In order to meet the new NH3 emission limits of China Ⅵ emission standards

a slightly-rich air-fuel ratio and ammonia slip catalyst(ASC) control strategy was developed and applied based on NH3 emission generation mechanism and a large amount of engineering test data. Besides

a matching development test was carried out on a certain natural gas engine

which was proved to meet the requirements of the China Ⅵ emission standards. The test results show that NH3 emissions are derived from the catalytic converter

not from the original emissions of natural gas engines. The coversion efficiency of ASC with 0.177×10-3g/cm3 precious metal content can reach 72.2%. And higher conversion efficiency cannot be achieved by further increasing the precious metal content. After post-processing with ASC with 0.177×10-3g/cm3 precious metal content

NH3 emission reaches the lowest level with air-fuel ratio 0.996

and the lowest level is lower than the standards.