Five myths about diesel engines

www.physorg.com ^ | June 14, 2011 | By Louise Lerner

[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

[Red Badger]

Argonne mechanical engineer Steve Ciatti takes a crack at some of the more persistent myths surrounding the technology of diesel engines. Credit: Argonne National Laboratory

[Red Badger]

Rest In Peace, old friend, your work is finished.....

If you want ON or OFF the DIESEL ”KnOcK” LIST just FReepmail me.....

This is a fairly HIGH VOLUME ping list on some days.....

[PSYCHO-FREEP]

You might also add, that Diesel engines generate a much longer and higher power band, as well as more HP, 3 times more torq and they get much better mileage to weight, per gallon.

I have a Duramax with 230K and it runs like it did the day it came off the show room floor. Never had to tune it up or do anything to it but change oil & filters. And I have worked it hard as a tow vehicle. I only wish GM had not changed because I would never buy a new one from them now. I'm forced to make this one last and it is doing a great job of doing just that.

[Big Horn]

Diesel engines, stink, very loud, and require regular maintenance, and #2 will jell in very cold weather.

[dangus]

I don’t care about the particulate matter; I care about the stink. VW diesels used to stink to high heaven. Are the new requirements doing anything about the stink, or just making it invisible?

[Red Badger]

#6

When the truck wears out, you can out a new body on your engine............

[Red Badger]

The new ones have a different odor, for sure. Removal of sulfur from fuel was a big help in the stink area. Newer fuel delivery systems have reduced the pollution and the particulates.
Now, they smell, to me anyway, like a campfire / wood stove burning..............

[CodeJockey]

Well I happen to love she smell of D2 in the morning.

[Red Badger]

The new ones don’t smell like the old ones.................

[mad_as_he$$]

What year is your truck?

[Dustoff45]

Diesel engines actually perform better at high altitudes than gasoline engines.

Last summer I transported GrandPa's Dodge Ram pickup from California to Virginia. Included in the back was a 1/2 ton of river rock from GrandPa's property as a special gift. So we were pulling some weight.

I remember climbing a fairly steep grade in Wyoming on I-80, at over 7500' at the time. I was holding the speed limit of 75, the overdrive was locked down, and I was passing everything in sight.

That was a mad moment!

[Red Badger]

Diesel engines, stink, very loud,

Don't get out much, do you?............

[PushinTin]

I bought a 2011 BMW X5 X35d and am VERY happy with the Diesel engine. It is a Blu-Tek Diesel and produces only Nitrogen and Oxygen. That's it. I got an $1,800.00 Tax credit because it was considered a green car. It has super power and gets 23 mpg. State inspection is about $20.00 in Texas. No emissions test required.

[paterfamilias]

I got my first diesel car in 1996, and never looked back. That one, I just sold (315,000 miles) to a friend, who loves it.

My 2nd diesel car has 148,000 miles on it (my daily driver), and I just got our 3rd diesel for my wife - brand new - about 400 miles.

[texas booster]

Diesel engines, stink, very loud, and require regular maintenance, and #2 will jell in very cold weather.

Well, bio-diesel solves some of the cold weather gelling issues.

If made from old oil from restaurants (now jealously guarded!) the exhaust can smell like any designer fragrance from french fires to fish.

[sasquatch]

Turbo diesel just won Le Mans...

[Red Badger]

I bet that has the Greenie-Weenies pulling their hair out...................

[arthurus]

Diesel engines, stink, very loud, and require regular maintenance, and #2 will jell in very cold weather.

20 years ago you would be closer to right. You are far off, now. They do not stink and the fuel in cold weather is not a problem, as it states in the article. The newer ones don't even rattle. Remember the diesel pickups in 1990? You couldn't carry on any sort of conversation near a running one. Now it is no worse than a car and depends entirely on the muffler used.

[Red Badger]

If it comes from a Chinese Restaurant it smells like #27................

[Jane Long]

The newer VW diesels are sweet.