The investigation presented in the paper concerns producer gas combustion in both the spark ignited (SI) and the dual-fuel compression ignition (CI) engine with a diesel pilot of 15% with respect to its nominal dose, at compression ratio (CR) of 8, 12 (for the SI engine) and 17 (for the CI engine). The research tasks were mainly focused on combustion instabilities such as engine work cycles unrepeatability and combustion knock onset. The investigation included also combustion of such gases as methane, biogas and hydrogen, which were taken for making comparison between them and the producer gas. The conducted analysis shows that producer gas is resistant to generate knock even if it contains significant hydrogen content of 16%. However, high work cycles unrepeatability is observed when producer gas is combusted in the SI engine. Obtained results led to conclusion that producer gas can be burnt more efficiently in the dual-fuel CI engine than the SI one. Neither misfiring nor knocking have occurred during its combustion in that engine.