Post on 03-Jan-2016
Cars and Drivers
210 million cars and light trucks
191 million licensed drivers
140 billion gallons gasoline/year
2.7 trillion vehicle miles
US Automobile Culture
Transportation consumes18% of Household Expenses
91% travel by private vehicles vs. 2% by mass transit
76% rides to work are solo
2.7 trillion vehicle miles per year
Carbon Emissions
US Automobiles add 1.3 billion metric tons of CO2 to atmosphere annually. (23% of US total emission)
Efficiency of cars is 20 miles/gallon
Drivers travel 14,000 miles annually
How do we reduce global impact of US transportation?
Raise CAFE Standards
Reduce Miles Traveled
New Technologies
Raise CAFE Standards
• Corporate Average Fuel Economy
• Established in 1975 to set U.S. mileage standards.
How can cars be more efficient?
• Smaller & more streamlined (wind resistance)
• Lighter (starting & stopping)• Less powerful (lower acceleration)
SUVs
• Mileage varies, but as low as 10 mpg as compared with 20 – 30 mpg for many cars and 50 mpg for hybrid electrics.
• Possible to achieve a more than 40% improvement with payback within ownership period.
Internal Combustion Engine
Engine – 20% efficient
Highway driving – Energy lost to air drag.
City driving – Energy lost during braking
Electric Car
Batteries are heavy and limit range to 100 miles.
Vehicles don’t have enough acceleration for traffic.
Not a practical solution.
Why do hybrids get better mileage?
Smaller engine. Electric motor boosts gas engine for acceleration.
Regenerative braking.
Electric motor runs at low speed where gas engine is very inefficient.
Electric motor shuts off when stopped.
Fuel Cells and the Hydrogen Economy
Fuels Cells use hydrogen to produce electrical energy
2H2 +O2 2H2O + energy
Fuel cells could be used to power cars with hydrogen as the fuel.
Clean fuel
Barriers to Hydrogen Cars
Availability of hydrogen fuel.
Storage of hydrogen fuel.
Expensive. Infrastructure
Fuel Cells
In development stage.
Currently very expensive.
Are not a source of energy.
Hydrogen must be supplied.
Hydrogen Sources
Steam reforming of natural gas:
CH4 +2H2O CO2 + 4H2
Electrolysis:
2H2O + energy 2H2 + O2
Energy Source for Electrolyzer
Electrolysis requires energy.
Energy could come from Solar, Nuclear, or Wind.
In the short term, it would probably come from coal.
Economics of Hydrogen Economy
Burning gasoline produces a therm for $1.50.
Coal can produce a therm for $0.08.
Coal burned at a power plant to produce electricity to run an electrolyzer could produce power cheaper than gasoline.
Vehicle Carbon Emission(grams per mile)
Fuel Cell with electricity from coal 440
Conventional with gasoline 370
Conventional with natural gas 310
Hybrid with gasoline 190
Hybrid with natural gas 170
Fuel Cell with hydrogen from reforming 140
Conclusions
Hybrid vehicles offer major short-term advantages
Fuel cells are expensive and have infrastructure issues.
Fuel cells based on electricity from coal plants could increase emissions
Mass Transit & other non-automotive options must be considered.