A Study On The Ignition Phase Control Of The Diesel Engine Under Premixed Combustion Mode

Premixed combustion diesel engines have become the focus because of their high efficiency, low NOx and soot emissions. But some problems of premixed diesel engine are still waiting to be solved, especially ignition time control. Therefore, the concept of Ignition-Chamber Pre-Mixed Diesel Engine system is introduced to solve the problem of ignition time control. An ignition-chamber is installed in the cylinder head, and the ignition-chamber is connected with the main chamber by one or several channels. Two injection systems are needed. Diesel injector is installed in the main chamber and gasoline injector as well as spark plug is installed in the ignition-chamber. The mixture is controlled to be under the self-ignition point by adjusting the compression ratio and the rate of EGR. After igniting the mixture of ignition-chamber, the flame will ignite the lean mixture in the main chamber. With reasonable design, the combustion stability will be enhanced and the ignition-timing could be controlled under different load. The numerical study on this engine is completed and the feasibility is investigated.According to the schematic of CF186F engine cylinder head, a new 3-D model of it is created by CAD software CATIA. Then the model and boundary conditions which are calculated by 1-D simulation software AVL BOOST are imported into AVL FIRE. Some typical processes of internal combustion engine are calculated and analyzed, including airflow process, fuel spray and atomization process, combustion processes and emission generating process. The influences of different injection timings, different ignition timings, different ignition frequencies and different nozzle angles on the performance of engine are also analyzed.The simulation results indicate:this system can receive the uniform distribution of fresh air. When the main chamber injection timing ranges from 70℃A to 90℃A BTDC, this system achieve excellent combustibility and emission behavior; the ignition timing of this system has a large range of crank angle from 20℃A BTDC to top dead center, the mixture around the spark plug has suitable equivalence ratio and is suitable for ignition and flame propagation; the combustion duration keeps nearly 20 crank angles, the mixture is extremely full burnt and mean temperature is lower than 1800K, all of which can reduce the amount of NOx and soot. The mixture isn't ignited before TDC when the engine runs in rated speed and the load is lower than 80%. External EGR is needed to control ignition time when the engine working under high load.The 3-D numerical simulation contributes to provide significant information about the process of combustion and emissions generation of ignition-chamber pre-mixed diesel engine, what's more, the simulation result can provide references for future experiment researches.