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非稳定工况是车用发动机最经常使用的工况，然而由于技术原因，对其工作过程的研究尚不够深入。本文定义了发动机非稳定工况与过渡过程的概念，按３种情况划分了加速过程。建立了适用于过渡过程的发动机缸内参数动态数据采集分析系统，利用该系统测取了４９２Ｑ汽油机加速过程的气缸内瞬时压力、空燃比等参数，并对加速过程进行了示功图分析。结果表明，与相应稳定工况比较，加速过程使混合气变稀、点火滞后、燃烧稳定性变差、循环动力性下降。
Unsteady conditions are the most frequently used operating conditions of vehicle engines. However, due to technical reasons, the research on their working processes is not yet in-depth. This paper defines the concept of engine unsteady conditions and transition process, according to three kinds of situations, the acceleration process is divided. A dynamic data acquisition and analysis system for engine cylinder parameters, which is suitable for transitional process, is established. By using this system, parameters such as instantaneous pressure, air-fuel ratio and other parameters in the acceleration process of 492Q gasoline engine are measured. The results show that, compared with the corresponding steady state, the acceleration process makes the mixture thinner, the ignition lags behind, the combustion stability deteriorates and the cycle dynamics declines.