Numerical Simulation Study Of Automotive Fuel Auxiliary Heater

For Chinese northern regions,the performance of automobile could decay with extreme low temperature circumstance.In consideration of this problem,the fuel automotive heater which is completely independent of engine-based heating device is used to improve the performance of vehicle starting.Therefore,it has great significance to research on how to enhance the performance of automotive fuel-assisted heater.In this paper,the influence of various structural parameters on performance was analyzed with numerical simulation,meanwhile improved model was proposed on the basis of original model by results.The main work is as follows:（1）The performance of combustion was simulated with FLUENT software,furthermore the distribution of temperature field and each component on Y=0 cross section were analyzed.The results show that the uniformity index of temperature is50.48%,the average mass fraction of NOx,CO and O₂,respectively,is 2.25×10^-7,0.046 and 0.039 in the outlet cross section.According to above data,not only be the distribution of internal temperature field proved uniform,but also the post-combustion phenomenon in the flame tube is serious.In addition,there is still margin decline though the overall emission load of NOx is low.Besides it can be inferred that nitrogen oxides are mainly caused by excessive local temperature from the temperature field of Y=0 cross section and the NOx distribution cloud chart,because it can be seen that high-concentration nitrogen oxides appear at higher temperature.（2）The effect of the single performance of the automotive fuel auxiliary heater with various structural parameters（temperature field uniformity index,and outlet nitrogen oxide content）were analyzed.It was found that when the nozzle radius R was changed,the temperature field uniformity index and the outlet nitrogen oxide content shows a downward trend.When the ratio of the amout of premariy and secondary air-intake is increased,the temperature field uniformity index is increasing,and the export nitrogen oxide content is decreasing.Influenced by the position of the deflector,when the nozzle distance L_k is changed,the temperature field of the combustion chamber fluctuates greatly,and the nitrogen oxide content of the outlet first decreases and then increases.When only the length L_r of the combustion chamber is changed,the temperature field uniformity index and the nitrogen oxide emission have an overall upward trend.（3）In view of the fact that the more single evaluation methods for automotive fuel auxiliary heaters are considered in some specific engineering applications,and each single performance index may affect each other,this paper aiming at the models of different structural parameters that have been simulated before established a comprehensive performance evaluation method,and the comprehensive performance scores of the selected 20 models were calculated and sorted.The single evaluation index considered in the comprehensive evaluation index added the export CO content and the export O₂ content besides the temperature field uniformity index and the export nitrogen oxide content.The result shows that the structural parameters of the model with the best overall performance are R=1.0mm,and the ratio of the primary air inlet is 0.0605,and L_k=31mm,and L_r=157mm.（4）In order to solve the problem that the function of changing the structural parameters to improve the temperature uniformity of automobile fuel auxiliary heater is not obvious,this paper proposed a new structure model with three different structural parameters and selected the best one.Further simulation analysis was carried out using the new structure and compared with the model with the best comprehensive performance before improvement.The result shows that the internal fluid of the improved automobile fuel auxiliary heater forms a circulating flow in the combustion chamber.The uniform index of the temperature field in the model combustion chamber is increased by 23.43%,the atomization of the diesel is more uniform,and the NOx emission is reduced by 98.10%.CO emmision is reduced by6.35%,and O₂ utilization is increased by 11.34%.