An Application of Model Based Combustion Control to Transient Cycle-by-Cycle Diesel Combustion 2008-01-1311
From the viewpoint of the global warming restraint, reduction of exhaust emissions from diesel engine is urgent demand. However, it needs further development in combustion control besides after treatment system. Larger amount of EGR (Exhaust Gas Recirculation) is effective to reduce NOx emission. On the other hand, in-cylinder physical conditions greatly influence on self-ignition and combustion process, especially low O2 fraction charged gas owing to excessive EGR causes misfire. A drastic solution for this problem, fuel injection timing should be optimally manipulated based on predicted ignition delay period before actual injection.
For this purpose, Toyota has developed a model based diesel combustion control concept to avoid the misfire and to keep low emission combustion includes in transient condition. The feed-forward self-ignition timing controller consists of the intake gas O2 fraction estimation model, the ignition timing prediction model, and the fuel injection timing finding function. On each cycle, the ignition timing prediction model makes a relational expression between fuel injection timing and predicted ignition timing. And the injection timing finding function finds the required injection timing to meet self-ignition timing to its target by using the expression. In the experiment, the controller prevents the transient excessive ignition delay, and the torque response and HC emission is improved. As a consequence, the control concept has been realized as a practical on-board control technology.