Heavy Duty Diesel Engine Starting And Load Step Conditions Control Strategy Design And Performance Optimization

As the the resource and emission problems getting more and more serious all over the world,more and more strigent rugulations concerning fuel consumption and emission limit are published.When it comes to China,the China VI emission regulation makes it more challenged for the transient cycle emissions.Based on above problems,the two typical transient conditions including starting and fast load step are researched,for the purpose of optimizing engine performance under that two conditins,a heavy duty diesel engine is used for research.Based on the problem that the starting injection quantity cannot fit the engine actual desired power input,the targent acceleration based starting fuel injection control strategy is proposed.The starting process desired torque is separated into a resistance torque and a acceleration torque,where the resistenc torque is fixed and it can be measured by dynamometer mortoring test,and the acceletation torquqe is acquired by calculation of the target acceleration model settled by author.Because the target acceleration based defined the power out put in detail and control the resistance torque and acceleration torque separately,the starting process injection quantity can match the engine power demand better.When comparing with the traditional starting control strategy,less engine speed overshoot during start to idle transient process,less accumulated fuel injection quantity during starting process and obvious HC,CO and NOx reduction are acquired from the target acceleration based starting control strategy.For the purpose of researching the influenc of different target acceleration on engine starting performace,different acceleration curve with different slope are designed.The reault shows that the acceleration with positive slope is helpful for reducing starting time,as well as reducing the starting process accumulated fuel injection quantity.There is great benefit for improving starting process combustion and emission performance by optimizing the start first cycle combustion quantity.From the various factors for influencing first cycle pergormance,injection strategy is relevant important.In this papar,the starting first cycle combustion and emission performance is optimized by means of optimizting first cycle injection strategy.Twice injection and triple injection mode are picked for reaearch.In twice injecition,the pilot injection quantity,pilot to main injection time and main injection time are the parameters to be adjusted,in triple injection,the first injection quantity,first injection to main injection time,the second injection quantity,the second to first injection time and the main injection timing are the paramenters to be adjusted.Because there is too much research parameters for optimization,the DoE method is used for research content design.For the purpose of securing the same first cycle boundary conditions to avoid the influence from boundary conditions,the CFD simulation is used and the same boundary is set in software.With the CFD calculation result,neural network modeling is realized by CAMEO and the twice injection and triple injection reaults are trained separately,where the input is the injection parameters and the out put is the first cycle accumulated heat,HC,CO and NOx emissions.With the relationship between input and output,the output is optimized by CAMEO and corresponding input is also acquired.The optimization result shows that HC,CO reduced and accumulated heat increased with NOx increased a little bit when comparing twice injection with triple injection.Base on the twice injection,the influenc of injection parameter on first cycle performance is analyzed.Results shows that as the pilot injection quantity increasing,more heat released by the pilot injection which is contributed for the main injection combustion,on the other hand,the increased pilot quantity show drawback on mixture formation,which can lead to uncompletely comnustion and increase HC emission.There is tradeoff between the benefit and drawback from pilot injection quantity increasing,with the reasonable optimization for pilot injection quantity,the first cycyle performance can be improved a lot.The pedal urgent load step increasing condition is one of the most common used transient conditions during the vehicle operational process.The engine dynamic performance demand of driver is in an uprush in short time,the intention is realized by the on the gas pedal,the transient fuel quantity is increasing fast after increasing of pedal open degree.While the responding speed can't meet the increasing speed of fuel quantity due to the higher fuel quantity and the lower intake quantity,which will lead to the worsen of emission performance;The fast increasing of fuel quantity due to the fast increasing of fuel pedal will lead to the fast increasing of vehicle speed which will affect the driving comfort,the progressive increasing of fuel quantity control strategy in urgent load step increasing speed aiming at the above question.The determine threshold of increasing speed is set firstly,the increasing speed of pedal is decided to overspeed of pedal when the increasing speed of fuel pedal is increasing to threshold,the progressive increasing function of pedal is active and the pedal open degree is switched to the opening of the provisional increasing as step;when the pedal degree is lower than the opening of the provisional,the peal progressive increasing restrict is stop and the pedal open degree is switched to the real open degree.The result shows that the increasing speed of fuel quantity is limited the rational scope after the restrict increasing speed of peal by progressive increasing control strategy of pedal,which improve the excess air coefficient and HC,CO and Soot emission.Under urgent load step condition,the intake mass increasing cannot mathc the fuel injection quantity increasing because of turbocharger delay,which can lead to obvious soot emission deterioration.Based on that problem,an EGR transient correction control strategy is proposed in this paper.During the early period of load step condition,the EGR valve is corrected to 0 by a correction factor,so that the intake air mass is increased and soot emission is reduced.During the later period of load step condition,the desired air mass MAP is corrected by the correction factor and the desire air mass is reduced so that the actual air mass can satisfied with the desied one earlier,which can lead to the earlier open of EGR valve,so the NOx emission is reduced during the later load step period.WHTC transient cycle was run based on the EGR transient correction control strategy,the result show that with EGR transient correction,the soot,NOx,CO and CO emissions all showed obvious reduction,but there is a bit fuel comsumption increasing when comparing with the originate control strategy.