Measurement for flame speed of CH₄/H₂ blends with ionic current method

Ionic current method was chosen to obtain the flame speed of CH₄/H₂ mixture over a wide range of excess air ratios and hydrogen fractions. The characteristic parameters of ionic current signal corresponding to the contact between spherical expanding flame and a pair of electrodes installed in a constant volume combustion bomb were investigated. Additionally, the flame speeds obtained with ionic current method were compared with those obtained by the traditional schlieren photography. The results show that for the CH₄/air mixture at the excess air ratios of 0.75, 0.8, 0.85, 0.9, 1.0 and 1.1, the flame propagating speeds measured with the ionic current method are 1.714, 1.935, 2.195, 2.250, 2.045 and 1.538 m/s, respectively, and the deviations from the speeds measured with the schlieren photography are 1.32%, 2.09%, 4.65%, 3.48%, 3.64% and 7.06%, respectively. For the CH₄/H₂ mixture at the excess air ratio of 0.8 and the hydrogen fraction of 0%-80% (10% increment), all the deviations between the flame propagating speeds measured with the ionic current method and the schlieren photography are less than 5%. This method is simple and practicable to achieve the flame speeds with higher accuracy and feasibility.