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This paper contains information about CNG technology for passenger car.
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AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 1
Entwicklungstrends Entwicklungstrends OttomotorOttomotorDaimlerChryslerDaimlerChrysler, Stuttgart 20.April 2004, Stuttgart 20.April 2004
AVL ITC, Technical Seminar
24. April 2007 Dr. Hubert FRIEDL
HighlyHighly AdvancedAdvanced CNG CNG EngineEngineTechnology Technology forfor PassengerPassenger Cars Cars
HigherHigher FuelFuel EfficiencyEfficiency and and lowerlower EmissionsEmissions
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 2
1. Market Trends1. Market Trends
2. Configurations of CNG SI2. Configurations of CNG SI--EnginesEngines
Turbo Charged BiTurbo Charged Bi--FuelFuel Mono Fuel CNG Direct InjectionMono Fuel CNG Direct Injection
3. Conclusion and Outlook3. Conclusion and Outlook
Content of Presentation
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 3
1.Market Trends
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 4
VolvoBMW
MercedesAudi
MazdaNissan
KiaHyundai
HondaSuzukiToyota
VWOpel
SkodaFord
PeugeotSeat
RenaultCitroen
Fiat
European European COCO22
Fleet Fleet DataData200520052012 2012
COCO22 LegislationLegislation as Technology Driver as Technology Driver forfor all all PassengerPassenger Car Brands in EuropeCar Brands in Europe
100 110 120 130 140 150 160 170 180 190 200
COCO22[g/km][g/km]
Extreme pressureto invest into high efficient powertraintechnology as well as to promotealternative fuels
EUROPE
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 5
VolvoBMW
MercedesAudi
MazdaNissan
KiaHyundai
HondaSuzukiToyota
VWOpel
SkodaFord
PeugeotSeat
RenaultCitroen
Fiat
European European COCO22
Fleet Fleet DataData200520052012 2012
100 110 120 130 140 150 160 170 180 190 200
COCO22[g/km][g/km]Super / Super / TurboTurbo--
ChargingCharging
CylinderCylinderDeactivationDeactivation
Variable Variable Charge MotionCharge Motion
GDIGDIStratifiedStratified
Variable Variable ValveValveActuationActuation
ControlledControlledAutoAuto--IgnitionIgnition
ReducedReducedparasiticparasiticlosseslosses
ImprovedImprovedenergyenergy
managemanage--mentment
EnergyEnergyrecoveryrecovery
Start / Start / StopStop
HybridHybrid--izationization
Alternative Alternative FuelsFuels
Technologies Technologies forfor GasolineGasoline EnginesEngines to to complycomply withwith forthcomingforthcoming CO2 CO2 TargetsTargets
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 6
Global PC and LD Vehicle Production by Propulsion Technology
15
30
45
60
75
90
1995 2000 2005 2010 2015
E
n
g
i
n
e
s
p
r
o
d
u
c
e
d
[
m
i
o
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]
DIESEL CHARGEDDIESEL NACNG/LPG/
ALCOHOL/FLEX FUEL
ALTERNATIVE FUELS
GASOLINE GDI
HYBRID
GASOLINE PFIGASOLINE Charged
Source: Global Insight
GasolineGasoline
DieselDiesel
20072007
GDIGDI
chargedcharged
Alternative Alternative FuelsFuels::CNG, EthanolCNG, Ethanol
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 7
0%
20%
40%
60%
80%
100%
S
o
u
t
h
A
m
.
2
0
0
6
E
U
R
O
P
E
2
0
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6
N
A
F
T
A
2
0
0
6
A
S
I
A
2
0
0
6
J
A
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A
N
2
0
0
6
R
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0
6
G
l
o
b
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6
2
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1
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2
0
1
0
2
0
1
0
2
0
1
0
2
0
1
0
2
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1
0
2
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1
5
2
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1
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2
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1
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1
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2
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1
5
2
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1
5
2
0
1
5
Region/Year
M
a
r
k
e
t
S
h
a
r
e
H2/ElectricHybridFlexFuel,Alcohol
CNG/LPGDiesel
Gasoline
Global Vehicle Production by Propulsion Technology
Source: Global Insight, AVL
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 8
2. Configurations for CNG SI-Engines
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 9
Diesel Gaso- Metha- Etha- LPG CNG DMEline nol nol
Chemical Formula (-) C15H28 C7H15 CH3OH C2H5OH C3H9 CH4 C2H6OMolecular Weight (-) 208 99 32 46 45 16 46Carbon Content (%m) 86.1 84.9 37.5 52.2 80.0 75.0 52.2Hydrogen Content (%m) 13.9 15.1 12.5 13.0 20.0 25.0 13.0Oxygen Content (%m) 0 0 50.0 34.8 0 0 34.8Density Liquid at 20 (kg/l) 0.840 0.740 0.795 0.790 0.540 - 0.668Lower Heating Value (MJ/kg) 42.7 42.5 19.7 26.8 46.0 47.7 28.4Heat of Evaporation (kJ/MJ) 6.0 8.0 56.4 33.8 8.6 - 14.4Octane Rating RON (-) - 95 >110 >100 100 130 -Cetane Number CN (-) 45-55 - - - - - >55CO2 Emission (g/MJ) 74.2 73.3 70.0 71.5 63.8 57.7 67.5
LPG: Liquified Petroleum mGas (50%mass C3H8 + 50% C4H10)
CNG: Compressed Natural Gas (mainly Methane CH4)
DME: Dimethylether
Properties of Fuels
Properties of CNG Properties of CNG most attractive most attractive for SIfor SI--Engines !Engines !
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 10
High knock resistance of CNG (RON 120-140) allows high compression ratio, but this leads to higher combustion pressure and higher mechanical loads
Higher ignition energy and different ignition timing compared toliquid fuels
CNG lacks cooling effect unlike other liquid fuels, but due to higher compression ratio the exhaust temperatures are lower
As CNG is gaseous and combustion is without soot formation, special attention has to paid for valve seat material
Max torque with CNG occurs very close to =1 and enrichment / leaning leads to drop in torque
Power drop in CNG 10 ~ 12 % (due to lower volumetric efficiency) Lean burn power drop 20 ~ 30% (partially compensated by turbocharging)
CNG in Combustion Process
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 11
Bi Bi fuelfuel
(Petrol or Gas)(Petrol or Gas)
Stoichiometric Stoichiometric ( ( == 1)1)
SI Spark IgnitionSI Spark Ignition
Lean burn ( Lean burn ( > 1)> 1)
Mono fuel Mono fuel
(Optimized for gas)(Optimized for gas)
Most common solutionMost common solution
Development Paths for CNG SI-Engines
Potential for higher Potential for higher fuel efficiencyfuel efficiency
Turbo ChargingTurbo Charging
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 12
Bi-Fuel vs. Dedicated Mono-Fuel CNG Engines
High compression ratio CH4 optimized catalyst CH4 optimized lambda control CH4 tolerant O2 sensors One set of fuel injectors Pressure regulator instead of
fuel pump
Monofuel PC gas engines
Knock limited CR (for gasoline) is compromising thermal efficiency
Gasoline optimized catalyst Lambda control optimized for
gasoline
Cold start usually with gasoline Two sets of fuel injectors and dual
tank infrastructure required
Bi-fuel PC gas engines
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 13
2.1 Turbo Charged Bi-Fuel Application
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 14
Development Tasks: Integration of CNG fuel system adapt mechanical system for specific
requirement when running engine with CNG (e.g. valve seat rings)
Key Tasks and Challenges for Turbo-charging Bi-Fuel CNG Engine
Challenges: provide similar power and torque for
CNG as with gasoline fuel
Fulfill stringent emission standards (ULEV, Euro 5) even maintaining with gasoline dedicated exhaust aftertreatment
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 15
BOSCH Natural Gas System (BiBOSCH Natural Gas System (Bi--Fuel)Fuel)
Source: Robert BOSCH GmbH, GS/EVP
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 16
Integration of CNG Fuel System to Engine
A combined CNG / gasoline fuel rail was designed for optimized packaging
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 17
Full Load Performance of 2.0L Turbo Engine CNG compared to Gasoline Fuel
0
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Engine speed [rpm]
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]
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P
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[
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]
CNG Torque [Nm]
Gasoline Torque [Nm]
CNG Power [kW]
Gasoline Power[kW]
Low end torque is lower onCNG compared to Gasoline.
CNG calibrated to 125kWGasoline std calibration 135kW
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 18
TEMPERATURES, PRESSURESCNG compered with gasoline at full load
0,1
0,2
0,3
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0 1000 2000 3000 4000 5000 6000 7000Engine [rpm]
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Full Load Conditions of 2.0L Turbo Engine CNG compared to Gasoline Fuel
Gasoline P Plenum
CNG P PlenumGasoline Cat 1 endCNG Cat 1 end
Catalyst Temperature Limit 950 C
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 19
Measures to reduce Exhaust Temperatures Measures to reduce Exhaust Temperatures with Turbowith Turbo--charged CNG Enginescharged CNG Engines
Integrated Exhaust ManifoldIntegrated Exhaust Manifold
Water Cooled Turbine
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 20
Slightly reduced power (7,5%) in CNG operation with 2.0L engine due to compromised layout for gasoline
Equalizing of performance gap to gasoline fuel operation feasible with higher compression ratio and further secondary measures (integrated exhaust manifold, cooled turbine)
Euro 5/ULEV Emission limits achieved in CNG operation due to optimized catalyst design and by calibrating lambda control as well as transient A/F control.
Results for Turbo charged Bi-FuelCNG Application Project
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 21
2.2 Mono Fuel CNG Direct Injection
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 22
Key Features of CNG Direct Injection Combustion System Application
Engine Capacity 450 ccm/cylinder
Compression ratio: 1:13
Injector: AVL proprietary DMI-Injector (Piezo Injector as Option)
CNG System Feed Pressure: 12 bar
Standard CNG pressure regulator and CNG system components as commercially available
Operation with homogeneous (=1) and stratified lean (>1) air/fuel ratio
Such dedicated system is able Such dedicated system is able to utilize the full potential and to utilize the full potential and advantages of CNG Fuel ! advantages of CNG Fuel !
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 23
CNG-supply
CNG / Mixture chamber (for pure CNGoperation and DMI operation)
Nozzle (different geometries)
HP-oil supply
solenoid valve
Actuation piston
Lift adjustment (0.6 and 0.3mm variant)
Oil leakage draining
CNG - DI Injector for combustion development(AVL Research Injector, no series product)
Key Features of CNG Direct Injection Combustion System Application
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 24
Principle of stratified CNG-DI Combustion Process
TDC
Swirl charge motion of intake air supports stratification of mixture cloud
[m2/s2]0.0 100
Turbulent Kinetic Energy
20 CA bTDC20 CA bTDC
CFD simulation shows toroidal rotation of mixture cloud
Key Features of CNG Direct Injection Combustion System Application
Central Injector Position, spark plug close to injector tip
Piston Bowl design for Wall-guided Mixture Formation
High turbulence due to gas-jet
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 25
CNG - DI Combustion CFD Simulation
CFD- Simulation for mixture formation in stratified and homogeneous operation (2000rpm / 3bar IMEP)
5 DEG CRA bTDC
x
y
30 DEG CRA bTDC
z
z
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x
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30 DEG CRA bTDC
z
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5 DEG CRA bTDC
y
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x
z
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Homogeneous early injection, A/F 1.0Stratified late injection, A/F 2.6Spark Plug
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 26
2000rpm / 3bar imep - isfc [g/kWh]
MFB 50% [deg CA aTDC]SO
I [deg
CA bT
DC]
isfc - OPT:SOI.....63 deg CA bTDCEGR...20 %MAP...810 mbarIGN....19 deg CA bTDC
Restrictions:CoV < 3 %isNOx < 3 g/kWh
i
s
f
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[
g
/
k
W
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]
201 g/kWh
2000rpm / 3bar imep - CoV [%]
MFB 50% [deg CA aTDC]SO
I [deg
CA bT
DC]
C
o
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[
%
]
3%
isfc - OPT
isfc - OPT:SOI.....63 deg CA bTDCEGR...20 %MAP...810 mbarIGN....19 deg CA bTDC
Restrictions:CoV < 3 %isNOx < 3 g/kWh
2000rpm / 3bar imep - isNOx [g/kWh]
MFB 50% [deg CA aTDC]SO
I [deg
CA bT
DC]
isfc - OPT:SOI.....63 deg CA bTDCEGR...20 %MAP...810 mbarIGN....19 deg CA bTDC
Restrictions:CoV < 3 %isNOx < 3 g/kWh
i
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]
3 g/kWh
isfc - OPT
2000rpm / 3bar imep - isHC [g/kWh]
MFB 50% [deg CA aTDC]SO
I [deg
CA bT
DC]
isfc - OPT:SOI.....63 deg CA bTDCEGR...20 %MAP...810 mbarIGN....19 deg CA bTDC
Restrictions:CoV < 3 %isNOx < 3 g/kWh
i
s
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C
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g
/
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]
14 g/kWh (at isfc - OPT)
Stratified CNG-DI: Very stable Operation (Part Load Optimisation with DoE)
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 27
Combustion simulation with different operation strategies in part load
The 3D-CFD combustion simulation shows the same tendency regarding combustion speed as the measurements. Due to the turbulence introduced by the DI-gas-jet the combustion speed increases significantly with late injection.
Heat release curves for different combustion strategies(CFD Simulation)
-1,0
0,0
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Crank Angle [deg CA]
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]
Homogeneous early - CFD Simulation
Homogeneous late - CFD Simulation
Stratified lean - CFD Simulation
Heat release curves for different combustion strategies(Measurement)
-1,0
0,0
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2,0
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-40 -30 -20 -10 0 10 20 30 40 50 60
Crank Angle [deg CA]
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Homogeneous early - Measurement
Homogeneous late - Measurement
Stratified lean - Measurement
Homogeneous early
Homogeneous late
Stratified lean
Flamefront 20deg CA after Ignition
CNG - DI Combustion CFD Simulation
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 28
0%
20%
40%
60%
80%
100%
Combustion Efficiency CO2 Emission
Homogeneous Gasoline DI
Homogeneous CNG DI
Stratified lean with EGRCNG DI
-40%-25%
Part Load: 2000 rpm3 bar IMEP
Improvement Potential for CNG Direct Injectioncompared to stoichiometric homogeneous GDI
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 29
Part load:Part load: The CNG The CNG -- DI combustion system shows 25% better efficiency DI combustion system shows 25% better efficiency
compared with homogeneous compared with homogeneous stoichiometricstoichiometric combustioncombustion Compared to homogeneous Compared to homogeneous stoichiometricstoichiometric combustion with combustion with
gasoline a CO2 reduction of more than 40% is possible due to gasoline a CO2 reduction of more than 40% is possible due to beneficial H/C ratio of CNGbeneficial H/C ratio of CNG
Full Load:Full Load: Reduced volumetric efficiency as it is known from manifold gas Reduced volumetric efficiency as it is known from manifold gas
injection can be fully compensated by late direct injection (aftinjection can be fully compensated by late direct injection (after er intake closing), which results in +12% charge mass in cylinderintake closing), which results in +12% charge mass in cylinder No necessity for spark retardation due to high knock resistance No necessity for spark retardation due to high knock resistance
of CNG, possibility to use a CR of 13, which gives 13% higher of CNG, possibility to use a CR of 13, which gives 13% higher efficiency in low end WOT compared to gasoline operationefficiency in low end WOT compared to gasoline operation Together with the beneficial H/C ratio of CNG also at full load Together with the beneficial H/C ratio of CNG also at full load a a
CO2 advantage of more than 30% is possibleCO2 advantage of more than 30% is possible
Results Achieved for CNG Direct Injection
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 30
3. Conclusion and Outlook
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 31
CNG is highly attractive fuel for vehicles and will become more CNG is highly attractive fuel for vehicles and will become more important due to the demand of CO2 reduction and have less important due to the demand of CO2 reduction and have less dependency on crude oildependency on crude oil
BiBi--fuel vehicles represent a short term solution to introduce fuel vehicles represent a short term solution to introduce CNG into the market on bigger scaleCNG into the market on bigger scale
CNG in combination with turbo charging reduces power gap CNG in combination with turbo charging reduces power gap compared to gasoline operation by achieving better volumetric compared to gasoline operation by achieving better volumetric efficiency, and turbo charging opens door for downsizing and efficiency, and turbo charging opens door for downsizing and achieving higher fuel efficiencyachieving higher fuel efficiency
New monoNew mono--fuel systems and technologies (e.g. Direct Injection) fuel systems and technologies (e.g. Direct Injection) are under development to utilize even more advantages of CNG are under development to utilize even more advantages of CNG operation for passenger cars in near futureoperation for passenger cars in near future
Conclusion and Outlook
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 32
ThankThank youyou veryvery muchmuchforfor youryour kindkind attentionattention !!
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 33
Abbreviations (1/2)
A/F Air-/Fuel Ratio of Mixture (Lambda)
CA Crank Angle
BMEP Brake Mean Effective Pressure
CNG Compressed natural Gas
CR Compression Ratio
DI Direct Injection
DeNOx Nitrogen oxide reducing catalyst
DMI Direct Mixture Injection (Air + Fuel pre-mixed)
DoE Design of Experiments
EGR Exhaust Gas Recirculation
EURO5 European Emission Limit Stage 5
FE Fuel Economy
FTP Federal Test Procedure (USA)
GDI Gasoline Direct Injection
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 34
Gen.1 Generation 1 (first development stage of engine technology)
HSDI High Speed Direct Injection (Diesel)
IMEP Indicated Mean Effective Pressure
LDV Light Duty Vehicle
LPG Liquified Petrol Gas
NA Naturally Aspirated
NEDC New European Driving Cycle
PC Passenger Cars
PFI Port Fuel Injection
ROW Rest of the World
SI Spark Ignition
SULEV Super Ultra Low Emission Vehicle
TWC 3-Way Catalyst
ULEV Ultra Low Emission Vehicle
Abbreviations (2/2)
AVL ITC 24.4.2007, Advanced CNG Engine Technology Page 35
Global PC and LD Vehicle Production by Propulsion TechnologyGlobal Vehicle Production by Propulsion TechnologyCNG in Combustion ProcessAbbreviations (1/2)Abbreviations (2/2)