by donshan » Tue 30 May 2006, 11:01:17
Here is a link to a good survey of diesel advantages and problems from the New York Times:
Diesel
It is only possible to get a limited amount of diesel fuel out of each barrel of oil with current refinery designs. Thus the popularity of diesel in Europe leads to a surplus of gasoline that is being exported to the USA. If the USA also went strongly to diesel, a shortage (and higher prices) would reduce the cost advantage.
$this->bbcode_second_pass_quote('', 'I')n Europe, diesel demand is high and growing by 1.5 percent a year, and "that's impossible to accommodate in a refinery," said Gene Tunison, manager of fuels development and policy planning at ExxonMobil.
Instead, European refineries are processing more crude oil to keep up with diesel demand and accumulating surplus gasoline that they export to the United States. That system is working because the United State has a shortage of refinery capacity, but if every country were to embark on a diesel strategy, refining would have to change radically, experts say.
However the diesel is clearly the winner on efficiency:
$this->bbcode_second_pass_quote('', 'B')ut the energy-consumption and environmental benefits are less clear. While there are more miles per gallon — 20 percent to 40 percent more, according to advocates — the reduction in global-warming gases is not as pronounced because diesel has more carbon in it than gasoline does, and thus produces more carbon dioxide per gallon burned.
Diesel goes farther for two reasons. One is that when the hydrocarbons in a barrel of oil are rearranged and sorted into a variety of products, the ones going into diesel have more energy than those that go into gasoline. A gallon of diesel has about 128,000 B.T.U.'s, while gasoline has about 115,000.
The second reason is energy efficiency. Diesel engines get more work out of each B.T.U. because they squeeze the fuel-air mixture tighter before combustion.
Advocates also say an advantage of burning diesel is that there are two sources for the fuel that have nothing to do with the petroleum. Substitutes can be made from coal and soybeans.
The popularity of the new hybrid cars has obscured a lot of disadvantages for long distance driving. The hybrid gets most of its great mileage in stop and go city driving since the braking system returns electric power to the battery when you stop, avoiding the energy loss to waste heating of brakes. On the highway the battery only will provide 30 miles of so of power and then you are running 100% on the gasoline engine in the hybrid. In in similar sized cars with similar performance, a high efficiency diesel only car will get much better highway mileage vs. the hybrid, especially considering it does not have to carry the dead weight of the hybrid battery and electric systems.
There will be a place for diesels for a long time to come since diesel fuel can be made from coal and soybeans. Nazi Germany ran their tanks on diesel made from coal!
I would love to see more high quality diesels in the USA. One of the problems in the past is US car makers skimped on diesel quality and a lot of problems developed that gave diesels a bad reputation that European designers avoided by better quality.
Also new low sulfur diesel regulations go into effect soon that will allow diesel designs to reduce the soot emmisson.
Also lost in the debate is E85 ethanol fuel has about 25% less energy per gallon than gasoline and is even worse vs diesel fuel. Thus diesel made from soybeans will have 30+ % better mileage than an E85 ethanol fueled car.