Laminar-burning velocities of hydrogen–air and hydrogen–methane–air mixtures: An experimental study

The laminar burning velocities of hydrogen–air and hydrogen–methane–air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of hydrogen–air and different composition of hydrogen–methane–air mixtures (from 100% hydrogen to 100% methane) have been measured at ambient temperatures for variable equivalence ratios (ER=0.8–3.2ER=0.8–3.2). A modified test rig has been developed from the former Cardiff University ‘Cloud Chamber’ for this experimental study. The rig comprises of a 250 mm length cylindrical stainless steel explosion bomb enclosed at one end with a stainless steel plug which houses an internal stirrer to allow mixing. The other end is sealed with a 120 mm diameter round quartz window. Optical access for filming flame propagation is afforded via two diametrically opposed quartz windows in both sides. Flame speeds are determined within the bomb using a high-speed Schlieren photographic technique. This method is an accurate way to determine the flame–speed and the burning velocities were then derived using a CHEMKIN computer model to provide the expansion ratio. The design of the test facility ensures the flame is laminar which results in a spherical flame which is not affected by buoyancy. The experimental study demonstrated that increasing the hydrogen percentage in the hydrogen–methane mixture brought about an increase in the resultant burning velocity and caused a widening of the flammability limits. This experiments also suggest that a hydrogen–methane mixture (i.e. 30% hydrogen+70% methane) could be a competitive alternative fuel for existing combustion plants.