10.1515/mecdc-2015-0009
BLOWBY GAS COMPOSITION IN SI ENGINES
KAREL PÁV
ŠKODA AUTO a.s., tř. Václava Klementa 869, Mladá Boleslav 293 60, Tel.: 326815450, Email: karel.pav@skoda‑auto.cz
SHRNUTÍ
Tento příspěvek se zabývá metodikou měření složení blow-by plynů v klikové skříni motoru s využitím konvenčních NDIR analyzátorů
výfukových plynů. Vyhodnocení je zaměřeno na určení podílu spalin, paliva a vodních par obsažených v těchto plynech. Určení podílu
spalin v blow-by plynech je založeno na měření koncentrace CO2. Výsledky měření na větším počtu zážehových motorů jsou statisticky
zhodnoceny s ohledem na provozní podmínky motoru. Je zde rovněž ukázán vliv různých provozních podmínek motoru a vliv různého
typu použitého paliva na složení blow-by plynů zážehových motorů s vnější tvorbou směsi.
KLÍČOVÁ SLOVA: B LOW-BY PLYNY, PODÍL VÝFUKOVÝCH PLYNŮ, PODÍL VODNÍCH PAR, ZÁŽEHOVÝ MOTOR, CNG MOTOR.
ABSTRACT
The paper deals with a procedure for measuring the composition of blowby gas in the engine crank case by means of a conventional
NDIR (Non-Dispersive Infra-Red) exhaust gas analyzer. This paper aims to evaluate the exhaust gas portion, as well as the fuel and
water vapor fraction in the raw blowby gas. Determination of the exhaust content in the blowby gas is based on CO2 concentration
measurement. The measurement results of several SI engines are statistically reviewed regarding the engine operational points. The
influence of different operational conditions and used fuel type is shown on raw blowby gas composition in port injection SI engines.
KEYWORDS: BLOWBY GAS, EXHAUST GAS FRACTION, WATER STEAM FRACTION, SI ENGINE, CNG ENGINE.
1. INTRODUCTION
The blowby flow into the crank case is caused by imperfect
sealing of the combustion chamber during the engine cycle. Due
to the leakage of piston rings, the working gas flows down along
the piston skirt. Dynamic movement of the piston rings is a very
complex issue and can be behind an unpredictable leakage.
Normally, the main flow occurs in the high pressure part of the
working cycle, but due to the piston ring movement or fluttering
a significant flow can also be observed in the low pressure part.
The blowby gas consists of fuel vapor which negatively affects
the oil in the oil sump and thereby contributes to oil degradation.
It leads to shorter oil life and deteriorating lubrication ability. As
well as fuel vapor, the blowby gas also includes water steam,
which can condensate at low temperatures and subsequently
freeze. This is a hazard, particularly with respect to oil pump
functionality and venting through the crank case ventilation
duct. The main source of the water steam is exhaust gas, which
contains water as a product of combustion depending on fuel
chemistry. CNG fuel produces a higher fraction of water vapor
in the exhaust gas. Numerous measurements carried out at the
Skoda Auto laboratories show that the composition of blowby
Blowby Gas Composition in SI Engines
Karel Páv
gas can be significantly influenced by piston ring and groove
design. Operational conditions of the engine also play an
essential role in blowby gas composition. The most important
factors are engine speed, EGR ratio (both internal and external),
ignition advance and burning rate.
Generally, the composition of raw blowby gas can be divided
into three fractions – fresh air, fuel vapor and exhaust gas. The
water steam is included in exhaust gas and to a small extent
also in wet air. The typical blowby composition of SI engines with
port injection technology is shown in Figure 1. The given ratio of
the individual fractions depends mainly on engine operational
point and piston design.
2. MEASUREMENT OF BLOWBY
GAS COMPOSITION
The direct measurement of species concentration in blowby
gas, including H2O content, is possible using a FTIR (Fast Fourier
Transform Infra-Red) technique with heated lines to the analyzer.
Even if the sampling lines are heated, the condensation of both
MECCA 03 2015 PAGE 01
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assuming that the H2O/CO2 ratio is constant and corresponds to
chemical
equilibrium
WetWet
Air Air at low temperatures (after chemical reaction
freezing
approx. 1700 K). This assumption is not far from
∼ 73%
∼at73%
reality because the blowby gas is formed by combustion products
until the flame front reaches the piston rings region. At this time
the temperature in the combustion chamber is usually bellow
2250 K thus the dissociation of combustion products declines
in importance. An example of indicated pressure and in cylinder
temperatures together with calculated equilibrium CO2 volumetric
fraction and H2O/CO2 ratio for fuel C8H15 is given in Figure 2.
The simplified calculation of chemical equilibrium was based on
equilibrium constants according to Schüle [1], which provides
results in good agreement with [2]. It is clear that rich mixtures
are affected by reaction temperatures even at lower temperatures.
Calculation analysis shows that the penetration of combustion
products through the piston rings area begins at several degrees
of crank angle after the end of burning. At this time the incylinder temperature is even lower. Here the assumption of
insignificant dissociation allows the use of CO2 as a tracking gas,
particularly for stoichiometric and lean mixtures. Rich mixtures
can be affected by small errors as can be seen in Figure 2.
Wet Exhaust ~25%
Water ~4%
Wet Air ~73%
FIGURE 1: Typical raw blowby gas composition of port injection
gasoline SI engines.
OBRÁZEK 1: Typické složení neředěných blowby plynů u benzínového
zážehového motoru s vnější tvorbou směsi.
50
50
40
40
30
30
20
20
10
10
0
Pressure
Pressure
T [K]
Burned
Zone Zone
Burned
Temperatute
Temperatute
2000 2000
60
40
ϕ [deg]
ϕ [deg]
0
0
80
60 100
80 120
100 120
0.04
0.02
0.00 0.00
2
2
0.06
RoB [1/deg]
yH O / yCO [-]
0.08
RoB [1/deg]
0.08
Unburned
Unburned1000 1000
0.06
Zone Zone
Temp.Temp.
0.04
500 500
Rate of
Rate
Burning
of Burning
0.02
λ = 1λ = 1
λ = 0.85
λ = 0.85
= 20 bar
p = 20p bar
p = 50p bar
= 50 bar
0.06 0.06
0.10 0.10
1500 1500
Mean Mean
Temp.Temp.
0
-80 -60
-80 -40
-60 -20
-40 TDC
-20 TDC
20 40
20
0.10 0.10
0.08 0.08
T [K]
2500 2500
0.12 0.12
2
3000 3000
1.6
1.6
1.4
1.4
1.2
1.2
2
60
/ yCO [-]
60
0.14 0.14
2O
3500 3500
Because of the use of conventional NDIR analyzers with a pre-chiller
refrigerating the sample to 4–8 °C it is necessary to take into account
condensed water in the gas samples. By means of experimental
work, it has been proved that only water condensation takes place
in the pre-chiller, there is negligible condensation of gasoline fuel
vapors. Assuming only water condensation in the sampling line, the
2
70
2.1 CALCULATION OF COMPONENT FRACTIONS BASED
ON MEASUREMENT
yCO [-]
70
p [bar]
p [bar]
the fuel vapor and the water steam in the cold crank case cannot
be completely avoided. Thus the measurement results can be
influenced by this issue. If it is not possible to totally prevent
the condensation, another method for this task can be applied.
The use of more common NDIR analyzers with pre-chiller used
routinely for exhaust gas analysis is also applicable. However,
in order to obtain proper results it is necessary to apply further
recalculation because of water removal from the sample.
The determination of blowby gas composition is mostly based on
a comparison between CO2 content in the blowby gas and exhaust
gas sampled upstream of the after treatment system [3]. Although
the H2O content is not measured directly, it can be calculated
1.0
yH
Water
Water
∼ 4%
∼ 4%
yCO [-]
Fuel ~2%
WetWet
Exhaust
Exhaust
∼ 25%
∼ 25%
0.8
1.0
λ = 0.85
λ = 0.85
λ = 1λ = 1
0.8
1000 1000
1250 1250
1500 1500
1750 1750
2000 2000
2250 2250
2500 2500
2750 2750
3000 3000
T [K]T [K]
FIGURE 2: Indicated pressure, unburned and burned zone temperatures, rate of burning (n = 4000 min-1, IMEP = 12.2 bar, l = 0.85), calculated CO2
equilibrium volumetric fraction and H2O/CO2 ratio in exhaust gas as a function of temperature and pressure for fuel C8H15.
OBRÁZEK 2: Indikovaný tlak, teplota v zóně neshořelé směsi a v zóně spalin, jednotková rychlost hoření (n = 4000 min-1, IMEP = 12.2 bar, l = 0.85),
vypočtený rovnovážný objemový podíl CO2 a poměr H2O/CO2 ve spalinách v závislosti na teplotě a tlaku pro palivo C8H15.
Blowby Gas Composition in SI Engines
Karel Páv
MECCA 03 2015 PAGE 02
Unauthenticated
Download Date | 6/16/17 4:05 PM
2
2
arly for stoichiometric and lean mixtures. Rich mixtures can be affected by small
2
ar,
CO
λ2 equilibrium
=λ 0.85),
calculated
volumetric
COthat
equilibrium
Hvolumetric
O/CO2 ratio
fraction
in* exhaust
and2 H
gas
as 2a ratio
in
exhaust
gas piston
as ay BB =
2culation
bar,
=analysis
0.85),
vypočtený
rovnovážný
podíl
CO
aBB
poměr
H2O/CO
2fraction
2objemový
2O/CO
Exh
*products
2 ve the
shows
theand
penetration
of
combustion
through
Exh
in
Figure
2.
y
y
on
sure
of
for
temperature
fuel
C
and
pressure
for
fuel
C
H
.
H
.
CO
CO
8
15
8
15
eplotě
a tlaku
pro degrees
palivo C8of
H15crank
.
2
egins at
several
angle after the end2 of burning.
At this time the in-cylinder
[ (
)
yCO22 − y Air yCO2 1 − yH 2 O + yCO2 yH 2 O
BB*
CO2
y
y
Exh
H 2O
Exh *
CO2
+y
(1 − y )
Exh
H 2O
zek
plota2:vIndikovaný
zóně neshořelé
tlak, směsi
teplotaa vv zóně
zóně neshořelé
spalin, jednotková
směsi a vrychlost
zóně spalin,
hořeníjednotková
(n =
rychlostExhhoření
(n =BB*
*
-1
yCOH2of
as
lower.
Here
the
of podíl
insignificant
dissociation
allows
use
CO22yve
CO2a
min
λis=even
0.85),
, IMEP
vypočtený
= 12.2
bar,
rovnovážný
λ =assumption
0.85),objemový
vypočtený
rovnovážný
CO2 a poměr
objemový
H2O/CO
podíl
CO2 a the
poměr
2 ve
2O/CO
BB
BB
BB
lysis
shows
that
the.inapenetration
of lean
combustion
products
through
the
piston
.
y
+
y
+
y
= in
1 exhaust
for
stoichiometric
and
mixtures.
Rich
mixtures
can
be
affected
by
small
fractions
blowby
and
exhaust
gas
before
and
after
sample
The
water
steam
fraction
gas can be expressed as
ách
a, particularly
tlaku
v závislosti
proCO
palivo
na
C
teplotě
tlaku
pro
palivo
C
H
H
.
Air
Exh
Fuel
8
15
8
15
2
of crank2.angle after the end of burning. At this time the in-cylinder
BB
BB
BB
neral
be degrees
seendrying
in Figure
are related by equations
y Air
+ yExh
+ yFuel
=1 .
er.
Here
the
assumption
ofofinsignificant
dissociation
allows
use of CO
2 as a the piston
shows
Calculation
that the
analysis
penetration
shows
that
combustion
the penetration
productsofthrough
combustion
thethe
piston
products
through
Exh*
k yCO2
yarea
forbegins
stoichiometric
and BB
lean
mixtures.
can
be affected
Exhsmall
egrees
of crank
atBB
several
angle after
degrees
the
end
crank
of burning.
angleRich
after
At mixtures
this
the time
end of
the
burning.
in-cylinder
At this yby
time
the in-cylinder
* of
, (5)
Exh*
H 2O =
y
y
Exh
CO
CO
k yCO
Figure
a
as *a − y*
erature
ere
the assumption
is2.even lower.
of Here
insignificant
the
dissociation
of insignificant
allows the use
dissociation
of CO2 asallows
the use 1of+CO
2
2 assumption
k y2CO
Exh
2
=
H
O
,
2
2
yH 2 O =
BB lean
Exh*
stoichiometric
ng gas, particularly
for1stoichiometric
mixtures.
mixtures
lean mixtures.
can be affected
Rich mixtures
by small
can be affected by small
− y H* O Richand
1 − yand
1 + k yCO
− yH* 2 O
Exh
Exh
H O
2
k
=
y
y
eas2.can be seen in2 Figure 2. 2 ,
H 2 O (1)
CO2
Exh
Exh BB
Exh * BB *
where ratio k = yHExh2O yCO
depends on used fuel, air/fuel ratio
y
y
yCO
y
2
CO
CO
CO
2
2
2
2
=
=
l
and
also
air
humidity.
For
the
purposes of this paper there are
1 − 1y HExh
−2 Oy HBB2 O1 − 1y H*−2 Oy H* 2 O
shown particular values of the ratio k for gasoline and CNG fuel
,
Exh
Exh *
in Figure 3. These values are calculated considering chemical
yCO 2
yCO 2with * denote
BB
BB *
where variables
marked
volumetric fractions after
y
y
=
CO
CO
kinetics at the temperature of reaction freezing according to [4].
2 *
2
=
1 −The
y HExh2volumetric
1 −BB
yfractions
drying.
of* CO2 and H2O in the blowby
O
H 2O
−
y
−
y
1
1
Hof
BB gas are
Airgiven
BB by the
ExhHcontribution
2 OBB
2 O both wet air and exhaust
yCO
= yyBB
BB * y Exh
,
CO 2 y Air + y
CO
2
2
y
Steady-state measurements carried out on port injection
Exh
Exh
*
CO 2
COthe
2
gas passing
through
piston
region
. yrings
y
BB
BB
BB
BB
*
*
=
CO
CO
BB
Air
BB
Exh
BB
2y
2
y
y
y
BB
*
engines confirm that the air/fuel ratio in the raw blowby gas
CO
CO 2=
yHCO
=−y=yHH2 OOyCOAir2 1+−yHy H2Exh
21
O y Exh
= * *2
2O
2
* 1 − y 2 O BB 1 − y
roughly corresponds to the air/fuel ratio in the exhaust gas.
H
O
Hy
O
,
Air
BB
Exh
BB
−
y
−
y
−
1 − yyHBB2BB
1
1
1
2
2
H 2O
O
= yCOH2 2yOAiry, Exh
+ y* COH22 Oy Exh
CO 2y Exh
,
This means that a nearly homogeneous mixture escapes the
CO
* 2 Exh BB* Air
BB* Exh BBCO 2AirExh *
(2)
. .Exh *
=
y2 CO
yCO
y
y
yCO
−2 yBBAir yExh
1
−
y
+
y
y
Air
BB
Exh
BB
CO
CO
CO
H
O
CO
H
O
*
2
2
2
combustion chamber by leakage through the piston rings area.
y1HBB2−O*=y=Exh
y 2 y Air
y =2 2 ,
− *y+2H y2 OHExh
=
2O
H 2 OH 2*O 1Exh
ExhExh1 − y *
−
−
1 − y HyExh2CO
y
1
y
+
y
1
−
y
O y1
H
O
H
O
H
O
Figure 4 shows sequences of different engine operational points
2 CO
2H O
2
H 2O
2
2
2
BB
Air
BB
Exh BB
for gasoline and CNG fuel comparing measured and calculated
*
* y Air +
* y
BB
BB yequation
Air = yCO
Air
Combining
systems
(1)yBB
and
CO
Exhresults in a formula for
2
2
2 (2)
yCO
− y Air
yCO
BB
CO2 1 − yH 2 O + yCO2 y H 2 O
BB
.
2
fuel volumetric fractions assuming measured values y Air but
,
yExh = the exhaust
BB fraction
Air* inBB
gas
blowby
gasy BB
BB* yExh
Exh
Exhy Exh
=
y
y
+
HO
H 2 O1BB
yCOAir2 yHExh
−AiryBBH 2 OH 2 OExh ExhBB
2 O + yCO
a homogenous mixture. Measured and theoretically calculated
2
BB
Air
BB
BBy Exh2 yAir
BB= BB
BB y BB
BB
y yBB
y AiryyCO
+Exh
y +Air2yy+
y
y
+
y
y
CO
Exh
.
yCOAir
=
1
2 2 +
2 CO
2
Exh
CO
CO
Air
CO
Exh
BBy*CO 2 = CO
Fuel2
2
2
fuel fractions in raw blowby gas display good mutual agreement.
.
.
.
O2 BB
BB ExhAirAirBB BB * Exh BB
BB* Air
BBAir
BB BB
BB AirBB*Exh
BB
y
−
y
y
1
−
y
+
y
y
=y AiryH+2CO
yH= OCO
yH 2 O =y Hy2HOBB
yy 2 Oyy+
yyH2Exh
y Air +H 2yOH 2 O yExh
Air
CO2 H 2 O
HExh
O
2O
2O
Exh2* 2
, (3)
= O k2HAir
yExh
BB* Exh
Exh *
Exh
y
BB
BB y
BB
CO2 y
2.2 SIMPLIFIED CALCULATION
Exh
+1, y.CO2 1 − yH 2 O
CO
H
O
y
+
y
+
y
=
y
=
2
2
Air Air*Exh
Fuel
* AirAir BB* Air
*
BB*
BB** *BB
BB* Air
H* 2 O AirBB
Exh
*BB
BBBB
−
y
y
1
−
y
y
+
−
y
y
y
y
1
−
y
+
y
y
Considerable simplification of the above-stated calculation
y O1CO− −y CO
y2HAir
*CO y AirBB
*y 21 +
+2CO
H
H
Oy2CO y H HO2 O
CO2 H 2 O
BByk
2 2O
COy2 − CO
Air
CO
O
B 2
, 2 Exh2*
,
yExh
=*2 2CO2 2 ExhHBB
CO
,
=
BB
*
Exh
Exh
*
Exh
Exh
2
procedure is possible by taking into account the following
hExh y
Exh+ y
yHy2 OBB+* yyExh
− Exh
yHy2*Exh
− yH 2 O CO2 volumetric
measured
CO2 where
O
Hy2 O directly
CO2 1
CO 1and
CO
1*2−yare
yCO
y2CO
CO2 H 2 O2 + ykCO
H 2O
2
Exh
assumptions:
2
Exh * fractions
BB=
* in exhaust and blowby gas
, respectively. The relationship
yH y2 OCO
BBExh* BB *
BB
yCO
2
2
.
y
+
y
+
y
=
1
• The inlet air contains neither CO2 nor H2O,
1 + k Air
ygas
−ExhyH 2 O Fuelis given by general mass balance
between blowby
CO2components
• Drying out of the sample is perfect without any residual
h
Exh
BB
BB
BB
BB
BB
BB
.y Air
+ yFuel
= 1 BB
+ yExh
+Exhy*Fuel
=1 .
O yyCO
Air2 + y Exh
BB
BB
water steam,
(4)
y Air + yExh Exh
+ y = 1 k. y CO2
,
yH 2 O Fuel
=
• There are no fuel vapors in blowby gas.
Exh* Exh**
Exh*
1 + k yCO
k yCO
k2 y−COy2 H 2 O
Exh
Exh
2
*,
,
y
=
Exh
H O =
k*yyExh
Exh*
Exh*
*
Exh
2.0 − y2.0 CO22
3.50
3.50
k H=2OyHExh
y
1
k
y
1
k
y
y
+
+
−
CO
H
O
CO
H
O
O
CO
,
y2H 2 O = 2 2
2
2
2
Exh*
* Gasoline
Gasoline
Fuel
Fuel
CNG Fuel
CNG Fuel
Exh 1 + Exh
ky
−y
[ (
1.6
1.6
()
)[ ] (
)
(
) (
]
)
])
]
)
H 2O
1.2
1.0
/ yCO
2O
1.4
k = yH
1.4
2O
/ yCO
2
1.8
k = yH
2
CO2
1.8
/ yCO
2O
y
k = yH 2O yCO2
k = yH
Exh
CO2
()
(
)
2
[ ([
]
1.2
pH O / pAtm
pH =O 0/ p÷Atm
0.05
= 0, Δ
÷ 0.05
= 0.01
, Δ = 0.01
1.0
2
2
0.8
0.8
0.70
0.70
0.75
0.75
0.80
0.80
0.85
0.85
0.90
λ [-]
λ [-]
0.90
0.95
0.95
1.00
1.00
3.25
3.25
3.00
3.00
2.75
2
(
)
)
/ yCO
(
]
2.50
2O
[ (
)
k = yH
[ (
2.75
2.50
2.25
2.25
2.00
2.00
1.75
1.75
pH
1.50
1.50
1.00
1.00
1.25
2O
/ pAtm
pH =O 0/ p÷Atm
0.05
= 0, Δ
÷=
0.05
0.01
, Δ = 0.01
2
1.25
1.50
1.50
1.75
1.75
2.00
λ [-]
λ [-]
2.00
2.25
2.25
2.50
2.50
FIGURE 3: Calculated H2O/CO2 ratio in exhaust gas as a function of air/fuel ratio l and partial water pressure in air for equivalent gasoline fuel
C7.76H14.67O0.12 (rich mixtures) and CNG fuel CH4 (lean mixtures).
OBRÁZEK 3: Vypočtený poměr objemových podílů H2O/CO2 ve spalinách v závislosti na součiniteli přebytku vzduchu l a na parciálním tlaku vodních
par ve vzduchu pro ekvivalentní palivo C7.76H14.67O0.12 (bohaté směsi) a CNG palivo CH4 (chudé směsi).
Blowby Gas Composition in SI Engines
Karel Páv
MECCA 03 2015 PAGE 03
Unauthenticated
Download Date | 6/16/17 4:05 PM
],
0.10
0.09
CNG Fuel
0.08
BB [-]
yFuel
0.07
0.06
0.05
Measurement
0.04
Theoretical Calculation
0.03
Gasoline Fuel
0.02
0.01
0.00
0
10
20
30
40
50
Engine Operational Point
60
70
80
FIGURE 4: Comparison of theoretically calculated and measured fuel volumetric fraction in raw blowby gas at different engine operational points
for gasoline and CNG fuel.
OBRÁZEK 4: Porovnání teoreticky spočítaných a změřených objemových podílů palivových par v neředěných blowby plynech při různých provozních
režimech benzínového motoru a CNG motoru.
In fact, the last assumption is only temporary. Applying equation
(5) and the above-stated assumptions to equation (3) provides
the final simplified form for calculation of the exhaust volumetric
fraction in blowby gas
TABLE 1: Compensation constants and H2O/CO2 ratios for different fuels.
TABULKA 1: Kompenzační konstanty a objemové podíly H2O/CO2
pro různá paliva.
Fuel
Gasoline
Constant K
Ratio kDryAir
0.8
5.630 – 8.078 l + 3.409 l2
(
) , (6) CNG (6)
1.7
2.037 – 0.019 l
y =!
y (1 +yK y(1 +)K y )
(6)
y =! replaced by the , constant K. The new constant
tio k has been formally
where theKwater fraction
in the sample after drying y ranges
(
)
y
1
K
y
+
for the influence
of
variable
H
O/CO
ratios,
but
also
for
the
presence
of
fuel
in
where the original ratio k has been formally replaced by the
from 0.006 to 0.01 depending on conditions in the pre-chiller.
BB
Exh
BB*
Exh *
yCO
1 + K yCO
2
2
Exh *
CO2
BB
Exh
BB*
BB* CO
2
CO2
Exh *
CO2 2
Exh *
CO2
BB*
2 CO2
*
H2O
ginal ratio
k has
been
formally
replaced
by fuel
the
constant
K. The
new
constant
particular
value
of
K depends
on the
according
toRatio
Table
1. for dryKair (p / p = 0) can be determined from
constant
K. constant
The new
constant
K compensates
notused
only for
the
kDryAir
H O
Atm
ot
only
for
the
influence
of
variable
H
O/CO
ratios,
but
also
for
the
presence
in 3 or 2can be calculated according to the
ained by influence
regression
analysisHofO/CO
measured
realthe
engines.
wasofin fuel
2 data
2 on for
of variable
ratios,
but also
presenceEquation
the(6)
charts
Figure 2
2
s. The
value ofinconstant
K depends
the
fuel
used
according
1.
ange
of particular
exhaust
the The
blowby
gas.value
Theonof
results
were
compared
withtoina Table
of fuel infractions
the blowby
gas.
particular
constant
formulas
Table 1.
were
obtained
by regression
analysis
of measured
on real
engines.
Equation (6) was
tion as
aK depends
reference.
error
resulting
from
usedata
ofThese
the
simplified
calculation
onThe
the fuel
used
according
to Table 1.
values
wide range of exhaust fractions in the blowby gas. The results were compared with a
were obtained by regression analysis of measured data on real
calculation as a reference. The error resulting from use of the simplified calculation
engines. Equation (6) was verified with a wide range of exhaust
All results presented in this paper are related to the raw blowby
Ratio kDryAir
Fuel
Constant K
fractions in the blowby gas. The results were compared with
gas even if an engine was equipped with a PCV (Positive Crank
2
Gasolinea non-simplified
0.8 calculation5.630
– 8.078 λThe
+ error
3.409resulting
λ
as
a reference.
case Ventilation) system. In this case the PCV system was
Ratio kDryAir
Fuel
Constant K
CNG from use of the
1.7simplified calculation
2.037
– 0.019
was
±2%. λ
2 deactivated for measurement purposes. The blowby gas was
0.8different fuels.
5.630 – 8.078 λ + 3.409 λ
onstants Gasoline
and
H2O/CO
2 ratios
Regarding
the
crankfor
case ventilation design it is desirable to
sampled from the crank case ventilation path downstream of
í konstantyCNG
a objemové podíly 1.7
H2O/CO2 pro různá paliva.
2.037 – 0.019 λ
estimate the amount of water vapor in blowby gas. It makes
the oil separator. Then the sample was led through the fine filter
ensation constants and H2O/CO2 ratios for different fuels.
sense
to
evaluate
the
occurrence
when
there
is
a thread
of
to avoid analyzer fouling. All the measurements were
O/CO
pro
různá
paliva.
mpenzační
konstanty
a
objemové
podíly
H
crank case ventilation design it is desirable
of water
2
2 to estimate the amountelement
water
freezing
inside
the
crank
case.
In
this
case
the
ambient
out under steady-state engine conditions.
It makes sense to evaluate the occurrence when there is a threadcarried
of water
isventilation
below
0 °C design
andtemperature
absolute
humidity
very
ding
the temperature
crank
it is air
desirable
tois estimate
amount
water
Numerous
results
show that the raw blowby gas composition
nk case.
In thiscase
case
the ambient
is below
0°Clow.
and the
absolute
airof
dry
air, the
water volumetric
fraction
the blowby
by gas. Assuming
Itdry
makes
sense
tovolumetric
evaluate
the
occurrence
when
there
a thread
of water
Assuming
air, the
water
fraction
in the inblowby
gas isisgiven
as mainly
depends
on engine speed and it almost independent
*
gas case.
is givenInasthis
e the crank
casey BB
the Exh
ambient
temperature is below 0°Cof and
absolute
aircharts in Figure 5 show possible values of
engine
load. The
kDryAir
Exh yCO2
ryyHBB
low.
Assuming
dry
air,
the
water
volumetric
fraction
in
the
blowby
gas
is
given
as
,
(7)
(
)
Dry
Air
=
exhaust gas fraction and of water steam content in blowby gas at
Exh *
2O
1 + kDryAir yCO
− yyH*BB2 O y Exh*
2
k
normal test cell environmental conditions. These measurements
DryAir Exh CO2
BB
, (7)
*
Air )drying
=
H 2 O ( Dry
Exh *
*
on in theysample
after
ranges
from
0.006
to
0.01
depending
oncarried(7)
y
have been
out on both port injection and direct injection
H 2O y
1 + kDryAir
y
−
CO2
H 2O
SI
engines.
The
depicted
fields are relatively large, but the area of
chiller.
Ratioin kthe
DryAir for dry air ( p H O / p*Atm = 0 ) can be determined from the
2
er fraction
sample after drying
yH 2 O ranges from 0.006 to 0.01 depending on
an be calculated according to the formulas in Table 1.
the pre-chiller. Ratio kDryAir for dry air ( pH 2 O / p Atm = 0 ) can be determined from the
3. MEASUREMENT RESULTS
e 3 or can be calculated according to the formulas in Table 1.
Blowby Gas Composition in SI Engines
Karel Páv
MECCA 03 2015 PAGE 04
Unauthenticated
Download Date | 6/16/17 4:05 PM
0.450.45
0.070.07
0.400.40
0.060.06
0.350.35
0.08
0.50
0.05
0.05
0.40
0.200.20
0.40
0.06
0.02
0.02
0.05
0.05
0.35
0.30
yH BB
O [-]
0.30
0.100.10
0.010.01
0.000.00
0.20
0.00
0.00
0.20
0.03 0
0
10001000200020003000300040004000500050006000600070007000
0 10001000200020003000300040004000500050006000600070007000
0
2
0.04
0.25
2
0.050.05
0.25
0.15
0.07
0.03
0.03
0.06
BB
BB [-]
yyHExh
O [-]
BB [-]
yExh
0.35
0.150.15
0.45
0.04
0.07
0.04
2
2
0.45 0.25
0.25
0.08
yH BB
O [-]
yH BB
O [-]
0.300.30
BB [-]
yExh
BB [-]
yExh
0.50
0.10
0.15
0.02
0.10
0.05
0.01
0.05
n [1/min]
n [1/min]
0.00
0.03
n [1/min]
n [1/min]
0.02
0.01
0.00
0
1000
2000
3000
4000
5000
6000
0.04
0.00
7000
0
1000
2000
3000
n [1/min]
4000
5000
6000
7000
n [1/min]
FIGURE 5: Exhaust gas and water steam fraction in raw blowby gas at normal test cell conditions (25 °C, wet air) as a function of engine speed for
different gasoline SI engines, highlighted characteristics of single engines.
OBRÁZEK 5: Objemové podíly spalin a vodní páry v neředěných blowby plynech při běžných okolních podmínkách (25 °C, vlhký vzduch) v závislosti
na otáčkách motoru pro různé benzínové zážehové motory, zvýrazněná úzká pole přísluší vždy jednomu konkrétnímu motoru.
1.100.850.85
18
18
20
20
20
20
22
22
23
23
18
18
19
19
20
20
21
21
23
23
23
23
19
19
20
21
20
21
23
23
24
24
25
25
21
21
22
22
19
19
21
21
BB [%vol.]
20
20
yExh
1.050.800.80
0.750.75
1.00
20
18
λ [-]
18
0.700.70
0.95
0 0 5
0.90
19
21
0.85
FIGURE 6:
Exhaust
21
20
21
20
20
21
21
23
21
21
22
21
21
23
24
26
24
26
27
27
24
24
26
28
24
24
26
28
28
24
24
24
29
28
29
-1 MAP = 574 mbar
n =222000
23 24 , 26
23 min
24 26
25
25
27
27
23
23
23
18
20
20
22
19
20
21
23
23
24
23
23
24
25
24
25
27
15
15
15
16
16
17
17
18
18
16
16
17
17
16
16
17
17
20
20
16
16
16
16
17
17
18
18
21
21
16
16
16
16
17
17
19
18
BB [%vol.]
17
yExh
17
y BB17[%vol.]
17
20 -120
-1
, MAP
= 22
574
= 2000
min
18n 18
19
=22mbar
528 mbar
n =19 4000
min
21, MAP
21
2015
18
18
20
17
21
0.950.95
27
27
15
1.001.00
24
27
20
21
24
25 [deg] 26
Ignition
Advance
Angle
Ignition
Advance
Angle
[deg]
1.10
0.85
0.85
1.10
Exh
0.80
0.80
1.05
1.05
1.00
21
22
23
24
27
16
0.900.90
0.750.75
1.00
24
16
18
18
17
17
18
15
0.90 0.90
16
21
20
16
20 2120
20
18
18
22
16
23
25
25
23
16
19
16
19
19
17 23 19
24
17
2618
21
19
17 23
30 30
17
21
18 25
0.70
26
27
28
29
22
23
24
19 27
20
21
35 35
26
21
2821
20
21
20
20
21
21
20
20
24
Ignition
Advance
Angle
[deg]
Ignition
Advance
Angle
[deg]
2116
18
24
gas volumetric fraction in raw blowby gas as28a function
advance and relative air/fuel ratio l,
20
20
20
21
21
21
2117
17
22
22
gasoline SI engine,
partial loads.
23
23
18
24 26 25
1924 26 25
21
27
0.80
0.80 0.80
20
20
20podíly 21
20 a součiniteli
OBRÁZEK 6: Objemové
spalin 23
v neředěných
blowby
plynech
v závislosti
na předstihu
zážehu
vzduchu l,
21
23 přebytku
23
23
24
24
17
25
25
18
18
27
19
19
0.75 středního zatížení benzínového motoru.
0.75 0.75
režimy
24
0.85
of
ignition
0.85
21
18
19
16
0.700.70
0.95
0.95
5 10 10 15 15 20 20 25 25 30 30 35 35 40 40 45 45
15
10 10 19 15 16
21
19
23
19
24
-1, MAP = 528 mbar
-1, MAP
= 4000
= 528 mbar
n = n4000
minmin
20
24 20
40 40
27
28
45 45
20
29 21
27 22
27 20
0.70 0.70
0
5
10load 15
partial
at
10 engine
15
20
0 values
5
15 engine
20 is relatively
25
30 narrow.
35 Examples
40
45
possible
for10a single
Advance Angle [deg]
of such measurementsIgnition
for three
specific engines at various
engine speeds and loads are given. These three highlighted areas
cover any possible fraction at any engine operation point. Along
with engine speed, the exhaust gas fraction also depends on
piston design and soot build up level within piston rings region.
Raw engines lie normally in lower range of the field and worn
engines lie in upper range.
Besides the engine speed and of course EGR rate there are
two more parameters influencing the blowby gas composition,
namely air/fuel ratio and ignition advance angle. The specific
influence of these two parameters has been investigated at
Blowby Gas Composition in SI Engines
Karel Páv
20 selected
30
35
40 40 45
two
operational
points.
The 45
25 25
30
35
Ignition
Advance
AngleAngle
[deg][deg]
Ignition
Advance
results of measurements
are
graphically
displayed in Figure 6.
The exhaust fraction in the blowby gas is strongly affected by
ignition timing because it shifts the angular position of the end of
combustion. The moment when the flame front reaches a distant
piston edge is the most important factor. Until then, only the
surrounding unburned mixture can pass through the piston rings
area. It is apparent that the air/fuel ratio also has a minor impact
on the resulting exhaust gas fraction in blowby gas, partly as the
mixture enrichment causes a slight increase in the amount of
residual gases passing through the piston rings region together
with the unburned mixture. It is generally known that the fastest
MECCA 03 2015 PAGE 05
Unauthenticated
Download Date | 6/16/17 4:05 PM
1.10
1.05
1.00
24 21
λ [-]
0.900.90
18
BB
BBy [%vol.]
yExh
Exh [%vol.]
λ [-]
λ [-]
λ [-]
0.950.95
18
1.051.05
λ [-]
1.001.00
1.101.10
-1, MAP = 574 mbar
-1, MAP
= 2000
n = n2000
minmin
= 574 mbar
λ [-]
1.051.05
BB
BBy [%vol.]
yExh
Exh [%vol.]
λ [-]
1.101.10
0.95
0.90
0.85
0.80
0.75
0.70
10
12
12
12 12
10
10
10 10
88
pe [bar]
p
pee [bar]
[bar]
pe [bar]
8
6
4
2
0
66
44
22
8
1616 17 1717
14 15 1515
1616 1616
16 17161717 14
14
14171515
141515 14
151516 1616 16
15
1717 1717 1818 1919
14
16
16
15
16
15
16
1616
1515
141414
17 17171817191815
19 15
16
21
21
15
15
15
16
16
15
15
16
16
1514
1416
2121
21
21
15
15
16
16
21
232321
161515 16
21
21
1717
1818
1313
1414
1616
1717
1414
1616
23
23
2424
21
2117
1718
1813
1314
1416
1617
1714
1416
1615
15
24
24
2525
2121
1919
1818
1414
1515
1414
1616
1515
1212
1515
25
2521
2119
1918
1814
1415
1514
1416
1615
1512
1215
15
16 1717
2626
2121
2121
1919 18 1818
1818 16
1717
1313
1111
1414
2019 1818
26
2621
2121 20
21
191818 1818 16181716 1717
1713
1311
1114
14
24
24
6
4
14
14
14 14
Gasoline
Fuel
Gasoline
Fuel
Gasoline
Fuel
Gasoline
Fuel
17
BB[%vol.]
BB
yBB
[%vol.]
BB
Exh
Exh
yyExh
y[%vol.]
Exh [%vol.]
20
20
141111
22 2323
2222
262624 22
2121
1818
1818
1616
1616 14
1212
1313
24
26
2622 22 222322 2321
2118
1818
1816
1616 14
1611 14 1112
1213
13
12
12
12 12
2727
2222
2323
2222
2020
1919
1515
1616
1111
1212
1111
27
2722
2223
2322
2220
2019
1915
1516
1611
1112
1211
11
26
26
26
26
28
28
2323
28
2823
12
12
12 13
12
13
1212
2323
2020
1818
1919
1717
1515
2323
2320
2018
1819
1917
1715
1512
1213
1010
1310
10
8
6
4
1212
1212
1111
12
1212
1211
11
2
88
1313
1313
1212
13
1313
1312
12
2
66
44
22
CNG
Fuel
CNG
Fuel
CNG
Fuel
CNG
Fuel
BB[%vol.]
BB
yBB
[%vol.]
BB
Exh
Exh
yyExh
y[%vol.]
Exh [%vol.]
10
10
10 10
pe [bar]
p
pee [bar]
[bar]
pe [bar]
14
14
14 14
8
6
4
1515 1616 1212
1414 1616
15 16151216 15
15 11 1313 1212
12
14 1614 16
15 1111
15 111213 13
13
1717 1717 1515 1313 1212
12
12 12 1515
13
1616
1515 1313
2222 202017 1717151713151212
11
13
13
12
15
12
1516
1615
1513
1313 1111
242422 2022 20
11
11
11
24
24
2626
11 13 11
262525 26 2020
1818
1616
1414
1616
1717
1515
1111
1111
13
25
2520
2018
1816
1614
1416
1617
1715
1511
1111
1113
13
16
16
16
16
2525
2121
2121
1717
1717
171716
16
1313
1414
1111
1111
25
2521
2121
2117
1717
1717
1716
1613
1314
1411
1111
11
121111
2424
2222
2121
2020
1717
1717
1818
1111
1313 12
1111
24
17
2422
2221
21
20
1717
1718
1811
1113 121311 12 1111
11
18
18
2020
20
20
2018
18
14
14
22 2323
14
12
2525
2323 22
2020
1919
1616
151514 12
1010
1010
1212
25
2523 22232322 2320
2019
1916
1615
1512
1210
1010
1012
12
24
24
24
24
2424
2222
24
2422
2222
1919
1919
1616
1616
1313
1212
1111
1111
2222
2219
1919
1916
1616
1613
1312
1211
1111
11
1313
1212
1010
13
1312
1210
10
2
1313
1212
1212
13
1312
1212
12
00
00
0
0
0
500 1000
1000 1500
1500 2000
2000 2500
2500 3000
3000 3500
3500 4000
4000 4500
4500 5000
5000 5500
5500 6000
6000 6500
6500
500 1000
1000 1500
1500 2000
2000 2500
2500 3000
3000 3500
3500 4000
4000 4500
4500 5000
5000 5500
5500 6000
6000 6500
6500
500
500
500 500
10001000
1500 1500
2000 2000
2500 2500
30003000
3500 3500
4000 4000
4500 4500
5000 5000
5500 5500
6000 6000
65006500
500 500
1000 1000
1500 1500
2000 2000
2500 2500
3000 3000
3500 3500
4000 4000
4500 4500
5000 5000
5500 5500
6000 6000
6500 6500
n[1/min]
[1/min]
nn[1/min]
n [1/min]
n[1/min]
[1/min]
nn[1/min]
n [1/min]
FIGURE 7: Engine map of exhaust volumetric fraction in raw blowby gas for gasoline and CNG fuel.
OBRÁZEK 7: Objemové podíly spalin v neředěných blowby plynech v úplné charakteristice motoru při provozu na benzín a CNG.
6060
60
60
5050
50
50
pp[bar]
p [bar]
[bar]
p [bar]
Pressure
Pressure
Pressure
Pressure
4040
40
40
8080
80
80
0.07
0.07
0.07
0.07
7070
70
70
0.06
0.06
0.06
0.06
6060
60
60
0.05
0.05
0.05
0.05
5050
50
50
0.04
0.04
0.04
0.04
4040
40
40
[deg]
[deg]
ϕϕϕ
[deg]
ϕ [deg]
6060
60
60
0.04
0.04
0.04
0.04
0.02
0.02
0.02
0.02
2020
20
20
0.02
0.02
0.02
0.02
0.01
0.01
0.01
0.01
1010
10
10
2020
20
20
000 0
-40-40 -20
-20-20 TDC
TDC
2020
-40
-20
TDC
20
-40
TDC 20
0.06
0.06
0.06
0.06
0.05
0.05
0.05
0.05
Pressure
Pressure
Pressure
Pressure
4040
40
40
0.07
0.07
0.07
0.07
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
Rate
Burning
Rate
Burning
Rate
ofofofBurning
Rate
of
Burning
λλλ==λ=11=1 1
3030
30
30
3030
30
30
1010
10
10
0.08
0.08
0.08
0.08
CNG
Fuel
CNG
Fuel
CNG
Fuel
CNG
Fuel
RoB
[1/deg]
RoB
RoB [1/deg]
[1/deg]
RoB [1/deg]
0.82
λλλ==λ=0.82
=0.82
0.82
0.08
0.08
0.08
0.08
pp[bar]
p [bar]
[bar]
p [bar]
7070
70
70
Gasoline
Fuel
Gasoline
Fuel
Gasoline
Fuel
Gasoline
Fuel
RoB
[1/deg]
RoB
RoB [1/deg]
[1/deg]
RoB [1/deg]
8080
80
80
0.00
0.00
0.00
0.00
8080
80
80
000 0
-40-40 -20
-20-20 TDC
TDC
2020
-40
-20
TDC
20
-40
TDC 20
Rate
Burning
Rate
Burning
Rate
ofofofBurning
Rate
of
Burning
4040
40
40
[deg]
[deg]
ϕϕϕ
[deg]
ϕ [deg]
6060
60
60
0.01
0.01
0.01
0.01
0.00
0.00
0.00
0.00
8080
80
80
FIGURE 8: Indicated cylinder pressure and normalized rate of burning at engine speed n = 6000 min-1 and full load for gasoline and CNG fuel.
OBRÁZEK 8: Indikovaný tlak ve válci motoru a jednotkový průběh hoření při otáčkách n = 6000 min-1 a plném zatížení motoru při provozu
na benzín a CNG.
combustion can be expected approximately at an air/fuel ratio
l = 0.85, which corresponds to the peaks in both charts.
For investigation of the fuel influence on blowby gas composition,
a fuel bivalent engine was chosen; specifically an SI engine of
swept volume 1.6 L with port fuel injection system designed to
run on gasoline or CNG fuel. The effect of used fuel on exhaust
volumetric fraction in blowby gas is presented in Figure 7. Some
differences in exhaust fractions are notable only at full load and
high engine speeds. The higher ratio of the exhaust in blowby
gas in the case of gasoline fuel is caused by faster combustion
of a gasoline rich mixture compared to a stoichiometric CNG
mixture as indicated in Figure 8.
Blowby Gas Composition in SI Engines
Karel Páv
4. CONCLUSION
Blowby gas flow within piston rings region is very complex.
However, a simplified explanation of the phenomena mentioned
above can be summarized as follows: The piston rings region can
be thought as a reservoir. The exhaust gas from the combustion
chamber cannot pass through this area until all the mixture in
this space is blown-by. There is more time for this phenomenon
at lower engine speeds. The higher the soot level, the smaller
space between piston rings and consequently more exhaust gas
flows through. The exhaust gas fraction in blowby is strongly
affected by the burning process in terms of angular position
of the end of combustion, which can be simply controlled by
MECCA 03 2015 PAGE 06
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ignition advance. Residual gases in the combustion chamber
contribute markedly to exhaust fraction in blowby gas. A nearly
homogeneous mixture escapes the combustion chamber by
leakage through the piston rings area in port injection engines.
The portion of the fuel vapor in the blowby gas strongly depends
on fuel type.
Knowledge of the water steam concentration in the crank case
is very important during engine development phase when the
crank case ventilation system is being tested and optimized.
Investigation of more engines shows their strong diversity.
Therefore, the direct measurement of blowby composition for
a particular engine is desirable.
The measurement results of raw blowby gas composition can be
utilized for a qualitative validation of the piston rings movement
simulation.
ACKNOWLEDGEMENT
This work was supported by ŠKODA AUTO a.s.
REFERENCES
[1] BURCAT, A., RUSCIC, A.: Third Millennium Ideal Gas
and Condensed Phase Thermochemical Database for
Combustion with Updates from Active Thermochemical
Tables, Argonne National Laboratory, TAE 960, 2005.
[2] GRILL, M.: Objektorientierte Prozessrechnung von
Verbrennungsmotoren, Dissertation, Universität
Stuttgart 2006.
[3] PÁV, K.: Measurement of Blow-by Gas Composition, XLV.
International Scientific Conference of Czech and Slovak
University Departments and Institutions Dealing with the
Research of Combustion Engines, str. 97 – 105, Kostelec nad
Černými lesy 2014, ISBN 978-80-7375-801-1.
[4] PÁV, K.: Složení výfukových plynů zážehových motorů,
Sborník přednášek mezinárodní konference Motor-Sympo,
str. 199 – 206, Vydalo ČVUT v Praze, ÚVMV s.r.o., Výzkumné
centrum Josefa Božka, Brno 2001,
ISBN 80-01-02382-6.
LIST OF NOTATIONS AND ABBREVIATIONS
Air
BB
CNG
DryAir
Exh
Fuel
H2O
IMEP
MAP
NDIR
RoB
SI
Wet air
Blow-by gas
Compressed natural gas
Dry air
Exhaust gas
Fuel vapour
Water steam
Indicated mean effective pressure
Manifold air pressure
Non-dispersive infra-red
Rate of burning
Spark ignition
k
n
p
pAtm
pe
pH O
2
T
y✳H O
2
yix
✳
yix
ϕ
l
Volumetric H2O/CO2 ratio [-]
Engine speed [1/min]
Indicated in-cylinder pressure [bar]
Atmospheric pressure [bar]
Engine brake mean effective pressure [bar]
Water vapour partial pressure in wet air [bar]
Calculated in-cylinder temperature [K]
Volumetric fraction of water steam in front-end
condenser [-]
Volumetric fraction of species i in matter x [-]
Volumetric fraction of species i in matter x after drying [-]
Crank angle [deg]
Relative dry air/fuel ratio [-]
Blowby Gas Composition in SI Engines
Karel Páv
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