Research On The LTC Low Load Combustion Control Based On Pressure Sensor Glow Plug

Low temperature combustion(LTC)is an advanced CI combustion mode,which can achieve low emissions of NOx and PM,and at the same time keep relatively high thermal efficiency.While as one of the major challenges for LTC combustion,at cold start compression ignition is hard to realize,combustion stability,thermal efficiency and emissions deteriorate,especially for gasoline or fuel with high octane number.In this thesis,LTC tests are conducted on a 1.9L common rail diesel engine,and engine performance at cold start and low load conditions is optimized based on a control platform and control algorithms for in-cylinder heating.The in-cylinder heating control platform is built for LTC combustion assist,which can realize the closed-loop control of in-cylinder heating based on feedback information like combustion states and engine operating condition.As a part of the control platform,a glow plug control unit(GPCU)is developed,capable of driving high current resistive loads,exchanging data with ECU through CAN communication and can realize independent control of the four cylinders.Further,glow plug surface temperature and electric power control algorithms are proposed.Open-loop control of glow plug surface temperature is achieved through lookup table,looking up the PWM pulse width.For the closed-loop control,temperature feedback is introduced.While the temperature of the glow plug can't be measured directly,it's estimated through a linear resistance-temperature model or a lumped capacitance temperature model,the latter one is more complicated but more precise.Because of limitation on response time and accuracy,power closed-loop control is preferred than temperature.The PID controller for closed-loop control of power has a cut-off frequency of 20 Hz,no steady-state error.LTC tests at cold start and low load conditions are conducted to optimize the engine performance.A blend fuel of diesel and gasoline is used,and the blending ratio of gasoline and diesel is 70:30 by volume.Test results show that in-cylinder heating has improved engine performance in aspects like combustion phase,efficiency,stability and emissions etc.At cold start conditions,through in-cylinder heating,COV IMEP is lowered to around 10% from 12%-37%;Combustion efficiency is 2% higher,and the highest combustion efficiency is larger than 99%,also indicated efficiency is 8% higher;Though NOx emissions deteriotate,it's still below the limiting values of the Stage V National Emissions Standard of China for diesel engines;At the same time PM emissions CO emissions and THC emissions are reduced greatly.At low load conditions,with the help of in-cylinder heating,COV IMEP is within 5% or 3%,which is a huge improvement compared with the original 3%-15%;Indicated efficiency is enhanced to 45%-51% from 35%-50%,combustion efficiency is around 5% higher;Except for NOx,all other major emissions are also reduced greatly.And NOx PM emissions are all below the limiting values of the Stage V National Emissions Standard of China for diesel engines.