Planes, trains and automobiles 27% of the total national energy budget goes into transportation Of this 27%, 35% is used by automobiles Autos are among the least energy efficient modes of transportation (Bicycles are number 1) Rely in the internal combustion engine

What does it take to move a car? Four force terms need to be considered: Force needed to accelerate the vehicle – F a = ma Force needed to climb any hills – F h =msg, where s is the slope of the hill Force needed to overcome internal energy losses (tire flexure, wheel bearings, friction with the road surface, etc) – F r = C r mv, where C r is a constant term Force needed to overcome aerodynamic drag on the vehicle, depends upon speed. – F ad = C D A f v 2 /370 where C D is the aerodynamic drag coefficient, A f is the frontal area of the vehicle. So the total force required is the sum of these 4 terms: – F T = F a + F h + F r + F ad

Energy required The energy required will be equal to the work done by the force over a given distance or – E = W = Fd or – E = Pt, where P is the power output and t is the time the vehicle is operated or – E = Fvt So to minimize energy, you need to minimize the forces.

Making current cars more efficient Minimize the force required: – ma+msg+ C r mv+C D A f v 2 /370 Make m small Make C r small Make C D small Make A f small Make v small Or any combination of reducing these values

Alternatives to the internal combustion engine Flywheels Electric batteries Hybrids Alcohol Hydrogen

Flywheels Energy storage device Flywheel is spun up and the energy is stored as rotational energy to be used at a later time Designed to resist losses of rotational energy due to friction, etc Energy stored is given by E k = Iω 2 where I = moment of inertial of the flywheel, and ω is the angular velocity. The moment of inertial is a function of the mass and the distance from the center of rotation So the structure of the flywheel and the rotational rate determine the amount of energy stored. Ultimate limit on the energy storage is the strength of the flywheel. Spin it too fast, and it will tear itself apart.

Flywheel vehicles Could extract energy from braking-rather than waste the energy into frictional heating of brakepads, reverse the engine and spin up the flywheel. Need to be recharged on the power gird, saves gas, but drains electricity The big implementation problem is materials which can withstand the stress needed to spin the flywheel fast enough to make this a worthwhile alternative. Prototype mass transportation vehicles have been built (In Sweden and by Lockheed) Used in Formula 1 racing to recover energy lost in braking and along with a continuously variable transmission to improve Formula one car acceleration. Also used in the incredible hulk roller coaster at Universal Islands of Adventure in Orlando, Fl. – Ride starts with an uphill acceleration, rather than a gravity drop. – Flywheels are used to provide the initial energy impulse, otherwise the park would brown out the local energy grid everytime the ride began.

Hybrids Still use gasoline powered engines, but combine them with (usually) batteries to achieve better fuel economy. Idea is to use as small as possible a gasoline engine, and only when it can be run at peak efficiency. Use excess power to recharge the battery (no need to tap the power grid) Use energy from braking (regenerative braking) to also charge the battery Work best in stop and go driving. Major initiative in the auto industry right now. Result in using less gas-stretching our fossil fuels

Pure electric vehicles Powered by an electric motor, rather than a gasoline engine Needs batteries – current generation of batteries have 520 times less energy density than gasoline. Need to be charged from the power grid If all the vehicles in the US were converted to electric cars, it would triple the current electric energy generation Recharging electric vehicles takes time- several hours, whereas it takes minutes to refill your gas tank Batteries have a finite lifetime, need to be replaced every 2-3 years at a current cost of 1000 Limited range (less than 100 miles before recharging is needed) Ultimate limit is current battery technology-current lead acid batteries have not changed much in 100 years. Environmental effects from the disposal of lead acid batteries No new promising battery technologies on the horizon to substantially help electric cars

Fuel cells An electrochemical conversion device Chemical reactions cause electrons (current) to flow Requires a fuel, an oxidant and an electrolyte ( a substance that contains free ions and acts as a conductor) Typical type of fuel cell is called a proton exchange membrane fuel cell (PEMFC)

Hydrogen Fuel Cells Clean-only emission is water Expensive to produce Highly efficient-in an automobile, efficiencies of converting fuel energy to mechanical energy of 60% could be achieved, almost double the current efficiencies Hydrogen itself has issues as a fuel source

Issues with Hydrogen Abundant in nature, but not a freely available fuel Must be unbound from compounds Currently obtained via steam reforming – Steam and a nickel catalyst react, producing H – Need steam at very high temperatures, 1600F In the future, H is anticipated to be produced by the electrolysis of water, requiring large amount of water and electricity

Electrolysis Pass an electrical current through water and obtain H Pass a direct current from a battery or other DC power supply through a cup of water (salt water solution increases the reaction intensity making it easier to observe). Using platinum electrodes, hydrogen gas will be seen to bubble up at the cathode, and oxygen will bubble at the anode. Choice of the electrode is critical, you do not want a metal that will react with oxygen

Issues with Hydrogen Storage-occurs in gas form at room temperature, hard to contain As a liquid, it can be stored, but needs temperatures of -253 C. – As a liquid, its energy density increases 1000 times – In principle, could replace gasoline as a liquid fuel, but not practical at this time One solution is to store it as a metallic hydride (the negative ion of Hydrogen in a compound with another element) at room T.

Issues with H Highly explosive – Forms a volatile mixture with air A mixture of 4-75% of H in air is explosive, compared with natural gas which is only explosive in a range of 5-15% concentration in air Ignition energy is small, needing only 2 x J (basically a spark of static electricity can ignite H) Only good news is its low density means if there is a H leak, it disperses quickly

Hydrogen Hindenburg disaster Hindenburg was a German passenger airship (zeppelins) built for transatlantic air flight. Filled with Hydrogen Something caused ignition of the Hydrogen- cause is debatable 36 fatalities out of 79 people onboard

Alchohol Use methanol or ethanol as a fuel – Already gone over ethanol Methanol is already in use at Indy 500 race – Proven that no significant loss of performance is experienced (though they are in the process of switching to ethanol) About ½ the energy content of gasoline Produces only CO 2 and water – Some nitrogen oxides produced in the engine Can be manufactured from re-newable sources (biomass for example) Technologies exist now.

Disadvantages Very dangerous – Burns with no visible flame-needs a colorant added – Fumes are toxic CO 2 is a greenhouse gas Currently made mostly from natural gas-a non-renewable fossil fuel Possibly more corrosive than ethanol to engine parts

Use in liquid fuel cells Another use is as a input to a liquid feed fuel cell In these cells, Methanol replaces hydrogen Methanol has a much higher energy density and is easier to store than H Current methanol fuel cells produce power too low for vehicles, but can be used in cell phones, laptops etc Advantage is that they store lots of power in a small space, which they over a long period of time