Q1. (Flames and Burners) [15 marks total] A non-premixed propane jet flame issues vertically from a tube with a cross-sectional area of 16 mm2 . The fuel is 298 K before leaving the fuel tube. You may assume the dynamic viscosity of propane as µF = 8.2×10-6 kg/m/s and the diffusion coefficient of propane in air is 0.11 cm2 /s at 298 K. a) Assuming the jet is round, and that the mass flowrate of fuel is 2 g/min, how long would the flame be if it is surrounded by air at 298 K? How do theoretical and experimental predictions compare? You may assume that the mean flame temperature is 65% of the maximum ?T due to combustion +Tintial, and that the adiabatic flame temperature is 2267 K. [8 marks] Suggestions: i) Check fuel jet Reynolds number (need calculation of exit fuel jet velocity) to evaluate if the jet is laminar or turbulent ii) Refer to slides 8 and 10 of “Lecs 11 12 – Key slides with equations for tutorial” for the definition of the theoretical and experimental flame length expressions b) What is the absolute maximum capacity of the non-premixed burner in part a), in kW? The HHV and LHV of propane are 50.35 MJ/kg and 46.35 MJ/kg, respectively, and the maximum laminar flame speed, sL,max, is 34.22 cm/s. [7 marks] Suggestions: i) Absolute maximum capacity requires calculation of the blow-off velocity Q2. (Flames and Burners) [10 marks total] a) Let’s consider a simple, turbulent non-premixed flame. What is the typical critical Reynolds number for the onset of the lift-off phenomenon? Describe this phenomenon and the safety risks associated with it. [5 marks] b) Suggest ways to increase the stability of the flame. [5 marks] Q3. (Heterogeneous Combustion) [10 marks total] A 100 µm char particle is burning in a furnace within a quiescent environment under these conditions: O2 partial pressure 0.1 atm, bulk gas temperature 1600 K, furnace wall temperature 1400 K, particle emissivity 0.9. Calculate the char particle temperature due to the reaction of C to CO at the char surface. Assume that the heat of reaction is 9.2 kJ/g and the char reaction rate constant is 0.071 g/(cm2 .s.atm O2).