Posted on 06/15/2011 6:07:50 AM PDT by Red Badger
Diesel engines, long confined to trucks and ships, are garnering more interest for their fuel efficiency and reduced carbon dioxide emissions, relative to gasoline engines. Argonne mechanical engineer Steve Ciatti takes a crack at some of the more persistent myths surrounding the technology.
Myth #1: Diesel is dirty.
"We all have this image of trucks belching out dirty black smoke," Ciatti said. This smoke is particulate matter from diesel exhaust: soot and small amounts of other chemicals produced by the engine.
But EPA emissions requirements have significantly tightened, and diesel engines now have to meet the same criteria as gasoline engines. They do this by adding a Diesel Particulate Filter (DPF), which removes visible smoke. "DPFs are very effective," Ciatti said. "They remove 95-plus percent of the mass of smoke."
The smoke, trapped in a ceramic matrix, accumulates until the car's computer determines it's time to clean it out in a process called a "regeneration cycle."
While running, a small amount of extra fuel is added to the combustion chambers in the engine; the resulting heat and oxygen activate a catalyst in the DPF to burn off the accumulated soot. This renders a small fuel consumption penalty.
"Visible smoke is essentially gone, as of the 2007-2010 regulations," Ciatti said. "If you're buying a diesel car from 2007 or later, it's no dirtier than a gasoline-powered vehicle."
And in the invisible range -- diesel engines actually emit less carbon dioxide than gasoline engines do.
Myth #2: Diesel engines won't start in the winter.
"Today's technologies for cold-start are very effective," Ciatti said. "Modern diesel engines start in cold weather with very little effort."
The problem is that diesel jells at low temperatures. Below about 40°F, certain hydrocarbons in diesel turn gelatinous. "Since an engine depends on aerosolizing fuel, you don't want goopy fuel," Ciatti explained.
Often this is remedied with glow plugs, which are heated by the battery and help warm up the fuel so it can vaporize.
Low temperatures aren't a problem for gasoline engines because gasoline is much more flammable than diesel. Even at room temperature and pressure, gasoline is partly vapor. "Toss a match into a pool of gasoline, and the match will never even hit the surface of the liquid; it will ignite the layer of vapor above the pool," Ciatti said. "That's why gasoline has to be handled extremely carefully around any ignition source. Diesel isn't so volatile; if you tossed that match into a pool of diesel, it would go out."
Glow plugs and other remedies, however, effectively vaporize diesel to prepare it for combustion.
Myth #3: Diesel cars don't perform well.
Because diesel engines are still most common in trucks, many people assume that diesel-powered cars would behave like a truck behaves: slow and sluggish. "But keep in mind, that truck's likely hauling around 50 tons," Ciatti said. "In fact, to some degree, some people who drive diesels find they perform better than gasoline engines."
That's because diesel-powered engines get their best power when the engine's revolutions per minute (RPM) are low -- that is, at speeds below 65 miles per hour, where most driving takes place. Gasoline engines, in contrast, get to peak power by running the engine very high and fast; a gasoline car only reaches its peak horsepower with the accelerator pedal to the floor and the engine running at 5,000 RPM.
"Diesel car performance is far better than the perceived horsepower rating, because you're getting all that power at speeds where you actually drive the vehicle," Ciatti said. "You've got more pulling power and more acceleration at those speeds."
Myth #4: You can't find diesel at the pump.
Diesel-powered pickups and cars are popular enough that the market has taken interest; most neighborhood gas stations now have automotive diesel pumps.
"I drove a diesel car myself for 10 years. I can count on one hand the number of times I had to actually search for a pump," Ciatti said.
Myth #5: Diesel fuel is more expensive than gasoline.
Though Chicagoland diesel prices are generally higher than gasoline, in most parts of the country, diesel fuel and gasoline are priced comparably. Today, Illinois taxes diesel at higher rates than gasoline.
"Diesel fuel is not more expensive to produce than gasoline," Ciatti explained. "Its price usually has to do with the local tax structure."
Bonus: One thing you may not know about diesel!
Diesel engines actually perform better at high altitudes than gasoline engines.
Why? Gasoline engines operate at a very specific ratio of fuel and air. At high altitudes, the air is thinner--literally: there are fewer molecules of air per cubic foot. In the mountains, then, gasoline engines have to add less fuel to keep the ratio perfect, which affects performance.
"But a diesel engine runs fuel-lean; you don't have to keep the ratio perfect," Ciatti said. Diesel engines have turbochargers, which are pumps driven by exhaust gas. They add more air to the combustion chamber, and more air means more fuel can be added. At altitude, it can pull in more air and more fuel, and thus gets more power than gasoline engines can. Turbochargers don't use extra energy; they run off thermodynamically "free" energy that would be lost as exhaust if not used.
"Drive a diesel at altitude and you'll see other cars struggling while you zip past," Ciatti said. "The effect is very noticeable."
Provided by Argonne National Laboratory
What part caught fire?
Fuel leaks on exhaust from deteriorated hoses or shorts from the batteries to chassis can cause a fire no matter the fuel..........
My guess is, with the way the International Fuel Tax Agreement (IFTA) works, is that truckers who drive into, or through Illinois, and fuel up there, are getting a net refund from Illinois on fuel taxes every quarter. Of course, that net refund will go to pay taxes in another jurisdiction.
For those not familiar with IFTA, the way it works is to allow interstate truckers to deal with (mostly diesel) fuel taxes for all the lower 48 states, and 10 Canadian provinces, with a single quarterly filing in your home jurisdiction (state or province). With diesel for interstate trucking, you only owe taxes on the fuel you consume in that state/province.
Example, say you drive 500 miles through three states, but you only fuel up in the last state (say 100 gallons for a net of 5 miles-per-gallon).
State A has a $0.23/gallon tax rate, state B has a $0.20/gallon tax rate, and state C has a $0.25/gallon tax rate. You drive 100 miles in state A, 250 miles in state B, and 150 miles in state C. So, you initially paid state C $25.00 in fuel taxes on that 100 gallons, but you only consumed 30 gallons there.
So on your quarterly IFTA return, you fill out that you drove a total of 500 miles, and consumed a total of 100 gallons, for a fleet average MPG of 5.0.
You drove 100 miles in state A for a taxable use of 20 gallons at $0.23/gallon, so you owe state A $4.60 in fuel taxes.
You drove 250 miles in state B for a taxable use of 50 gallons at $0.20/gallon, so you owe state B $10.00 in fuel taxes.
You drove 150 miles in state C for a taxable use of 30 gallons at $0.25/gallon, so you owe state C $7.50 in fuel taxes, but you paid state C that initial $25.00 at the pump, so you get to net the $7.50 due against the $25.00 paid, for a refund of $17.50 from state C.
So, out of that $17.50, you pay state A and C (all netted on the form) the taxes due them (a total of $14.60). Then, at the bottom of the form, you net all the taxes due against the all the taxes paid (due $22.10) and all the taxes paid ($25.00) and get a total due or refund. In this case, you'll get $2.90 back.
The forms get sent, electronically, to the IFTA clearing house for all jurisdictional taxes due/paid, and the jurisdictions settle these taxes amongst themselves based on the filed returns. You only pay the net due to, or get the net refund paid to you by, your home jurisdiction.
No math required....diesel here is pricier than gasoline, irregardless.
Should be states A and B, not A and C.
Or keep the batteries and you have a diesel/electric hybrid. The Germans are experts with those - think U-boat.
One thing I haven’t understood since they started coming out with hybrid cars, is why noone is doing a hybrid with diesel. I would think it was a natural to use as a generator. A diesel engine will run forever at a set rpm.
I well remember when Blajoavitch first took office, he proposed a special tax on in state trucking companies. A group of owners got an audience with him and let him know just how mobile their business was and promised him that they would set up operations in neighboring states, if he pursued that "special" tax on them. He quietly dropped his efforts.
I think that should be "below about -40F" (which is also -40C). I think the author goofed on this one.
“Here in Southern California, diesel is 35 to 40 cents higher...so no “myth” around these parts.”
Diesel at 35 to 40 cents more is about 10% more expensive. However, you get between a 25% to 35% mileage increase over a comparable gas engine because diesel contains more energy per gallon.
So, it’s still a net savings - and your engine will likely last far longer to boot. Not to mention that there’s no ethanol in diesel. ;-)
I’m planning on going diesel for my next vehicle.
Yup, especially those ford powder stroke (miss sp intended) diesels. I hate those stinky things.
Could be a printer’s mistake................
Do you have any idea why here is such a cost premium for the diesel Sportwagen? I understand that diesel engines are more expensive to produce but is there really a $5,000 cost differential?
This explains the whole process....
I know how diesels work but CO2 is an unavoidable by product of hydrocarbon combustion.
My comment was directed at your statement that the exhaust only includes oxygen and nitrogen...
“Often this is remedied with glow plugs, which are heated by the battery and help warm up the fuel so it can vaporize.”
In trucks in cold climats they sell #1 diesel instead of #2 which doesn’t gell and has a lower flash point.
If you go into cold climate with a load of #2 all you have to do is add 1 quart of ATF per 50 gallons of #2 and you have #1.
“#2 will jell in very cold weather.”
Add a quart of ATF per 50 gallons of #2 and you have #1 which won’t jell.
THAT’S GOOD INFO!..............
Yes my 93 Dodge 1 ton is noisy, a little smelly but by no means slow. Everyone that I let drive it remarks how peppy it is for a 7000 lb truck. I could probably fix some of the noisy if I stuck a muffler on it. It gets 16mpg as versus my former F250 that approached 11 if the stars were properly aligned with its 5l gas engine. The Dodge will pull anything the Ford always hated a trailer. The chevy b4 the Ford was killed several times (expensive repairs) by trailer pulling. Now if you want to talk slow I have an 81 Mercedes 240D 4 cyl stick no turbo that basically defines slow boat.
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