Control And Optimization Of Diesel Substitution Rate For Diesel-natural Gas Dual Fuel Engine

With the increasingly stringent emissions regulations and the growing shortage of fossil fuels,diesel-natural gas dual fuel engine has been attracting much attention in recent years because of its good power,economy and low emissions.However,in actual operation,the diesel-natural gas dual fuel engine frequently encounters the reliability problems such as ‘melting top' and ‘scrapping cylinder',and its emissions are still difficult to meet the increasingly stringent emission standards,resulting in its commercial application is not successful.The reasons for the frequent occurrence of reliability problems for diesel-natural gas dual fuel engines are as follows: 1)The electronic control system of diesel-natural gas dual fuel engine can not achieve the optimal co-combustion of dual fuels;2)The setting and control of diesel substitution rate(DSR)is unreasonable,which leads the actual DSR deviates the ideal setpoint.In view of the above reasons,my research focus on the development of electronic control system and the setting,control and optimization of DSR.1.According to the modification requirements of diesel-natural gas dual-fuel engine,a set of parallel co-combustion electronic control system,which can achieve the optimal cocombustion of dual fuels,is developed.An active co-combustion mode switching board is designed to realize the flexible switching of the two working modes of the diesel-natural gas dual fuel engine.A diesel nozzle physical simulator with the energy feedback function is developed.The developed diesel nozzle physical simulator can accept the output pulse of the original diesel electronic control unit(ECU)in the dual fuel co-combustion mode,which avoids the unnecessary fault alarm of the original diesel ECU and the re-development of the complex torque-based total fuel control strategy.A dual fuel ECU with the ability to independently drive the diesel fuel nozzle is developed,so as to optimize the diesel injection law under the dual fuel co-combustion mode.2.The piston maximum temperature(PMT)restriction is introduced,and the DSR is calibrated by compromising the PMT,the cylinder pressure maximum rise rate,emissions and economy,which avoids the occurrence of a too-high calibrated DSR.The PMT restriction is that the PMT does not exceed its safe limit.The PMT is calculated by the finite element analysis software ANSYS.3.A closed-loop control strategy of DSR is proposed.A DSR estimation model is established using the support vector regression(SVR)theory.The estimation model inputs are composed of diesel cycle injection quantity,natural gas cycle injection quantity,engine speed,inlet air flow and excess air coefficient.The DSR estimation model is embedded into the dual fuel ECU for real-timely estimating the DSR.The estiamted DSR is used as a feedback signal,and the the dual fuel ECU control parameters is adjusted based on the feedback signal,which achieves a closed-loop control of DSR.4.For the heavy-load condition,an online optimization strategy of DSR setpoint is proposed.Two simple PMT pattern classifiers are designed using v-support vector machine(vSVM).The feature variables of the classifiers consist of engine speed,NOx emission,intake manifold pressure and excess air coefficient,respectively.Two classifiers are embedded into the dual fuel ECU,and the on-line pattern recognition of PMT is realized.According to the PMT pattern recognition results,the DSR setpoint is adjusted in real time,so that the DSR is in the real-time optimal state,which ensures the real-time reliability of the diesel-natural gas dual fuel engine.