Diesel Pollutants vs. Gasoline, electric, etc.
Question:
>Gasoline requires more energy to refine, and you get less gas per barrel of >crude. Diesel produces more pollutants (at least solids, right?) but goes >farther on less crude.
The way a modern catalytic cracking refinery works, lighter fractions like gasoline are "cracked" from heavier fractions. Thus it’s possible to make nearly the entire barrel into gasoline, but it’s not possible to make the entire barrel into diesel. Crude has fractions ranging from very light product like some of the naphthas, down to residual fuel oils and tars. Many of the fractions in a barrel of crude are heavier than gasoline and can be cracked to it. Diesel is generally considered a byproduct of gasoline refining, an intermediate step if you will, and it’s price and availablity are a function of gasoline demand. A cat cracker uses less than 5% of the energy content of a barrel of oil to refine that barrel of oil and the ratio of gasoline to diesel has very little effect on refinery energy consumption. Diesel, because it contains more carbon than gasoline, has a somewhat higher energy content per gallon, but the primary efficiency advantage lies in the engine, not the fuel. Direct injection diesels have high compression ratios. Within reason, the higher the compression ratio, the more efficient the engine. An internal combustion engine is basically an air pump. The less restriction to air flow the engine has, the lower it’s losses. Because direct injection allows a diesel to be built without a throttle plate restricting the air intake, the diesel is a more efficient air pump at part throttle than a gasoline engine. Engine output of a diesel is controlled exclusively by the quanity of fuel injected into the cylinders. Because of it’s high compression ratio, a diesel can produce more nitrogen oxides (NOx) than a gasoline engine of the same size. And, when it is heavily loaded, a diesel can produce unburned carbon in the form of soot, the black smoke you see coming from laboring trucks. Both of these can be minimized with proper design, tuning, and maintenance, but you can’t just slap a catalytic converter on the output and clean up whatever noxious pollution the engine may generate as you can with a gasoline engine. (cat converters aren’t without their costs either, and can’t clean up everything, but they do compensate somewhat for out-of-tune engines) Depending on the weight of your fifth wheel trailer, I’d give a look to some of the intermediate sized pickups on the market. The Jeep Commanche for example can handle a 2,000 pound trailer without special equipment. It’s 4.0 liter straight six produces 190 hp and mine gets 24 MPG around town. If your loads are heavier, the GMC 6 liter diesel is well thought of around here. Either would probably be a better choice than a gas V8, though my previous truck was a diesel, and they can be a pain, especially in cold weather. Diesel engines are more expensive to purchase than gas engines, and diesel fuel is currently $0.10 a gallon more expensive than gas thanks to an increased Federal tax on diesel. So your mileage has to be very much better than the gas engine to break even. Gary
Response:
I live in south-central Texas — I drive about 750 miles/week (work and back) + an average of 200 miles on a weekend, and need to replace my old pickup truck with a new one. I’m interested in what the real pollutant counts for Diesel engines vs. Gasoline engines (and storage electrics, et al). My supposition is that a Gasoline powered pickup gets about 10-15 mpg empty (I have to pull a fifth wheel trailer with it, so it needs at least a 351 C.I.D. V8). For a Diesel, I’d get about 18-22 mpg empty. Gasoline requires more energy to refine, and you get less gas per barrel of crude. Diesel produces more pollutants (at least solids, right?) but goes farther on less crude. If you include the energy cost of refining, and the total pollutant output per mile (including refining), what is "really" better? I’m also interested in knowing how the relative pollutant output per mile traveled of electrics, hybrid electrics, and alternative fuels (natural gas, etc.) might be. Please post any information you might have that would contribute to a solution to my problem (you can exclude my moving closer to work…my wife would then put the 750 miles a week on her vehicle:). Looking forward to a spirited concensus on this topic, Tom Stewart – Pencom Software – we know AIX personally "I am irritated" —- Lt. Worf, ST-TNG
