| In the recent years, with the increasingly prominent of stringent emission regulations and environmental issues, clean and efficient diesel combustion with low-carbon smoke emissions has become a hot trend. Because of the potential to achieve ultra-low emissions of soot, low temperature pre- mixed combustion(PLTC) technology has become one of the important means to achieve efficient and clean combustion. However, compared with the traditional mode, the PLTC mode shows a completely different combustion characteristics, resulting in the difference of soot formation characteristics. With the further development of PLTC diesel combustion technology, characteristics of soot formation of new combustion mode need to be researched.In this paper, the research was conducted by the method of CFD numerical simulation, based on the engine bench test. The effects of control parameters and multiple injection strategy on the soot formation characteristic of PLTC were conducted, and the results are as follows:(1) The soot formation characteristics of PLTC and traditional combustion mode were researched. The result shows that the combustion process and soot emissions between PLTC and conventional combustion mode has a great difference. The ignition delay of PLTC with early injection strategy is longer and the mixture is more uniform for the early injection coupling EGR. And the ?- T distribution turns to be a concentrated and small trend, and that in traditional combustion turns to be diffused with overgenerous equivalence ratio area. The in-cylinder combustion temperature got better control by high EGR rate, so that it achieve a lower soot emissions compared to traditional combustion mode.(2) The influence of control parameters such as injection timing and EGR rate on the combustion characteristics of soot formation on diesel PLTC was analyzed. The result shows that: the formation and oxidation of soot are promoted and the oxidation of soot holds dominant position with a timely early injection timing, which leads to a low soot emission. When the injection timing is too early, although it can restrain the soot formation and oxidation, the soot formation dominates the role. And the soot get a rise. The increase of EGR restrain the formation and oxidation of soot, the suppression of soot oxidation holds dominant position, and it will increase soot emission. With the further increase of EGR rate, the suppression of soot formation dominates the role, for which the soot emission decreases.(3) The effect of multiple injection strategy on diesel PLTC soot formation characteristics was conducted. The results show that: with the advancement of pilot injection timing, the C2H2 and OH formation get a rise, which will promote the oxidation and formation of soot. But the effect on soot formation holds dominant position, which leads to a rise of soot emission. With the further advance ment of pilot injection timing, the OH formation decreases, the accelerated effect on soot oxidation further weakened, soot emission increases accordingly. With the increase of pilot injection amount, the C2H2 and OH get a rise, which will promote the soot formation and oxidation. The effect on soot oxidation holds dominant position, and the soot emission decreases. When the pilot injection fuel mass is increased, although the C 2H2 decreases and the OH increases, the accelerated effect on soot formation holds dominant position, and it makes the soot emission get a rise. There is a suitable scope of pilot injection timing and pilot injection quantity to achieve lower soot emissions. With the increase of timing interval between main injection and post injection, the soot associated components get a two levels change, and the start of change puts off. And soot was first on the rise after a downward trend. With the increase of the post-injection of fuel, the soot associated components get a two levels change, the variation of change increases. Soot emission get a upward trend. |
PDF Full Text Request