The main aim of the study was to develop and investigate a small-scale experimental gasification technique for the effective thermal decomposition of pelletized renewable fuels (wood sawdust, wheat straw). The technical solution of the biomass gasifier for gasification of renewable fuels presents a downdraft gasifier with controllable additional heat energy supply to the biomass using the radial propane flame injection into the bottom part of the biomass layer. From the kinetic study of the mass conversion rate of pelletized biomass and variations of the composition of produced gas it is concluded that the process of biomass gasification is strongly influenced by the amount of additional heat energy and air supply into the biomass. The results of experimental measurements of the composition of produced gas have shown that under the conditions of the sub-stoichiometric air supply into the layer of pelletized wood biomass (α < 0.3) increasing additional heat energy supply in a range from 60 kJ up to 130 kJ leads to an enhanced mass loss of pelletized biomass and enhanced formation of volatiles (CO, H2) in the flaming pyrolysis zone. For the wood biomass the average content of CO in the products can be increased from 73 g/m3 up to 97 g/m3, while the average content of H2 increases from 4.7 g/m3 up to 6.2 g/m3. Similar variations of the composition of products are observed during the enhanced gasification of the wheat straw. At constant rate of additional heat energy supply and the sub-stoichiometric combustion conditions (α ≈ 0.17-0.30), a faster thermal decomposition of the pelletized biomass and larger average amount of the produced volatiles (CO, H2) can be obtained by increasing the air supply rate from 0.27 to 0.43 g/s, determining the variations of air-to-fuel ratio in a range from 1.3 up to 1.6.