Evaluating Vehicle Fuel Consumption And Nitrogen Oxides Emission Characteristics Based On On-board Diagnostic Approach

As the divergence between real-world and official vehicle fuel consumption and emissions are getting larger in recent years,collecting on-road vehicle fuel consumption and emissions is the foundation to formulate effective vehicle pollution control regulations,and it has much significance to reduce energy consumption and to improve urban air quality.The on-board diagnostic(OBD)is one of promising and next-generation in-use vehicle monitoring methods.Not only can it collect instantaneous fuel consumption and emission data,it can also send the data to the monitor center by wireless communication and thus allow authorities to track high-emission vehicles in time.This study collects second-by-second on-road test data in a combination of several methods: 1)collects on-road fuel consumption data for 4 passenger cars by using OBD method,2)collects nitrogen oxides(NO_x)emission data for 8 heavy-duty vehicles(HDVs)by using portable emission measurement systems(PEMS)and OBD method together,3)collects long-term fuel consumption and NO_x emissions data for 6 buses using remote OBD systems.Based on real-world data,this study explores the relationship between operation and engine conditions with fuel consumption and NO_x emissions,establishes the correlations between average speeds and fuel consumption and NO_x emission factors.For HDVs,averaging window method(AWM)is used to evaluate in-use compliance of NO_x emissions.Furthermore,this study analyses the divergence of NO_x emissions and its possible reason between conventional diesel buses and hybrid diesel buses.For passenger cars,fuel consumption derived by OBD method and measured by chassis dynamometer are strongly correlated(R2=0.98),and corrected OBD fuel consumption are on average 5% less than laboratory test results.The fuel consumption of passenger cars correlates significantly with average speed(R2=0.91),while 80 km/h is the speed with minimum distance-specific fuel consumption.For HDVs,high NO_x emissions occur in high VSP(vehicle specific power)driving conditions,which needs to be paid more attention as these driving conditions have the largest time share in real-world driving for heavy duty trucks.The fuel consumption and NO_x emission factors for conventional diesel buses calculated by remote OBD method are respectively 34.5±3.4 L/100 km and 11.7 ± 0.3 g/km,and are quite close(average discrepancies within 1%)to our previous results by using PEMS method.The average fuel consumption for hybrid diesel buses indicate an overall reduction of 20% relative to their conventional counterparts,but the uncertainty still remains in the NO_x control benefit from hybrid bus technologies and the correlation between average speed and NO_x emission factors,which is likely due to the different catalyst temperature of different energy control strategies of hybrid models.Speed is the leading parameter affecting on-road fuel consumption and NO_x emissions for diesel buses.If the average speed increases from 10 km/h to 20 km/h,estimated fuel consumption and NO_x emission factors of diesel buses would be both decreased by 28%.Therefore,effective traffic measures(e.g.,dedicated bus lanes and bus rapid transit)could bring benefits in fuel consumption and NO_x emission control by improving traffic conditions.As the urban public buses usually operate under low-speed and low-load conditions in China,AWM would be a suitable in-use compliance analyzing method for China.However,the 20% window power threshold set by Europe does not suit urban buses in China.The on-road test results further support to set the window power threshold of 15% by the proposed China AWM regulation.This study can provide important reference for in-use vehicle fuel consumption and emissions regulations for China in the future.