Study On The Emission And Test Methods Of Vehicle Compared With Diesel Engine Bench Based On China VI Emission Standard Heavy-duty Vehicles

Diesel engine is the main power source of heavy commercial vehicles in China and the emission characteristic of diesel engine determines the emission level of vehicle.Testing technology,measuring working condition and testing boundary conditions have a great impact on the measurement results of vehicle and diesel engine.Compared with China V emission standards,the cycle has been changed in China VI emission standards.The vehicle road test method,vehicle laboratory test method,engine system durability,vehicle OBD information and remote emission management were added.The emission influence factors of the heavy-duty vehicle test and engine test were discussed in this paper.The variation of pollutants emitted from diesel engine and vehicle with environment,boundary conditions,load,test conditions and other factors were summarized.It has important academic value and great significance for the implementation of emission standard VI of heavy-duty vehicle in China.There are seven chapters in this paper.Diesel engines bench test and vehicle test were carried out.By combining experimental research and simulation,the pollutant test methods,influencing factors and emission correlation were studied.It is revealed that the test condition and test equipment are the main factors for the big difference in NOx emission between the vehicle drum test and vehicle road test.By analyzing the influence of test fuel,load,test working condition and driving resistance on vehicle emission,the emission factors measured by sliding test resistance are higher than those measured by the recommended formula resistance.The influence of the test boundary condition on emission was studied through the diesel engine bench test and the influence of test temperature and test sequence on emission results was found out.In order to investigate the influence of diesel engine DPF durability degradation of pollutants,the operation condition of the vehicle and the transformation model of the working condition of diesel engine test bench was established.The correlation between vehicle testing conditions and diesel engine bench working conditions was studied.The relationship between vehicle operating point and emission sharing rate of diesel engine test points was put forward.The influencing factors of vehicle emission were studied and the effects of diesel engine performance,fuel physical and chemical characteristics,aftertreatment system,operating parameters and operating environment on vehicle pollutants were discussed.The advantages and limitations of drum test,vehicle road test,tunnel test and remote sensing test were analyzed.Through the study of emission characterization parameters,specific power and window method were selected as the calculation method of pollutants in the road test.Without changing vehicle parameters,vehicle speed,load,environmental temperature,altitude and other factors have a greater impact on vehicle emissions.The test environmental conditions can be controlled precisely in the drum test and the test has the advantages of high accuracy and good repeatability.The instantaneous pollutant emission of the vehicle running on the actual road can be obtained through the vehiclemounted emission test.Remote sensing test is very fast and can be used for road test stably and conveniently.The road tests and drum tests for China VI standard diesel vehicle were carried out and the test conditions,exhaust temperature and pollutant emissions were studied.The emission factors under different fuel,load,cycle condition and driving resistance conditions were tested and the variation law of the vehicle emission with the test parameters were analyzed.The change trend of pollutants under different operating conditions of the vehicle was studied,and the differences and reasons of pollutants discharged from vehicle drum test and road test were analyzed.Studies have shown that the NOx emission of the vehicle fueled with Beijing-VI diesel fuel is about 18% lower and the PM emission is about 25% than that of the diesel fueled with China V diesel fuel.The PM emissions are 23% and NOx emissions are 30% greater with full load than empty load.The emissions of HC,CO,NOx and PM in C-WTVC(China-World Transit Vehicle Cycle)are 27%,14%,25% and 15% higher than that in ETC(European Transient Cycle).According to the standard of ‘Fuel Consumption Test Methods for Heavy-duty Commercial Vehicles’,the driving resistance of vehicle is obtained and the emissions test under sliding resistance and formula resistance are carried out.The NOx emissions of vehicle under sliding resistance is about 25% higher than that under formula resistance.The NOx instantaneous emission varies greatly with the driving conditions,and is highest in urban conditions,while that in suburban and high-speed conditions is basically the same.By comparing the vehicle drum and road emissions,it is found that the exhaust temperature and NOx emissions of the vehicle are quite different due to different test conditions and environment.The average exhaust temperature of vehicle under drum test is about 25 ℃ higher than that of road test.The key components of diesel engine after-treatment for the vehicle emissions were studied.The differences among data of emission measurements under conditions of the WHSC(World Harmonized Steady-State Cycle),WHTC(World Harmonized Transient Cycle)and WNTE(World Not-To-Exceed)were analyzed.The effects of durability and test boundary conditions of DPF(Diesel Particulate Filter)on pollutants such as NOx,THC,PM and PN before and after regeneration were studied by diesel engine bench test.The change trend of pollutants in WHTC test before and after DPF regeneration was discussed,and the influence of mileage on diesel engine pollutant degradation was studied.By changing the inlet boundary temperature,the intercooled temperature,the inlet temperature and other test boundary conditions and the WNTE test sequence,the influence of the test boundary conditions on the emissions of diesel engine bench was studied.Studies show that the NOx emissions of diesel engine benches using WHTC testing are much higher than those of diesel engines using WHSC testing and WNTE testing.Under the WHTC condition,the NOx emission of the diesel engine before DPF regeneration is 0.287g/kWh,the NOx emission after regeneration is 0.197g/kWh,and the NOx emission of the diesel engine after DPF regeneration decreases by about 31%.With the intake air temperature raising from 20 °C to 40 °C,the NOx emission decrease by 0.021g/kWh.With the temperature increasing from 30 ° C to 50 ° C after mid-cooling,NOx emission decreases by about 46%.With the fuel inlet temperature raising from 20 ° C to 40 ° C,the NOx emission decreases by about 41%.And WNTE test sequence has little effect on diesel engine emissions.According to the "Durability requirements and test methods for heavy-duty vehicle exhaust pollutant emission control system"(GB20890-2007),the 1500-hour endurance test was carried out,and the pollutants were measured on the diesel engine test bench under WHTC conditions and WHSC conditions.And the results show that the HC emission of the test sample does not change with the using time.After long time engine test operating,the NOx emissions increases rapidly.After 23300 km running mileage,the NOx emissions of the test engine prototypes increases by 0.0115g/kWh,which should be paid attention to during actual use.In order to reveal the relationship between the exhaust pollutants of the whole vehicle drum and the diesel engine bench test,the conversion model of the vehicle operating condition and the diesel engine bench working condition was established by using Matlab software to realize estimation of emissions of pollutants of the diesel engine test bench and the vehicle test cycle based on the grey relational theory.Through the comparison test,the measured actual speed and gear position data verify the accuracy of the model,and analyze the emission correlation between the vehicle C-WTVC working condition and the diesel engine WHSC working condition.The research shows that the parameters of the diesel engine speed and instantaneous vehicle speed calculated by the working condition conversion model have a good linear relationship.The high acceleration interval model is used in the high-grade position,which is different from the actual operation of the driver.The NOx emission sharing rate is the highest under the conditions of high-acceleration and high-speed of the vehicle under C-WTVC conditions,reaching 18.7% and 16.5%.The NOx emission sharing rate of the diesel engine bench test at WHSC cycle operating point 10 is the highest,reaching 15.2%.The working condition point 3 of the vehicle C-WTVC working condition has the highest correlation with the working condition point 10 and 1 of the diesel engine WHSC working condition,reaching 0.8 and 0.79.The high speed and high load conditions are the main conditions of emissions.The emission of diesel engine road and the effects of post-processing were studied by simulation.The simulation models of diesel engine and vehicle were established by GT-Power software and the models were verified.The effects of FTP working condition and NEDC working condition on vehicle emissions were analyzed.The variation trend of NOx emissions of vehicle under different load conditions is discussed.The research shows that the changes of NOx emission and exhaust temperature of the vehicle are relatively flat under the NEDC condition.Under the FTP condition,the vehicle is under running conditions of acceleration,deceleration and parking frequently,and the NOx emission changes drastically.When the vehicle is accelerated,the NOx emission is high.