Fuel Utilization in Advanced Spark-Ignition Engines · Fuel Utilization in Advanced Spark-Ignition...

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.


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)



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



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



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



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



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



Spark-ignition engine efficiency is constrained by different factors at low and high load


• 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


• 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?



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




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




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



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…?



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…?



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…?



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…?



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



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


‘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


21



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


Refinery Blendstock (RON 90) + Methanol Utilization of the ‘Leveraging’ Fuel

Incre

asin

g H

igh O

cta

ne

Fuel U

tiliz

ation

22



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)


Combined BSFC by Volume

Differences due to

fuel properties

23

Potential Implications for Vehicle Fuel

Consumption and Lifecycle CO2

Emissions



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


WLTP Drive Cycle US06 Drive Cycle


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




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



FTP-City Drive Cycle FTP-City Drive Cycle

-20%

+2%

(RON 75) (RON 61) (RON 75) (RON 61)


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



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



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



30

Acknowledgements


• 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


Questions

[email protected]

Fuel Utilization in Advanced Spark-Ignition Engines · Fuel Utilization in Advanced Spark-Ignition...

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