ME 102 APPLIED THERMODYNAMICS

ME606 Fundamentals of Combustion

Tutorial Sheet No. 6/2008 (Premixed flame propagation)

1. A stoichiometric mixture of Butane and air is kept at 1 bar, 300 K in a long, open cylindrical tube. The adiabatic temperature for the stoichiometric mixture can be taken as 2270 K. The molecular weight of the mixture can be taken as 30. The burning of the fuel is described by a single step reaction of the form

The following table can be used to calculate the thermal properties of the mixture:

Temperature T (K)Specific heat Cp (J/kg K)Thermal conductivity k (W/m K)

3009900.026

60010200.047

100011000.067

180012000.120

240015000.196

Find the laminar flame speed of the fuel air mixture at 1 bar, 300 K. If the unburnt mixture temperature is increased to 400 K at the pressure of 1 bar (and the corresponding adiabatic flame temperature is 2300 K), find the laminar flame speed. Also find the laminar flame speed if the pressure of the unburnt mixture is increased to 5 bar at 300 K, assuming that the mixture thermal properties given in the table are functions of temperature only. 2. Take the constant factor b equal to 64 and find the quenching distance for the unburnt mixture conditions of (i) p = 1 bar, T = 300 K (ii) p = 1 bar, T = 400 K (iii) p = 5 bar and T = 300 K.

3. Calculate the minimum ignition energy values for the conditions mentioned in Pb.2.

4. A fuel air mixture of molecular weight 29 and specific heat ratio () 1.4 is initially at 1 bar and 300 K. During combustion, the heat release from the mixture is 3 MJ/kg. Calculate the conditions across the combustion wave for the mass flux value of (i) 2500 kg/s m2 (ii) 2.5 kg/s m2. Discuss which states these correspond to._1284835180.unknown