Experimental investigations with a combustion bomb have been carried out with mixtures of methane and producer gas produced by thermal gasification of biomass. The investigations showed that the lamin ar flame speed increased and the amount of UHC decreased for increasing amount of producer gas in the fuel. Application of mathematical models for calculations of quench distances near the bomb walls and post oxidation reactions has led to the conclusion that the amount of unburned fuel is reduced primarily due to a promotion of post oxidation processes. Engine experiments have been carried out applying mixtures of natural gas and gasification gas as fuel for different air-fuel ratios. These investigation showed that substituting 16% (Vol.) of the natural gas by producer gas resulted in a decrease of 50% (Vol.) of the UHC from the combustion for lean mixtures.