Development And Experimental Research On Ionization Current Detection System In The Cylinder Of A Gasoline Engine

Detection and diagnosis of engine cylinder combustion is an important measure to improve engine combustion efficiency and reduce emissions of the engine. The ion current detection and diagnosis technology gradually became a current method utilized to research combustion state of the engines, for its low cost and acceptable usability. Rely on the Hunan Provincial Science and Technology Department research for innovation (project number:2012TT2043), the research work for the ionic current technology used to detect and diagnose combustion state of engines was carried out, as the details and the key conclusions are listed as following:(1)As abundant literature were referred to, the ionization process and mechanism for the gas mixture in the cylinder were analyzed to study the mixture in the combustion process, the reaction temperature and the mixture was heated to effect the process of ionization process. The result showed that the ion current is mainly affected by chemical and thermal ionization effect.(2)With a set of ionic current detection system designed, mainly including detection circuit, MC9S12XS128microcontroller and program loaded in it, the build-in A/D module of the microcontroller were utilized to measure the voltage across the resistor that set for measurement, and acquired data was sent to upper computer through Serial Communication Interface(SCI) for further analysis.(3)Wavelet analysis were used, when analyzing the ionic current data mixed with noise, to removes noise from the signal, subsequently the true signals of the ion current were acquired. Feature value of the true signal, which can be used for judging the misfire or the knock in the engine, were counted, including peak value, number of peaks, peak position and the integrated value.(4)Based on the test device built on a single-cylinder gasoline engine, the ionic current detection experiments under idle condition were conducted. Experimental results show that, when the engine ran under idle condition, the speed can be reduced for a lower fuel consumption, with the choke adjusted to50%-100%opening for better combustion of the mixture; higher DC voltage can be more accurate to capture the peak current signal, and excessively low DC voltage may affect the ion current detection. The center electrode configurations of the spark plug have a greater influence on the ion current, and the negative electrode was weak to influence the ion current. Misfire and knock of the engine could be distinguished precisely by the detection system.