柴油引擎噴射系統故障與噴射壓力波形之關聯性

Observations on the Malfunctions of a Disel Injection System and Its Injection Pressure Waveform

本文以數值模擬的方法來探討柴油引擎之噴射系統元件發生故障時，所表現出來的噴射壓力波形特徵。數學模式所使用的統御方程式為準一維可壓縮的流體方程式配合能量方程式，模式中並考慮噴射系統中高壓油管受柴油高低壓震盪所引起的膨脹收縮行為。文中模擬了噴油嘴開啟壓力、柱塞磨損、噴嘴阻塞與擅調等情形對噴油率與高壓油管壓力傳播之影響，用來了解這些故障對高壓油管內之壓力特徵的影響。計算結果指出：欲使用高壓油管內之壓力來診斷柴油噴射系統時，建議以較靠近噴油嘴端來量測較佳，此處壓力微分後的局部最大值（噴油嘴開啟時）或局部之最小值（噴油嘴關閉時），可用來診斷噴油率之持續時間的重要參數與特徵。

This study is undertaken to develop methods and technology of usingthe injection pressure waveform to diagnose, on-line the malfunctions of adiesel injection system. Emphasis is placed on the establishment of thedatabase to identify malfunction characteristics in the injection pressurewaveform. For this study, numerical investigation is proposed to find thecharacteristics of the injection pressure waveform while the components ofthe injection system are out of order. The governing equations used hereare quasi-one dimensional compressible flow equations and an energyconservation equation. The compliance of the fuel tube is also modeled inthis mathematical model. The numerical codes are verified and validatedby comparison with the experimental data. Several types of malfunction aresimulated to find their effect on the pressure waveform, including abnormalinjector opening pressure, plunger corrosion, plugged injector and illegaltuning. The results also recommend that the measuring point should be nearthe injector side using on-line diagnosis instruments. Also, the localmaximum and local minimum of the first derivative of pressure would be indications of injector opening and close. The duration time is assumed tobe the important parameter for smoke generation.