Thermal processes and power generation systems may employ producer gas generated through gasification as a green alternative to replace natural gas (NG). However, pure producer gas in engines is associated with a significant power derating that can be mitigated by blending it with other biofuels. In this proposal, an optically accessible research engine was used to study the influence of the addition of hydrogen and methane to producer gas in terms of combustion characteristics, thermodynamic efficiency and emissions. The results demonstrated that the addition of 25% methane to producer gas is enough to sustain the combustion reaction with good stability and a power derating of 10.8% compared to Natural Gas. The addition of 50% methane to producer gas attains efficiency and combustion characteristics remarkably similar to pure natural gas with a power derating of 5.4%. Emissions indicated that CO has decreased with the addition of methane to producer gas from 85 to 3.43 g/kWh, NOx emissions have increased from 0 to 8.85 g/kWh. In the case of unburned hydrocarbons (UHC), emissions did not considerably change before the addition of 25% methane to producer gas and remained constant at approximately 10 g/kWh. Engines designed to run on natural gas could use this mixture without significant modifications to the combustion chamber with improvements in the NOx emissions. This work also evaluated the effects of hydrogen and producer gas blends on the performance of a research SI engine. The results have shown that the addition of 29 to 36% of hydrogen to producer gas are the most relevant to improve the combustion intricate phenomena with lower cycle-to-cycle variation. These mixtures are strong candidates to be used as substitutes of NG in the near future due to similar flame propagation speed, rate of heat release and flame geometry characteristics. Hydrogen increased the flame propagation speed, lowered the centroid displacement and the Heywood circularity factor. In the range from 16 to 62% of hydrogen in the producer gas, the emissions indicated that the presence of hydrogen increased NOx emissions from 0 to 12 g/kWh while decreased CO emissions from 25 to 14 g/kWh. The presence of 36 and 44% of hydrogen in the producer gas mitigated the relative emissions of UHC from 0.5 to 0.