Analysis on Emission Characteristics of Urban Buses Based on Remote Online Monitoring

<div class="section abstract"><div class="htmlview paragraph">In this study, a new system of assessment method was developed to evaluate the characteristics of urban buses based on remote online monitoring. Four types of buses, including China V emission standards diesel bus, lean-burn CNG bus, air-fuel equivalence ratio combustion CNG bus and gas-electric hybrid bus, were chosen as samples to analyze the emission characteristics of urban buses with different engine types in urban scenario. Based on the traffic conditions in Beijing, the actual emission characteristics of buses under newly-built driving conditions were analyzed. Moreover, the emission factor database of urban buses in Beijing was established to analyze the characteristics of excess emission. The research results are shown as follows. 1) Compared with other types of buses, NO_X emission factor and emission rate of lean-burn CNG bus are much higher. The equivalent air-fuel ratio CNG engine combined with TWC catalytic converter and hybrid power technology can better reduce NO_X emission. 2) There is difference between the type certification under standard operating conditions and the emission results in actual operation to a varying degree. The evaluation of emission performance based on actual operation can more truly reflect the actual performance of the bus. The BJ-FPC (Beijing flat peak cycle) developed in this paper is closer to the actual operating conditions of the sample bus in terms of VSP Bin proportional distribution. 3) As to weighted NO_X emission factors, the BJ-HPC (Beijing high peak cycle) of different types of buses are higher than BJ-FPC and actual operating conditions. 4) Based on the excessive emission method assessment, the NO_X of China V diesel bus easily exceeds the emissions limits, and the NOx concentration of lean-burn CNG bus is high, and both the NOx over-limit ratio and the quantity of excessive emission buses are also high. Gas-electric hybrid bus can better reduce the NO_X emission and the excessive emission frequency under the urban operating condition.</div></div>