基于离子电流为信号源的发动机燃烧诊断的基础研究

Ion current measurement is a neotype on-line survey method for SI (spark ignition) engine. Due to its low cost, simple structure, no modification to engine and excellent response performance,ion current diagnostics is proved an effective approach and much effort has been devoted to it. Currently, the main problem of ion current method is that the dominant factors and the principle of detection for combustion information are ambiguous.This proposed work involves two aspects but related research work: 1) Componet effect of synthesis gas (CH4/CO/H2) on the ion curent will be investigated. Multiple ion current sensors are designed and located at different positions in a constant combustion bomb, ion current generated during combustion of pre-mixture will be detected. This aspect aims to find the dominant ionization process of ion current, and confirm the contributing proportion of chemical ionization reaction and thermal ionization reaction.Concentration of component related to the charged particles will be calculated with CHEMKIN software to analyze generation mechanism of ion current. Ion current obtained with different electrodes will be compared to find the optimized location of ion sensor for combustion detection. Additionally, a multiple ignition system will be designed to the simulate of abnormal combustion including knock and pre-ignition condition, this aims to achieve mechanism of abnormal combustion detection using ion current method through analysis of frequency quality of ion current. 2) The second aspect is to acquire the behaviour of ion current generated during combustion in automobile engine. Multiple ion current sensors are located central symmetrically in the gasket between the cylinder and its head. Relationship between ion curent and pressure will be established, and artifical neural network method is chosen to predict pressure based on ion current parameters. Data obtained in this proposal research could be used to guide reasonable installation of ion sensor to get combustion parameters with high quality for electrical controll, and provide feasibility scheme for on-line detection system based on ion current signal for for automobile engine, thus this work has great importance in scientific research and engineering application.

离子电流法是一种新型的在线测量技术，相比于传统的压力传感器、激光法等，由于其具有结构简单、价格低廉、响应性能好等优点，现已成为发动机电控领域的研究热点。目前，离子电流法应用于电控系统的"瓶颈"问题是：离子电流的主导因素与获取燃烧信息的原理不明确。本项目将研究：1)分析定容燃烧装置中不同比例的CH4/CO/H2混合气燃烧过程中产生的离子电流变化规律，采用CHEMKIN化学反应动力学软件计算燃烧中间产物的浓度分布，从化学反应元素源头推导主导离子电流的离子化反应种类，提炼通过离子电流提取燃烧与排放信息的原理；2）在发动机汽缸垫上布置多个电极，根据各电极测得的离子电流提取压力、火焰传播以及发动机运转工况等信息，并结合神经网络算法预测缸内燃烧状态，阐明离子电流测量非正常燃烧的机理。本项目研究所得的数据可以用于指导开发基于离子电流为信号源的新型发动机电控系统，具有重要的科学意义与工程价值。

针对离子电流法应用于电控系统存在一个“瓶颈”问题：离子电流的主导因素和获取燃烧信息的原理不明确，项目通过在容弹试验装置上改变测量电极的布置方式、混合气燃料的种类，以及在发动机试验装置上汽缸垫周围安装多个测量电极等试验方法，重点研究了测量电极的布置方式和几何结构、燃料中化学元素（N、H、C）、火焰碰壁对离子电流特征峰的影响，深入分析了离子电流特征峰的成因，详尽探讨了火焰与电极接触时火焰前锋面内带电粒子被电极吸收在离子电流形成中起到的作用，揭示了NO热离子化在焰后区离子电流形成中发挥的作用。本项目还提出了利用离子电流法获取层流燃烧信息的方法。在定容燃烧弹布置一对测量电极，通过测量和分析燃烧过程中的离子电流信号，提出离子电流法测量平均火焰传播速度与前锋面火焰厚度的方法，并对常温下不同过量空气系数（lamda=0.75~1.1）、掺氢比（0~80%，10%递增）和预混压力（P0=0.8atm、1.0atm、1.2atm）下CH4/空气混合气燃烧火焰的平均传播速度和前锋面火焰厚度进行了测量，并与传统光学纹影法的测量结果进行了对比.结果发现：对于常压下过量空气系数为0.8的CH4/空气/H2混合气预混燃烧，在掺氢比0~80%时，利用离子电流法测得的平均火焰传播速度随掺氢比增大而增大，而前锋面火焰厚度随掺氢比增大而减小，测得的火焰速度分别为2.02、2.14、2.43、2.65、2.95、3.40、4.29、5.81、8.18 m/s，而火焰厚度分别为1.46、1.37、1.22、1.11、1.06、0.95、0.86、0.87、0.82 mm，相对于纹影法的误差均在5%之内。验证了本方法的可行性，为离子电流法测量层流火焰传播特性的新方法提供了理论和试验依据。