The emission of ammonia from an equivalent ratio natural gas engine was studied by using Fourier transform infrared spectrometer. The emissions of NOx

CO and CH4 at the upstream of the three-way catalyst (TWC) and the emission of ammonia at the downstream of the TWC in different operating conditions were analyzed. The results show that there is no ammonia emission in the original exhaust gas from the equivalent ratio natural gas engine. The catalytic reaction of engine exhaust gas in the TWC is the real reason of the ammonia emission. When the concentration of original CO and CH4 remains stable

higher NOx concentration can restrain the ammonia emission. Higher EGR rate at full load can promote the ammonia emission by reducing the NOx emissions and increasing the CO and CH4 emissions. Different engine loading speeds can result in different amounts of ammonia emission by affecting the original CO and CH4 emissions

and higher loading speed can promote the production of ammonia. Difference in fuel composition has no effect on the power and gaseous emissions of the natural gas engine if it has a self-adaptability for fuel. When the TWC inlet temperature is in the range of normal operating temperature of the catalyst

a lower temperature will promote the ammonia emission.