VOCs emission characteristics in motorcycle exhaust with different emission control devices

Speciated VOCs and regulated air pollutant emissions (CO, HC and NO) of carburetor (CB) and fuel injection (FI) motorcycles were evaluated based on engine dynamometer tests. Effects of engine loads and emission control systems were evaluated. CB was equipped with oxidation catalytic converter (OCC) and secondary air system (SAS) while FI had three-way catalytic converter (TWC) and oxygen sensor (OS). Under normal operation of the control devices, the emissions of regulated pollutants and the sum of detected VOCs (Sigma VOC) were higher in CB than in FI motorcycle. Alkanes and aromatics had the highest concentrations contributing approximately 90% to the Sigma VOC while xylene and toluene were most abundant among the BTEX, in both motorcycles. Emissions of all regulated pollutants and Sigma VOC increased with increase in engine load. The emission control devices showed differential efficiencies on different VOC groups. Average emission reduction efficiencies of OCC with SAS (CB motorcycle) were 45.4% (Sigma VOC) and 48.6% (BTEX) and TWC with OS (FI motorcycle) were 74.4% (Sigma VOC) and 88.0% (BTEX). Without SAS, the efficiency of OCC dropped to 30.2% (Sigma VOC) and 34.9% (BTEX) in CB motorcycle. Similarly, the efficiency of TWC reduced to 69.0% (Sigma VOC) and 85.2% (BTEX) when the OS was blocked in FI motorcycle. The ozone formation potentials of VOCs ranged from 500 mg-O-3/m(3) (FI motorcycle with TWC and OS, TO 20%) to 2218 mg-O-3/m(3) (CB motorcycle without control system, TO 30%).