber,which is conducive to more complete combustion of the mixture in the pre-combustion chamber.The influence of initial pressure on jet characteristics is generally consistent with temperature,and higher pressure is conducive to improving the density and heat release of the mixture in the pre-combustion chamber.Under passive pre-chamber jet ignition conditions,high peak pressures can be obtained at stoichiometric ratio for mixture concentration control.3)Study the influence of its geometric volume and position on engine performance.This section studies the volume ratio of the pre-combustion chamber to the main combustion chamber and its arrangement depth in the main combustion chamber,and summarizes the calculation models to calculate the thermal efficiency.The results show that the pre-combustion chamber with a small volume has better responsiveness with the change of ignition advance angle,weakens the combustion lag phenomenon,and has better combustion acceleration.When the arrangement depth is L=22.5,the maximum pressure in the cylinder after ignition is higher than the simulation data of the original machine,the peak phase is shifted forward,the combustion duration period is shortened,and the combustion concentration of the mixture is improved.During the structural optimization study of the passive pre-combustion chamber,the effective thermal efficiency was increased by up to 1.16%.In summary,when the volume ratio of pre-combustion chamber to combustion chamber is 1.5%,the number of pre-combustion chamber jet holes is 6 holes,the arrangement depth is L=5.5,the orifice cone angle is 67.5°,and the ignition advance angle is-18°CA ATDC,the effective thermal efficiency is increased by up to 1.16%,so it can be considered that the passive pre-combustion chamber has a good improvement effect on the thermal efficiency of the research prototype. |
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