At present there are detailed studies of the phenomenon of auto-ignition in liquid fuels and even for natural gas, but studies to syngas is very limited, and existing are focused primarily on combustion kinetics, and do not study phenomenon of knocking before ignition point. This paper presents the development of a thermodynamic model to study the phenomenon of auto-ignition in gaseous alternative fuels during the compression stroke in the spark ignition internal combustion engine. The model takes into account the fuel composition, process parameters and the variation thereof with the pressure and temperature. For this, a formulation is used from the viewpoint of equilibrium thermodynamics, allowing easily estimate the engine operating condition. The results allow us to provide applications in heat engines, generating power with syngas as fuel, where a low number of methane is handled, but with adequate compression ratios can get a good efficiency, compared with natural gas.