## The Automobile

### U.S. Energy consumption by sector

U.S. Energy consumption, by economic sector

### U.S. Transportation energy

U.S. direct transportation energy consumed by each transportation mode.

### Internal combustion engines

150 kW internal combustion engine.

Best theoretical engine efficiency ~ 30%.

But typically, 15-20%.

### Energy flow for gas-fueled car

What is the efficiency of this car?

eff=10/70 = 1/7 ~14%

### Electric cars

Comuta-Car... in Goshen

Is an electric car a zero-emission vehicle? If not, where are the emissions happening?

'electric' mileage: $(5 mi) / (kwh)$ works out to 103 miles for the 2009 cost of 1 gallon of gas.

$CO_2$ emissions: equivalent to a 48 mpg gasoline car.

Top-speed: ~35 mph (30 mph in the winter).

Range: 40 miles fully charged. (Average 2nd car in the U.S. driven 27 miles per week).

Conversion of ElectricE -> MechanicalE in a DC motor: >90% efficient.

Cost in 1993: used 1980s model ~$2500. Cost of replacing batteries ~$800.

2010: Chevy Volt estimated to cost $33,000 after rebates has a small gas engine (to charge batteries) as well as batteries. Cost of replacement batteries... unknown. For Honda Civic hybrids, costs range from$2,000-4,300.

### Efficiency - revisited

Is there a better way than "miles per gallon" to measure transportation efficiency?

Particularly if you want to take into account how many people are being transported?

Choose between mpg / # of people or # of people $\cdot$ mpg ...?

people $\cdot$ miles per gallon is the measure of efficiency we want! It's a number that gets larger the more people we put in the vehicle.

### Comparing transportation

* The energy content of gasoline is converted to food Calories to figure the energy efficiency of humans.

### Sample test question

"Which is more efficient: 3 people driving in a van that gets 21 mpg, or 1 person driving a Prius that gets 48 mpg?"

The van is getting 3 passengers $\cdot 21 mpg$
$= 63$(passenger miles) $/ (gal)$.

The Prius is getting 1 passenger $\cdot 48 mpg$
$= 48$(passenger miles) $/ (gal)$.

### Sample life question

"Which investment is more likely to save more energy: buying a 48 mpg Prius or buying a house within less than a mile from where you work?"

### Moving freight

The equivalent efficiency criteria for moving freight is to multiply the "gas mileage" times the weight (or, ahem, mass) moved.

Why might the barge come out the best?

* TDM encyclopedia from vtpi.org

### Animal kingdom

Comparing many different animals by the number of kg $\cdot$ km they can move on 1 MJ of energy

Maybe that's why he's smiling?

Small group discussion:
* Other than technical improvements to vehicles, how could you reduce the amount of energy you personally expend on transportation?   * Which of these suggestions involve *no* negative "quality of life" impact?

### Steam-electric plant

80% of electricity is produced in steam-electric power plants. This includes both coal- and nuclear- plants.

### Steam turbine

The steam expands in several stages as it moves through the turbine blades.

### CO2 emissions from coal

Howstuffworks addresses the cost of powering one lightbulb. They find that when burning 714 lbs of coal, a total of 1852 lbs of $CO_2$ is produced. How is it possible to have a greater weight of $CO_2$ emitted tham the weight of what we started burning??

$CH_n +$ several$O_2 \rightarrow CO_2 +$ several$H_2O$

Carbon comes from coal, Oxygen comes from atmosphere.

### Energy flow: electric generator

Efficiency : 900 MW / 2500 MW = 0.36 = 36%

### Cogeneration

Efficiency: (900 + 1200)/2500 = 84%

Also called "Combined Heat and Power" (CHP).

Mirant Kendall Cogeneration Station (1949), in Cambridge, Massachusetts.

### Suggested Exercises

Conceptual exercises, Chapter 7: 25, 27, 28, 30, 33, 35

### Image Credits

Chad Conway, MissMass, Fletcher