Unburned Methane emissions from gas engines are of concern because of their contribution on global warming. Formaldehyde – a toxic interstage product of the Methane oxidation process – is known for its strong smell and carcinogenic properties. The amount of and the reasons for these emissions depend very much on the gas engine design and its combustion system. This results in different engine internal and engine external strategies for optimizing Methane and Formaldehyde emissions. Due to their combustion system lean burn Otto-Gas-Engines generally show the highest rates of unburned Methane emissions among different gas engine concepts. But compared to Diesel engines modern gas engines definitely contribute to an effective reduction of NOx, CO2 and other toxic emissions in the exhaust gas. Due to their savings in CO2-emissions gas engines even with unburned Methane emissions close to 2% still show a lower Green House Gas (GHG) factor than comparable Diesel engines.
After treatment systems for Formaldehyde-oxidation are proven technology (for natural gas) and already in use in the gas engine market. However, reliable after treatment systems with catalysts to oxidize the residuals of unburned Methane are not available yet. For current systems the exhaust gas temperature of gas engines is significantly lower than that needed for efficient conversion. After treatment systems for Methane-oxidation definitely require further development.
The further optimization of the gas engine combustion process, the gas engine design and the after-treatment system is a major interest of the gas engine industry. Much effort is spent on the continuous development of new improved solutions.