Why would gases
“have to come “down” to burn”?
You need 3 things for a fire: something to burn, oxygen, and heat, so as long as newly released gas comes into contact with burning gas in the presence of oxygen, it will burn.
That need not be near the exit of the gas main (for an extreme example, look at a flame thrower (military ones typically use liquid, but commercial ones typically use gases such as propane)
Efficiency and cleanliness of burning will likely go down, but I would think the design of gas exits isn’t that critical to keep a flame burning. One reason could be that, initially, it isn’t density that controls whether gas goes up or down, but gas pressure.
