Control Of Diesel LTC Combustion Using Cold-Hot EGR And Two-pulse Injection

Low temperature combustion(LTC) has become one of the hottest research focuses on engine combustion as an efficient and cleaning technique in recent years. However, due to the lack of direct combustion control method on LTC, the control on combustion and mode switching process of LTC was still a research difficulty.A research idea was presented that a cooperative control method using multi-pulse fuel injection and cold-hot EGR to control the air-fuel mixture of LTC and the control of combustion process. The effect of multi-pulse injection parameters on the steady-state performance and emission performance of LTC was investigated. The control action of cold-hot EGR system on EGR rate and intake temperature was argued. The optimum control strategy of steady-state performance was studied with the combination of multi-pulse fuel injection and cold-hot EGR. The transient control method was determined to achieve the smooth transition for the switching process from LTC mode to CI mode.Firstly, experiment study on the effect of multi-pulse injection parameters on the steady-state emission performance of LTC was conducted in a test bench on HC concentration distribution. The effect of time space, injection timing and injection mass ratio on the spray atomization was revealed. On the basis, effect of two-pulse fuel injection on LTC combustion and emissions were studied, and effect of fuel injection interval, timing and ratio on LTC combustion and emissions were revealed. Also, the control strategy of two-pulse fuel injection was confirmed from the evaluation of fuel consumption and NOx emission.Secondly, on the cold-hot double-loop EGR engine test bench, the concept of cooperative control method by EGR amount and intake mixture temperature was introduced. With the cooperative control of cold EGR valve, hot EGR valve and back pressure valve, the precise control of EGR amount and intake mixture temperature was achieved. The effect of EGR rate and intake temperature on the combustion process and emission performance was investigated, and the results showed that the increase of intake temperature provides more effect than the decrease of air mass flow with the same EGR rate at low speeds. The EGR control strategy was achieved at different operating conditions. The small amount of high temperature EGR was introduced to promote the evaporation and atomization of fuel at low speed and light load. The high rate of cooled EGR was introduced to maintain better control of combustion phase at high speed.Thirdly, combining two-pulse injection and cold-hot EGR, the effect of the changing ratio of two-pulse injection fuel on the combustion and emission performance was investigated with the action of EGR on the test bench of cold-hot EGR double-loop. The results showed that the larger fuel amount of the 2nd injection, the effect of EGR on the combustion retard becomes more obvious. The atomizing and evaporation effects of the 2nd injection also become more sufficient, and the cooperative control of EGR and two-pulse injection were determined.Finally, the smooth characteristic of indicated mean effective pressure(IMEP) and transient HC emission were investigated in the switching process from LTC mode to CI mode. The peak value of HC emission emerges after the switching process. During the strategy of regulating the ratio of two-pulse injection in two transition cycles was proposed to reduce coefficient of variation(COV). The problem of output power decrease was solved at the beginning period of switching process. During LTC-CI switching process, the strategy of regulating the gradually increasing amount of single injection in five transition cycles was introduced, which eliminate the peak value phenomenon of transient HC emissions and reduced COV of IMEP after switching.