Power Consumption in Transportation To this point in the class, we've talked about: Electrical science "The Grid" Power Production technologies, including:

Power Consumption in Transportation

To this point in the class, we've talked about:

Electrical science

"The Grid"

Power Production technologies, including:

Alternative means of producing power

Total resource costs of that power

The surprisingly strong need for energy storage

The quirks of attaching renewable power sources to the grid

Possible breakthroughs in power production

Today we finally turn to Power Consumption

An Introduction to Sustainable Energy Systems: www.virlab.virginia.edu/Energy_class/Energy_class.htm

World per capita energy consumption:

From the International Energy Agency (2003):

http://en.wikipedia.org/wiki/List_of_countries_by_energy_consumption_per_capita

For perspective, an abbreviated bar graph: Or, in rank order:

Some lower ranked but affluent industrial economies:

Germany 4003.3

France 4030.5

Japan 3898.4

More quantitatively:


(World Bank 2011)

We North Americans are profligate energy consumers

But, yes, our Canadian neighbors have hung right in there with us!

We're in a club whose other members are either the world's oil producers

Or where something really strange is going on:

Iceland: Cold as heck + most abundant/cheap geothermal in the world?

Finland: Damn cold (=> saunas?), but how on earth can they afford it?

Trinidad and Tobago: I haven't a clue

So not only are we the climate change bad guys

But maintaining our economy and lifestyle is going to be particularly difficult

E.G., about 75% more difficult than for even economic leader, Germany!

Message received?


And are THEY the big culprits? For example "they" = the military industrial complex

Or some other "they" over which you feel almost no personal control?

Or are WE the big culprits?

We humble U.S. citizens in our apartments & 3 BDRM homes

The U.S. Energy Information Agency's Breakdown (as of 2014):

SupplyConsumption

So how do we in the U.S. consume so much energy?

Source: EIA 2014 - http://www.eia.gov/todayinenergy/detail.cfm?id=16511&src=Total-b1

Converting the consumption end to an easier to read pie chart:

(also omitting the EIA's embarrassing use of antiquated BTU units)

Exports (fuels): 12.01%

Commerce: 17.93%

Residential: 21.13%

Transportation: 27.01%

Industrial: 31.48%

Industry + Commerce = 45%

No big surprise

Residential + Transportation = 44%

Big Surprise! / Big Deal!

http://news.thomasnet.com/IMT/2012/03/12/the-damage-done-gas-addiction-edition-how-detrimental-is-petrol/

But is that really about me (personally)?

The 21.13% residential figure is certainly all about your personal choices

And as for how the 27.01% transportation figure breaks down

Plotted from 2009 EIA data:Whoops!

59.7% = "Light Vehicle"

= You and Me (directly!)

Plus 7.7% Air

Probably still pretty much us directly

Plus 22.1% Truck

Us directly/indirectly

Pogo, by Walt Kelly, Post Hall Syndicate

As immortalized in the 1971 Earth Day comic strip Pogo, by Walt Kelly:

The complete strip of that day:

Even more iconic for older Americans: Images from the "Gas Crises"

President Carter's "sweater" speech: New national speed limit:

The seemingly incontrovertible messages (loathed by many Americans to this day):

Energy Conservation = Being cold

Energy Conservation = Going really slow

Yes, if (absent foresight) you must cut your energy consumption right now!

But DO note that above was the latest in decade long series of gas crises!


However, (at least in the U.S.) cold and slow aren't really required:

Because in the last century we got really used to being a big energy producer

Not just in isolated TX or PA oilfields, but in even "downtown" LA !

Long Beach CA Venice CA

Signal Hill CA Beverly Hills High School Placentia CA

Photos from: http://www.theatlantic.com/photo/2014/08/the-urban-oil-fields-of-los-angeles/100799/

Which led us to becoming really great . . .. well . . . energy wasters

Which, ironically, means that we now have an exceptionally large number,

of often painless (or almost painless) ways

in which we can drastically reduce our energy consumption

While not only remaining warm, but living in more comfortable homes

While still driving quickly, alone, in our big cars

While personally saving a lot of money doing this

While simultaneously creating jobs

While stimulating our economy

Indeed, reducing energy consumption is easy compared to increasing production!

Photos from: http://www.theatlantic.com/photo/2014/08/the-urban-oil-fields-of-los-angeles/100799/

http://news.thomasnet.com/IMT/2012/03/12/the-damage-done-gas-addiction-edition-how-detrimental-is-petrol/

Today let's focus on transportation (with a later lecture on housing):

Look again at that plot of U.S. energy consumption in transportation:

As engineers our first instinct is to dive into efficiencies

Especially efficiencies of things affected by our engineering field

But for maximum impact, we must address technologies using the most energy

Regardless of whether they are now efficiency winners or losers


So focusing on impact:

For best perspective we might convert above data to "per-ton" or "person-mile"

But even without such corrections, the message is crystal clear:

Don't focus on buses or trains - They are doing just fine!

Shipping (despite turbulent wakes) also looks pretty damned good

So we can't just blame it all on importing too much from China

And I don't know what can be done to improve pipelines

As turbulence and oil/fuel viscosity are hard to beat

And vehicular transport alternatives (below) are hugely worse

Leaving us with the inescapable baddies: Cars, Trucks and Planes

So how could you improve the efficiency of automobiles?

The list of possibilities is very long

And it can be very hard to sort which ideas offer the greatest impact

Especially as many of those ideas are just that: ideas

Or are clouded by marketing hype

But there's one sure way of gaining perspective: Old fashioned Newtonian Physics

It can't tell us what technology will achieve

But it will tell us what technology cannot possibly achieve

So to identify mechanisms and limits, I am going to follow our textbook's lead

And do some calculations on both auto and airplane physics

Which, even if you studied the book's technical chapters,

Might still be helped by a little review and clarification


The physics of automobile transportation:

CASE 1) City driving (stop and go)

Here power goes mostly into the car's own kinetic energy

Which is SPENT on every acceleration, then LOST on every braking

Approximate the car's city driving (stop and go) as:

Driving a distance d, at velocity vcity, stopping, then all of this repeating

Ignoring lesser energy losses to air resistance and rolling friction

In each of those intervals, fuel energy goes into kinetic energy of:

Ekcar_kinetic = ½ Mcar vcity 2

It spends that much energy (getting going) once every time interval = d / vcity

So average power (energy/time) = Pcity = Mcar vcity 3 / 2 d

So how do you increase car's city driving efficiency?

Answers are going to come right out of: Pcity = Mcar vcity 3 / 2 d

1) Slow down (reduce vcity)

2) Find route with fewer stop signs / stop lights (increase d)

3) Decrease car's weight:

Buy a smaller car ("But that's downright un-American!!")

AND/OR buy a car built using lighter materials

Electric car's heavy batteries are going to be a problem!

4) Don't throw kinetic energy away every time you stop!

That is, rather than heating brake discs/shoes, RECAPTURE that energy

Its called "Regenerative Braking" - I'll come back to this a bit later


CASE 2) Highway driving:

The interval between accelerations is now vastly stretched out

Diluting the (acceleration) kinetic energy expenditures of CASE 1

Dominant energy loss then becomes the loss to air friction (a.k.a. "drag")

That is, passage of car accelerates a volume of air up to almost the car's speed:

=> Transferring kinetic energy to individual air molecules

Volume then gradually slows and expands, as Ekinetic of 1st air molecules

is then shared with vastly larger number of air molecules Car image from: www.clipartlord.com/category/transportation-clip-art/

Energy loss to drag can be modeled as follows:

Consider cylinder of air dragged immediately behind car

It will attain almost the car's velocity

But its cross-section will depend on car's streamlining

Better streamlining, less air accelerated => smaller cross-section (A):

Aair = cdrag Acar That is, it will be car's frontal cross-section x cdrag

With cdrag likely being < 1 and decreasing with streamlining

Behind car, in time t, will be accelerated air volume = Aair (vcar t). Moving at ~ vcar

Then, for air of density rair, can calculate that air's gained kinetic energyAn Introduction to Sustainable Energy Systems: www.virlab.virginia.edu/Energy_class/Energy_class.htm

Kinetic energy gained by car's trailing cylinder of air:

Eair_kinetic = Edrag = ½ Mair vair 2 = ½ rair (volume of air) vair

2 which becomes

= ½ rair (Aair vcar t ) vair2 = ½ rair (cdrag Acar vcar t ) vair

3

Power = Energy / time = (equation above) / t: Pdrag = ½ rair cdrag Acar vair

3

From this, how do you increase car's highway efficiency?

1) Slow down

Reduce vair

2) Reduce the car's drag

By reducing cdrag (involving the shape of the car)

Or by reducing Acar (involving the size of the car)


Two ways of reducing a car's drag:

1) Drag Coefficient (cdrag), relating to the streamlining of the car:

Honda Insight 0.25

Prius 0.26

Renault 25 0.28

Honda Civic 0.31

Volkswagen Polo 0.32

Peugeot 206 0.33

Ford Siesta 0.34

Audi TT 0.35

Honda Civic 0.36

Citroen 2CV 0.51

After "Sustainable Energy without the Hot Air" (page 257)

For modern cars (≠ Citroen 2CV):

Streamlining => diminishing returns

- Somewhat boxy Polo: cdrag = 0.32

- Teardrop shaped Insight: cdrag = 0.25

- Total range: Ratio of 1.5 to 1

So more severe, streamlining is not

likely to be a "silver bullet" solution

Especially as we are already cutting into:

head &, cargo room, general utility

Second way of reducing a car's drag:

1) Drag Area (cdrag Acar) in m2:

After "Sustainable Energy without the Hot Air" (page 257)

For modern cars (≠ Citroen 2CV):

SIZE MATTERS A LOT!

- Small Honda Insight: 0.47

- "Typical Car:" 0.8

Sub-range: Ratio of almost 2 to 1

- Land Rover pushes ratio to almost 3:1

- As would popular large U.S. SUV's

Full range: Ratio of 3 to 1

("We have met the enemy, and he is us")

Honda Insight 0.47

Volkswagen Polo 0.65

Honda Civic 0.68

"Typical Car" 0.8

Volvo 740 0.81

Land Rover Discovery 1.6

OK, but that physics ignores energy losses IN the car:

That is, preceding accounts only for energy used in ideal movement of the car

Equaling the kinetic energies imparted to the masses of the car and air

But to supply that energy, we are going to have to use a lot more energy

With difference going into inefficiencies of engine, drive train . . .

As manifested by all sorts of things heating up

With that waste buying us nothing in the way of movement

So where IS car's input energy (from gas, diesel or batteries)

used?


For city driving:

Where the energy goes in a 2005 Toyota Camry:

Only 13% of the fuel's energy makes it into things we calculated above!

From MIT lecture "Electric Cars 101" by Dan Lauber:http://www.slidefinder.net/e/electric_vehicles_101_introduction_dan/evs101-11-13-09%28web%29/10697203

Engine Loss76%

Engine

Idling8%

DrivelineLosses

3%

Driveline

Aero3%

Rolling4%

Braking6%

Fuel Tank100%

16% 13%

POWERTRAIN VEHICLE-Related

For highway driving:

Where the energy goes in a 2005 Toyota Camry:

Still use only 19% of the fuel's energy!

From MIT lecture "Electric Cars 101" by Dan Lauber:http://www.slidefinder.net/e/electric_vehicles_101_introduction_dan/evs101-11-13-09%28web%29/10697203

Engine Loss77%

Engine

Idling0%

DrivelineLosses

4%

Driveline

Aero10%

Rolling7%

Braking2%

Fuel Tank100%

23% 19%

POWERTRAIN VEHICLE-Related

Internal combustion engines waste ¾ of the energy!!!

Question #1) Where the heck is all of that energy going?

Into heat of exhaust gas + Heat of that massive engine system itself

Question #2) Isn't this a one line (killer) argument for electric cars?

After all, aren't electric motors more like 80-90% efficient?

Department of Energy / EPA webpage seems to support that conclusion:1

Electric vehicles convert about 59%–62% of the electrical energy from the grid to power at the wheels—conventional gasoline vehicles only convert about 17%–21% of the energy stored in gasoline to power at the wheels.

But let's think about this a little more deeply:

- Car's battery is charged from our largely hydrocarbon powered grid

- Power plants convert hydrocarbon fuel to electricity with efficiency ~ 33%2

1) http://www.fueleconomy.gov/feg/evtech.shtml 2) http://en.wikipedia.org/wiki/Fossil-fuel_power_station

So the true "apples to apples" comparison should be:

Hydrocarbon energy to car movement energy conversion efficiency:

Gas powered cars: 17-21%

Electric cars: (59-62%) x (33%) = 19.5 – 20.5%

Add to that the facts that:

For decades we have worked hard to clean up automobile exhaust

But have put FAR less effort into cleaning up coal/oil power plant exhaust

Result: Per gram hydrocarbon burned, cars release less CO2 than power plants

Putting this all together (for our current types of power plants):

Total energy efficiency of gas vs. electric cars is a dead heat

With gasoline cars now having a significantly lower net carbon footprint


What I just did, shown diagrammatically:

It's as if both cars come attached to an oil well + refinery OR a coal mine

But electric car then adds on a coal-fired OR oil-fired electric power plant


+

OR

17 – 21%

x 59 – 62%

x 33%

19.5-20.5%

x 17 – 21%

= 1

Gasoline CarEfficiency:

Electric CarEfficiency:

What about "hybrid" cars like the Prius?

Hybrids ALSO use gas as their energy source, bypassing coal power plant

AND they use that gas more efficiently (via some of the tricks that follow)An Introduction to Sustainable Energy Systems: www.virlab.virginia.edu/Energy_class/Energy_class.htm

+

OR

17 – 21%

x 59 – 62%

x 33%

19.5-20.5%

x 17 – 21%

= 1

Gas Car Efficiency:

Electric CarEfficiency:

x 25 - 35% ?

25 - 35% ?

Hybrid Efficiency:

Yes, when our power plants are more efficient and cleaner

ELECTRIC CAR'S total efficiency and cleanliness WILL improve!

For example, if all our power came from hydro, solar, wind and nuclear

THEN electric car's energy/greenhouse gas footprints will be due to only:

Getting materials for, and manufacture of, the power plants and the car

=>"Life cycle carbon & energy footprints" = Topic of a later lecture

But, at least for now, we cannot write off the good old internal combustion engine

For which the obvious action is to, somehow, make it more efficient!

But during "gas crises" of 70's & 80's, manufacturers swore little could be done

Were they right?An Introduction to Sustainable Energy Systems: www.virlab.virginia.edu/Energy_class/Energy_class.htm

EPA data on gasoline IC engine carbon footprint & fuel economy:

1975-2013: Internal combustion car's CO2 emissions/mile fell by 50%

1975-2013: Fuel economy figures rose by 100%

(Although, in fine print, EPA confesses that gas mileages are all inflated by 20%)Source: www.epa.gov/otaq/fetrends.htm

With shape of the data telling a really interesting story:

Gas Crises => Action

Source: www.epa.gov/otaq/fetrends.htm

Oil state wars etc. => Renewed ActionNeglect

With clear implications:

- Technological fixes were pretty EASY

- Willpower fixes were the hard part

Leading to:

New CAFE (Corporate Average Fuel Economy) standards requiring another 100% improvement in fuel economy (to 55 mpg!)

This time the industry did NOT oppose and instead only wanted to ensure a level playing field between competing companies

http://www.washingtonpost.com/business/economy/americas-best-selling-cars-and-trucks-are-built-on-lies-the-rise-of-fake-engine-noise/2015/01/21/6db09a10-a0ba-11e4-b146-577832eafcb4_story.html

A problem(?): As engines get more efficient, they also get quieter

From the 21 January 2015 business section of the Washington Post:

“America’s best-selling cars and trucks are built on lies:

The rise of fake engine noise”

“Stomp on the gas of a new Ford Mustang or F-150 an you’ll hear a throaty rumble – the same style of roar that Americans have associated with auto power and

performance for decades. It’s a sham.”

Fearing a loss of vroom-vroom (male U.S.) customers:

Ford has created artificial engine noises and is secretly

piping them in through the vehicle’s hi-fi system speakers

Vs. a serious Idea: Keep engine nearer to its most efficient speed

This relates to what is called an engine's "Torque Band," with possibilities such as:

For two alternative engines:

<= RPM for max power OR max torque

For optimum power and efficiency let'sguess that sweet spot is slower, say 4000

RPM

But a CAR must go a full range of speeds, so add the gear ratios of a transmission:

http://en.wikipedia.org/wiki/Power_band

Engine's Speed

Car's Speed

4000 RPM

0 MPH

1st Gear 2nd Gear 3rd Gear 4th Gear

70 MPH

That only sort of works:

With acceleration, transmission allows us to repeatedly drop down engine speed

So engine spends more of its time vaguely near target of 4000 RPM

But what if we had an infinite number of possible gear ratios?

So that whatever the car's speed, motor could stay at ~ optimum speed?

Thus my wife's new Subaru has a "Continuously Variable Transmission" (CVT)

It uses a chain belt running between two continuously adjustable pulleys:

5:1 Ratio 1:1 Ratio

Gear equivalents at bottom

http://nissanaltimaaustin.com/altimas-cvt-keeps-moving/

Another serious idea: Regenerative Braking:

Above, "city driving" figure stated ~6% of power went into heating of the brakes

But this is probably a bit of an underestimate

Physics said that in city driving, air turbulence, friction . . . were insignificant

Energy use was ALL about putting kinetic energy into the motion of the car

And then throwing it away every time you stopped!

What if, instead, you could STORE that energy as you stopped

And then just reapply it, to accelerate back up to speed?

Then (from physics standpoint): Only energy spent is that of the FIRST acceleration

Instead of saving 6% in brake heat, you might save almost full 13% sent to wheels

Plus, if you shut down the motor when stopped, save 8% of power lost when idling

Total possible savings => ~ 20% !

How might you store that energy as you stop?

In an electric car, or hybrid electric car, the answer is really simple:

Use torque from slowing wheels to turn electric motor into a generator

As is done in gas-powered HYBRID CARS, such as the Prius

Which also switches off its engine when stationary:

http://www.cvel.clemson.edu/auto/systems/regenerative_braking.html

Kinetic Energy Recovery Systems (KERS) of Formula I race cars store energy in:

Heavy, metal, flywheels

A new flywheel-based KERS system being tested in Jaguar's cars:

But what if it's not an electric car?

http://www.wired.com/2010/10/flywheel-hybrid-system-for-premium-vehicles/

Flywheel

Continuously Variable Transmission

Differential / Coupling Gear

Or Mazda's unique approach: "i-ELOOP"

Car engines normally drive car PLUS an "alternator" to charge the battery

Battery then runs the starter PLUS air-conditioner, HiFi, WiFi, GPS, videos . . .

An "alternator" is just another name for a generator/motor

But driving it continuously adds to the load on the engine (eating fuel)

With i-ELOOP, the alternator is driven only when your foot is off the accelerator

During that deceleration, the alternator quickly charges a super-capacitor

When foot returns to accelerator, super-capacitor energy is transferred to battery

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Mazda6 with i-ELOOP => 40 MPG highway / 28 MPG city:


Can do same things for Trucks - So let's move on to airplanes:

Does air travel being such a "bad actor" somewhat surprise YOU?

After all, how many trips do we (or "average U.S. citizens") take per year?

One, a few, a half dozen? (even including business travelers?)

Or could all of our Amazon.com airfreight deliveries have really hurt that much?

I made a half-hearted (but unsuccessful) try at answering both questions

But I'm pretty sure that real answer is that Flight uses LOTs of fuel!

(Which will come back to haunt us in the Carbon Footprint lecture)

So let's again follow Sustainable Energy Without the Hot Air's lead and now learn a bit more about the physics of flight:

First, to offset gravity, airplanes REALLY want to have lift:

To offset force of gravity, exploiting Newton's "Action = Reaction"

An airplane MUST steadily push LARGE volume of air downward (caused by wings)

Omitting details (such as wingtip vortices) and approximating as a simple cylinder:

Masscylinder = density x volume = ρair x (vplane t Arealift_cylinder)

Where ρ is air density, A is cylinder's cross-sectional area

And (vplane t ) is the distance the plane flies in a time t

Jet image from: www.clipartlord.com/category/transportation-clip-art/

(continuing)

If, due to plane's passage, that air is forced downward at a velocity uair:

Cylinder's downward momentum = Mair uair = ρair vplane Alift uair t

Downward force = D Momentum per time which is then:

Forceair = ρair vplane Alift uair

Which must be in balance with the force of gravity = Mplane g

Equating and solving for uair = Mplane g / (ρair vplane Alift)

Use this to calculate the kinetic energy lost to that now downward moving air:

½ Mair uair2 = ½ (ρair vplane t Areacylinder)(Mplane g / (ρair vplane Alift))2

= t (Mplane g)2 / (2 ρair vplane Alift)

So power (energy/time) in that lift air is Plift = (Mplane g)2 / (2 ρair vplane Alift)

But in addition to energy expended on lift is energy to drag:

For which the analysis is just like that for the earlier highway-driving car

And which (after updating the subscripts) gives us:

Pdrag = ½ ρair cdrag Aplane vplane3

Combining (and color coding) both LIFT and DRAG power expenditures:

Ptotal = Plift + Pdrag = (Mplane g)2 / 2 ρair vplane Alift + ½ cdrag ρair Aplane vplane3

With: Alift: Circle ~ size of plane's wingspan, Aplane: Circle ~ size of fuselage Xsec

Converting power per time to energy per distance:

Energy / distance = (Energy / time) (time / distance) = Power / velocity =>

Eper_distance = (Mplane g)2 / 2 ρair vplane2

Alift + ½ cdrag ρair Aplane vplane3

(To figure out fuel used, we'll need to factor in jet engine's efficiency )e

To minimize this (absolutely essential for airline's economic survival!) must have:

d/dvplane (Energy / distance) => 0

After some math (which I did, to check the book) you find that:

ρair vplane_optimum2 = Mplane g / (cdrag Aplane Alift)1/2

Left side = Things WE can tweak: speed and altitude (which affects air density)

Right side = Fixed things + plane's decreasing weight as it burns off fuel

Which brings us to some surprising conclusions:

From optimization: ρair vplane_optimum2 = Mplane g / (cdrag Aplane Alift)1/2

Conclude (unlike cars) that for planes going slower is NOT better

In fact, if go higher (into thinner air) plane should speed up!

If this optimum speed condition is substituted into energy consumption equation:

Eper_distance = (Mplane g)2 / 2 ρair vplane2

Alift + ½ cdrag ρair Aplane vplane3

Find that, at optimum speed, first (lift) and second (drag) term are equal, thus:

At most efficient speed, plane spends ½ its power on lift, ½ on drag

With the total energy spent per distance then becoming:

Eper_distance_at optimum_speed = (cdrag Aplane / Alift)1/2 x Mplane g

Working from that final optimized equation:

Eper_distance_at optimum_speed = (cdrag Aplane / Alift)1/2 x Mplane g

Plane's ENERGY EFFICIENCY is not improved by:

- Making plane bigger or smaller: Changes in A's cancel, negating effect

- Changing altitude: Because air density has dropped out!

(But at higher altitude can go faster for same energy per mile)

Plane's ENERGY EFFICIENCY is improved by:

- Decreasing drag coefficient by making plane more "streamlined"

Limited by need to retain space for paying passengers / cargo!

- Making the plane lighter, which could be done three ways

By building it with lighter structural materials OR

Or hauling less/fewer passengers, cargo, bags OR lighter fuel


And they ARE indeed working on making planes lighter:

By (where possible) removing metal in favor of lightweight plastic composites

And discouraging (or charging for!) excess luggage

However, short of ALSO charging passengers for their weight

Which HAS been suggested and would reflect real airline costs!

The only remaining "knob to turn" would seem to be the fuel weight:

But to travel the same passenger/cargo distance,

You can't just cut the amount of fuel, unless:

You get more energy per kilogram out of that fuel

Leading us to this table and its rather surprising (and disappointing) entries:

Energy density of fuels (and would-be fuels / energy sources):

Conventional Battery = 0.001 x Gasoline's energy density

PC Battery = 0.01 x Gasoline's energy density

TNT (0.65 Cal/gm) = 1/15 x Gasoline's energy density

Butyl alcohol = 0.9 x Gasoline's energy density

Kerosene / JP-4 / Jet Fuel = 0.93 x Gasoline's energy density

Gas / Diesel = 1 x Gasoline's energy density

Liquid Natural Gas = 1.3 x Gasoline's energy density

Hydrogen = 2.6 x Gasoline's energy density

(Uranium or Plutonium = 106 x Gasoline's energy density)

Only significant improvements to kerosene/JP-4 are:

Liquid or pressurized gases!

Which would THEN require MUCH heavier fuel tanks (!@#!!$#!)Data mostly from from Richard A. Muller's book "Physics for Future Presidents"

They are certainly working on jet engine efficiencies

Often via better materials that are lighter and/or more heat tolerant

But they've also been tinkering with the basic operation of the jet engine

E.G. by increasing the size of the up front air-driving "fan" blades:

Early "turbojet" jet engine Later "bypass turbofan" jet engine

Modern turbofan with even more pronounced enlargement of front fan blades:

OK, but what about engine efficiency (as overlooked by physics)?

http://en.wikipedia.org/wiki/Jet_engine http://aviation.stackexchange.com/questions/11586/what-is-a-high-bypass-geared-turbofan-and-why-is-it-so-much-more-efficient

Then there is United Technologies' "Billion Dollar Bet" 1 on: The Geared Turbofan

The idea:

- You push more air by making the front blades bigger than the rest of the engine

- But those "fan" blades push most efficiently when turning at modest speeds

- Where later blades of fuel-burning section of jet work best at higher speeds

- But in conventional turbofan, they are on the same shaft, turning at same speed

So add a gearbox between them (allowing front fan blades to slow down): 2

1) http://www.forbes.com/sites/danielfisher/2013/01/23/the-billion-dollar-bet-on-jet-tech-thats-making-flying-more-efficient/2) http://www.airplanegeeks.com/2012/01/24/episode-182-alan-epstein-and-the-geared-turbofan-engine/

Or, if you want all of the details: 3

3) http://airinsight.com/2012/10/02/airinsight-technical-analysis-the-core-of-the-pw1000g-geared-turbo-fan/#.VN40n8bPeEQ

4) United Technologies full page ads running in the Washington Post, February 2015

The goal:

"16% greater fuel efficiency while reducing the noise footprint by up to 75% 4

*Source: EPA automobile fuel economy chart from an earlier slide

16% would be nice, but it's still not an air travel game changer

So how DOES flight consume ~ 1/3 of truck OR ~ 1/10 of car fuel total?

Well let's work out some simple fuel consumption numbers:

Say as "average American" I drive my car (mostly alone) 12,000 miles per year:

Which (at least if its a new car) is supposed to get ~ 24 miles /gal*

I would then personally consume 508 gallons of gasoline per year

Say, in a plane, I also took one cross-country flight per year (not alone!)

JFK to LAX to JFK = 2 x 2775 miles = 5550 miles = 8880 km

With "Hot Air's" 747 plane number of 25 passenger-km / liter of fuel =>

=> 355 liters ~ 80 gal which is already over 1/10 of my car's consumption!

NOTE HOWEVER PER KM: Car ~ 9.4 km/liter Plane ~ 25 km / liter


What about saving energy in other modes of transportation?

I dismissed ships, busses and trains because of their small overall contribution

But, shouldn't we still try to make them more efficient? Yes, of course!

For instance, most all of the above suggestions for cars will also apply to busses

But trains are going to be hard to improve, because:

As one long body they are already well streamlined (Pdrag = small)

And, they already minimize starting and stopping (Pkinetic = small)

And with steel wheels on steel tracks, running friction is small

And finally, they already avoid going up and down hills

And surprisingly (at least to me) slow cargo ships are almost as efficient

After figure in "Sustainable Energy without the Hot air" page 92

Yielding energy per freight load mass per distance transported:

Energy (kW-h / tonne / km)

Images from: www.clipartlord.com/category/transportation-clip-art/ and https://lionelllc.wordpress.com/page/2/

Speed (km / h)

1.5

1.0

0.5

025 50 75 900

After figure in "Sustainable Energy without the Hot air" page 128

Or energy per passenger per distance transported:

Energy (kW-h / 100 passengers / km)

Images from: www.clipartlord.com/category/transportation-clip-art/

Speed (km / h)

150

75

50

050 100 150 900200

25

Cars (gas or electric): Assuming single passenger

Plane/Ship: Assuming full-ish passenger load

SUMMARIZING: To cut energy in transportation, priorities should be:

Cars and Trucks (assuming we will resist buying smaller and/or slowing down):

Streamline (where possible) or at least reduce forward cross-section

Continue improving engines / transmissions

Add regenerative braking

Airplanes: BIGGEST IMPACT = Fly less Teleconferences! / Local Vacations!

Short term (small gain): Further trim plane's weight / develop engines

Medium term: An opportunity for otherwise questionable biofuels?

Long term: Figure out lightweight tanks for compressed gasses?

Trains: Damned good as they are but we should certainly USE THESE MORE!

Ships: Sure, some gain from less cross-oceanic importing, however:

Impact on total energy spent is still small compared to things above

Credits / Acknowledgements

Some materials used in this class were developed under a National Science Foundation "Research Initiation Grant in Engineering Education" (RIGEE).

Other materials, including the "UVA Virtual Lab" science education website, were developed under even earlier NSF "Course, Curriculum and Laboratory Improvement" (CCLI) and "Nanoscience Undergraduate Education" (NUE) awards.

This set of notes was authored by John C. Bean who also created all figures not explicitly credited above.

Copyright John C. Bean (2015)

(However, permission is granted for use by individual instructors in non-profit academic institutions)


Documents

Power Consumption in Transportation To this point in the class, we've talked about: Electrical science "The Grid" Power Production technologies, including: