Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric Cars, plug-ins? Why not CNG?

  1. Jan 21, 2009 #1
    Natural Gas, It's the only logical substitute to Crude Oil. The mechanics of the vehicle are almost identical to gasoline, base infrastructure is already in place (pipelines), Although the major Oil producers also produce Natural gas, the US has reserves that match that of Saudi Arabia and UAE.

    21% of all electricity in the US is produced by Natural Gas, 50% by Coal, 1% by petroleum

    I don't get what the point is to use electricity created from natural gas to run a car, and not just use natural gas itself.

    Just look at the numbers (all data from eia) This is just a rough estimate, world reserves accuracy isn't validated, and prices don't account for the different grades of product

    NYMEX->1/21/09

    Price
    Oil - $40.34/barrel
    Ngas-$4.6350/mbtu
    Diesel-$1.3656/gal
    Gasoline-$1.1340/gal

    World Reserves
    Oil- 1,332,000,000,000 barrels
    Naturalgas- 61,941,925,400,000 mbtu

    Market Cap
    Oil-----$53,732,880,000,000
    Ngas--$287,100,824,229,000

    Total World btu
    Oil-----7,725,600,000,000,000,000
    Ngas--61,941,925,400,000,000,000

    btu/$1
    Oil-----143,777
    Ngas---215,749
    diesel---109,614
    gasoline-110,229
     
  2. jcsd
  3. Jan 21, 2009 #2

    russ_watters

    User Avatar

    Staff: Mentor

    It is certainly a possibility, but the difficulty with natural gas is the storage. It is tough to get any kind of decent range with a pressurized tank.
     
  4. Jan 21, 2009 #3
    Perhaps efficiency - gas-fired CCGT power plants can achieve 60% thermodynamic efficiency, twice that of an internal combustion engine. I don't know the figures for gas turbine cars, but from general principle I doubt they're 60%.

    http://en.wikipedia.org/wiki/Fossil_fuel_power_plant#Gas_turbine_combined-cycle_plants

    Yes it is! Besides, of course, hydrogen fuel cells, hydrogen internal combustion engines, methanol combustion or direct methanol fuel cells, bioethanol (from miscnathus grass, sugar cane, or blue-green algae), biodiesel (methyl or ethyl esters of lipids), alkali metal hydrides (such as LiAlH4 or NaBH4), chemical electric batteries (Li ion or NiCad), ultracapacitors, synthetic hydrocarbons from biomass (via CO, Fischer-Tropsch), synthetic butanol, dimethyl ether (from methanol), solid boron, or ammonia. But besides those, it's the only logical substitute for oil.
     
    Last edited: Jan 21, 2009
  5. Jan 21, 2009 #4

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    It's completely standard in europe. You can modify a gasoline engine for about $1000, it still uses gasoline as well (most can't start on LPG).
    There were even grants to pay for it and LPG is about 1/2 the price at the pumps because of lower tax
    The main reason for not doing it is the worry that once you have paid for the conversion they will put the same tax on LPG as they do on petrol/diesel.

    CNG is a bit trickier. LPG gives about half the range of diesel and CNG about half again. It also needs high pressure tanks to store it rather than just a barbecue type propane cyliner
     
    Last edited: Jan 21, 2009
  6. Jan 21, 2009 #5
    I agree, we should work more towards natural gas. As russ said there is a range problem but for the typical daily commuter it is a cleaner/cheaper alternative to gasoline that can easily be used by the general public. More so than electric cars in my opinion. I'm a firm believer that burning a fuel is the most practical way to move a vehicle (and be able to provide enough heating & AC energy).
     
  7. Jan 21, 2009 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Burning natural gas to make electricity is especially dumb.
    The only reason to do it is that it is very cheap to build a gas fired plant compared to any other, you can even build a small 100-200Mw almost off the shelf by bolting together backup generator sized units.
    Expensive to run and they only have a short life but if you manage the contracts for power generation wrongly this is what you get.
     
  8. Jan 21, 2009 #7
    It's not dumb at all! As I pointed out, gas-fired CCGTs achieve the highest thermodynamic efficiencies - 60% even. This is not a cheap off-the-shelf solution, it is a capital-intensive power plant which uses more than one thermodynamic cycle - for example, a high-temperature Brayton cycle (a gas turbine) with a lower temperature Rankine cycle (a steam turbine).

    http://en.wikipedia.org/wiki/Fossil_fuel_power_plant#Gas_turbine_combined-cycle_plants

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

    Together with the much lower CO2 intensity of natural gas (half that of coal), CCGT baseload power is a very reasonable short-term reduction strategy for GHGs. For example, a 60% efficiency gas-fired CCGT will emit 1/4th the CO2 per kWh of a 30% efficiency coal plant. It is less capital-intensive and much faster to construct than nuclear power, so it could be a transition strategy.

    http://en.wikipedia.org/wiki/File:BiodieselsCountryOfOrigin.jpg

    Utilities build (non-CCGT) gas power plants because they are economic for peaking power (fast, on demand load balancing in peak hours). This is because the upfront capital costs are cheap, so amortized, running gas power at very low capacity factor is cheaper than anything else at low capacity factor, except maybe hydroelectric dams. The fuel costs may be high, but at low capacity factor that is less important. See for instance:

    http://www.iea.org/Textbase/publications/free_new_Desc.asp?PUBS_ID=1472

    [​IMG]
     
  9. Jan 21, 2009 #8

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Thermodynamic efficiency doesn't matter if your fuel is more expensive.

    Then using that electricity to electrically heat houses and run stoves instead of piping gas directly to them is about as bright as burning diesel in a power plant to create electricity for plug-in EVs.
     
  10. Jan 21, 2009 #9
    They are not mutually exclusive. The economy still has non-heating needs for electricity.

    It does, because less is needed as a result, which lowers the effective fuel costs. Additionally there is the large CO2 advantage of natural gas - add in a carbon tax and the economics change. For instance, from a 2008 Canadian study:

    $/MWh vs. $/MTCO2 (Canadian $)
    [​IMG]

    http://www.cbo.gov/ftpdocs/91xx/doc9133/Chapter1.4.1.shtml#1088555

    http://www.cbo.gov/ftpdocs/91xx/doc9133/toc.htm
     
    Last edited: Jan 21, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?