PG (producer gas) from biomass gasification can be used either in SI (spark ignited) or CI (compressed ignited) engine. Present study evaluates fundamental combustion characteristics of SI CPG (compressed producer gas) in a CVCC (constant volume combustion chamber) at various equivalence ratios (phi) using optical technique. The combustion characteristics were compared to common fuels: gasoline, CNG (compressed natural gas) and LPG (liquefied petroleum gas). The amount of air required for each phi was calculated based on fixed mass of gasoline injected. For optimization study, CPG was tested at different MIF (mass increase factors): MIF = 0% (minimum configuration), MIF = 25% (middle configuration) and MIF = 50% (maximum configuration) by using DOE (design of experiment). ANOVA (analysis of variance) was conducted and the values of experimental reliability were 0.9775 and 0.9875% for flame speed and peak pressure, respectively. From the experiments, the flame speed and peak pressure of CPG were found to be 3.15 m/s and 312.09 kPa, respectively. These were lower compared to gasoline, LPG and CNG. Optimization analysis shows that CPG peak pressure is comparable to gasoline and achieve its maximum flame speed at phi = 1.1 and MIF = 35%. (C) 2014 Elsevier Ltd. All rights reserved.