Untitled - Aerobib - Universidad Politécnica de Madrid

6.14. HYDRAZINE DECOMPOSITION FLAME 179
Theoretical
(Spalding)
Experimental
Hot flame 190 cm/s 185 cm/s (Murray-Hall)
Cold flame 12 cm/s 10 cm/s (Adams-Stocks)
Table 6.4: Propagation velocity of the flame in cm/s.
As Spalding points out the excellent numerical agreement is casual to a certain
extent since there are doubts respect to the correct values of the transport coefficients.
Moreover, Spalding did not include the influence of the variation of such coefficients
with the temperature across the flame. More interesting is the fact that Spalding’s
results predict correctly the influence of the combustion temperature on the velocity
of the flame.
Spalding also concludes that the propagation velocity of the flame that would
be obtained when calculating the radical distributions by means of the steady state
assumption would be much too large. He bases this conclusion upon the fact that
the distribution of radicals obtained with the steady state assumption is considerably
larger, at temperatures close to combustion temperature, than the distribution given by
correct calculation.
Millán and Sanz [30] calculated the propagation velocity of hydrazine decomposition
flame applying the same simplified model proposed by Adams and Stocks.
Two cases were considered, the first assuming steady state for concentration of radicals
and solving the flame equations through Kármán’s method; the second, for which
an approximate calculation method was developed to obtain flame velocity without
considering the steady state assumption. The authors concluded that the results obtained
applying the steady state assumption to the radical concentrations are satisfactory
when compared to those corresponding to a more correct distribution for the
same.
Simultaneously, Gilbert and Altman [38] obtained the flame propagation velocity
corresponding to complete kinetic model proposed by Adams and Stocks [36]
through the application of the Boys-Corner method in finding the solution of the flame
equations and calculating the concentration of radicals throughout the flame under the
steady state assumption introduced by Kármán and Penner [6].
Recently [39] a new analysis of the problem was conducted using the complete
kinetic model of Adams and Stocks, and adopting the steady state assumption for the
determination of the concentration of radicals, with Kármán’s method in calculating
the solution.