Quantifying Platoon Fuel Savings: 1999 Field Experiments

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Quantifying PlatoonFuel Savings1999 Field
Experiments
Drivers Benedicte Bougler Dan Empey Pushkar
Hingewe Xiao-Yun Lu David Nelson Han-Shue Tan

• By Mark Michaelian and Fred Browand
• University of Southern California

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Motivation/Overview

• 1999 Field Experiments included
• Accurate measurements of instantaneous fuel
  consumption
• Up to 10 fuel savings as result of platooning
• Previous USC windtunnel experiments have shown
  quantitative drag info on individual cars in
  platoons.
• How does this drag information compare to real
  cars on the real highway?

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Test Procedures

• Utilized 2.4km section of I-15 freeway HOV lanes
  from 930AM-130PM.
• Topography - 12m elevation rise - thus testing
  included going both directions.
• Measured temperature and wind speed on test
  segment.
• Safety protocols followed.

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Test Protocols

• Single vehicle tests (indivdual vehicle
  baseline).
• Platoon tests at 3m, 4m, 5m, 6m separations.
• 22 separate round trips.
• Some results averaged over 2 or more
  realizations, some are single realization.

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Data Acquisition/Reduction

• 30 engine parameters stored - eng. fuel inj.,
  eng. RPM, veh. speed, abs. marker pos., intake
  manifold press., brake press. - most important
  for this study.
• Data sampled at 100Hz (time).
• Signals vs. abs. position interpolated to
  2000pt. Grid (2.4km) smoothed w/ cubic spline.

Forward speed
Engine RPM
Fuel injector pulse width
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Fuel expenditure expression

• Fuel expended rate of fuel usage
• C1 ? grams fuel delivered during single pulse ?
  pulse width (PW)
• Buick LeSabre injector, C1 0.002826 gm/ms
• Results expr. as ratio of platoon fuel
  consumption to indiv. fuel consumption.
• Ratio independent of C1, C2
• graciously provided by Andy Degner, Delphi
  Automotive Systems

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Individual car fuel consumption (single vehicle)

• 25 difference between South-to-North runs and
  North-to-South runs using full 2.4km test
  circuit, 10 for 1.8km circuit w/o steepest road
  slope.
• Trip averages virtually identical! (0.1)
• Fuel consumption independent of particular path.

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Fuel consumption reliablility estimate
1.2
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Individual car fuel consumption(in platoon)

• Fuel consumption savings in platoon DO NOT depend
  on particular round-trip path chosen.

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Fuel consumption as a matter of position in
platoon

• Interior vehicles gain most benefit from
  platooning
• Interior cars consume 10 less fuel _at_ closest
  spacing
• Trailing vehicle saves 7 _at_ closest spacing
• Extrapolating to gaps consumes less fuel than trail vehicle!
• Drag behavior qual. consistent w/ prev. expts.

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Average fuel consumption as function of spacing
fraction of vehicle length

• Vehicle separation normalized by vehicle length
• Predictions based on EPA Highway Driving Cycle
• Optimal based on prev. windtunnel studies using
  Lumina vans
• Overestimate

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Average fuel consumption as function of spacing
fraction of sq. root of frontal area

• Vehicle separation normalized by the square root
  of the vehicle frontal area
• Flow within gap controlled by size and shape of
  cross section locally
• Still an overprediction

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Average fuel consumption as function of spacing
fract. sq. rt. front. area below window

• Vehicle separation normalized by the square root
  of the frontal area below the windshield
• Assume aero. Flow in gap deter. By effective
  frontal area
• Closer overall agreement
• Geometrically averaged

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Conclusions

• Fuel injector signals give inst. fuel
  consumption,
• Round trip measurements important, fuel
  consumption not roadway path dependent
• Platooning gives drag savings of up to 10 (3
  vehicles _at_ 3m gap)
• Interior vehicles - best fuel savings, front veh.
  surpasses trail veh. _at_ 1.5-2m
• Square root of frontal area below windshield best
  length scale - shows closest agreement with
  windtunnel observations

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Platoon - 2 cars
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Platoon - 4 cars