Study of Spherical Turbulent Flame Using a Single-Step Chemical Reaction

hammercoupleMécanique

22 févr. 2014 (il y a 3 années et 4 mois)

540 vue(s)

Study

of
Spherical Turbulen
t

Flame



Using

a Single
-
Step Chemical Reaction

Fandi D. Suprianto

Jurusan Teknik mesin, Universitas Kristen Petra

Jl. Siwalankerto 121
-
131, Surabaya

60236, Telp: 031
-
8494830 psw.3464

Email: fandi@peter.petra.ac.id


Over the past

3
0 years significant progress has been made in the development

of
modelling

for turbulent premixed flames.

Experiments are mostly conducted using
complex chemical kinetics mixtures while the theories are always assumed using very
simple chemical kinetics
mixtures.
They usually involve hydrogen or hydrocarbons
as fuels because their chemical kinetics mechanism is simple and contain fewer steps
than other fuels. There are also some other substances which the chemical kinetics
mechanism is simpler than that o
f hydrocarbon combustion, such as ozone, and
hydrazine decomposition flames. Nevertheless these substances are still characterized
by at least two step chemical kinetics, and they require special handling because of
either high toxicity or difficulty in pr
eparing the stable premixtures.
A better
prediction of turbulent premixed combustion can be obtained if the fuel contains very
simple chemical kinetics. The thermal decomposition flame of di
-
tert
-
butyl
-
peroxide
(DTBP) is well describe by a single, first or
der reaction and therefore, a suitable
solution to fulfil the single chemical kinetics assumption.

The subject of this
writing

is the modelling of spherical premixed DTBP + N
2

flames. The main goal is to investigate the behaviour of these flames by using
e
xperimental method and numerical method and make a comparison between those
methods.

For the experimental method, explosions were performed in a fan
-
stirred
combustion vessel of total volume 30.1 dm
3

or 19.5 cm radius, with a centrally
located spark that g
enerate an initial flame kernel in the shape of a smooth sphere of
radius 0.3 cm.

The turbulence is created by fans and the flow has been shown to be
nearly homogeneous and isotropic, mainly in at the central region of the vessel. The
fan speed can be adju
sted to allow rms
fluctuation

velocity up to 10 m/sec to be
generated. Flame propagation was captured using high speed schlieren cinematograph
and the results showed that in reality, the flame contour always non
-
spherical and that
the turbulent flame propa
gation is unsteady and is characterized with the mass
burning rate increasing in time.

For numerical method, t
urbulent premixed flames of DTBP is modeled in a
one dimensional spherical co
-
ordinate. Balance equation is derived in terms of
progress variable
and calculated numerically using routines from NAG Fortran
library. The parameters chosen here were adopted from parameters used in the
experimental work which has been done
before
. Values of obtained progress
variables were
plotted

against radius/distance

and the results were compared with the
experimental results.

Although it seems like

similar, but

t
he mass burning rates obtained from
modelling

are constant, different from the experimental results which show that the
mass burning rates are accelerating.

This difference is suspected because of
assumption used in simplifying source term which eliminates the effect of chemistry.


Key
words: Turbulent, Flame, Single
-
step reaction.