Investigation of the detection of knock and misfire of a spark ignition engine with the ionic current method

This paper reports an investigation of detection of knock and misfire in the spark ignition engine by means of the ionic current method. In the knock experiments, two detecting methods are used. One is the ionic current method. High frequency signals will be added to the ionic current signals where knocking is happening, which can be detected by picking up these signals. The other is the engine block vibration method. Knock can also be detected by monitoring signals of the vibration sensor in a proper position. The signals of the two kinds of methods are recorded at the same time with a dual-channel oscilloscope. With wave comparison and fast Fourier transform analysis, the advantages of the ionic current method can be shown and its feasibility and reliability can be proved further. In misfire experiments, misfire can occur by adjusting spark plug gap, adding carbon deposits and cutting out high voltages. A remarkable difference exists between misfire and non-misfire ionic current signals in shape and amplitude. By detecting these changes, misfire detection can be realized. The experiments prove that using the ionic current method to detect knock and misfire is simple, visual and cheap.