63.83.220.234 Comments Measurements of flame temperature and energy are taken at a neutral flame setting. By definition, a neutral flame is the proper combination of fuel gas and oxgyen so that both are consumed in the flame.
Every fuel gas has variation in properties, including temperature and BTU delivery.
All fuel gases produce more heat and higher flame temperature when combined with oxygen. In approximate value, acetylene is a 6000 degree flame, producing 1450 BTU's, per cubic foot of gas. Propane has an approximate flame temperature of 5000 degrees, producing 2600 BTU's of heat per cubic foot of gas. One reason for propane to be able to deliver more heat energy is how the flame releases heat. Propane releases its heat in a wider pattern, from farther out in the flame.