Experimental study on transient emissions characteristics of a heavy duty natural gas engine under world harmonized transient cycle

Abstract

In this study, the transient emissions characteristics under WHTC for both cases with and without an aftertreatment system (AS) were investigated. The engine operating parameters were measured to reveal the factors influencing the emissions. The effects of engine thermal state (the oil temperature, coolant temperature and exhaust temperature) on emissions and AS were analyzed. The results show that emissions under WHTC are influenced by engine operating conditions and are higher in the cold start test. The CO emissions are sensitive to changes in the excess air coefficient. The NOx emissions are highly consistent with changes in the engine throttle values. The HC emissions are almost dominated by variations of the engine torque at high speeds. In addition, the exhaust temperature has a significant impact on AS performance. The conversion efficiencies of CO, NOx, and HC in the cold start test are respectively 95.8%, 97.5%, and 88.3%, while those of CO, NOx, and HC in the hot start test are respectively 98.4%, 99%, and 99.1%. Overall, the CNG engine with AS can meet the China VI emission limits and even more stringent emission standards in the future. This study provides a reference for exploring methods of emission reduction for CNG engines.

Keywords

• CNG engine
• Transient emissions
• Aftertreatment system
• World harmonized transient cycle
• Cold start