Does Density Ratio Significantly Affect Turbulent Flame Speed?
Journal article, 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

Thermodynamics

v456

iences

Mechanics

spherically expanding flames

burned gas-distribution

surface

definition

Low Turbulent

Thermal expansion

scalar transport

Density ratio

g-equation

Expanding spherical flame

isotropic turbulence

high-temperature

premixed flames

p1997

pressure burning velocities

propagating

Turbulent flame speed

Author

Andrei Lipatnikov

Dynamics

Chalmers, Applied Mechanics, Combustion and Propulsion Systems

Wun-yi Li

National Central University

L. J. Jiang

National Central University

Shenqyang Shy

National Central University

Flow, Turbulence and Combustion

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

Vol. 98 4 1153-1172

Subject Categories

Mechanical Engineering

Materials Engineering

Driving Forces

Sustainable development

Areas of Advance

Transport

Building Futures (2010-2018)

Energy

Roots

Basic sciences

DOI

10.1007/s10494-017-9801-6

More information

Latest update

11/16/2022