基于灰色关联理论和神经网络的掺氢汽油机性能及排放研究

发布时间：2018-05-09 13:11

本文选题：汽油机 + 掺氢　；参考：《吉林大学》2017年博士论文

【摘要】：在我国经济快速发展的背景下,汽车的保有量逐年攀升,这就使我国的石油需求量不断增加,而对于我国这样一个石油资源贫乏的国家来说已成为限制国家发展的一个重要因素。同时,汽车尾气带来的空气污染已严重的影响了人们的生活。因此,全世界都在致力于开发代用燃料和减少汽车尾气排放的研究。而氢气既可以作为代用燃料,又可以将其加入汽油机中来调节汽油机的性能及排放。目前为止所查阅到的关于掺氢汽油机的文献中大多以氢气和汽油都为进气道喷射的研究为主,而本文所进行的试验采用了氢气缸内直喷、汽油进气道喷射的方式,其最大的优势是可以有效的避免回火现象的产生。本文首先对喷氢过程进行了仿真以确定最佳的喷氢时刻。然后,进行了氢气汽油混合燃料火花点火发动机的台架试验,并分析了掺氢比,过量空气系数、点火提前角和EGR率对掺氢汽油机性能和排放的影响。利用台架试验所得的数据通过灰色关联度计算方法求出了每个影响因素与掺氢汽油机各个性能及排放参数之间的灰色关联度,并使用灰色关联分析法分析了掺氢汽油机性能和排放的各个参数受哪些因素的影响及影响程度。最后建立了神经网络模型,并对掺氢汽油机的性能和排放进行了预测。本文主要的结论总结如下:随着点火提前角的增大,NOX、HC和CO排放都随之增加。最佳点火提前角随着掺氢体积分数的增加而减小。随着过量空气系数的增加有效功逐渐降低,压力升高率持续减小,平均指示压力的循环变动系数增大,且压力升高率和平均指示压力的循环变动系数都随掺氢体积分数的增加而减小。掺氢体积分数的增加使热效率增大,NOX排放增加,未燃HC排放减少。汽油机加氢可以同时降低缸内最大压力的循环变动系数和平均指示压力的循环变动系数,而且缸内最大压力的循环变动系数和平均指示压力的循环变动系数都随着点火提前角的增加而减小。在加入EGR后,EGR率的增加使NOX排放显著降低,HC排放升高,瞬时放热率的峰值降低,其峰值所对应的相位也逐渐推迟,平均指示压力的循环变动系数先减小后增大,而掺氢能量分数对降低平均指示压力的循环变动系数的效果更加明显。在不使用EGR的条件下,过量空气系数是影响扭矩和功率的主要因素。掺氢比、过量空气系数和点火提前角对CO排放的影响作用基本相同且都较大。对于CO2排放和HC排放来说都是过量空气系数的影响作用最大。而掺氢比是3因素中对NOX排放影响最大的。加入EGR后掺氢比是影响扭矩和功率的主要因素。掺氢比、EGR率和点火提前角对CO排放的影响作用都很大。掺氢比和点火提前角对CO2排放的影响基本相同,但比EGR率的影响略大。对于HC和NOX排放来说都是点火提前角的影响最大,但对于NOX排放EGR率的影响相对于掺氢比和点火提前角有一定的差距。利用BP神经网络模型对掺氢汽油机性能及排放的分析结果为:在过量空气系数为1.5时,掺氢汽油机的扭矩随着掺氢比的增加和点火提前角的减小而增大,HC排放量随着掺氢比的减少和点火提前角的增大而增加,NOX排放量随着掺氢比的增加和点火提前角的增大而增加。在加入EGR后,掺氢比为25%时点火提前角较小的情况下扭矩随EGR率的增加而降低,而在点火提前角较大的情况下扭矩随EGR率的增加呈现出上升的趋势。HC排放随着点火提前角和EGR率的增大而增加,NOX排放量随着点火提前角的减小和EGR率的增加而减少。
[Abstract]:In the background of China's rapid economic development, the number of cars keeps rising year by year, which makes the demand for oil in our country increasing, and it has become an important factor restricting the development of the country as a country with poor oil resources. At the same time, the air pollution caused by automobile exhaust has seriously affected people's life. As a result, the world is working on developing alternative fuels and reducing exhaust emissions. Hydrogen can be used as a substitute fuel and can be added to a gasoline engine to regulate the performance and emissions of gasoline engines. The main advantages of this paper are the direct injection of hydrogen in the cylinder and the injection of gasoline intake, which can effectively avoid the occurrence of tempering. In this paper, the simulation of hydrogen injection process is carried out to determine the best time for hydrogen injection. Then, the spark ignition of hydrogen gasoline mixture fuel is carried out. The effect of hydrogen doping ratio, excess air coefficient, ignition advance angle and EGR rate on the performance and emission of hydrogen doped gasoline engine was analyzed. The grey correlation degree between each influence factor and each performance and emission parameter of the hydrogenated gasoline engine was calculated by the data of the bench test. The influence and influence degree of the parameters of the performance and emission of the hydrogen doped gasoline engine are analyzed by the grey correlation analysis method. Finally, the neural network model is established, and the performance and emission of the hydrogen doped gasoline engine are predicted. The main conclusions are as follows: with the increase of the point fire advance angle, the NOX, HC and CO emissions are all followed. The optimum ignition advance angle decreases with the increase of the volume fraction of hydrogen. With the increase of the excess air coefficient, the effective work gradually decreases, the pressure increase rate decreases continuously, the cyclic variation coefficient of the mean indicator pressure increases, and the pressure rise rate and the average indicator pressure cyclic variation coefficient decrease with the increase of the volume fraction of hydrogen. The increase of the volume fraction of hydrogen makes the thermal efficiency increase, the NOX emission increases and the unburned HC emission decreases. The gasoline engine hydrogenation can simultaneously reduce the cyclic variation coefficient of the maximum pressure in the cylinder and the cyclic variation coefficient of the mean indicator pressure, and the cyclic variation coefficient of the maximum pressure in the cylinder and the cyclic variation coefficient of the mean indicator pressure are all along with the coefficient of variation of the cyclic variation coefficient of the average pressure and the mean pressure. The increase of ignition advance angle decreases. After adding EGR, the increase of EGR rate makes the emission of NOX significantly lower, the emission of HC increases, the peak value of instantaneous exothermic rate decreases, the phase corresponding to the peak value gradually postpones, and the cyclic variation coefficient of the mean indicator pressure decreases first and then increases, and the hydrogen doping energy fraction can reduce the cyclic variation of the mean indicator pressure. The effect of dynamic coefficient is more obvious. Excessive air coefficient is the main factor affecting torque and power without using EGR. The effect of hydrogen ratio, excess air coefficient and ignition advance angle on CO emission is basically the same and larger. For CO2 emission and HC emission, the effect of excess air coefficient is the greatest. The ratio of hydrogen is the most important factor affecting the NOX emission in the 3 factor. The ratio of hydrogen doping is the main factor affecting the torque and power after the addition of EGR. The ratio of hydrogen doping, EGR and ignition advance angle have great influence on the CO emission. The effect of hydrogen doping ratio and ignition advance angle on CO2 emission is basically the same, but it has a little influence on the EGR rate. For HC and NOX emissions are all The effect of ignition advance angle is the greatest, but there is a gap between the effect of NOX emission EGR ratio and ignition advance angle. The analysis results of the performance and emission of hydrogen doped gasoline engine by BP neural network model are as follows: when the excess air coefficient is 1.5, the torsional moment of the hydrogen doped gasoline engine increases with the ratio of hydrogen and ignition advance angle. With the decrease of the hydrogen ratio and the increase of ignition advance angle, the emission of HC increases with the increase of hydrogen doping ratio and the increase of ignition advance angle. When the ratio of hydrogen is added to EGR, the torque of the ignition advance angle decreases with the increase of the ignition advance angle when the ratio of hydrogen is 25%, and the ignition advance angle is larger. The downward torque increases with the increase of EGR rate and increases with the increase of ignition advance angle and EGR rate. The emission of NOX decreases with the decrease of ignition advance angle and the increase of EGR rate.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK411

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