Research On Effects Of Fuel Tank Permeation And Intake & Exhaust System On China 6 Vehicle Evaporative Emission

With the rapid increasment of vehicle population and the continuing upgrade of exhaust emissions,the importance have beening more important in China.In China VI emission standard,the control of evaporative emissions was tightened fisrt time in last 20 years.The test duration of the diurnal emission of the type IV evaporative emission tests changed to 48 hours.The temperature in the Imtech variable-temperature SHED during hot soak test changed from the 20-30 ° C to 38 ± 2 ° C.While the limited value have dropped from 2 g/test to 0.7 g/test.With a stringent emission standard,control of caniste emissions would not meet the requirement of new standard,permeation emissions and emissions from the intake&exhaust system are more important than before.In order to provide basic emission data of different material tanks under the China VI standard test and the measured data of the influence of the intake and exhaust systems on evaporative emissions,quantitatively evaluate the tank permeability and the influence of the intake and exhaust system on the China VI evaporative emissions.System experiments were conducted with three different material fuel tanks(metal,conventional plastic and low-permeability plastic),two fuel injections(multi-point EFI and direct Injection)and two thermal cycles(Otto cycle and Miller cycle)gasoline vehicles.27 hot soak tests and 21 diurnal emission tests with both China V and China VI emission standards were conducted in this study.Hot soak emissions using conventional plastic fuel tanks was 0.178 g/hour,which was28.0% and 63.3% higher than that of metal fuel tanks and low-permeability plastic fuel tanks,respectively.And emissions using China VI procedures were 1.85,1.12,and 1.25 time those using China V procedures.Similarly,for diurnal emission test,emissions using China 6 test procedure was 1.4 times.From the China V emission standard to China VI emission standard,since the temperature of vehicle soak and precondition driving become much higher,the final emission become more sensitive to the permeability of the fuel tank material.The permeability of the fuel tank material has become more important for China VI evaporative emission tests.Emissions from the intake system contributed up to 60% of hot soak emissions for China 5 vehicle.The multi-point EFI fuel supply method can promote the emission from the intake system compared with the in-cylinder direct injection oil supply mode.And the degree is greater than the increased emissions of exhaust system promoted by the direct oil supply mode.When using the Otto cycle engine,the fuel supply mode of the multi-point EFI is equivalent to the promotion of the intake system discharge by the direct injection in the cylinder and the promotion of the intake system by the Miller cycle in the direct injection mode.Both are 0.1 g/hour.The thermal cycle is negligible compared to the effect of the fuel supply on the exhaust system emissions.The emission of the intake system using the Otto cycle multi-point EFI and the Miller cycle direct injection is similar,and the promotion of the multi-point EFI to the intake system is almost identical to the promotion of the Miller cycle.For the diurnal emission test,the total emissions of the intake and exhaust system for two days were less than 0.05 g.The effect of the intake and exhaust system on diurnal emissions is almost negligible compared to hot soak emissions.Whether it is a direct injection engine or a multi-point EFI engine,the physical cleaning of the injector carbon deposits will reduce the evaporation of the intake system and exhaust system.