An imbert 'throated' gasifier which has hourglass heart and varying axial area and nozzles for injection of gasification agents has been studied. The transport of reacting gas-solid two-phase mixture through the gasifier has been mathematically modeled transiently. Downdraft gasification in such a complex system has so many variables and is quite cumbersome to describe. For the first time throated gasifiers are modeled as realistically as possible. The resulting set of transport, structural, kinetic and auxiliary equations was solved via numerical methods. The modeling work was experimentally validated using a 10 kW gasifier. The actual geometry of the experimental setup was used in the model. The model results were in line with the experimental results. Throated combustion zone causes better distribution of heat and reduces heat loss. With the same core size and solid consumption, stratified gasifier output was 24.5% less than throated one. The model exit had 25.85% CO; 18.25% H-2; 7.84% CO2; 2.9% CH4; while the experiment had 35.07-20.77% CO; 18.30-13.66% H-2; 13.68-5.95% CO2; 6.7-1.2% CH4; the rest was N-2. The model can be applied to different geometries. (C) 2015 Elsevier B.V. All rights reserved.