Reduction of natural gas engine emissions using catalysts

In order to diminish the environmental and health effects and to comply with tightening emission limits, exhaust after-treatment systems are going to be increasingly utilized also in the natural gas engine applications. In this work, we study both oxidation catalyst and se-lective catalytic reduction systems to solve how the catalysts influence on e.g. hydrocar-bons, NOx and particles existing in natural gas engine exhaust. A passenger car engine modified to run with natural gas was used in a laboratory research facility equipped with a possibility to modify the exhaust gas properties. In addition, the role of lubricating oil on the emission formation was also studied. When using selective catalytic reduction, high NOx reductions were observed. To oxidize methane a highly efficient oxidation catalyst was needed while other hydrocarbons were more easily oxidized. Catalyst systems were found to have significant effects on particulate emission also. Especially at high exhaust tem-peratures, high nanoparticle concentrations were observed downstream of the catalysts. Changing the lubricating oil was also found to have an effect on the particle emission.