基于缸压信号的柴油机NO_x排放建模

Modeling of Diesel Engine NO_x Emission Based on Cylinder Pressure Signal

在1台缸内直喷、增压中冷柴油机上建立了基于缸压信号的NOx排放经验模型。利用iCAT采集缸压信号,基于缸压信号计算得到燃烧放热率、燃烧累计放热量,建立了零维双区燃烧模型并由此得到了全局温度、未燃区温度和已燃区温度。结合NOx的生成机理,从燃烧过程曲线中提取了与NOx排放相关的燃烧状态参数,并根据固定工况试验分析了燃烧状态参数与排放的相关性,结果表明最大缸压、最大压升率、最大燃烧放热率相位、50%燃烧放热量相位、已燃区最高温度和高温NO生成面积与NOx排放具有强相关性,可以作为NOx排放模型的输入。进行了稳态多工况建模和验证试验,根据建模试验建立了NOx排放的二次多项式模型,通过验证试验验证了所建排放模型的预测精度。结果表明,基于缸压信号的NOx排放经验模型结构简单,预测精度高,可写入iCAT中用于NOx排放的实时预测。

The empirical model of NOx emission for an in-cylinder direct injection, turbocharged and intercooled diesel engine was established based on the cylinder pressure signal. Cylinder pressure signal was collected by iCAT. The heat release rate and accumulated heat release were calculated based on cylinder pressure signal. The zero-dimensional dual-zone combustion model was built, from which the global, unburned zone and burned zone temperature were acquired. Combined with the forma- tion mechanism of NOx, the combustion state parameters related with NOx emission were extracted from the combustion curve. The correlation between combustion state parameters and emission was further analyzed under the fixed operating conditions. The test results show that the maximum cylinder pressure, maximum rate of pressure rise, phase of maximum heat release rate, phase of 50% total heat release, maximum temperature of burned zone and formation area of high temperature NO have strong relations with NOx emission and can be used as the inputs of emission model. The modeling and verification of steady state and multiple operating conditions were carried out and the quadratic polynomial model of NOx emission was built. Through the experiment, the prediction accuracy of NOx emission model was verified. The results show that the empirical mod- el of NOx emission based on cylinder pressure signal has simple structure, high prediction accuracy and hence can be written in- to iCAT for the real-time prediction of NOx emission.