Does Density Ratio Significantly Affect Turbulent Flame Speed?
Artikel i vetenskaplig tidskrift, 2017

In order to experimentally study whether or not the density ratio sigma substantially affects flame displacement speed at low and moderate turbulent intensities, two stoichiometric methane/oxygen/nitrogen mixtures characterized by the same laminar flame speed S-L = 0.36 m/s, but substantially different sigma were designed using (i) preheating from T-u = 298 to 423 K in order to increase S (L) , but to decrease sigma, and (ii) dilution with nitrogen in order to further decrease sigma and to reduce S (L) back to the initial value. As a result, the density ratio was reduced from 7.52 to 4.95. In both reference and preheated/diluted cases, direct images of statistically spherical laminar and turbulent flames that expanded after spark ignition in the center of a large 3D cruciform burner were recorded and processed in order to evaluate the mean flame radius and flame displacement speed with respect to unburned gas. The use of two counter-rotating fans and perforated plates for near-isotropic turbulence generation allowed us to vary the rms turbulent velocity by changing the fan frequency. In this study, was varied from 0.14 to 1.39 m/s. For each set of initial conditions (two different mixture compositions, two different temperatures T-u , and six different , five (respectively, three) statistically equivalent runs were performed in turbulent (respectively, laminar) environment. The obtained experimental data do not show any significant effect of the density ratio on S-t . Moreover, the flame displacement speeds measured at u'/S-L = 0.4 are close to the laminar flame speeds in all investigated cases. These results imply, in particular, a minor effect of the density ratio on flame displacement speed in spark ignition engines and support simulations of the engine combustion using models that (i) do not allow for effects of the density ratio on S-t and (ii) have been validated against experimental data obtained under the room conditions, i.e. at higher sigma. DELGAYED RG, 1987, PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL

cruciform burner

Density ratio

Thermal expansion

burned gas-distribution

p1997

Expanding spherical flame

v456

iences

isotropic turbulence

pressure burning velocities

Thermodynamics

propagating

g-equation

Mechanics

definition

premixed flames

Turbulent flame speed

spherically expanding flames

surface

Low Turbulent

scalar transport

high-temperature

Författare

Andrei Lipatnikov

Dynamik

Chalmers, Tillämpad mekanik, Förbränning

Wun-yi Li

National Central University Taiwan

L. J. Jiang

National Central University Taiwan

Shenqyang Shy

National Central University Taiwan

Flow, Turbulence and Combustion

1386-6184 (ISSN) 1573-1987 (eISSN)

Vol. 98 4 1153-1172

Ämneskategorier

Maskinteknik

Materialteknik

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Building Futures

Energi

Fundament

Grundläggande vetenskaper

DOI

10.1007/s10494-017-9801-6