Electric Vehicles
Hybrid-Electric Vehicles
Fuel Cell Vehicles and the Hydrogen Economy
An electric vehicle (EV) is powered not by fossil fuel but by its battery. "Battery" literally means a battery of electrochemical cells, just as we speak of a battery of artillery or a battery of tests: more than one cell hooked together in series or in parallel. You should know how a battery works. Whether it is a wet cell or a dry cell, rechargeable or nonrechargeable, the basic idea is that two chemical half-reactions (a reduction reaction and an oxidation reaction) occur at two separate electrodes (the cathode and the anode); free electrons are liberated at the anode and are required as reactants at the cathode. Although ions can move (and generally must move) between the two electrodes through the electrolyte, free electrons can't, so they must instead travel through the wire you provide: a current. The particular set of chemical reactions that occurs determines the battery's emf.
The battery provides energy to the car's electric motor. We saw that electromagnetism is at the heart of an electric motor: When the current from the battery passes through a coil of wire, the coil becomes an electromagnet with a north pole and a south pole. If the coil ("armature") is free to spin, and if it is in the vicinity of a strong stationary magnet, it will indeed spin so as to get its north pole as close as possible to the stationary magnet's south pole. To see how the armature of a DC motor continues to spin -- that is, how it's prevented from achieving the happy state in which its north pole is close to the stationary magnet's south pole -- review the online article and check out the role of the commutator. For an AC motor, this isn't a problem (why not?).
Electric generators are used by EVs (and by hybrid-electric vehicles) for regenerative braking purposes. Generators are essentially the opposite of electric motors: rather than converting electrical energy to rotational kinetic energy, they convert rotational kinetic energy to electrical energy. They accomplish this via electromagnetic induction, the fundamental behavior of nature by which an emf is induced (generated) whenever a magnetic field is in the process of changing its strength or its direction. So if a coil of wire is made to spin in the presence of a strong stationary magnet, from the coil's "perspective" it's the magnet which is spinning, with the result that the magnetic field produced by the magnet is constantly changing direction: an emf is induced in the coil. Since the coil is a conductor, electrons in the coil can move in response to this emf: an AC current is generated. This in turn can be "rectified" to a DC current if desired, meaning that the current is made to travel in the same direction at all times rather than switching back and forth.
And why was the coil spinning in the first place? In a braking car, this might be related to the spinning of the tires, with the generated current used to partially recharge the batteries. In a power plant, you might have burned coal to boil water to produce high-pressure steam which rushes past turbine blades, causing a shaft (with our coil at the other end) to spin. Or you might have allowed water to fall through a dam, rushing past turbine blades, etc.
Now that you have those crucial EV components under control, you should reread the article about them (but don't try to learn the details of how to retrofit your car to be an EV). What other components, such as the DC controller, are present? What are the drawbacks of EVs that have caused them not to be commercial successes so far? What kinds of new EVs are in the works? How does the scheme of Better Place differ from those used for past EVs?
If we combine two different power sources, we have a hybrid vehicle. For cars, the hybrids on the road today are hybrid-electric vehicles (HEVs): Gasoline-powered internal combustion engines (ICEs) combined with electric motors. There are other hybrids, like diesel-electric trains, nuclear-electric submarines, experimental gasoline-hydrogen ICE cars, but we won't talk about those here.
Having these two sources of power to the wheels means that the car can be more efficient -- which the driver sees as better mileage. Why? We also talked about improving efficiency by implementing one or another scheme for regenerative braking, and you should understand these schemes. And there are still other ways in which HEVs are designed for improved mileage, and you should review the online article to see what they are.
As for individual cars that are already on the road, the articles you read focused on three: the Insight, the Prius, and the Escape. You should be able to describe one or two of them to show how they operate and how they differ from other HEV models. You should also be able to discuss how the Chevrolet Volt will be different from any of these once it's in production.
You should understand how a fuel cell works, as exemplified by the hydrogen fuel cell. How is it similar to a battery, and how is it different? What are the reactants and the product? What role does the electrolyte in the middle play?
There were a number of particular kinds of fuel cells discussed in class and online: PEM, alkaline, SOFC, etc. You don't need to know the detailed chemistry of them but you should be able to write a bit about how they differ from each other and what their relative pros and cons are. Note that they differ primarily in the electrolyte used rather than the fuel used.
What's a fuel processor (a.k.a. reformer) and how does one work? What are the pros and cons of using one?
You've seen online links to fuel-cell vehicles from two companies: the GM Hy-Wire (and its successor the Chevrolet Equinox); and the Honda FCX Clarity. You should be able to give an overview of either one, and you should be able to pick one of them and discuss in detail how it works. For example, what's the skateboard concept? What's drive-by-wire technology? How far can you drive the FCX Clarity -- and who gets to drive it so far?
Carefully reread the online article that takes a skeptical look at the viability of a hydrogen economy. More specifically, you should be able to answer a full-page question summarizing and discussing this article.
Energy efficiency, environmental impact, and cost are three important considerations for choosing our future transportation mode. What is "well-to-wheels efficiency" and what do we learn by analyzing various vehicles in this way? Why is hydrogen referred to as an "energy carrier"? How do we produce hydrogen (H2) gas, and is this the best use of the energy required to produce it? In what sense is hydrogen a clean transportation fuel, and in what sense is it not? Hydrogen can be transported from place to place -- but how easily?