Design And Experimental Study On Exhaust Gas Ejector Of Diesel Engine Cooling System

As an important system of a vehicle,the cooling system plays an important role in maintaining the normal operation of the engine.Because of the special structure power carbin,the military armored vehicles’ requirements for the cooling system are more harsher.Generally speaking,the military armored vehicles’ cooling system use cooling fan which is a mature technology to cool the radiator forcely,but the cooling system which using fan will occupy huge spac and be noisy.Comparatively,the exhaust gas ejector cooling system co-ol down the engine’s temperature by using the energy of the exhaust gas from the engineer to suck the the air to achieve cooling the radiator,whose structure is simple and can w-ork efficiently.In this paper,the exhaust gas cooling system is studied considering there are few research on the exhaust gas ejector cooling system,.Firstly,the work environment of the military armored vehicle is studied.Having considering the characteristic of the ejector,the minimum ejector ratio which the exhaust gas cooling system must meet is derivated by using the traditional heat transfer model and the formula using in the design of the cooling system.Furthermore,putting out a design method for the ejector’s design according to the current literature.Taking a heavy-duty special vehicle as an example,a single-tube ejector structure suitable for the exhaust emission cooling system of the vehicle is designed.Then simplifying the ejector’s model reasonably,establishing the ejector’s calculated model by CATIA which is a classical three-dimensional modeling software in the world,meshing the model by ICEM CFD,porous jump model is used to simulate the pressure drop generated by the radiator for simplifying meshing and simulating the flow field numerically by using the computational fluid dynamics software FLUENT.Analysis the key factors’ influence on the ejector’s flow field and entrainment ratio,such as the length to diameter ratio of the ejector’s mixing section、the distance between the nozzle and the entrance of the mixing section and the angle of the diffuser tube.A series of ejector structures were designed,and the optimum ejector structure whose the length to diameter ratio、nozzle distance、diffuser angle and aperture ratio is respectively 4、0.75、10°、2.According to the obtained model and the laboratory’s the actual conditions,the experimental model of the ejector was established.The exhaust gas expe-riment was carried out on the engine bench.By changing the exhaust mass flow,the temperature,pressure and flow were measured at the key position.And the parameters such as the ejection coefficient,the total pressure loss coefficient,the outlet velocity uniformity and the outlet temperature of the ejector under different working conditions were obtained.The results were compared with the numerical results.The average error was 8% The simulation model is verified to be reliable and correct.At the same time,the conclusions are drawn as follows: 1)there is a positive correlation between the ejection coefficient and the main flow rate;2)the higher the intake air temperature,the greater the increase of the ejection coefficient.