How the engine dynamic characteristics affect the blow-by gasses
| Author | Erjon Selmani |
| Position | Polytechnic University of Tirana, Albania |
| Pages | 52-64 |
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52
H
ow the engine d
y
namic characteristics a ect the blow-b
y
gasses
Er
j
on Selman
i
Polytechnic
U
niversity o
f
Tirana,
A
lbania
Abs
tr
ac
t
The combustion chamber is ought to be perfectly sealed, however, part of the air and fuel
mixture can escape from it.
A
mong the several losses there is the gas fl ow from the inter-ring
crevices, which is always present. This leakage is known as blow-by, and a ects e ciency,
correct lubrication and emissions. The amount of leakage is dependent on many factors, and
among the most important are the engine speed and load, which are able to a ect the system
through the forces applied on it. The aim of this paper was to understand in a more detailed
way how the engine speed and load could a ect the sealing e ciency of a ring-pack. For this
purpose, a complete range of speeds and loads were used in the simulations. The equations o
f
the ring motions and gas dynamicshas been implemented and solved in ©Ricardo R
I
NGP
A
K
solver. The results showed that inertia and inter-ring gas pressures drives the sealing behavior
of the rings. The blow-by trend showed to decrease with the speed and increase with the
load, exception made for the idle condition where the values were di erent to the other cases,
especially at higher speeds.
A
mong the two parameters, the engine speed resulted to a ect
more signifi cantly the blow-by trend.
K
e
y
words:
B
low-by, internal combustion engines, speed, load, ring dynamics.
I
ntr
oduc
t
io
n
T
h
e
p
iston an
d
p
iston-ro
d
mec
h
anism, are
p
owere
d
by
t
h
e gas
p
ressure o
b
taine
d
f
rom the combustion inside the chamber.
I
n order to allow the
p
iston to move and
slide over the c
y
linder liner, a
p
ack o
f
rings is mounted into the
p
iston crown. The
p
iston rings main dut
y
is to seal o
the combustion chamber, however, their tightness
is not
p
er
f
ect and
p
art o
f
the intake gas mixture is lost toward the crankcase. This
p
henomenon is commonl
y
known as blow-b
y
gas, and was recognized to brink
negative e
ects on
p
er
f
ormances, lubrication and emissions [1-5].
I
nitial studies [6-7]
have anal
y
sed the ring motions in the axial direction,
f
urther studies [8-9] have also
inc
l
u
d
e
d
t
h
e motions in t
h
e ot
h
er
d
irections. W
h
en t
h
e ring moves insi
d
e its groove,
t
h
e a
b
i
l
it
y
to sea
l
t
h
e com
b
ustion c
h
am
b
er is ex
p
ecte
d
to
d
ecrease. T
h
is motion is
called radial colla
p
se [10], and was seen to occur when the ring li
s-o
f
rom the
contact with the c
y
linder liner.
I
n the above mentioned re
f
erences, the colla
p
se tended
to increase with s
p
eed and load.
I
n re
f
erences [11-14], the ring was accounted also
with the third de
g
ree o
f
f
reedom, the twist around the axis o
f
the rin
g
cross section.
I
n all cases, the ring motions and gas d
y
namics are related to a wide set o
f
p
arameters
a
ectin
g
them. Some are static, such as desi
g
n, materials and sur
f
aces. Some others
a
re
dy
namic, suc
h
as
l
u
b
rication, tem
p
erature variation an
d
engine s
p
ee
d
an
d
l
oa
d
.
I
n the
p
revious studies,Curtis [18] states that the engine s
p
eed is a
p
arameter which
ma
y
a
ect the ring d
y
namics and gas
fl
ow. Kim et. al. in [19] states that the blow-b
y
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