The Performance Simulation And Optimization Of Diesel Engine For Construction Machinery Under Plateau Conditions

Abstract:The working environment of construction machinery is complex. The most prominent thing is that the decrease of atmospheric pressure caused by altitudes will lead to the power, fuel economy and emissions of diesel engines for construction machinery worse.The work condition of construction machinery is very bad,which makes the transient performance of engine for construction machinery deteriorated. The stability performance simulation model and transient performance simulation model of diesel engine were built based on GT-Power software. The influence of steady-state performance caused by altitudes and the influence of transient performance caused by fluctuating load were researched based on the models. The main research work was as follows:(1)The influence on intake flowrate, combustion temperature, cylinder pressure and P-V diagram caused by different atmospheric pressure was researched. The study showed that the power of engine was reduced with the decrease of atmospheric pressure. The turbocharger became overspeed and overtemperature easily under plateau conditions, which made the power compensation of turbocharger deteriorated. The turbocharger had a lower comprehensive efficiency on the low-speed conditions.(2) The influence on ignition delay, cylinder pressure and temperature under different advanced injection angles was researched. The study showed that advanced injection angles had a significant effect on the ignition delay. Ignition delay showed a half U-shaped curve under advanced injection angles. The engine power increased with advanced injection angle increased,while specific fuel consumption decreasing.(3) Combining the above two aspects researched,aiming at the problem that the performance of diesel engine for construction machinery on plateau conditions deteriorated, a way that optimizing advanced injection angles was put forward. The study showed that with the increase of altitudes,rising the advanced injection angle of diesel engine according to certain rule could improve the plateau performance of engine effectively.(4) The load of hydraulic excavators had periodic,which could be seen as a combination of different load-changed-rate load and sine-wave-form load. The engine’s dynamic process under the different load-changed-rate load and the sine-wave-form load were researched based on the transient performance model of diesel engine. With the load-changed-rate increased, the engine speed reduced severely, resulting in fuel injection quantity overshooting seriously, but intake flowrate did not change significantly. When the frequency of the sine-wave-form load exceeded a certain value, engine speed was no longer changed by load,the impact on the speed caused by variation amplitude was very little.