Research On Combustion Close-loop Control Of Diesel Engine Based On In-cylinder Pressure

As the situation of energy shortage and environment pollution is getting worse, fuel saving and emission reduction are the most urgent tasks for the automotive industry, especially in the research field of internal combustion engine. Traditional diesel engine is well known for its high combustion efficiency, low fuel consumption and strong power output, but its high emission is always a serious concern. The rise of HCCI and the popularization of alternative fuel indicate a promising developing way for diesel engine, however, both technologies are facing combustion process control problem in practical application. Therefore, a combustion close-loop control system of diesel engine based on in-cylinder pressure was designed and developed in this paper. It was then applied in a HCCI-CI prototype engine, evaluating its influence in improving engine performance.Combustion close-loop control system was developed from an electrical control platform of diesel engine, by adding mass produced pressure sensor glow plugs as feedback source of each cylinder. Distributed structure was applied, so there were two control units in this control system. In-cylinder Combustion Analysis Tools (iCAT) was in charge of feedback, and Engine Control Unit (ECU) was in charge of control. They communicated with each other through CAN.iCAT was a totally new developed signal processing unit. With proper design of hardware and software, iCAT could collect and deal with in-cylinder pressure signals from 4 cylinders continuously, and all combustion related indices of current working cycle could be calculated and sent to ECU before the arrival of next working cycle's combustion process. The calculation results were as good as those calculated by Combustion Analysis System (CAS) which was specially designed for in-cylinder combustion research. Close-loop control algorithm was added to the software framework of ECU, while its hardware kept same as original electrical control platform. By choosing IMEP and CA50 as feedback variables, amount of cycle fuel and timing of fuel injection as control variables, it could effectively reduce the combustion unevenness of each cylinder.The combustion close-loop control system was applied in the prototype engine and conclusions could be drawn from the test results. In CI mode, combustion close-loop control showed no significant influence in reducing engine emission. In HCCI mode, combustion close-loop control could help to avoid incomplete or instable combustion in middle and small load, leading to reduction of THC and CO emission, and it could also help to prevent CA50 from mass soot generation area, leading to reduction of soot emission. When GTL was applied in the prototype engine with combustion close-loop control, the torque output could be kept same as when diesel was applied, if engine speed and the position of accelerator pedal were same.