Combustion of fuels leads to the formation of gaseous and particulate matter pollutants that have an impact on air quality and the environment. Comparison to the gaseous emissions from stack, measuring of particulate matter (PM) needs extra attention because particles do not behave as a continuum. Dilution tunnels are used with the PM measuring instruments to dilute the hot exhaust gases leaving from the stack. The main focus of this study was to investigate the dilution ratio results obtained from a partial flow dilution tunnel. The partial flow dilution system consists of a porous tube diluter, an ejector diluter and an air heater. The dilution air flow settings into the porous tube diluter and ejector diluter are selected for a wide range of dilution ratios. Two mass flow controllers were used to regulate the flow of dilution air into the diluters. The experiments were conducted at the Renewable Energy Laboratory of the Vrije Universiteit Brussel (VUB).There were a total of fifteen experiments with four flow settings conducted. Dilution ratio (DR) is evaluated based on the ratio of the CO2 (dry) concentration in the raw sample to the diluted sample. The results obtained from the experiments with the partial flow diluters are limited between 34 and 110. The experimental results are also compared with other works and found quite similar