To investigate the influence of different dry-wet correction methods on the measurement results of CO2 emissions during the cold start phase of a compressed natural gas(CNG)heavy-duty vehicle,cold start tests are conducted on a CHINA 6 CNG vehicle under different test cycles using a chassis dynamometer.The CO2 emissions during the cold start phase of the vehicle are calculated using the dry-wet correction method recommended by CHINA 6 regulations and the dry-based correction method based on the volume fraction of H2 O in the exhaust gas.The results indicate that during the cold start phase of vehicles,the CO2 emissions calculated using the dry-wet correction method recommended by CHINA 6 have a significant deviation.After sufficient heating,the calculation results of the two methods tend to be consistent.When using the recommended method of China 6 for correction,compared to direct wet-based measurement results,the CO2 emissions during the cold start are about 14%lower.For the calculation of CO2 emissions during the cold start phase of CNG,methanol,gasoline and other vehicles with high exhaust water content,using the volume fraction of H2 O in the exhaust to calculate the CO2 dry-wet correction factor yields more accurate results.
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