Download Flame structures of turbulent premixed methane and alcohol flames

Flame structures of turbulent premixed methane and alcohol flames inferred
from 2D OH-PLIF
J. Trabold(1), S.M. Walther(1), C. Becker(1), A. Johchi(2), B. Böhm(2), A. Dreizler(2), D.
Geyer(1*)
1
Thermodynamics & Alternative Propulsion Systems, Univ. of Appl. Sciences, Darmstadt, Germany
FG Reactive Flows and Diagnostics (RSM), Center of Smart Interfaces, TU Darmstadt, Germany
* Corresponding author; e-mail address: [email protected]
2
A novel Temperature Controlled Piloted Jet Burner (TCPJB) has been developed to
study the effect of turbulence-chemistry interaction of liquid fuels in the gaseous phase.
The liquid fuels were pre-vaporized and mixed with air upstream of the TCPJB to
generate a gaseous fuel/air mixture. To prevent condensation of the fuel/air mixture at
cold spots the flow system as well as the burner assembly including the jet tube
(diameter 11.4 mm) were electrically heated. The flow system of the TCPJB allows to
control the temperature of the fuel/air mixtures in a range up to ~450 K with a precision
of +/- 1K at the nozzle exit. A co-annular pilot flame is utilized to enable the stabilization
of turbulent jet flames of gaseous and pre-vaporized liquid fuels over a wide range of
equivalence ratios as well as Reynolds numbers. In the current study the pilot was
fueled by five gases (H2, C2H2, N2, CO2, air) to establish a lean premixed stabilization
flame. The mixture of the five gases was adjusted to meet both the C/H atom ratio and
the adiabatic flame temperature of the corresponding fuel/air mixture in the inner jet at
an equivalence ratio of 0.7. In summary, parameter relevant for turbulence-chemistry
interaction such as equivalence ratio and fuel/air mixture can be varied independently
for a variety of fuels in the novel TCPJB.
In a first study, turbulent premixed flames fueled by the alcohols methanol, ethanol, 2propanol and 2-butanol at slightly lean (=0.90) and slightly rich (=1.05) conditions
have been stabilized at Reynolds numbers of 12 000 and 18 000 respectively on the
TCPJB. Moreover, flames of the simplest alkane methane at identical conditions
served as reference cases. Global fuel effects are discussed in terms of the jet’s
Reynolds number and the laminar flame velocity of the fuels respectively.
Planar laser induced fluorescence of the hydroxyl radical (2D-OH PLIF) was employed
to characterize the flame structure of the various premixed turbulent flames at six axial
locations. The statistics of the flame position derived from OH PLIF in terms of the
mean and the fluctuations are compared for the different fuels. Curvature and wrinkling
of the OH contour are employed to characterize the flame structure. Finally, the
interaction of the turbulent flow field with the fuel dependent chemistry is investigated
by exploring the flame surface density. This allows for an assessment of the local
reaction rate of the four alcohols in comparison to the alkane methane for the turbulent
premixed jet flames presented here.