Investigation On Performance Of STC Diesel Engine During Transient Process With Intake Manifold Air Injection

The sequential turbocharging technology is one of the most effective method that can improves the performance of diesel engine at low load.But in the process of diesel engine sequential turbocharging switching in and switching out,if the switch delay and switch point of sequential turbocharging system is not suitable,it will result in some problem such as compressor surge,engine speed fluctuations,smoke increases and so on.it is hard to find the application of air injection technology in sequential turbocharging diesel engine.Air injection technology was applied to improve the process of accelerate and loading for sequential turbocharging diesel engine.The high pressure compress air was jetted into engine intake pipe.There are different influence for diesel engine performance about its transient performance combustion process and exhaust pollution at all kinds of jet pressure and jet duration.All of above works can supply the fundamental of control theories for sequential trubocharging diesel engine.The intake and exhaust pipe transform were done base on TBD234V12 diesel engine test bed.The air injection experiment was done in the process of switching,accelerating,loading for diesel engine.The influence law was investigated on different air jet duration and different air jet pressure about smoke,and the strategy of air injection was achieved.Through the calculation analysis of the inlet and combustion process in cylinder,the jet and speed up the process of diesel engine sequential turbocharing switching load in the process of the gas flow rule and the rule of the combustion in cylinder.The main research results are as follows:(1)The experiment were done in the process of diesel engine sequential turbocharging switching in and switching out.The switching in test showed that:in the process of swtiching in,the delay time is too long or too short is unreasonable,when the time is too short,diesel engine inlet pressure decrease rapidly,resulting in deterioration of diesel engine and diesel engine cylinder explosion pressure is reduced,increase the smoke of the engine.When the time is too long,the basic turbocharger for energy reduction,decreasing the inlet pressure of diesel engine,the combustion in cylinder,which can lead to the maximum explosion pressure in cylinder and corresponding reduced,smoke increase rapidly.The best value of the switching delay time is carried according to analyzing experimental data.The switching out transient test showed that when the gas valve is turned off,the controlled turbocharger has not enough energy boost pressure,and basic turbocharger itself has a certain inertia,the establishment of the supercharging pressure needs a certain amount of time,therefore,diesel engine intake can not meet the diesel engine combustion air amount,which can lead to worse instant diesel engine and smoke intensity increases,and the longer the delay time,smoke intensity values.Air valve and gas valve closed at the same time,we can achieve the best result of smoke of engine exhaust in switching out process.(2)The air injection test in sequential turbocharging switching process were done.the result showed that in the process of sequential turbocharging switch,After using jet technology,the diesel engine intake pressure stabilization time is shortened,engine speed fluctuations reduced and transient emissions have been greatly improved.Through the study of different jet pressure got influence of air pressure on the handover process:the higher the air pressure,the higher the engine intake pressure,the settling time is also shorter;through the study of different jet starting time got the air injection start time influence of the switching process:The best jet starting time is the gas valve to open or close time,ahead of the jet time has little effect on the process of switching transient performance,but it will lead to an increase of NOx emissions before switching;Through the study of the different durations of jet,the jet has been the influence of the duration of the handover procedure:the duration of the jet pressure to the feed gas pressure reaches the switching time of the steady operation of the engine is best if the time is too short jet,diesel the smoke increased,if the time is too long jet,diesel NOx emissions increase.(3)The air injection experiment has been carried out in the process of acceleration and loading.The experimental results showed that:in the process of acceleration and loading,the diesel engine rotating speed and torque increase,the throttle opening increases suddenly,the fuel injection in cylinder increased,Because of the characteristic of air compression and the turbocharger response lag factors,instantaneous air-fuel ratio dropped significantly,deterioration of the combustion in cylinder,resulting in the smoke emission increases sharply.The air injection has been applied to turbocharged engine,due to the air amount increase,diesel engine intake pipe pressure stable time shortened,the smoke of diesel engine,HC and CO emissions will decreased,but NOx will increase.The air injection pressure is higher,the higher the inlet pressure of the diesel engine,the shorter in the time of diesel engine intake pipe pressure stability.The improvement is more obvious in the process of acceleration and loading transient performance.When the air injection pressure hold on,we should holding air injection until the engine intake pipe pressure become stability.If the air injection time is too short,diesel engine exhaust smoke will increase.(4)Investigation on influence of intake,combustion,emission of diesel engine in the process for air injection technology.The results show that in intake pipe pressure difference increases after air injection,in cylinder air flow velocity increases,the diesel engine scavenging effect is strengthening,inlet valve closing time in cylinder pressure increases,diesel engine air inflow.The air injection makes the main combustion period increases,little influence on early combustion.Because of the air injection in cylinder the air amount increase,the oxygen content increases,therefore,the content of soot decreased.In short,in order to improve the switching process sequentially turbocharged diesel engine and accelerate the process of transient performance,this paper presents the intake manifold air injection program and experimental research.Studies have shown that:air injection can significantly reduce the smoke of diesel engine transient process,sequentially turbocharged diesel engine is an effective way to accelerate the handover process and transient performance process solutions.