Upload
others
View
15
Download
0
Embed Size (px)
Citation preview
Fuel Utilization in Advanced Spark-Ignition Engines
Kai J. Morganti, Ph.D.
Fuel Technology R&D Division, Saudi Aramco R&DC
Dhahran, Saudi Arabia
KAUST Future Fuels Workshop
March 7 – 9, 2016
Thuwal, Saudi Arabia
2
Presentation Overview
1. Background
2. Snapshot of the Light-duty Vehicle Fleet: 1975 – 2014
3. Fundamentals of the “Downsize and Boost” Strategy
4. Implications of Modern Engine Designs on Fuel Utilization
5. Where are Future Vehicle Efficiency Gains Likely to be Found?
- Can we better leverage petroleum-derived fuels to enable additional gains?
- How is this likely to impact lifecycle CO2 emissions?
6. Summary and Questions
Fuel Technology R&D Division.
Copyright 2016, Saudi Aramco. All Rights Reserved.
3
Background
1Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
4
Reciprocating engines will remain attractive for achieving cost-effective CO2 mitigation ($/kg CO2)
• Proven technology platform, with cost advantages over competing technologies
• Comprehensive global fuel production and distribution network
• Low cost “bolt-on” technologies will continue to benefit fuel consumption
• Further efficiency improvements are still possible from engine downsizing (with the right fuels)
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Opportunities and Challenges for the Transport Sector
Ford Motor Company
5
Reciprocating engines will remain attractive for achieving cost-effective CO2 mitigation ($/kg CO2)
• Proven technology platform, with cost advantages over competing technologies
• Comprehensive global fuel production and distribution network
• Low cost “bolt-on” technologies will continue to benefit fuel consumption
• Further efficiency improvements are still possible from engine downsizing (with the right fuels)
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Con
trib
utio
n p
er
Ve
hic
le
Vehicle Production Volume
HEV
PHEV
BEV
CO2
Mitigation
IC Engines + Advanced Features
FC
Opportunities and Challenges for the Transport Sector
Evolution on a large scale can be a far more significant contributor than revolution on a smaller scale
6
Snapshot of the US Light-duty Vehicle Fleet: 1975 – 2014
Engine Displacement
Large decline in the 1970s as gasoline
prices increased. Technologies that
enable engine downsizing at equivalent
or enhanced performance have been a
key driver in recent years
Engine Power
Largely driven by consumer preference
for enhanced vehicle performance.
Increased power output is also often
required to offset an increase in the
vehicle mass
Average Specific Power
Power density has continued to increase
since 1975. This trend may not continue
in the future due to the competing
demands of regulators, automakers,
consumers and fuel producers
Fuel Technology R&D Division.
Copyright 2016, Saudi Aramco. All Rights Reserved.
LDVs have evolved significantly since 1975, with these changes driven by a range of factors
• Corporate Average Fuel Economy standards (US) and other environmental regulations
• Consumer preference for both performance and fuel economy
US Environmental Protection Agency, “Light-Duty Automotive Technology, Carbon Dioxide
Emissions, and Fuel Economy Trends: 1975 Through 2014,” Washington, DC (2014)
7
Snapshot of the US Light-duty Vehicle Fleet: 1975 – 2014
Fuel Technology R&D Division.
Copyright 2016, Saudi Aramco. All Rights Reserved.
Efficiency gains have enabled power to increase at a faster rate than fuel consumption
• Widespread adoption of turbocharged engines has been a key driver of recent efficiency gains
• This is despite more stringent vehicle safety continuing to be a “headwind” for fuel consumption
“Improvements over time have resulted in impressive performance, fuel economy and CO2 emissions”
8
Fundamentals of the “Downsize and
Boost” Strategy
2Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
9
Limitations on Spark-Ignition Engine Efficiency
Brake Thermal Efficiency
Higher fuel anti-knock quality is only
useful when the engine is knock-limited
at higher load
Combustion Phasing (CA50)
Fuels with higher anti-knock quality
enable higher loads to be attained
before spark retard must be applied
Fuel Enrichment (λ)
Used for hardware durability purposes to
maintain TWC/turbine within temp limits.
Since λ<1, TWC conversion efficiency is
significantly degraded and the excess fuel
energy is wasted
Fuel Technology R&D Division.
Copyright 2016, Saudi Aramco. All Rights Reserved.
Spark-ignition engine efficiency is constrained by different factors at low and high load
• Pumping losses at low load from throttling
• Spark retard at high load prevents knock, but significantly degrades efficiency and torque capability
Example of loads sweeps at 2000 rpm, three different liquid fuels (RON 91, 96 and 101)
CR 10:1
Adapted from Leone et al., SAE Int. J. Fuels Lubr. 7(1):2014
10
Limitations on Spark-Ignition Engine Efficiency
Fuel Technology R&D Division.
Copyright 2016, Saudi Aramco. All Rights Reserved.
Spark-ignition engine efficiency is constrained by different factors at low and high load
• Pumping losses at low load from throttling
• Spark retard at high load prevents knock, but significantly degrades efficiency and torque capability
These factors can be observed in the brake specific fuel consumption (BSFC) map
• Load limit will vary with fuel anti-knock quality, compression ratio, degree of spark retard/enrichment, etc.
spark retard spark retard + enrichment
11
Naturally aspirated PFI engines can be very efficient, but only within a narrow operating range
• Pumping losses at low load from throttling
• Spark retard and enrichment at high load to prevent knock and maintain hardware durability
Modest specific power (~50 kW/L) with good minimum BSFC, but the fuel consumption is only favorable
at high engine loads
How can Turbocharging Improve Vehicle Fuel Economy?
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
BMEP vs RPMBSFC vs BMEP: 2000 rpm
Efficiency degraded due
to spark retard and then
fuel enrichment
12
Boosting the engine (and adding fuel) enables higher loads to be attained
• Pumping losses can be mitigated by operating at higher loads where throttling is reduced
• Nonetheless, spark retard and enrichment are still required at high load
Specific power increased by 60% (~80 kW/L) while maintaining a good minimum BSFC. The fuel
consumption is also favorable over a much wider range of engine loads
How can Turbocharging Improve Vehicle Fuel Economy?
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
BMEP vs RPMBSFC vs BMEP: 2000 rpm
13
The engine is typically downsized to match the power of a larger naturally aspirated engine
• Rule of thumb is 30% reduction in displacement, e.g. V6 → I4
• Shifts the region of good BSFC into the area of high utilization
Excess torque can be used for downspeeding (lower gear/axle ratios) or using the engine in a larger vehicle
How can Turbocharging Improve Vehicle Fuel Economy?
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Torque vs RPM
14
The “downsize and boost” strategy allows the vehicle to be operated more frequently at the
most efficient operating conditions
• Performance envelopes for Class E vehicle equipped with two different powertrains (US06 drive cycle)
- 2.5 L naturally aspired engine
- 1.6 L turbocharged engine (downsized at equivalent performance)
Implications of Modern Engine Designs on Fuel Utilization
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
However, the traditional constraints on
operating the engine at high load still remain…
• Engine becomes more frequently knock-limited
• Average fuel octane requirement increases
• Since efficiency is degraded approaching the
load limit, too much downsizing can increase
the specific fuel consumption
- “Downsizing” vs “Rightsizing”
15
Where are Future Efficiency Gains
Likely to be Found…?
3Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
16
Future efficiency gains will be derived from continuing to operate the engine more frequently
in regions of the load-speed map that provide favorable BSFC
1. Reduce or eliminate engine operation at low loads → powertrain design
2. Increase the frequency of engine operation at high loads → powertrain + fuel design
3. Expand the favorable BSFC region of the load-speed map → powertrain + fuel design
Where are Future Efficiency Gains Likely to be Found…?
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
17
Future efficiency gains will be derived from continuing to operate the engine more frequently
in regions of the load-speed map that provide favorable BSFC
1. Reduce or eliminate engine operation at low loads → powertrain design
2. Increase the frequency of engine operation at high loads → powertrain + fuel design
3. Expand the favorable BSFC region of the load-speed map → powertrain + fuel design
Where are Future Efficiency Gains Likely to be Found…?
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Advantages Disadvantages
Advanced “bolt-on” features
Cylinder deactivation
Start-stop systems
Cost, shifts operation to higher loads
Cost, eliminates some low load operation
Increases average octane requirement, NVH limitations
Benefits not always realized, e.g. using air-conditioning
HybridizationEliminates low load operation (extent varies
depending on the degree of hybridization)
Generally more costly than a downsized engine with
advanced features, with fuel economy benefits dependent
upon vehicle size, driving conditions, etc.
Extreme engine downsizing
with turbocharging and
downspeeding
Cost, shifts operation to even higher loads that
can provide improved efficiency
Light-duty diesel engine structure required (200 bar)
Increases average octane requirement, with benefits only
realized if adequate fuel anti-knock quality is available
Supercharging or advanced controls required to enhance
low speed torque, with the latter constrained by durability
Miller/Atkinson cycle with
high geometric CR
(“Rightsizing”)
Cost, high geometric CR improves efficiency at
low and intermediate loads, thereby expanding
the favorable BSFC region
Vehicle performance is degraded due to the lower engine
load attained at the knock limit
Fuel Design
Higher anti-knock quality fuels are generally an
enabler for the above technologies
Increase the high load limit and potential to expand
the favorable BSFC region
Refinery octane addition can be costly/energy intensive
High octane fuels with lower volumetric energy densities
need to be utilized appropriately
18
How Can the Fuel be an Enabler for
Lower Vehicle Fuel Consumption…?
4Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
19
Higher octane fuels generally enable the factors that degrade efficiency to be shifted to higher
engine loads. But does this always expand the favorable BSFC region…?
No… the increase in efficiency must offset the additional fuel consumption that enables higher loads
Efficiency vs. Fuel Consumption: Higher Octane Fuels
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Extreme case: most efficient
conversion of fuel into effective
work, and yet higher overall
volumetric fuel consumption
Leone et al., SAE Int. J. Fuels Lubr. 7(1):2014
20
Two tanks – Two fuels
One potential Octane-on-Demand configuration
Octane-on-Demand uses two fuels to attain only the necessary level of fuel anti-knock quality
based on the real-time engine requirements
• Lower octane fuel (RON ~70 - 90)
- Ideally provides a high energy density and
moderate anti-knock quality for urban driving
- Examples: lower octane gasolines, refinery blendstocks
• High octane fuel (RON ~105 - 110)
- Only used to extend the performance envelope
of the lower octane fuel, when required
- Examples: methanol, ethanol, butanol, bio-ETBE
Copyright 2016, Saudi Aramco. All Rights Reserved
‘Leveraging’ to Improve Petroleum-Derived Fuel Utilization
Can the favorable BSFC region be further expanded by instead ‘leveraging’ a high octane fuel
to improve the engine’s utilization of the petroleum-derived fuel…?
• Leverage only when necessary, rather than just displacing
• Avoid degrading the volumetric energy density at low and intermediate loads, where high
fuel anti-knock quality provides few benefits
Fuel Technology R&D Division
21
Copyright 2016, Saudi Aramco. All Rights Reserved
‘Leveraging’ to Improve Petroleum-Derived Fuel Utilization
Can the favorable BSFC region be further expanded by instead ‘leveraging’ a high octane fuel
to improve the engine’s utilization of the petroleum-derived fuel…?
• Leverage only when necessary, rather than just displacing
• Avoid degrading the volumetric energy density at low and intermediate loads, where high
fuel anti-knock quality provides few benefits
CA50 and λ held constant with increasing load – no spark retard or fuel enrichment
Fuel Technology R&D Division
Refinery Blendstock (RON 90) + Methanol Utilization of the ‘Leveraging’ Fuel
Incre
asin
g H
igh O
cta
ne
Fuel U
tiliz
ation
22
Copyright 2016, Saudi Aramco. All Rights Reserved
‘Leveraging’ to Improve Petroleum-Derived Fuel Utilization
Since the high octane fuel acts as the primary means of load extension…
• The new BSFC constraint becomes the tradeoff between higher rates of fuel consumption
and the efficiency increase that this can enable via further load extension
- This tradeoff varies with the fuel properties (∆hvap, LHV, RON, etc)
The traditional durability constraints at high load are eliminated independent of BSFC → shifts to a peak
cylinder pressure constraint (rather than exhaust temperature)
Fuel Technology R&D Division
Combined BSFC by Volume
Differences due to
fuel properties
23
Potential Implications for Vehicle Fuel
Consumption and Lifecycle CO2
Emissions
5Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
24
Drive cycle simulations for a 1600 kg vehicle with 1.6L downsized engine
• Three base fuels: Naphtha (RON 61 and 75) and refinery blendstock (RON 90)
• Preliminary vehicle simulation results indicate fuel economy benefits of up to 8% relative to
the same vehicle operated on gasoline (RON 95)
- Outcome is sensitive to both the fuel properties and drive cycle characteristics
Copyright 2016, Saudi Aramco. All Rights Reserved
WLTP Drive Cycle US06 Drive Cycle
Fuel Technology R&D Division
Potential Implications for Vehicle Fuel Consumption
+2%
-8%
(RON 61) (RON 75) (RON 90) (RON 61) (RON 75) (RON 90)
Morganti et al., SAE Paper 2016-01-0683 (2016)
25
Life Cycle Assessment (LCA) can be used to assess the broader environmental impact
• Well-to-Tank CO2 emissions estimated using the GREET model
• Tank-to-Wheel CO2 emissions obtained from vehicle drive cycle simulations
Alternative feedstocks can be used to produce most fuels, and this affects the carbon intensity
• Gasoline: Conventional Petroleum (baseline case)
• Naphtha: Conventional Petroleum or Natural Gas
• Methanol: Natural Gas or Coal
Well-to-Wheel CO2 Emissions Breakdown
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Morganti et al., SAE Paper 2016-01-0683 (2016)
26
Extreme lower and upper well-to-wheel CO2 emissions for different feedstocks
• Net 2% increase in well-to-wheel CO2 emissions for highest carbon intensity feedstocks
• Best Case: RON 75 Naphtha (Petroleum) – Methanol (Natural Gas) → -20%
• Worst Case: RON 61 Naphtha (Natural Gas) – Methanol (Coal) → +2%
Well-to-Wheel CO2 Emissions Breakdown
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
FTP-City Drive Cycle FTP-City Drive Cycle
-20%
+2%
(RON 75) (RON 61) (RON 75) (RON 61)
Morganti et al., SAE Paper 2016-01-0683 (2016)
27
Mitigation of CO2 is still almost always possible relative to an equivalent gasoline vehicle, but
the feedstock affects the extent of these benefits
Well-to-Wheel CO2 Emissions Mitigation: FTP-City
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
Net increase
P = Petroleum, NG = Natural Gas, C = Coal Morganti et al., SAE Paper 2016-01-0683 (2016)
FTP-City Drive Cycle
(RO
N 6
1)
(RO
N 7
5)
(RO
N 9
0)
28
Summary and Questions
6Copyright 2016, Saudi Aramco. All Rights Reserved.
Fuel Technology R&D Division.
29
• Reciprocating engines will remain attractive for cost-effective CO2 mitigation ($/kg CO2)
- Evolution on a large scale can be a larger contributor than revolution on a small scale
• Engine improvements over time have resulted in impressive performance, fuel economy
and CO2 emissions
• Recent improvements have been largely driven by downsizing and turbocharging
- Enables the favorable BSFC region to be expanded
- Increases average octane requirement and frequency of knock-limited engine operation
• Future efficiency gains will be driven by continuing to operating engines more frequently in
regions that offer favorable BSFC
- Both powertrain and fuel design can be an enabler for these gains
• Higher octane fuels will be an important factor in future efficiency gains
- ‘Leveraging’ a high octane fuel to improve the engine’s utilization of a petroleum-derived
fuel can enable the favorable BSFC region to be expanded (i.e. Octane-on-Demand)
- Lifecycle CO2 mitigation is also possible, but requires careful consideration of the fuel
production method and feedstock
Summary and Conclusions
Fuel Technology R&D Division
Copyright 2016, Saudi Aramco. All Rights Reserved
30
Acknowledgements
Copyright 2016, Saudi Aramco. All Rights Reserved.
• Yoann Violet, Robert Head → Interpretation of engine data
• Marwan Abdullah → Vehicle drive cycle modeling
• Abdullah Zubail → Life Cycle Assessment (LCA) modeling
• Hassan Babiker and Gautam Kalghatgi → Useful discussions
Fuel Technology R&D Division.
Questions