天然气发动机起动控制参数对排气特性影响的模拟研究

Simulation on the Effects of Start Control Parameters on the Exhaust Characteristics of CNG Engine

利用GT-Power和FIRE软件建立了天然气发动机一维仿真模型和排气系统三维模型,并得到了试验验证。通过仿真,研究了天然气发动机起动阶段点火时刻和怠速转速对排气特性的影响。结果表明:推迟点火时刻和提高怠速转速可明显提高排气温度、催化器入口高温区域的面积和排气质量流量;适当推迟点火会提高催化器入口排气的流速分布均匀性;发动机与催化器的匹配存在一个使催化器入口流速分布均匀性最佳的点火时刻和怠速转速;合理选择发动机起动阶段的点火时刻和怠速转速,可在满足起燃温度要求的同时使催化器入口流速分布更均匀。

A 1D model for CNG engine and a 3D model for its exhaust system are built with software GTPower and FIRE, and are validated by tests. Simulations are conducted to study the effects of ignition timing and idle speed on the exhaust characteristics of CNG engine at start phase. The results show that retarding the ignition timing and increasing the idle speed can markedly increase the exhaust gas temperature, the area of high-temperature region at the inlet of catalytic converter and exhaust gas mass flow rate. Reasonably retarding ignition timing can improve the uniformity of exhaust gas flow velocity at the inlet of catalytic converter. In matching catalytic converter with engine, there is an optimal ignition timing and idle speed to obtain the best uniformity of exhaust gas flow velocity at the inlet of catalytic converter. More uniform distribution of exhaust gas flow velocity at catalytic converter inlet can be achieved by the proper selection of ignition timing and idle speed at start phase while meeting the requirement of light-off temperature.