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Scarce resources of fossil fuels and increasingly stringent exhaust emission legislation push towards a stronger focus to alternative fuels. Natural gas is considered a promising solution for small engines and passenger cars due to its high availability and low carbon dioxide emissions. Furthermore, natural gas indicates great potential of increased engine efficiency at lean-burn operation. However, the ignition of these lean air/fuel mixtures leads to new challenges, which can be met by fuel scavenged prechambers. At the Institute of Internal Combustion Engines of the Technische Universitaet Muenchen an air cooled natural gas engine with a single cylinder displacement volume of 0.5 L is equipped with a methane scavenged prechamber for investigations of the combustion process under real engine conditions. The main combustion chamber is supplied with a lean premixed air/fuel mixture.

Polyoxymethylene dimethyl ethers (OME) are synthetic fuels, which offer the property of sustainability because the reactants of production base on hydrogen and carbon dioxide on the one hand, and the air pollution control in consequence of a soot-free combustion in a diesel engine on the other hand. High exhaust gas recirculation (EGR) rates are a promising measure for nitrogen oxide (NOx) reduction without increasing particle emissions because of the resolved soot-NOx trade-off. However, EGR rates towards stoichiometric combustion in OME operation reveals other trade-offs such as methane and formaldehyde emissions. To avoid these, a lean mixture with a combination of EGR and exhaust after-treatment with selective catalytic reduction (SCR) is useful. The limitation of urea dosing due to the light-off temperature of SCR systems requires heating measures.