Closed Loop Combustion Control

of IC Engines

Professor Guoming (George) Zhu

Department of Mechanical Engineering

Michigan State University

Abstract:

Maximum Brake Torque (MBT) timing for an Internal Combustion (IC) engine is the minimum advance of spark timing for best torque or, in other words, for best fuel economy. But MBT timing is often limited by engine knock in advanced direction, and spark timing is also constrained by partial burn and misfire in retard direction. It is preferred to operate IC engines at MBT timing when it is not knock limited and at borderline knock limit when it is knock limited. During the cold start it is desired to operate IC engines at its maximum retard limit subject to combustion stability limits to reduce catalyst light-off time. Traditionally, both MBT timing and retard spark limit are open loop feedforward controls whose values are experimentally determined by conducting spark sweeps at different speed and load points, and at different environmental conditions. The borderline knock limit is controlled by a dual-rate count-up/count-down closed loop control utilizing deterministic information from engine knock sensors.

Exhaust Gas Recirculation (EGR) is a well-known practice to improve engine fuel economy and reduce NOx emissions in certain operating regimes. A portion of the exhaust gas is either recirculated back to intake manifold through a link between the intake and exhaust manifolds (external EGR) or trapped inside the cylinder through valve timing control (internal EGR) in order to mix with the fresh air for the next combustion event. Dilution of the fresh air-charge mixture with the inert exhaust gas lowers the combustion temperature and therefore suppresses the NOx formation. The conventional approach of EGR control for a given engine operational condition is pre-determined by extensive engine calibrations and implemented in real time utilizing the stored maps in an open loop control setting, and hence is relatively conservative.

This presentation addresses a closed loop control scheme for both spark timing and EGR rate using an in-cylinder ionization signal, where both borderline knock and retard spark limits are regulated using closed loop stochastic limit controls, and engine MBT timing and EGR rate are controlled using an extremum seeking algorithm. The presentation will discuss two main closed loop control strategies: a) the stochastic knock spark limit control, and b) MBT timing and EGR rate control using an extreme seeking algorithm.

Friday, September 26, 2008

3:30 – 4:30 p.m.

Rm. 1500 EECS