Gasification can be seen as a process in which solid biomass is converted into a mixture of combustible gases, which complete their combustion in a second device, usually a reciprocating internal combustion engine (RICE). Downdraft moving-bed gasifiers coupled with RICE are a good choice for moderate quantities of available biomass, the equivalent of up to 500 kW of electric power. The producer gas must be mixed with additional air in order to have a stoichiometric mixture to fuel the RICE. To predict the engine performance working with such a fuel, a so-called Engine Fuel Quality (EFQ) parameter has been developed by the authors. This parameter considers the combined effect of stoichiometric air-fuel ratio and stoichiometric mixture heating value, both depending on the producer gas composition. The estimation of engine power made by using the EFQ parameter indicates that power at full load is reduced at about two-thirds of the maximum obtained with a conventional liquid fuel. A more detailed prediction of engine performance requires the use of computer simulation of several types. The authors have used successfully a two-zone thermodynamic model to predict engine performance. Model results include the fraction of mass burned, the pressure and temperature evolution, and pollutant emissions. The detailed results for power confirm the first order prediction based on the EFQ parameter. (c) 2005 Elsevier B.V. All rights reserved.