Combustion

Combustion

1. (10 points) The overall reaction order n for a global one-step hydrocarbon-air mechanism is given to
   be n = 1.75, where the global reaction rate is expressed in standard Arrhenius form:
   ( ) exp{ } R T
   E k T A
   U
   − A = . What are the units (SI units, as we have been using in lecture) for the preexponential factor A in this case?
2. (10 points) Consider a steady one-dimensional laminar premixed flame with hydrocarbon-air
   reactants (a non-methane paraffin fuel). For a reference condition of ambient pressure and
   temperature reactants (p = 1 atm, Tu = 298 K) and no dilution (Ydil = 0), the laminar flame speed is
   approximately sl,ref = 0.5 m/s at an equivalence ratio of Φ = 1.1. Use the Metghalchi & Keck laminar
   flame speed correlation (with BM = 0.5 m/s, B2 = -3 BM , ΦM = 1.1) to estimate the laminar flame
   speed sl for each of the following sets of conditions:
   a. p = 1 atm, Tu = 600 K, Φ = 1.1, Ydil = 0
   b. p = 10 atm, Tu = 298 K, Φ = 1.1, Ydil = 0
   c. p = 1 atm, Tu = 298 K, Φ = 0.7, Ydil = 0
   d. p = 1 atm, Tu = 298 K, Φ = 1.1, Ydil = 0.10
3. (10 points) Consider a fully turbulent momentum-dominated axisymmetric hydrocarbon-air
   jet flame. By approximately what factor does the mean flame length change with:
   a. A factor of two increase in fuel nozzle diameter (fixed flowrate and fuel type)?
   b. A factor of two increase in fuel flow rate (fixed nozzle diameter and fuel type)?
   c. A switch in fuel from propane to hydrogen (fixed nozzle diameter and flowrate)?
   d. A switch in fuel from propane to methanol (fixed nozzle diameter and flowrate)?