采用离子电流法的甲醇发动机失火诊断

Misfire Diagnosis of Methanol Engine with Ion Current Method

在一台由四缸柴油机改装而成的甲醇发动机上,采用以火花塞作为传感器的离子电流测量法在线获得了发动机正常燃烧和3种典型失火工况时的离子电流信号,分析了它们之间的异同,给出了3种典型失火工况的离子电流信号特征值,并利用离子电流的焰后区峰值幅值及峰值位置量化了试验用甲醇发动机发生失火的判定依据。结果表明:当发动机正常燃烧时,离子电流曲线只含有前锋区和焰后区;当火焰不能连续传播而引起失火时,离子电流信号在上止点附近出现若干尖峰;当断油引起失火时,离子电流只出现点火信号;当缓慢燃烧引起失火时,离子电流波形分别在前锋区和焰后区出现峰值。该结果可为离子电流法在点燃式甲醇发动机中的应用提供理论依据。

The ion current signals of normal combustion and three kinds of typical misfire conditions were obtained with ion current method from a methanol engine refitted by a four- cylinder diesel engine, where the spark plug was served as a sensor. A comparative analysis of shapes was carried out between the ion current signals obtained under normal and abnormal combustion conditions. Analyzing their similarities and differences, the characteristic values of the ion current signals under three kinds of typical misfire conditions were given. The misfire criterion of methanol engine was established according to the peak value and the timing of the peak value of ion current. The ion current curve contains only front flame and post flame under normal condition. When misfire occurs under different operating conditions, the shape of the ion current becomes quite different. The ion current curve possesses a number of peaks as interrupted flame occurs; the ion current just has one peak as fuel is not supplied; for part-combustion, the ion current curve possesses two peaks at the front and post zones. Thus a misfire evaluation criterion is established according to the peak value of post-flame current and appearance of the peaks.