Predicting relationship among hydrogen flame length, flame ports, and volume flow for efficient burner design: an experimentally validated theoretical approach

A total shift from fossil fuel based economy to green hydrogen based economy requires major technological upgrades and theoretical understanding. Hydrogen is a difficult fuel and unlike other fossil fuels, its flame characteristics differ in terms of flame speed, flashback, length, heat transfer, visibility, etc. In this study, a theoretical approach has been presented to estimate flame length in relation to orifice size, number of orifices, and volume flow rate of hydrogen. The theoretical approach is based on velocity and volume flow changes with reference to orifice size. The approach has been validated experimentally using various volume flow rates and orifice sizes. It has been observed that flame length has a permanent direct relation (increase in mass flow increases flame length) with flow rates. However, the flame length increases with an increase in orifice size (by keeping the flow rate constant) to a certain orifice size, and then starts decreasing. Further increase in orifice size results in flashback. It has been estimated that the flashback occurs when the velocity of hydrogen falls below a certain value i.e. 10 m/s. Moreover, gas velocities, higher than optimum due to very small orifice size prevent ignition to occur at all.