Methane is a very important fuel, methane as the main component of methane is an important energy. Many laboratories and equipment are powered by methane gas. But it's well known that combustible gases have an explosion limit, an optimal ignition point, and when methane concentrations are too high they don't burn enough because of the lack of oxygen, so another gas is needed to dilute the methane gas. Chen Jun-hsun from Taiwan studied the combustion flame experiment by adding nitrogen to the methane gas to dilute it.

This experiment is to study the flame conversion of a single porous cylindrical burner in a wind tunnel at the intake velocity (Uin), the methane gas-nitrogen mass ratio, and the fixed injection velocity (0.05m/SEC). During the experiment, the methane gas - nitrogen mass ratio of fixed fuel was changed from 0.41 m to 2.63 m/ SEC to observe the related flame structure changes. In the experiment, it was found that the methane gas-nitrogen mass ratio was higher than that. When the intake velocity increased, the flame structure changed from enveloping flame, conversion flame and tail flame in sequence. The transition zone exists between the enveloped flame and the tail flame. The flame oscillates back and forth in this region for only 5 to 8 seconds. The flame is highly unstable in this area. It may be an ascending flame, a trailing flame, or an extinguished flame. On the other hand, when the methane-nitrogen mass ratio is below 60%, the flame changes directly from the enveloped flame to the tail flame when the intake velocity gradually increases to the limit and no conversion flame exists in this area. In addition, the study found that when the mass of methane gas in the fuel mixture becomes low, the flame conversion limit velocity will also become low. In addition, the picture shows the change of stand-off distance, flame thickness and attached Angle to understand the physical mechanism of relevant flames. The flame temperature distribution along the vertical center line of a porous cylinder burner is measured in the enveloped-flame and tail flame to understand the flame variation trend. Finally, the experimental results are compared with relevant numerical simulations to verify the correctness of the experiment. The comparison results show the same trend with the experimental results. It was found that the experimental results were higher than the numerical prediction when the mass ratio of methane gas to ultrapure nitrogen was changed from enveloping flame to tail flame and from enveloping flame to conversion flame and then to stable tail flame. The flame thickness obtained by the experiment and the standoff distance were found to be lower than the numerical simulation, and the attached Angle obtained by the experiment was higher than the numerical simulation.