Optimal Control Of Oil-gas Switch Of CNG/diesel Dual Fuel Engine

Along with the development of automobile industry and the rapid increase of automobile amount, the environment problem and oil crisis are even worse, these enforce people to find the alternative cleanly resources. CNG (Compressed Natural Gas), as an alternative engine fuel, can alleviate these conflict effectively. CNG/diesel dual fuel engine has been receiving more and more attention for its advantages such as good performance, convenient refitting and flexible use.The power, economy and emission of the dual fuel engine are worse at low load condition. In order to improve the performance, combusting pure diesel is a better method at low load condition. There is a process from pure diesel condition to dual fuel condition. Engine speed will fluctuate sharply and emission will be worse if the engine is not effectively controlled in this process.In order to eliminate the speed fluctuation of the compressed natural gas (CNG) /diesel dual fuel engine in the oil-gas switch process from pure diesel condition to dual fuel condition and cost less fuel, this paper analyzed the performance of CNG/diesel dual fuel engine based on the relative research. The reason that makes the low load performance of the engine be worse and the reason that makes the speed of the switch process fluctuate were analyzed. The oil-gas switch system was developed based on existent fuel supplying system. Optimal control object that is comprised of power and economy was provided basis of the practical condition. According to the variational methods and the theory and practice of engine, the math model of the oil-gas switch process was built.The engine has time-delay, non-certain, nonlinear and time-varying characters. In order to control it, there need a fast response, reliable and effective control algorithm. This paper analyzed kinds of control algorithm and control model of engine. Through analyzed predictive control in detail, the supplying fuel of engine was governed by GPC (Generalized Predictive Control) and optimal control was realized in the oil-gas switch process. Optimal control was simulated by MATLAB and the simulation result was analyzed. The validity and usefulness of this model and control algorithm were showed.