Ammonia and nitrous oxide emissions of a stoichiometric natural gas engine operating with high caloric value and low caloric value fuels

With the implement of the increasingly stringent emission standards, natural gas engines feature stoichiometric operation with three way catalyst (TWC) have been put into focus due to their low-cost and high-efficient aftertreatment system. In this paper, the ammonia and nitrous oxide emissions during both steady-state and transient test cycles are analyzed with the aid of the regulated emission values and the temperatures in the TWC system. The results indicated that in the steady-state test cycle, NH3 are highest at low-speed high-load condition and N2O emissions are at extremely low levels during the whole test cycle. At most operating modes of the steady-state test cycle, NH3 and N2O emissions exhibit higher values when operated with high caloric value fuel. In both cold and hot start world harmonized transient cycle(WHTC) tests, motorway sub-cycle has the highest average NH3 emissions and adopting low caloric value fuel could reduce the tendency of NH3 formation; N2O emissions are mainly generated in the engine starting period. In the cold start WHTC tests, adopting fuel with high caloric value is favorable for the abatement of N2O emissions while in the hot start WHTC tests, using fuel with low caloric value would be a better choice for the control of N2O emissions.

Automated summary

This study analyzed the emissions of ammonia and nitrous oxide in steady-state and transient test cycles using natural gas engines with TWC system, finding that NH3 emissions are highest at low-speed high-load conditions, and N2O emissions mainly occur during engine starting, with high caloric value fuel beneficial for reducing N2O emissions.