This research study explores the technology of biomass syngas production by using an experimental downdraft fixed-bed gasifier coupled to a two-cylinder engine, designed and implemented at the Polytechnic University of Valencia, Spain. Furthermore, it deals with the study of the experimental and analytical relations between the driving thermodynamic parameters that control the gasification process, in order to contribute to the development of a theoretical model for the design of a small-scale gasification facility. Different experiments have been performed to investigate the variations in parameters such as low heating values, the air–syngas ratio, the reduction and combustion temperature, efficiency, and electrical power generation during the continuous functioning of the gasification power production facility. The results obtained show that the low heating value is directly related to the inlet air flow rate, so that it increases when the air flow increases, while the increase in the inlet air flow of the gasifier makes both the reduction and the combustion temperature increase. Moreover, the efficiency of the motor–generator reaches a maximum value of 0.204 at the maximum power (around 5 kW), being characterized by an excellent operating range for the air–fuel ratio of a gasification facility.