Study On The Coupling Control Of In-cylinder Temperature And Exhaust Gas Ratio In A Gasoline Low Temperature And High Efficiency Combustion Engine

The global issues of energy conservation and environment protection are demanding improvements in engine technologies. Based on the "saving-oriented" national policy, technological upgrade of traditional gasoline engines is regarded as one of the most prospective alternatives for development of car industries currently in China. Low temperature and high efficiency combustion of gasoline engine, represented by homogeneous charge compression ignition (HCCI) combustion, is attracting more and more attention for its capability of improving fuel consumption and NOx emissions simultaneously. However, gasoline HCCI is still confronted with the problem of a limited operation range and thus is not practically applicable. In order to achieve low temperature and high efficiency combustion at all engine loads, this research, based on the exhaust gas management strategy of HCCI combustion, develops a method to cooperatively control the in-cylinder temperature and exhaust gas ratio by coupling the technologies of fully variable valve actuations and exhaust gas recirculation.In the research, the flexible control strategy of in-cylinder temperature and exhaust gas ratio is studied on a single-cylinder gasoline HCCI principle prototype engine, through the combination of experiments and simulations. By effectively controlling the in-cylinder temperature and exhaust gas ratio, HCCI combustion can be extended to low and idle loads, and hybrid combustion and optimal spark ignition (SI) can be applied outside the HCCI operation range. In this way, the desired low temperature and high efficiency combustion can be realized at all engine loads.High exhaust gas ratio and low exhaust gas temperature inside the cylinder are the two major factors that hinder HCCI combustion at low loads. In this research, an innovative method is proposed to achieve spatial decoupling of temperature and exhaust gas in the combustion chamber by controlling the intake backflows through intake valve actuations. In this way, the low load boundary of HCCI combustion is expanded and stable HCCI combustion can be obtained in the low load operation range. In idle conditions, over 10% and 90% improvements can be obtained in fuel consumption and NOx emissions respectively when this method is applied, in comparison with the cases when only SI combustion is employed. The state-of-the-art HCCI combustion engines can only work at part loads. In this research, the operation range of low temperature and high efficiency combustion is extended through the introduction of hybrid combustion and optimal SI combustion modes. Stable hybrid combustion can be achieved and high cyclic variation can be avoided by effectively controlling the in-cylinder temperature and exhaust gas ratio. The hybrid combustion could meet the requirements of low temperature and high efficiency combustion, and can cover a part of operation range. The load continuous adjustment with temperature and exhaust gas ratio could be achieved by using hybrid combustion, which could eliminate the concept of combustion mode switching in control. SI combustion can be optimized through coupling control of internal and external exhaust gas, leading to improvements in both fuel consumption and NOx emissions.Effective in-cylinder temperature and exhaust gas ratio control is necessary for the achievement of low temperature and high efficiency combustion managed by exhaust gas. In this research, A T50-Total EGR schematic diagram is designed based on detailed experimental data, as guidance for the development of continuous load control strategy at all loads. The design principles of the valve parameters of low temperature and high efficiency is proposed, namely the principle of continuity, the principle of global optimization, the principle of stability and the principle of timing. On the basis of the aforementioned principles, a way how to design the valve parameters in the all loads is brought up. This research is of great significance for the practical application of the low temperature and high efficiency combustion technology on gasoline engines.