v8 engine breathing revisited - gamma technologies
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Autor - Dateiname.ppt 1
GT-SUITE Conference 2007
Frankfurt/Main 2007-10-08, Birmingham/MI, 2007-11-13
V8 Engine Breathing Revisited A GT-POWER Analysis of AFR Control and Performance Issues
Christof Schernus
FEV Motorentechnik GmbH, Aachen, Germany
schernus@fev.de
� Acknowledgements:
� Mr. Andrea Dutto, FEV Motorentechnik GmbH
� Prof. Federico Millo, Politecnico di Torino
This presentation is intended to be a compilation of V8 engine related issues that
may be known to most engine developers who have already dealt with this type of
engines. Nonetheless, talking to professionals around in the industry, I found, V8
engines are often overestimated regarding the uniformity of their cylinder process.
Those deviations from the engine average of individual cylinders will be the focus
of my presentation.
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V8 Engine Breathing Revisited
V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Contents
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Here is a brief outline:
After the introduction, I will mention some basics about exhaust manifold layouts.
Then, different firing orders of V8 engines will be addressed.
They will cause differences in engine breathing behavior at full load and part load
that is of concern for air flow control.
Further observations refer to oxygen sensing.
A summary closes the presentation.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Introduction
First V8 engines came up 102 years
ago
� 1905: Rolls-Royce V-8
� 3535 cm³, 120° flat-plane
� Intended to replace electric cars
� 1914: Cadillac Type 51 with L-Head Engine
� 341 in³ (5588 cm³), 90° side-valve, 70 hp
� First cross-plane V8
� First mass produced V8
8-cylinder engines are appreciated as
a prime mover of superior comfort
� 90° firing interval ⇒ Small torque fluctuations
� Cross-plane enables second order mass
balance w/o balance shafts
� Sound
Rolls-Royce V8 1905 [1]
Cadillac Type 53 Cabriolet, 1916 [2]
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
V8 engines are more than 100 years old. The first one was built by RR in 1905. It
was a 3.5 liter 120° V engine and like all early V8 engines it had a flat crankshaft
just like a double straight-4 engine. Interestingly, RR wanted to replace electric cars
that were much common that time. So to be competitive, the engine had to be very
smooth, silent and smoke-free.
The first cross-plane crankshafts came up in 1914 with the famous Cadillac L-Head
engine sharing a patent with Peerless. It was the first mass produced V8 engine, and
in the next decades America became the home of V8s.
So since its first introduction, 8-cylinder engines were appreciated as a prime mover
of comfortable and luxury and/or sporty cars.
The short firing interval produces small torque fluctuations, the cross-plane
crankshaft design enables balancing of 2nd order forces and many love the sound of
V8s, too.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Introduction
Despite of their smooth torque
delivery, V8‘s may sometimes be
cross-grained
� Flat-plane crankshafts need balance shafts for
2nd order mass balance like straight-4’s
� Cross-plane crankshafts have large inertia
(counterweights against 1st order moment)
and odd firing along each bank
Odd firing of cross-plane crankshafts
may reportedly cause non-uniform air
supply
� Although as old as cross-plane V8s, this effect
shall be revisited with respect to engine
control
WOT Volumetric Efficiency
Source: Millo et al
GT-SUITE User‘s
Conference, 2003
WOT Volumetric Efficiency
Source: Millo et al
GT-SUITE User‘s
Conference, 2003
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
[3]
Nonetheless, V8s may surprise us with some characteristics that do not fit very well
with these expectations.
Flat-plane crankshafts without balance shafts have vibrations just like straight-4
engines.
Cross-plane crankshafts need large counterweights against 1st order moments
causing a larger inertia, and they have odd firing intervals along each bank.
This can cause significant differences in volumetric efficiency, as was shown four
years ago by Prof. Millo in his investigation of the Maserati Spyder engine.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Basic Exhaust Manifold Layouts
General Rule for Firing Order Exhaust Manifold:
� Join primary runners of cylinders without interference of exhaust events
� Most preferred, if 2 x 360° or 3 x 240°
� Periodical blow-downs eliminate 0.5th order and provide preconditions for equal gas exchange for each cylinder
� Typical arrangement for V8 with cross-plane crank shaft: 270° + 450°
� Base harmonic = 0.5th order
� Different exhaust pressure level for each
cylinder during exhaust and overlap
� (Characteristic V8 sound)
1 2 3 4
1 2 3
4 5 6
5 6 7 8
1 2 3 4Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
There is a simple rule for exhaust manifold layout:
When connecting primary runners, try to avoid interference of exhaust events.
Three or six cylinder engines with 240° intervals make this pretty easy. Straight-4’s
allow to join cylinders with 360°. All of these solutions allow to eliminate the half
order pressure fluctuation, because the firings of connected cylinders are periodical
and equidistant.
Conventional manifolds for cross-plane V8s allow to connect pairs of cylinders with
270 and 450°, respectively. The unequal intervals does not enable the extinction of
the half order. Therefore, the exhaust pressure level during valve overlap is different
for each cylinder.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
5 6 7 8
1 2 3 4
V8 Engine Firing Orders
„Natural“ V-Angle: 90°
� 90° firing interval without split-pin crank throws
Cross Plane Crankshaft
� Complete 2nd order mass balance
� Bank-wise odd firing featuring intervals
of 90°, 270° and 180°
Flat Crankshaft
� Basically two I4 engines
� Equal firing intervals @ each bank
� Balance shaft required for
2nd order mass balance
1,5
4,8
2,6
3,7
1,5
4,8
2,6
3,7
1-8-6-2-7-3-4-51-8-4-5-7-3-6-21-5-4-3-7-2-6-8
1 2 3 4
5 6 7 8
1,54,8
2,63,7
1-6-3-5-4-7-2-81-6-3-8-4-7-2-51-7-3-5-4-6-2-81-6-2-8-4-7-3-5
RLLRLRRLRLLRLRRLRLLRLRRLRLLRLRRLRLLRLRRLRLLRLRRL
RLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRL
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The „natural“ V-angle of an 8-cylinder engine is 90°. It allows to split the 720°
degrees of a cycle in steps of 90° without need for split-pin crank throws.
The mass balance of a cross-plane crankshaft is paid for by odd firing intervals of
90, 180 and 270° on each bank.
(*) The many possible firing orders depend on the arrangement of cranks and sense
of rotation. But their basic pattern remains the same. After alternating the banks, a
double firing occurs on the same bank, as you can see from the black letters in the
Left-Right sequence.
A flat-plane crankshaft makes each bank a inline 4-cylinder engine with equal firing
orders. The banks alternate their firing. First order mass balance comes for free, but
second order forces require balance shafts for comfort.
(*) denotes a keystroke or mouse-click to initiate an animation
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
V8 Engine Firing Orders
Flat-plane Intake and Exhaust Flow Rates
1-6-3-5-4-7-2-8
(counterclockwise)
Each bank:
� ∆ϕ=180°
� 1-3-4-2-1
6-5-7-8-6
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
In a GT-POWER model of a flat-plane crankshaft engine, the valve mass flow rates
of the different cylinders highlight the even firing order of both banks.
Basically, both banks here have a 1-3-4-2 firing order, just in this case the left bank
is delayed by 270°.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
V8 Engine Firing Orders
Cross-plane Intake and Exhaust Flow Rates
1-8-4-5-7-3-6-2
(counterclockwise)
Right bank:
� Cyl. /∆ϕ=
� 1-4: 180°
� 4-3: 270°
� 3-2: 180°
� 2-1: 90°
Left bank:
� Cyl. /∆ϕ=
� 5-7: 90°
� 7-6: 180°
� 6-8: 270°
� 8-5: 180°
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
In the engine model with cross-plane crankshaft, you find the short firing intervals
between cylinders 2 and 1 on the right-hand side, and between cylinders 5 and 7 on
the left-hand side.
A long break occurs between the blow-downs of cylinders 4 and 3 and between 6
and 8.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
V8 Engine Firing Orders
Flat-plane vs. Cross-plane exhaust pressure
Flat-plane
� Rather uniform
pressure pulses
� Constant average,
no 0.5th order
Cross-plane
� Backpressure drops
btw 4-3 and 6-8
� Short interval btw 2-1,
5-7 leads to higher
backpressure for
cylinders 1 and 7
� FFT results in
remaining 0.5th order
4
3
21
8
6 57
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
1 3 4
2
65 78
Looking at the exhaust pressure in front of the catalyst, you find two times four (*)
rather equidistant pressure pulses of similar magnitude for the flat-plane engine,
plotted in red. The low pass filter reveals no half order, but a (*) constant average
pressure.
The cross-plane engine has that gap after the pulses of cylinders 4 (*) and 6, in
which the manifold is depleted, and the pressure falls. But during the shortening
firing intervals after that gap, the manifold is recharged with exhaust gas and hence
the (*) pressure increases again to its maximum at cylinders 1 and 7, i.e. those
cylinders blowing 90° after their predecessors. (*) This low frequency pressure
fluctuation from odd firing is noted as half order.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Flat-plane WOT Volumetric Efficiency Scatter
Flat crankshaft has
some scatter
� Compact exhaust
manifold with different
primary runner lengths
� Side mounted throttle on
intake plenum causes
different resonances
along entire intake
system
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Because of its more uniform backpressure, the engine with flat-plane crankshaft has
just a small scatter of full load volumetric efficiency. Intake cam phaser angle was
optimized at each speed in a trade off between volumetric efficiency and cam phaser
excursion. The observed variation of volumetric efficiency is related to intake and
exhaust manifold asymmetries. (The compact exhaust manifold features different
primary runner lengths. And feeding the intake plenum through a side mounted
throttle creates different system modes or wavelengths, respectively, between
cylinders and upstream pressure nodes, like air cleaner or snorkel inlet.)
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Cross-plane WOT Volumetric Efficiency Scatter
Cross-plane has
significantly higher
scatter
� same intake manifold
� 4-in-2-in-1 exhaust
manifolds combining
cylinders with 270/450°
intervals
5 6 7 8
1 2 3 4
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The intake system is the same for the cross-plane engine. And the exhaust manifold
combines primary runners of large firing intervals. Nonetheless, we see a large
scatter band of volumetric efficiency. The right bank shows a (*) significant non-
uniformity at 3500 rpm, that we will take a closer look at.
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V8 Engine Breathing Revisited
V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Cross-plane gas exchange at 3500 rpm, WOT, Cylinder 1
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The valve timing is set equal for all eight cylinders.
Looking at the intake and exhaust pressures at cylinder 1, we see a (*) suction wave
coming back to the exhaust valve while the intake pressure is on a higher level. The
gas exchange profits from this pressure gradient by (*) scavenging residuals as
indicated by the positive mass flow rates in intake and exhaust.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Cross-plane gas exchange at 3500 rpm, WOT, Cylinder 3
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The situation is the same for cylinder three
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Cross-plane gas exchange at 3500 rpm, WOT, Cylinder 4
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
And can still be found at cylinder 4, although a bit weaker
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V8 Engine Breathing Revisited
V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Cross-plane gas exchange at 3500 rpm, WOT, Cylinder 2
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
But it is just the contrary at cylinder 2. Because the exhaust valve of cylinder 1
opens just 90° after cylinder 2, its blow-down pressure pulse hits cylinder 2 in the
(*) last 45° of its exhaust stroke. It causes even some (*) backflow from the exhaust
into the cylinder against the upward moving piston and spoils the overlap. Instead of
residuals scavenging, we see backflow of exhaust gas into the intake system. And
where exhaust gas has to be ingested during suction, there is no more room for fresh
air. This explains the low volumetric efficiency of cylinder 2.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Full Load Engine Breathing
Comparison of cross-plane and flat-plane engine
� Cross-plane exhibits
significantly larger
standard deviation
at certain engine
speeds
� Issues:
� Knock control
� AFR uniformity
� Misfire detection
� Comfort
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
All over the speed range of our example engine, we see no clear drawbacks or
advantages for either firing order regarding average volumetric efficiency and
residual gas fraction. But there is a clear disadvantage for the cross-plane engine in
terms of standard deviation. While the flat-plane engine stays below 2%, the cross-
plane always exhibits much higher or in the best case equal standard deviation of
volumetric efficiency. Similar deviations apply to residuals. From this non-
uniformity follow differences in AFR, knock behavior, and – under certain
circumstances – fluctuations of torsional speed and vibrations.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Air Flow Modeling for Controls
Approach based on filling straight line
p0pV
∆∆η
Two stage model: ( )( )
( )( )VVTrpm
VVTrpm
VVVTrpmp pp
pEffVol ,0
,
,,. −
∆∆
=η
Cross-plane2000 rpm
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Now this may pose challenges to engine air flow control, too. Engine controls often employ two
stage models for air flow.
To create a two stage model, volumetric efficiency is measured in manifold pressure sweeps at
constant valve timings and fixed engine speeds. Typically a linear correlation of volumetric
efficiency and manifold pressure is found. At a still positive pressure p0 (*), the extrapolated
volumetric efficiency would be zero, and the slope of volumetric efficiency should be a constant
gradient (*).
These two parameters of the linear equation, p0 and gradient, have to be found for any engine
speed, intake valve lift and intake and exhaust cam phasing.
Please note that for small valve overlap, we see just a small scatter of these characteristics for
the different cylinders even in case of the cross-plane crankshaft.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Local model of breathing straight line
Air Flow Modeling for Controls
Two stage model based on breathing straight line
Manifold
air pressure
Engine
Speed
Var. Valve
Actuation
Global model
vol.eff. gradient
p
V
∆∆η
Global model
Pressure Offset
0p
( )p
pp VV ∆
∆−=
ηη 0
Intake
Lift
Cam
Angles
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Now this is the structure of such an air flow two stage model. We don’t build a model of air
flow rate or volumetric efficiency for the complete set of operation point parameters including
manifold pressure. Once the local pressure offsets p0 and gradients of volumetric efficiency
have been determined, we can fit global Response Surface Models to these sweep variables
using polynomials or non-linear functions for the entire range of VVA parameters and engine
speeds.
The resulting two stage model can be used in the ECU or in Hardware-in-the-Loop Simulation
to predict the amount of air ingested by the engine based on VVT settings, engine speed and
manifold air pressure.
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© by FEV – all rights reserved. Confidential – no passing on to third parties
Air Flow Modeling for Controls
Linear fit less appropriate at large overlap
� Cross-plane, large
valve overlap
� Curvature causes
problems for linear fit
� Higher order
polynomials no good
option either
Two stage model: ( )( )
( )( )VVTrpm
VVTrpm
VVVTrpmp pp
pEffVol ,0
,
,,. −
∆∆
=η
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Unfortunately, that linear correlation is not always sufficiently accurate. Such significant
curvature (*) of the breathing line may be found where overlap cross sections are no longer
small compared to the intake suction area. Higher order polynomials may not comply with the
required monotony of the model and therefore provide unphysical results.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Air Flow Modeling for Controls
Linear fit less appropriate at large overlap
� Cross-plane, large
valve overlap
� Curvature causes
problems for linear fit
� Higher order
polynomials no good
option either
� Cross-plane: large
relative deviations
� Workaround:
Hardwired correlation
of overlap and load
map enables linear
approach for air flow
with local validity
� Reduced overlap at
low load improves
scatter width of ηV and AFR Two stage model: ( )
( )( )( )VVTrpm
VVTrpm
VVVTrpmp pp
pEffVol ,0
,
,,. −
∆∆
=η
-60%
-40%
-20%
0%
20%
40%
60%
80%
100%
0 0.2 0.4 0.6 0.8 1
manifold pressure (bar)
vol.eff. deviation from average
cyl.1
cyl.2
cyl.3
cyl.4
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The situation becomes more difficult, (*) because the scatter of the cross-plane V8 engine
produces a relative deviation from average volumetric efficiency that increases towards low
manifold pressures. This may result in large lambda changes and misfire. Similar reasons may
be found for poor idle stability of V8’s with cross-plane crankshaft.
(*) A workaround is available through a hardwired correlation of cam phasing and target load,
significantly reducing overlap toward lower manifold pressures. Then, the linear equation may
still be valid in a limited pressure range around the target value. (*) And the scatter of
volumetric efficiency can be handled, too.
Let me add the note that the flat-plane V8 engine is much less sensitive to this effect due to its
even firing order.
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Exhaust Oxygen Sensing
TWC has to operate at λλλλ=1� Cylinders deliver different amounts of gas at different λ� Some run rich, others lean
� Catalyst relevant λ is mass average:
EGO sensor signal influenced by oxygen partial pressure @ ZrO2 sond
� Effected by exposure time fraction of exhaust gas
� Under stationary conditions, cycle average λ signal should be proportional to the average cylinder mass fractions in the EGO body
� Transport of gas from different cylinders into the lambda sond plays important role
( )∑
∑=icyl
icylicyl
m
m
,
,, λλ
∫∫∑
∫∫∑ =∝
dt
dt
dt
dt icyl
icyl
icylicyl
EGO
,
,
,, ξλ
λξλ
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The AFR excursions lead to the next paragraph, how to obtain reliable information
about at which lambda the engine is operating.
Let me suppose the gases are distributed uniformly in the all cross sections, well
knowing there are many effects related to 3D flow that could blur the 1D findings
we discuss here.
Especially cylinders of a cross-plane V8 may run at unequal lambda. Some run rich,
others lean. If these deviations cannot be reduced, at least the mass average lambda
shall be correct to keep the 3-way catalyst working.
The oxygen sensor however will provide a signal based on the oxygen partial
pressure on the surface of the electrode. And after low pass filtering this signal is
rather a time-mass average of the gases in touch with the electrode.
Now, how do gases get from the cylinders to the electrode?
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Exhaust Oxygen Sensing
Cylinder Tracking in the exhaust line
Tracer Gas Injection
� Tracer gas is injected into each cylinder before EVO proportional to it‘s amount of fresh air (0.01%)
� This gas can be traced all along the exhaust system
by sensors
� The normalized mass fractions of tracer gas represent
the local composition as of the cylinders
Oxygen Sensor Model
� EGO sensors commonly consist of a ceramic sensor
element inside a metal heat shield
� Exhaust gas is transferred in and out through holes on
the front of the heat shield
� Compression and expansion is the dominant mechanism of mass exchange
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
To model this transport we inject 0.01% of the ingested air mass as tracer gas into
each cylinder before EVO.
Using sensors, we can trace these gases all along the exhaust system model and tell
at each place and time to which proportion the cylinders have contributed to the gas
mixture.
(Click movie) From CFD we have learned that for the typical oxygen sensors with
holes on the tip, compression and expansion is the dominant mechanism of mass
exchange. Gas will flow into the heat shield and change the composition inside,
when the pressure increases, and the heat shield will be depleted without changing
mass fractions when the pressure falls.
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Exhaust Oxygen Sensing
UEGO Sensor Model
GT-POWER (U)EGO sensor model
� Volume of heat shield connected to
catalyst inlet cone by orifices
� Lambda sensed inside heat shield
� Tracer gas mass fractions sensed and
normalized
� inside heat shield and
� at inlet cone
� Pressure changes will cause mass
exchange by compression/expansion of
gas inside heat shield
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
Our GT-POWER model reflects this by a small volume representing the heat shield
connected to the converter inlet cone by orifices – the small holes in the sensor tip.
Here we can now sense lambda and the mass fractions of the tracer gas.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Exhaust Oxygen Sensing
Cylinder Signature of Flat-Plane Engine
� 3000 rpm,
BMEP=3 bar
� Flat-plane engine
shows similar
signatures inside
UEGO sensor
heat shield
� Signatures ∝cylinder vol.eff.
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
At 3000 rpm and 3 bar BMEP we first look at the flat-plane engine. We find rather
similar pressure pulses every 180°.
Every increase of pressure causes flow into the heat shield and will cause a change
of composition.
Because of the uniform transport conditions along the cycle, the cylinder signature
inside the oxygen sensor is closely related to the variation of volumetric efficiency.
These are good preconditions for AFR control.
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Exhaust Oxygen Sensing
Cylinder Signature of Cross-Plane Engine
� 3000 rpm,
BMEP=3 bar
� Cross-plane
engine: cyl. 4 is
outlier
� More frequent
and larger rises
of pressure when
cylinder 4 gas
present in front
of UEGO sensor
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
The cross-plane engine does it an other way.
During the rising slope of the half order pressure fluctuation, we see more frequent
and higher pressure increases, and hence, larger mass flow pulses into the sensor.
During this period, cylinder 4 is present in the cone with higher concentration than
the others. Therefore, its concentration in the heat shield is higher, too. The AFR
signal will therefore emphasize the value of cylinder 4 lambda. If this one runs lean,
the AFR control may turn the entire engine too rich. (Which cylinder is over- or
underrepresented depends on the firing order, on the exhaust manifold volume
between valves and oxygen sensor and to some extent also on engine load.)
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
Exhaust Oxygen Sensing
Cylinder Signature Flat Plane Eng. w/ Cross-Plane Manif.
� 3000 rpm,
BMEP=3 bar
� Flat-plane firing
order with cross
plane manifold
⇒ lower deviation
of signatures
� Periodic
pressure
amplitudes w/o
0.5th order do
not emphasize
individual
cylindersIntroduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
To validate, if this effect would not be caused by improper layout of the exhaust
manifold, we simply ran the flat-plane firing order on the engine with cross-plane
exhaust manifold. And see, the correlation between volumetric efficiency and
cylinder signature in the sensor has become much better.
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© by FEV – all rights reserved. Confidential – no passing on to third parties
Summary
Cross-plane crankshaft: Odd firing order
� 0.5th order pressure fluctuations in conventional exhaust manifolds
� Different conditions during valve overlap
� Non-uniform internal EGR and volumetric efficiency
� Scatters of volumetric efficiency can be reduced by small overlap
� AFR sensor signal may ignore or emphasize individual cylinders due to coincidence of
pressure pulse frequency and presence of gas in front of EGO sensor
� While differences in air flow may be minimized by proper tuning of manifolds and valve
timing, there is no ultimate panacea for AFR sensor errors
Flat-plane engine
� Preferred solution for sports and racing applications
� Comfort reasons may require balance shaft for 2nd order mass forces
Introduction
Basic Exhaust Manifold Layouts
V8 Engine Firing Orders
Full Load Engine Breathing
Air Flow Modeling for Controls
Exhaust Oxygen Sensing
Summary
…
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V8 Engine Breathing Revisited
© by FEV – all rights reserved. Confidential – no passing on to third parties
References
[1] "Rolls-Royce V-8 (1905)." Wikipedia, The Free Encyclopedia. 1 Oct 2007, 09:27 UTC.
Wikimedia Foundation, Inc. 07 Oct 2007 <http://en.wikipedia.org/w/index.php?title=Rolls-
Royce_V-8_%281905%29&oldid=161509935>.
[2] "Cadillac Type 51." Wikipedia, The Free Encyclopedia. 26 Jan 2007, 11:18 UTC. Wikimedia
Foundation, Inc. 07 Oct 2007
<http://en.wikipedia.org/w/index.php?title=Cadillac_Type_51&oldid=103355675>.
[3] „Improving Misfire Detection in an 8-Cylinder FERRARI Engine.“ F. Millo, F. Mallamo, R.
DiGiovanni (Politecnico di Torino) and A. Dominici (Ferrari Auto S.p.A). GT-SUITE
European User‘s Conference, 20 Oct 2003, Frankfurt/Main, Germany. 07 Oct 2007
<http://www.gtisoft.com/confarch/MisfireDetect.ZIP>
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