| Rotary engine has been widely used in many fields such as automobile,UAV and power generation because of its advantages such as: its simple structure,its high power to weight ratio and easy miniaturization of the whole machine.However,the rapid development of the rotary engine,which is fueled with traditional fuels such as gasoline,diesel,aviation kerosene,has been restricted by its high fuel consumption and excessive emission.Therefore,under the background of the increasingly depleting oil energy and the urgent need for environmental protection,the importance of developing and using clean and efficient alternative fuels is self-evident for rotary engines.Thehydrogen doped natural gas is considered as one of the most promising alternative fuels in the future of rotary engine.This is because the mixture of natural gas and hydrogen combines the advantage of the two fuels i.e.the exixtence of abundant natural gas reserves and fast combustion rate of hydrogen.However,even if natural gas in admixture with hydrogen is used to power rotary engine,its combustion efficiency still needs to be improved.This is because the special structure and operation mode of the rotary engine leading to narrow shape and large face to volume ratio of the cylinder.In addition,the air flow in the cylinder is mainly one-way flow at the ignition time,which makes it difficult for the flame in the cylinder to propagate to the back of the cylinder against the direction of the air flow.Therefore,regardless of the fuel type used in the rotary engine,the aforementioned problem is still a major concern.In order to solve this problem,an in-depth study of the flow motion and combustion mechanism of natural gas hydrogenated rotary engine is necessary.On this basis,the combustion process can be improved by organizing the distribution of the gas mixture and coupling the flow field in the cylinder.In addition,it is not to be ignored that the special structure and operation mode of rotary engine will lead to the problem of radial seal air leakage.Both natural gas and hydrogen are gaseous fuels,which are more likely to leak in radial seal air leakage.Therefore,the influence of radial seal leakage on the flow field and combustion in cylinder cannot be ignored for the study of combustion process in the cylinder of natural gas hydrogen doped rotary engine.In this paper,a three-dimensional dynamic numerical simulation model considering radial seal air leakage is established,and the flow field test data and cylinder pressure test data obtained from experiments were used to verify the numerical simulation model.On the basis of this model,the effects of radial leakage gap and fuel injection strategy on the in cylinder flow evolution,combustion process and pollutant generation of a peripheral intake rotary engine were studied by numerical simulation.The results are as follows:(1)The influence of the radial seal leakage flow on the three-dimensional flow field in the cylinder of the peripheral intake rotary engine was revealed.The specific contents are as follows: in the early stage of the intake phase,the air leakage impacted the vortex formed in the early stage of the intake phase and accelerated the breakup of the vortices.In the later stage of the intake phase,the strength of the vortices formed in the later stage of the intake phase increased due to the leakage flow.In the later stage of compression,the one-way flow in the cylinder is divided into two parts,namely "leakage area" and "main flow area".The air flow direction of "leakage area" is opposite to that of "main flow area".In addition,for different leakage gaps,with the increase of leakage gap,the intensity of leakage air flow continued to increase,and the impact of the leakage air flow became stronger and stronger.For different engine speeds,with the speed increases,the leakage became smaller and smaller,and the influence of leakage air flow on in-cylinder flow became weaker and weaker.(2)The influence of the injection position ofhydrogen doped natural gas on the fuel distribution and combustion process in the cylinder under the action of radial air leakage was obtained.The results showed that: when the nozzle is located at A(the upper part of the long axis of the cylinder profile,50 mm away from the long axis of the cylinder profile)and B(the long axis of the cylinder profile line),with the delay of the fuel injection time,the fuel continuously accumulates from the uniform distribution to the front of the cylinder.When the nozzle is located at C(the lower part of the long axis of the cylinder profile,50 mm away from the long axis of the cylinder profile),with the delay of the fuel injection time,the fuel distribution area changes from the main distribution in the rear of the cylinder to the whole cylinder,and the fuel stratification degree became higher and higher.In addition,compared with other conditions,Case: B-150(injection position B,injection time 150°CA(BTDC))condition has the highest peak combustion pressure.This is mainly because: in Case:B-150 working condition,the fuel in the cylinder is mainly distributed in the middle and front of the cylinder,keeping a high concentration near the spark plug.This kind of fuel distribution is not only conducive to the formation of fire core in the early stage of the combustion,but also can avoid the phenomenon that a large amount of mixture left behind the cylinder can not be burned in time.(3)The effect of injection angle ofhydrogen doped natural gas on fuel distribution and combustion process in cylinder under the action of radial air leakage was clarified.The results showed that when the fuel injection time is in the early and middle stage of the intake stroke,the injection angle has little effect on the fuel distribution in cylinder at ignition time.When the fuel injection time is at the later stage of the compression stroke,the injection angle has a significant effect on the fuel distribution in the cylinder at the ignition time.In addition,compared with other conditions,the peak value of combustion pressure in Case: 220+60(injection timing 220°CA(BTDC),injection Angle 60°)and Case: 150+0(injection timing 150°CA(BTDC),injection Angle 0°)conditions is very close,but also significantly higher than other conditions.This is also because: This is also because: in Case: 220+60 and Case: 150+0 working conditions,the fuel in the cylinder is mainly distributed in the middle and front of the cylinder,and a high fuel concentration is maintained near the spark plug.This ideal fuel distribution form is conducive to improving the ignition stability and flame propagation rate. |
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