Study Of Diesel Spray Heat Transfer Characteristics Of Spray Wall-impingement

The spray impingement has become an inescapable phenomenon with the continuously per power requirement,and lead to the wall-film formationand near wall dense mixture,which were the main reasons of the wall-burning and the incomplete combustion.As a result,it aggravates the thermal load,reliability and emission problems.Therefore,the experiment and numerical simulation about the dieselspray wall interaction and the heat transfer process are carried out in this paper.The visual diesel spray impingement test bench has been built.It mainly includes the common rail system,the heating and temperature controlling device,the transient temperature sensor,DEWETRON data acquisition instrument and the high-speed camera.Besides,the design of temperature heating device,the selection of the transient temperature sensor and the parameter setting of the high speed camera are introduced in detail in this paper.Successfully,the bench can record the development and heat transfer processof diesel spray impingement under the different pressure(0～120MPa),impingement distance(0～20cm)and wall temperature(25℃～250℃).The visual research show that the spray development is undesirable when the impingement distance is too small or too large.While the spray distance is 8cm and10cm,it can successfully form the preferable effect of the diesel atomization and the relatively perfect spray morphology in a short time.In addition,the increase of injection pressure and the rise of wall temperature both make the spray diffusion radius and the spray entrainment height increase obviously,and optimize the diesel atomization effect.However,the increasing tendency of the spray diffusion radius and the spray entrainment height is weakened with the increase of pressure.By comparing the growth rate,it is found that the wall temperature has a relatively significant influence on the spray entrainment height.Nevertheless,the spray distance and the spray pressure have great influence on the spray diffusion radius,that is to say,the increase of distance or pressure causes the spray diffusion radius change obviously.The experiment results of the heat transfer characteristics of the diesel spray impingement show that the heat transfer capacity gradually increased with the increase of the jet distance,but the further increase of spray distance impact on heat transfer slightly.Furthermore,the rising of wall temperature and the injection pressure benefits the forced convection heat transfer and the oil film evaporation heat transfer.While the further increase of the injection pressure weakens the effect of forced convection heat transfer.When the wall temperature increases from 120 to 210degrees,heat flux increases from 6.20MW/m~2 to 15.90MW/m~2.Comparatively,it is found that the effect of temperature on the spray impingement heat transfer is far more than the jet pressure and jet distance,and fit a dimensionless company,which considered the pres0sure,distance and temperature effects.Meanwhile,3D numerical model was utilized to simulate the diesel spray impingement process by CFD tool Fluent.Compared the simulation data with the experimental data,the simulated results show good agreement with the measurement,and the difference of the wall maximum temperature is within 10%and the curve trend is approximately the same.The rationality of the simulation model is verified successfully.Then use the model to know the higher temperature simulation.