Effects Of Open Combustion Chamber And Oil-gas-Chamber Matching On Heat Transfer Loss And Thermal Efficiency Of Diesel Engine

Reducing the heat transfer loss of the engine is an important way to improve the thermal efficiency of the engine,this paper proposes an idea of reducing heat transfer loss and realizing high efficiency combustion of diesel engine by oil-gas-chamber matching based on low swirl open combustion chamber.Based on a six-cylinder step combustion chamber diesel engine,first,reduce the heat transfer loss in the cylinder through different open combustion chambers and swirl ratios,and then the fuel injection system was matched to improve the combustion efficiency and reduce the heat transfer loss.Finally,the improvement space of heat transfer loss and thermal efficiency in different open combustion chambers was explored through the combustion system matching.Firstly,the influence of open combustion chamber and swirl ratio on the heat balance law of diesel engine is studied.By comparing the thermal balance law between the step and open combustion chamber,the results show that because of the smaller piston depth and the larger shrinkage radius,the high temperature area of the open combustion chamber is closer to the cylinder head and cylinder liner than the step combustion chamber.and the piston heat transfer amount of the open combustion chamber is smaller,but the the cylinder head and the cylinder liner heat transfer amount of the open combustion chamber of is larger.In view of the large heat transfer between the cylinder head and cylinder liner of the open combustion chamber,it is hoped to change the distribution position of the high temperature zone in the cylinder by changing the open combustion chamber line type.The influence of five different open combustion chamber line types on the heat balance law of diesel engine is studied.The results show that the larger boss height and piston depth(V3 open combustion chamber)can slow down the development speed of the high temperature zone to the cylinder head and cylinder liner,thus reducing the heat transfer of the cylinder head and cylinder liner,however,the mixing capacity of oil-gas is also weakened,and the combustion loss is increased.Aiming at the V3 open combustion chamber with low heat loss and high combustion loss,the influence of swirl ratio on its heat balance law is studied.The results show that the increase of swirl ratio does no promoting the mixing ability of oil-gas,instead will increase the high temperature distribution in circumferential direction of the position,so as to increase the heat transfer loss,and the low swirl ratio causes less heat transfer loss in the cylinder.Then,the matching of the injection system to the low swirl V3 open combustion chamber is carried out,and the influence of the number of nozzles and the angle of fuel injection on the heat transfer loss and thermal efficiency is studied.The results show that increasing the number of nozzles can make the fuel more evenly distributed in the circumferential direction,the oil-gas mixing ability increases,and the indicated thermal efficiency increases.However,an excessive increase in the number of nozzles results in an overlap between the oil bundles,which increases the combustion loss and reduce the indicated thermal efficiency.Increasing the number of nozzles will result in less oil being sprayed by a single orifice,slower fuel movement and later reaching the wall of the combustion chamber.For the piston,because the fuel is distributed evenly in the circumferential direction,the slower fuel movement has little effect on the heat transfer of the piston,but the heat transfer in the cylinder head decreases greatly,which leads to the decrease of the total heat transfer loss in the cylinder with the increase of the number of nozzles.Increasing the angle of the fuel injection makes the surface of the oil bundle have better contact with the air,and the mixing ability of the oil-gas in the cylinder is enhanced,indicating that the indicated thermal efficiency is increased.Increasing the angle of the fuel injection will make the center line of the oil bundle close to the cylinder head.The fuel near the cylinder head increases,at the same time,the drop point of the oil bundle on the circular arc of the piston moves up,making more fuel move to the bottom of the piston,increasing the heat transfer of the piston and the cylinder head,and increasing the heat transfer loss in the cylinder.Finally,the effects of combustion chambers,swirl ratios,number of nozzles and injection angles four parameters matching on the heat transfer loss and thermal efficiency of the diesel engine in the combustion system were studied in two steps.On the basis of 0.4 swirl ratio and 16 nozzles with different combustion chambers and fuel injection angles matching,the results show that the larger and smaller injection angles can not make the indicated thermal efficiency higher for all combustion chambers.The energy distribution of the OPEN type open combustion chamber and the injection angle of 79° matching is better;The number of nozzles and the swirl ratio are matched based on the OPEN type open combustion chamber and fuel injection Angle 79 °,the results show that for all the nozzles,increasing the swirl ratio appropriately is beneficial to improve the indicated thermal efficiency,but the indicated thermal efficiency will decrease if the swirl ratio is too large.In the condition of small swirl ratio,increasing the number of nozzles can improve the indicated heat efficiency in the cylinder and reduce the heat transfer loss in the cylinder.The 16 holes and swirl ratios of 0.4,1 and 1.5 have lower heat transfer losses and higher indicated thermal efficiency in the cylinder,and achieved high efficiency combustion with low heat transfer loss of diesel compared with the original step combustion chamber.