Question

The laminar flame speed of a premixed stoichiometric mixture of propaneair at 1 atm and 298 K is 0.4 m/s. If the nitrogen is replaced with helium, estimate the flame speed using the thermal flame theory. Assume that the temperature does not change. The thermal conductivity of the helium mixture is 0.36 W/m . K at 298 K. Assume it increases as a function of T 1/2. Use cp = 2.5R for helium and cp = 3.5R for nitrogen. In reality the flame temperature will increase because the specific heat of the helium is lower than that of nitrogen. Explain quantitatively how this would change the flame speed estimated above.