<div class="section abstract"><div class="htmlview paragraph">Experimental investigations have been conducted with two identical small scale SI gas engines gen-sets operating on biomass producer gas from thermal gasification of wood. The engines where operated with two different compression ratios, one with the original compression ratio for natural gas operation 9.5:1, and the second with a compression ratio of 18.5:1. It was shown that high compression ratio SI engine operation was possible when operating on biomass producer gas from a TwoStage gasifier. The results showed an increase in the electrical efficiency from 31% to 35% when the compression ratio was increased.</div><div class="htmlview paragraph">The influence of ignition timing on emissions was investigated during high compression ratio operation. It was shown that for λ=1.4 the NO_x emission decreases by almost a factor 3, when the timing is retarded from 13° to 7° before top dead center. In order to further investigate the combustion properties of the biomass producer gas, the laminar flames speed has been determined from experiments and a thermodynamic model. The experiments have been done in a constant volume combustion bomb, and measurements with Danish natural gas have been conducted for comparison. The natural gas with a methane content of 90% had a flame speed of 0.32-0.33 m/s at λ=1.22, while, the laminar flame speed for the biomass producer gas was determined to 0.45 m/s at λ=1.05 and 0.35 m/s at λ=1.44.</div></div>