Research On The Combustion Control Of A Flex-fuel Engine Based On Closed-loop Combustion Control

It is a huge challenge for the automotive industry to both increaseengine efficiency and reduceengine out emission at the same time. Traditional single fuel(gasoline or diesel) engines have met problems in realizing clean combustion udel to the fuel properties, so flexible-fuel or blended fuel could be a potential solution to the problems by fully utilizing the different properties of different fuels. However, problems remain in precicely controlling the combustion, extending the load range, and realizing fuel-adaptive capabilities. With closed-loop combustion control measures, this paper conducts deepresearch on the combustion optimization control of the flexible-fuel engine from two aspects, the hybrid combustion aspect and the hybrid fuel(flex-fuel) aspect.Firstly, closed-loop combustion control technology is the key control technology of the flexible-fuel engine. Previous closed-loop combustion control system with one in-cylinder pressure sensor in each cylinder is very expensive, while the traditional method based only on engine instantaneous speed analysis requires too complicated algorithm, and the precision is not very good either. In order to deal with the problems of previous measures,an innovative combustion state parameters estimation method is proposed in this paper, which integrates one in-cylinder pressure sensor and the engine instantaneous speed sensor together through sensor fusion algorithm and based on experimental study results. The method proposed in this study could reduce both system setup cost and algorithm complexity at the same time, so it has both high theoretical value and practical value.Secondly, a new multi-mode compound combustion control strategy is proposed in this paper in order to deal with the problems met at small load condition(combustion instability) and large load condition(emission deterioration) in realizing clean and efficient combustion. The multi-mode compound combustion control strategy is proposed based on experimental study results of different advanced combustion modes with dieseline of different blend ratios. The comparative experimental study between partially premixed combustion and late injection low temperature combustion has finallyled to the multi-mode compound combustion strategy: at the very small load range, glow-plug aided combustion strategy or ultra-low pressure injection compression ignition mode should be utilized to stabilize the combustion; at the small to medium load range, partially premixed combustion mode should be utilized to achieve clean and efficient combustion; at the medium to high load range, late injection low temperature combustion mode should be utilized to realize clean combustion; and at the high load range, traditional compression ignition mode should be utilized. The operation range of different combustion modes will change with the blend ratio between gasoline and diesel, but the multi-mode compound combustion strategy is the optimal strategy for combustion control in the whole load range.Thirdly, flex-fuel engine optimization control research is conducted to make the engine adaptive to different kinds of fuels using two kinds of methods, the open-loop control method and the closed-loop control method. The open-loop control method is based on on-line fuel blend ratio detection. One energy based fuel detection method, one ignition delay based fuel detection method and one multi-factor fuel detection method are proposed through theoretical analysis of the chemical and physical characteristics of different fuels and experimental study of the combustion state parameters. All fuel detection methods have been verified.The open-loop control method has the drawback of demanding too much calibration effort and requiring very high precision. In order to improve the open-loop control method, a closed-loop control method is proposed. In order to meet the torque output and engine efficiency requirements, closed-loop control strategies aredesigned to deal with the torque output difference problem and the thermal efficiency optimization problem respectively when using different fuels. The closed-loop control methods feature both feed-forward and feed-back controllers to realize engine break torque output management and engine thermal efficiency optimization targets. In conclusion, a foundamental flex-fuel enginemanagement system has been establishedduring this research.