A team at Michigan State University is proposing a new transition strategy for switching between spark ignition (SI) combustion and homogeneous charge compression ignition (HCCI) combustion for a transition boundary in which the engine speed is between 1100 and 2000 rpm and the corresponding load (indicated mean effective pressure, IMEP) is between 3.8 bar and 5.0 bar.
It is fairly challenging to achieve a smooth mode transition between spark ignition combustion and for a spark ignition engine capable of homogeneous charge compression ignition, because their in-cylinder thermal and charge mixture properties are quite different owing to the distinct combustion characteristics.—Zhang et al.
The two combustion modes have distinct engine operating parameters, along with distinct cycle-to-cycle residue gas dynamics during the mode transition.
In their approach, they opened the throttle step-by-step to its wide-open position for the transition from SI to HCCI or closed it directly to the target position for the transition from HCCI to SI. The hybrid combustion mode was employed with spark assistance to change gradually to the desired HCCI mode or SI combustion mode respectively, by increasing or decreasing the percentage of homogeneous charge compression ignition combustion during the hybrid combustion operation.
They experimentally validated the mode transition strategy on a spark ignition engine capable of HCCI equipped with electric variable-valve-timing systems, dual-lift valves and an electronic throttle control system. Because of the limitation on the electric variable-valve-timing response time, it takes 5–10 cycles of the engine, depending on the engine speed, to complete the mode transition.
During the transition and steady-state HCCI operation, they maintained the normalized air-to-fuel ratio between 1.0 and 1.3; the charge air was heated by a manifold charge cooler heated by the engine coolant; and a test gasoline fuel with a research octane number of 85 was used for all the experiments conducted.
The researchers demonstrated that the strategy is able to achieve a smooth combustion mode transition with the net mean effective pressure and the combustion phase fluctuations at the level of stable spark ignition and homogeneous charge compression ignition combustion.
Shupeng Zhang, Andrew Huisjen, Guoming G Zhu, Harold Schock (2015) “Improvement in the combustion mode transition for a spark ignition engine capable of homogeneous charge compression ignition” Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering doi: 10.1177/0954407015583599
Shupeng Zhang and Guoming G. Zhu (2014) “Model-Based Mode Transition Control Between SI and HCCI Combustion” ASME 2014 Dynamic Systems and Control Conference doi: 10.1115/DSCC2014-6148
Xiaojian Yang; Guoming Zhu (2013) “SI and HCCI Combustion Mode Transition Control of an HCCI Capable SI Engine,” Control Systems Technology, IEEE Transactions on,” vol. 21, no. 5, pp. 1558,1569 doi: 10.1109/TCST.2012.2201719