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Engine experiments have been conducted on a gas fueled SI engine. The engine was fueled with natural gas and mixtures of natural gas and hydrogen containing producer gas in order to examine the effect of addition of producer gas on the combustion process and the engine-out emissions. The experiments showed that addition of producer gas decreased the UHC emission at conditions leaner than λ=1.40. The CO emission was increased by addition of producer gas. This was mainly caused by unburned fuel CO from the producer gas. No effect of producer gas on the NOx emission was detected. Formaldehyde, which is suspected to cause odor problems from natural gas fired engine based power plants, was measured using FTIR. The investigation showed that the formaldehyde emission was decreased significantly by addition of producer gas to natural gas.

Experiments have been conducted on a gas fueled spark ignition engine using natural gas and two hydrogen containing fuels. The hydrogen containing fuels are Reformulated Natural Gas (RNG) and a mixture of 50% (Vol.) natural gas and 50% (Vol.) producer gas. The producer gas is a synthetic gas with the same composition as a gas produced by gasification of biomass. The hydrocarbon emission, measured as the percentage of hydrocarbons in the fuel, which passes unburned through the engine, was for the mixture of natural gas and producer gas up to 50% lower than the UHC emissions using natural gas as fuel. The UHC emission from the experiments using reformulated natural gas was 15% lower at lean conditions. Furthermore, both hydrogen-containing fuels have a leaner lean burn limit than natural gas. The combustion processes from the experiments have been analyzed using a three-zone heat release model, which is taking the effect of crevices into account.

Application of a known hydrogen containing fuel called reformed natural gas (RNG) has been realized in a stationary combustion engine with success. The aim for this is to reduce unburned hydrogen emissions (UHC) from the engine together with an increase in efficiency. The fuel contains mainly methane, hydrogen and minor amounts of carbon dioxide. A small-scale unit for onboard production of RNG has been built in order to avoid the dependence of artificial supplementation of hydrogen. The production is carried out through means of steam reforming of natural gas. The RNG-unit together with theoretical considerations for estimating fuel composition and issues of caution are described. Theoretical studies show a potential for varying the hydrogen content between 8 and 30 vol%. Studies also show potential for remarkable increases in the methane number relative to that of the natural gas. A test engine has been fueled with RNG.

In-cylinder post flame oxidation of unburned hydrocarbons from crevices in a lean burn spark ignition engine has been examined for natural gas and mixtures of natural gas and a hydrogen containing producer gas. For this purpose a model was developed to describe the mixing of cold unburned reactants from crevices and hot burned bulk gas and to describe the oxidation of the unburned fuel. The post oxidation was described by a single step chemical reaction mechanism instead of detailed chemical kinetics in order to reduce the calculation time. However, the exploited Arrhenius expressions used to describe the chemical reactions were deduced from a detailed reaction mechanism. Different detailed reaction mechanisms were compared with results from combustion reactor experiments. Experiments and simulations were compared at different pressures and excesses of air similar to the conditions present during in-cylinder post oxidation.