In

Cylinder Pressure and Flame Measurement
Dr. Manoochehr Rashidi
Engine Research Center
Shiraz University
http://succ.shirazu.ac.ir/~motor/
motor@shirazu.ac.ir
Part 2
Flame Observation
and Measurement
Schematic arrangement of the transparent piston engine
Quartz piston assembly used for obtaining
high speed motion picture of flame
HYCAM rotating prism camera, 10 000 frames/sec on 16
mm film
1.
Object lens
2.
Image size limiter
3.
Segment shutter
4.
1st field lens
5.
1st prism
6.
plane compensation
prism
7
2nd field lens
8
2nd prism
9
Intermediate lens
10
U prism
11
Image
12
Prism
13
Ocular
14
Synchronized gear
drive
Color
photographs
from
high
speed
movie
of
spark
ignition
engine
combustion
process,
taken
through
glass
piston
.
Ignition
timing
30
before
TC,
1430
rpm
.
لاعتشا هقرج روتوم رد هلعش تکرح
Non uniform flame propagation is one of
the causes of cyclic variation in engine
Microshadowgraphs of flame at
various engine speeds showing effect
of turbulence
Schematic arrangement of the transparent piston engine
Synchronization arrangement, for simultaneous
flame front and pressure measurement.
Typical profile of flame front at various crank angle
Inner circle is the visible part of the combustion chamber
Consecutive measured pressure
Variation of flame radius with crank angle or time
Measured flame velocity from photographs
Calculated gas velocity just ahead of flame
Entrained (or burning) velocity
Full line is least square, and doted line is from model
Variation
of
flame
geometry
and
velocity
parameters
during
four
individual
combustion
cycles
.
Variables
shown
in
the
figure
are,
flame
radius
r
f
,
burned
gas
radius
r
b
,
normalized
entrained
volume
y
f
,
burned
volume
y
b
,
.
normalized
flame
front
area
a
f
,
laminar
area
a
L
,
flame
front
speed
u
b
,
burning
speed
S
b
,
and
laminar
flame
speed
S
L
.
Figure
in
previous
page
shows
results
from
an
analysis
of
cylinder
pressure
data
and
the
corresponding
flame
front
location
information
(determined
from
high

speed
movies
through
a
window
in
the
piston)
of
several
individual
engine
operating
cycles
.
The
combustion
chamber
was
a
typical
wedge
design
with
a
bore
of
102
mm
and
a
compression
ratio
of
7
.
9
.
The
flame
radius
initially
grows
at
a
rate
that
increases
with
time
and
exhibits
substantial
cycle

by

cycle
variation
in
its
early
development
(Fig
.
a)
.
Later
(r
f
>
30
mm)
the
growth
rate,
which
approximates
the
expansion
speed
u
b
,
reaches
an
essentially
constant
value
.
The
flame
radius
r
f
is
initially
equal
to
the
burned
gas
radius
r
b
it
increases
above
r
b
as
the
flame
grows
and
becomes
increasingly
distorted
by
the
turbulent
flow
field
(Fig
.
b)
.
Eventually
r
f

r
b
goes
to
an
essentially
constant
value
of
about
6
mm
.
This
difference,
is
approximately
half
the
thickness
of
the
turbulent
flame
brush
.
Normalized
enflamed
and
burned
volumes,
and
flame
front
area
and
laminar
burning
area,
are
shown
in
Fig
.
c
.
Volumes
are
normalized
by
the
cylinder
volume,
and
areas
by
Rh,
where
h
is
the
average
clearance
height
and
R
the
cylinder
radius
.
Discontinuities
occur
in
the
flame
area
a
f
at
the
points
where
the
flame
front
contacts
first
the
piston
face
and
then
the
near
cylinder
wall
.
The
laminar
area
A
L
is
initially
close
to
the
flame
area
A
f
and
then
increases
rapidly
as
the
flame
grows
beyond
10
mm
in
radius
.
During
the
rapid
burning
combustion
phase
(y
f
>
0
.
2
)
the
value
of
y
f
is
significantly
greater
than
y
b
.
During
this
phase,
the
laminar
area
exceeds
the
flame
area
by
almost
an
order
of
magnitude
.
These
observations
indicate
the
existence
of
substantial
pockets
of
unburned
mixture
behind
the
leading
edge
of
the
flame
.
The
ratio
of
the
volume
of
the
unburned
mixture
within
the
turbulent
flame
zone,
to
the
reaction

sheet
area
within
the
flame
zone,
defines
a
characteristic
length
l
r
,
which
can
be
thought
of
as
the
scale
of
the
pockets
of
unburned
mixture
within
the
flame
.
l
r
is
approximately
constant
and
of
order
I
mm
.
These
flame
geometry
results
would
be
expected
from
the
photographic
observations
of
how
the
flame
grows
from
a
small
approximately
spherical
smooth

surfaced
kernel
shortly
after
ignition
to
a
highly
wrinkled
reaction

sheet
turbulent
flame
of
substantial
overall
thickness
.
Initially,
the
amount
of
unburned
gas
within
the
enflamed
volume
is
small
.
During
the
rapid
burning
phase
of
the
combustion
process,
however,
a
significant
fraction
(about
25
percent)
of
the
gas
entrained
into
the
flame
zone
is
unburned
.
The
front
expansion
speed
u
f
,
burning
speed
S
b
,
and
laminar
flame
speed
S
L
are
shown
in
Fig
.
d
.
The
expansion
speed
increases
as
the
flame
develops
to
a
maximum
value
that
is
several
times
the
mean
piston
speed
of
3
.
1
m/s
and
is
comparable
to
the
mean
flow
velocity
through
the
inlet
valve
of
18
m/s
.
The
burning
speed
increases
steadily
from
a
value
close
to
the
laminar
flame
speed
at
early
times
to
almost
an
order
of
magnitude
greater
than
S
L
during
the
rapid
burning
phase
.
During
this
rapid
burning
phase,
since
(r
f
–
r
b
)
is
approximately
constant,
the
flame
front
expansion
speed
and
the
mean
burned
gas
expansion
speed
are
essentially
equal
.
The
difference
between
u
b
and
S
b
is
the
unburned
gas
speed
u
g
just
ahead
of
the
flame
front
.
Note
that
the
ratio
u
f
/S
b
decreases
monotonically
from
a
value
equal
to
the
expansion
ratio
e
u
/e
b
at
spark
to
unity
as
the
flame
approaches
the
far
wall
.
Superimposed
tracings
of
flame
fronts
.
Illustration
showing
best
fit
circle
to
the
18
th
flame
front
.
Schematic
diagram
of
combustion
chamber
geometry
and
spherical
flame
front
.
Angle
versus
distance,
showing
qualitative
trajectories
for
flame
center,
flame
fronts,
and
gas
particle
.
CONCLUSIONS
Simultaneous
pressure
measurements
and
highs
peed
motion
pictures
of
the
visible
flame
in
a
spark
ignition
engine
show
that
the
initial
flame
front
propagation
speed
is
very
close
to
that
of
a
laminar
flame
for
the
same
charge
.
As
the
flame
grows,
its
speed
increases
rapidly
to
a
quasi

steady
value
of
order
10
times
the
laminar
value
.
During
the
rapid
quasi

steady
propagation
phase,
a
significant
fraction
of
the
gas
entrained
behind
the
visible
flame
front
is
unburned
.
The
measurements
also
suggest
that
the
final
combustion
phase
can
be
approximated
by
an
exponentially
decreasing
burning
rate
with
a
time
constant
of
order
1
ms
.
Detailed
analysis
of
the
data
has
led
to
the
development
of
a
set
of
empirical
differential
equations
that
correlate
well
the
experimental
observations
.
The
burning
equations
contain
three
parameters
:
the
laminar
burning
speed
of
the
charge
S
L
,
a
characteristic
speed
u
T
,
and
a
characteristic
length
l
T
.
Measurements
of
S
L
under
engine
like
conditions
can
be
made
in
constant
volume
combustion
bombs,
and
values
for
a
number
of
common
fuels
are
available
.
Values
for
u
T
and
l
T
can
be
obtained
from
engine
experiments,
and
preliminary
correlation
for
relating
these
parameters
to
engine
geometry
and
operating
variables
have
been
given
.
The
data
suggest
that
u
T
increases
and
l
T
decreases
during
compression
of
the
unburned
gas
.
For
a
given
engine
cycle,
the
parameters
in
the
burning
equations
can
be
adjusted
to
fit
the
observed
pressure
curve
.
Cycle

to

cycle
fluctuations
in
pressure
can
be
caused
by
variations
in
any
of
the
parameters
S
L
,
u
T
,
and
l
T
.
Variations
in
S
L
can
be
caused
by
incomplete
mixing
of
the
fresh
charge
with
burned
residual
gas
in
the
cylinder
and
by
variations
in
the
stoichiometry
of
the
fresh
charge
.
Variations
in
u
T
,
and
l
T
are
presumably
associated
with
the
statistical
character
of
turbulence
.
An
additional
parameter
required
to
close
the
burning
equations
with
a
geometrical
description
of
the
enflamed
region
is
the
vector
r
e
giving
the
position
of
the
apparent
flame
center
.
The
nominal
value
of
r
e
is
determined
by
spark
plug
position,
but
convection
of
the
flame
kernel
at
early
times
during
propagation
can
produce
significant
displacement
.
It
is
observed
that
substantial
cycle

to

cycle
fluctuations
can
be
caused
by
variations
in
the
parameter
r
e
.
Variations
in
r
e
are
presumably
caused
by
convection
of
the
initial
flame
kernel
in
the
flow
field
near
the
spark
plug
.
In
this
connection,
it
may
be
noted
that
a
correlation
between
the
pressure
and
the
flow
velocity
.
r
e
near
the
spark
has
been
observed
in
laser
doppler
measurements
.
Although
the
proposed
empirical
burning
equations
provide
a
relatively
simple
and
accurate
method
of
predicting
the
observed
burning
rates
in
spark
ignition
engines,
the
range
of
engine
geometry
and
operating
variables
investigated
in
this
experiment
is
relatively
small
and
needs
to
be
considerably
extended
.
In
particular,
systematic
investigations
over
a
wide
range
of
engine
speeds,
spark
angles,
valve
lifts,
and
compression
ratios
are
needed
to
establish
the
proper
correlation
for
u
T
,
and
l
T
.
the
origin
of
the
cyclic
variations
in
the
values
of
S
L
,
u
T
,
l
T
and
r
e
needs
to
be
more
closely
examined,
and
correlation
for
relating
their
magnitudes
to
engine
geometry
and
operating
conditions
need
to
be
developed
.
The
range
of
validity
of
the
burning
equations
and
their
applicability,
for
example,
to
engines
with
significant
swirl
and
squish
also
needs
to
be
established
.
Finally,
the
experimental
evidence
presented
and
the
proposed
empirical
equations
need
to
be
better
understood
in
terms
of
the
underlying
physical
mechanisms
.
References
1.
C
.
R
.
Ferguson,
“Internal
combustion
engines
applied
thermodynamics”
Wiley,
1985
.
2.
R
.
Stone,
“Introduction
to
internal
combustion
engines”
Macmillan
Press,
1999
.
3.
J
.
B
.
Heywood,
“Internal
combustion
engine
fundamentals”
McGraw
Hill
1988
.
4.
G
.
P
.
Beretta,
M
.
Rashidi,
J
.
C
.
Keck,
"Turbulent
flame
propagation
and
combustion
in
spark
ignition
engines"
.
Combustion
and
flame,
V
52
,
N
3
,
P
217
,
1983
.
5.
M
.
Rashidi,
"The
nature
of
cycle

by

cycle
variation
in
the
SI
engine
from
high
speed
photographs"
.
Combustion
and
flame
.
V
42
,
P
111
,
1981
.
6.
M
.
Rashidi,
"Calculation
of
equilibrium
composition
in
combustion
products
.
"
Journal
of
applied
thermal
engineering,
V
18
,
No
3

4
,
pp
.
103

109
,
1998
7.
M
.
Rashidi,
"Measurement
of
flame
velocity
and
entrained
velocity
from
high
speed
photographs
in
the
SI
engine"
.
The
institution
of
mechanical
engineers
.
Proceedings
.
V
194
,
N
21
,
P
231
,
1980
.
8.
M
.
Rashidi,
"The
sensitivity
of
elementary
reactions
for
hydrogen
oxygen
in
a
well
stirred
rector"
.
International
journal
of
hydrogen
energy
.
V
5
,
P
515
,
1980
9.
M
.
Rashidi,
M
.
S
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Massoudi,
"A
study
of
the
relationship
of
street
level
carbon
monoxide
concentrations
to
traffic
parameters"
.
Journal
of
atmospheric
environment
.
V
14
,
P
27
,
1980
10.
G
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P
.
Beretta,
M
.
Rashidi,
J
.
C
.
Keck,
"Thermodynamic
analysis
of
turbulent
combustion
in
a
spark
ignition
engine
;
experimental
evidence"
.
Paper
WSS/CI
80
/
20
presented
at
the
spring
meeting
of
the
western
states
section
of
the
combustion
institute
.
April
1980
11.
M
.
Rashidi,
M
.
S
.
Massoudi,
"The
use
of
gas
engines
for
motor
vehicles
in
oil
exporting
countries"
.
SAE
paper
770145
,
1977
.
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