Downsized and Supercharged
Hybrid-Pneumatic Engine
C. Dönitz, C. Onder, I. Vasile, C. Voser, L. Guzzella
Nothing New (the Parsey Locomotive, 1847)
Source: http://www.dself.dsl.pipex.com/MUSEUM/TRANSPORT/comprair/comprair.htm
2
Dickson Locomotive, 1899
Mass 16 t, storage 40 bar, working 10 bar, volume 4.8 m3
Source: http://www.dself.dsl.pipex.com/MUSEUM/TRANSPORT/comprair/comprair.htm
3
Compressed Air as Fuel?
45 MJ/100km
η2= 44%
η1= 90%
η4= 80%
Ptank=300 bar
Ttank= 300 K
η3= 81%
ηtot  0.25
Necessary energy in air tank 70 MJ, which corresponds to
320 kg air mass and 200 kg tank mass (kevlar composite) and
925 l tank volume.
Compare that to BEV: plug-to-wheel efficiency of ηtot= 0.75 and
150 kg battery mass (Li-ion batteries with 100 Wh/kg useful
energy density).
4
Pneumatic Hybrid Powertrains?
 Internal combustion
engine as range
extender: too many
components and
poor fuel economy
 Hybrid pneumatic engine:
 1 main energy supply
 1 energy buffer
 1 energy conversion device
5
Directly vs. Indirectly Connected Air Tank
Indirectly Connected Air Tank:
+ Only limited changes in valve
actuation system needed
+ No major cylinder head changes
− Mode changes difficult/restricted
− Reduced actual pumping
compression ratio
Directly Connected Air Tank
− Add charge valve actuation to
system
− Cylinder head redesign
+ Mode changes easy
+ Pumping compression ratio not
compromised
Adapted from:
A. Fazeli, A. Khajepour, C. Devaud,
and N. Lashgarian Azad. A new air
hybrid engine using throttle control.
SAE Paper 2009-01-1319
6
Downsizing and Supercharging (DSC)
• “downsizing” V-6
T
Replace a V-6
by an R-3
with turbocharger
R-3
• “supercharging”
0.3
0.36
0.35
0.33

0.36
0.35
0.33
0.25
0.3
0.2
0.25
0.1
0.2
0.1
n
7
7
Willans Behavior
output
x=0.37
full load input
x=0.27
x=0.17
full load
output
0
input
idle input
8
Problems DSC
?
Drivability
9
The Hybrid Pneumatic Engine (HPE) Idea
 Previous work by
Herrera (1998),
Schechter (1999),
and Higelin (2001)
 Air tank as energy
buffer
 Recuperation and
pneumatic driving
 Pneumatic modes
are 2-stroke based,
all valves variable
10
Comparison Valve Actuation Modes
IV – Intake Valve
EV – Exhaust Valve
CV – Charge Valve
– ETH Modes
 2-stroke modes require variable actuation for all valves
 4-stroke concept is cheaper and less complex
11
The ETH DSC HPE Concept
12
Operating Modes
Engine
Mode
Torque
Uses
Gasoline
Air Tank
Pressure
Pump
+
no
no
↑
↓
Conv.
Combustion
+
yes
→
most often used engine mode
Supercharged
+
yes
↓
transients only,
overcoming turbo lag
Recharge
(>= 4 cyl.)
+
yes
↑
e.g. 2 cylinders pump,
2 cylinders burn,
shifting operating point
Pneumatic
Motor
Usage
vehicle braking
rapid pneumatic engine start
(avoids idling) & cruising
13
Additional Engine Modes
a)
b)
c)
-
Pump mode: throttle always open
Pneumatic motor mode: closes throttle for higher torque
Supercharged mode: air injection at start of compression
Recharge mode: 2 cylinders conventional, 2 cylinders pump
a)
b)
c)
14
Simulation Vehicle & Engine Parameters
 Base vehicle weight 1450 kg, engine weight: 67kg/l
 Rated power: 100kW for all engines, baseline is 2.0l NA
gasoline engine
 Auxiliaries consume 400 W
 Gearbox: manual, 5-speed, η=93%
 Mid-size vehicle, A
c
0
.8
3
f
d
 Tank volume 30 liters
 Effect of reduced compression ratio on engine efficiency
considered
 Variable valve actuation energy accounted for according
to number of used EHVS.
15
Baseline Engine as Willans Machine
16
Engine Scaling
 Account for reduced internal
efficiency when reducing the
compression ratio due to
supercharging
 Values obtained using engine
process simulation
engine ε
k(ε)
2.0l NA
10.5
1
1.6l TC
9.5
0.978
1.4l TC
9.5
0.978
1.2l TC
9.0
0.966
1.0l TC
9.0
0.966
17
Variable Valve Actuation Energy
 Energy demand for EHVS is added to demanded torque
 Hydraulic pump efficiency of ηHyd=0.6 assumed



[
b
a
r
]

m
i
n
m
a
x
8

p
,
5
0
,
2
0
0
T

V

p

z
/
4
 p








H
y
d
T
a
n
k
H
y
d
H
y
d
,
i
H
y
d
i H
y
d
i

C
V
,
E
V
,
I
V


 zi is the number of
variably actuated
valves per 2
revolutions
Valve
# per
yHyd
Zylinder
type
Charge Valve CV
1
5 mm
V0.5
Intake Valves IV
2
10 mm
V0.7
Exhaust Valves EV 2
10 mm
V0.7
18
Simulations (1): Fuel Economy
MVEG-95, 1550 kg vehicle
19
QSS & Dynamic Programming
 Additional degree of freedom, additional state: Internal
energy of air tank
 Use quasi-static simulation (QSS) and engine mode maps
and reduce to
Dynamic Programming:




One state: tank pressure
One input: engine mode choice
Disturbance: drive cycle
Cost: fuel consumed
20
Simulations (2): Influence Tank Volume
21
Simulations (3): Overcoming the Turbo-lag
Simulation for 1500 kg vehicle in
4th gear with 0.75 liter engine
22
The ETH DSC HPE Test Engine
Main Ideas
 Strong downsizing to
improve fuel economy
 Connect pressurized air
tank directly to engine
cylinders: enables
excellent driveability
Engine Type
 PFI/stoich gasoline engine
 Asymmetric turbo charger
Additional Hardware:
 Variable valve actuation system for CV only
 Air tank (cold tank strategy)
23
Hardware (1): Modified Engine MPE750
engine data
manufacturer
Weber Automotive GmbH (WENKO)
displaced volume
0.75 liter
# cylinders
2, parallel twin 360°
compression ratio
9.0
fuel
gasoline port fuel injection
# valves
2 IV, 2 EV per cylinder
turbocharger
Garrett GT 12 (C) – 14(T)
rated power
61 kW
24
Hardware (2): Modified Engine MPE750
25
Electro-Hydraulic Valve Actuation System
 EHVS provides fully variable valve actuation for the CV:
opening
closing
07.04.2015
K. Mischker and D. Denger. Requirements for a fully variable
valvetrain and realization with the electro-hydraulic valvetrain
system EHVS. VDI-Fortschritt-Berichte, 12(539), 2003.
26
Hardware (3): Engine on testbench
Air tank 30 liters,
steel, not
insulated for
cold-tank
strategy
Engine equipped
with GT12
compressor &
GT14 turbine
Electric
wastegate
actuator
27
A (virtual) lab visit
… or come and visit us!
28
Hardware (4): Engine Control Systems
29
Engine Controls:
Vehicle Emulation Control Architecture
 Dynamometer
controls torque
(behaves like a
vehicle in drive
cycle)
 Engine controls
speed
 Supervisory control
determines engine
mode f(pT)
30
Measurements (1): The Supercharged Mode
31
Measurements (2): The Supercharged Mode
Test at constant intake pressure (550 mbar)
32
Measurement (3): Overcoming the Turbolag
N = 2000 rpm
33
Measurements (4): Rapid Pneumatic Start
 Rapid engine start
enables start/stop
operation and thus
the elimination of
idling.
 Pneumatic engine
start < 350ms for
pT= 10 bar.
pT = 10 bar
34
Optimization Results Pneumatic Modes
 Pneumatic motor
mode: only for
low engine speeds
 Pump mode:
operating area
strongly limited
35
Measurements (4): Recuperation Efficiency
m 
 Teff 
air

max
 max



T
mair p.mot
 eff pump

36
Remark: Recuperation using Alternator
 Recuperation: pumping is limited by four-stroke mode
 In the MVEG-95 ~500 kJ cannot be recuperated by
pumping air in braking phases
 Excess energy can be used for:
 EHVS actuation: 104 kJ needed to drive MVEG-95 (assuming 60%
efficiency for the alternator & 60% efficiency for an electric hydraulic
pump)
 Electric auxiliaries need 300 W at the crankshaft for 1200 s, i.e.,
360 kJ are needed for the drive cycle
 Fuel consumption can be further reduced
37
Experiment: VW Polo, MVEG-95
38
Engine Mode Determined Using DP
39
Experiment: Nissan Micra, FTP
40
Engine Mode Determined Using DP
41
Fuel Consumption Measurement Results
 Engines of approximately same maximum power are compared
 Comparison to NA SI engines in series production cars
Measured Fuel Consumption Reduction (MVEG-95)
42
Result Overview, MVEG-95
Vehicle
VW Polo
(2005)
VW Polo
(2009)
Nissan
Micra
Nissan
Micra
Toyota
Prius II
Engine Vd
1390 ccm
1390 ccm
1240 ccm
1386 ccm
1497 ccm
Rated power
59 kW
63 kW
59 kW
65 kW
57 kW
Weight
1088 kg
1070 kg
1065 kg
1075 kg
1400 kg**
Price (CHF)
19’770
22’600
16’897
20’090
38’950
ECE / EUDC /
NEDC (l/100km)
8.3 / 5.2 /
6.3
8.0 / 4.7 /
5.9
7.4 / 5.1 /
5.9
7.9 / 5.4 /
6.3
5.0 / 4.2 /
4.3
Hybrid Pneumatic MPE750 (61kW), 30l Air Tank
ECE / EUDC /
4.2 / 4.0 /
NEDC (l/100 km) 4.1
(4.2 / 3.9 /
4.0)*
4.3 / 4.6 /
4.4
4.2 / 4.5 /
4.4
(4.5 / 4.4 /
4.5)**
Fuel savings
- 49.4 % /
- 23.2 % /
- 35.4 %
(- 47.2 % /
- 17.5 % /
- 31.9 %)*
- 42.6 % /
- 10.5 % /
- 24.6 %
- 46.3 % /
- 16.2 % /
- 29.8 %
(- 9.1 % /
+ 5.0 % /
+ 3.7 %)**
Δ rated power
+ 3.4 %
- 3.2 %
+ 3.4 %
- 6.2 %
+ 7.0 %**
43
Result for FTP, Nissan Micra
Vehicle
Nissan Micra (visia)
Engine Vd
1240 ccm
Rated Power
59 kW
Weight
1065 kg
Price (CHF)
16’897
FTP part 1 / 2 / 3 / comb.
6.2 / 6.5 / 5.6 / 6.1 (l/100km)
Hybrid Pneumatic MPE750 (61kW), 30l Air Tank
FTP part 1 / 2 / 3 / comb.
4.8 / 4.4 / 4.6 / 4.6 (l/100km)
Fuel Savings
- 22.4 % / - 32.7 % / - 17.9 % / - 24.9 %
Data sources: Touring Club Switzerland
www.tcs.ch, EMPA Switzerland, OEM webpages
44
Electric Hybridization vs. DSC HPE Concept
Cost vs. Mileage
60.0
mileage (rated power and
vehicle base mass adjusted)
55.0
HPE: Estimated added
cost for EHVS & tank:
1500 CHF (conservative)
DSC & pneum.
hybridization
50.0
Polo & Micra
electric
hybridization
45.0
Prius
40.0
Hybrid Pneumatic Engine in
Polo & Micra
35.0
30.0
15000
20000
25000
30000
price (CHF)
35000
40000
For normalization:
base rated power 61 kW
base weight 1080 kg (Prius
base weight 1250 kg)
45
Thank you for your attention!
46
Compressed Air in a Series Hybrid?
ICE 20 kW
comp. 20 kW
1-stage
adiabatic
tank, ~50 l
pneum.motor 60 kW
ptank=20-30 bar
Ttank= 700-800 K
η1= 35%
COP = 1
η2= 80%
ICE 20 kW
comp. 20 kW
2-stages
η11= 35%
COP = 0.5
η12= 80%
Q21 = 65%
η22= 50%
η4= 81% η5= 80%
η3= 80%
ηtot  0.15
air tanks ~50 l and
ptank~ 80 bar
Ttank= 400 K
η13= 95%
45 MJ / 100km
~10 l
Expand
and
heat up
η23= 50%
pneum.motor 60 kW
45 MJ / 100km
η4= 81% η5= 80%
ηtot  0.19
47
Reproduceability of Measurements
4.0%
3.0%
Polo 05
ECE
Polo 05
EUDC
Polo 05
NEDC
Prius
ECE
Prius
EUDC
Prius
NEDC
Micra 1.2l
FTP
2.0%
min
1.0%
max
0.0%
127.3g
-1.0%
207.9g
335.2g
137.9g
229.5g
367.4g
615.0g
Mean measured fuel
consumption (g)
-2.0%
-3.0%
-4.0%
Deviations from mean values (exemplary, 3 measurements per cycle)
48
Pneumatic Modes Control
Pneumatic Pump Mode:
 Feedforward only
 Braking torque is limited a
priori if too high
Pneumatic Motor Mode:
 Throttle feedforward only
 Feedback uses as ΔMV2O
as control signal
49
Supervisory Control – Dynamic
Programming
 3 states:
 2 inputs:
tank pressure, old engine mode, and old gear
engine mode, gear switching
 allows engine start & gear switching penalty
 For the MVEG-95, gears are pre-defined, so 2 states and 1 input
results.
50