Research On Low Temperature Combustion Close-loop Control For Diesel Engine Under Transient Operations

With the depletion of fossil oil resources in the world, as well as the increasingly stringent exhaust emission regulation, in recent years, low temperature combustion(LTC) technology for diesel engine was widely investigated in the world in order to achieve high efficiency clean combustion and reduce system cost. Although the pollutant emission can be reduced in LTC mode which was accomplished by employing high EGR and sigle late injection, there was also problems about combustion stability and fuel economy. In this study, the combustion characteristics of LTC mode was invetigated, and the close-loop control strategy was studied when combustion mode switched between traditional combustion mode and LTC mode through the combination of bench test and simulation methods.The test rig and acquisition system were built, and the combustion control parameters, including EGR rate, EGR temperature, injection timing and injection pressure, on combustion and emission characteristics were investigated, and the control problem were disscussed. At the same time, EGR chemical kinetic equilibrium in transient process was analyzed. And the relationship between intake/exhaust oxygen concentration and EGR/ excess air coefficient was concluded.In order to identify current in-cylinder combustion mode, and guarantee combustion stability and emission performance, LTC chemical kinetic theory was analyzed, and the main effect mechanism to achieve LTC mode was got. Among in-cylinder pressure, in-cylinder rise rate and heat release rate(HRR) parameters, HRR was adopted to indentify the different combustion mode. A GT-Power engine simulation model, which employed DI-Jet combustion model, was built to analyze in-cylinder equivalence ratio–combustion temperature change between traditional combustion mode and LTC mode.Meanwhile, in order to solve the problem about lower power output and poor fuel economy during combustion mode switch, the GT-Power and Matlab/simulink joint simulation platform was built to carry out combustion mode switch control method research and to optimize fuel economy in LTC mode. Firstly, based on model based calibration(MBC) method, the optimized control aim parameters were calibrated in LTC mode. Following, a two-input and two-output control relay feedback method was implemented to turn coupled parameters and solve the problem about calibration workload issues.Eventually, based on LTC joint simulation platform, the TITO closed-loop method and single input and single output closed-loop control model was carried out, respectively, to contrast the engine fuel economy. And the result showed that, without deteriorating emission performance, the TITO control method could improve fuel economy both in LTC model and in combustion mode switch process under transient conditions.