Impact of altitude on the real driving emission (RDE) results calculated in accordance to moving averaging window (MAW) method

Over half of the high altitude RDE tests failed to pass trip validity verification. To find out the reason and proper solution, vehicles were tested over The Worldwide harmonized Light vehicles Test Cycles (WLTC)/RDE at various altitudes and RDE tests were calculated using different WLTC reference data. Generally, the higher the altitude, the lower the vehicle CO2 emission and CO2 emission of naturally aspirated test vehicle has a linear correlation with altitudes: every 1000 m the altitude rise, WLTC CO2 emission will decrease 5.31%. The reasons for urban trip validity verification failure are the intensity of test cycles, different calculation methods and lower air resistance at high altitude, while for rural/motorway trip validity verification failure, lower air resistance is the only reason. Both high altitude reference data and sea level reference data with coefficients are plausible for high altitude RDE calculation. At 2400 m, the coefficients are 0.98, 0.91 and 0.86 for urban, rural and motorway respectively, but the calculation of the coefficients needs to be verified by more study. No correlation was found between reference data and RDE results.