To analyze the emission characteristics of NOx during cold-start of heavy-duty diesel non-urban vehicles on actual roads,20 heavy-duty diesel vehicles meeting China Ⅵ standards were selected for on-road emission testing using the Portable Emission Meas-urement System(PEMS).By defining the coolant temperature reaching 70℃ as the boundary,the cold and hot states of the engine were distinguished to analyze the emission characteristics during the cold-start phase.The test results indicated that the cold-start phase typically occurs within 600 seconds,accounting for less than 8％of the total duration.However,during this phase,the specific NOx emissions exceeded 1593.6 mg/(kW·h),significantly higher than China Ⅵ standard limit of 690 mg/(kW·h).To more accurately reflect the actual emission levels of vehicles on the road,it is recommended to introduce an emission assessment method incorpora-ting the cold-start phase in the next phase of emission standards,thus improving the vehicle-level PEMS emission evaluation system.
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