Experimental investigation of the influence of turbulence on the transient premixed flame propagation inside closed vessels

Abstract

The emphasis of the present work is the systematic study of the effect of turbulent flow exerted on explosive reactions in the deflagrative range inside closed vessels, in order to gain insight into the fundamental processes governing turbulent combustion. In the experiments performed, premixed fuel/air mixtures of varied stoichiometry were ignited by electrical sparks in two pressurized vessels of different size. Using various measurement techniques, the flow and turbulence field, pressure, temperature and flame front position were measured and interpreted as a function of time. For all investigated fuel/air mixtures a universal, linear dependency between the extrapolated turbulent flame velocity and the RMS-values of the velocity-fluctuations could be evaluated. The inclination of this linear dependency turned out to be a function of the laminar flame velocity of the particular mixture. In the range of laminar flame velocity between 0.2 m/s to 3.0 m/s and for the velocity fluctuation RMS-values between 0 m/s and 2.4 m/s , the following relation was obtained: S t S l = 1 + S l 0.25 u t ′ S l (1) The dependency of the turbulent flame velocity on the turbulent length scale of the flow could not be determined, since the experimental setup used in the present study did not permit sufficiently large variations of the length scale. It can, however, be expected that a relation between flame velocity and length scale will render the above equation dimensionless.