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Diesels: So Bad?

by Donal 5/22/2012 - 11:05 am   |

My mama didn't hate them, but I never knew much about diesels. During the late 70s fuel scare, one of my many bosses bought an Olds diesel, probably with the 350cc engine, to try to get better economy without buying a small car. He complained about it constantly, and the 350 is now considered one of the worst engines of all time. I drove my aunt's big Mercedes turbo-diesel a few times, but never, ever considered buying a diesel myself. But diesel keeps cropping up in articles, and clean diesels regularly figure in green car competitions. If you've got a pile of cash, you can buy the world green car of 2012, the Mercedes Benz S 250 CDI Blue Efficiency (below) for under $70,000, except that it doesn't seem to be sold in the US.

Diesel has always been popular in Europe, and TTAC has cited reports that diesel sales are up 27%, from a miniscule 0.4% to 0.5% of US sales, and beginning to make some inroads in Japan.

Even with higher taxes and low-sulfur environmental regulations, diesel used to be competitive with gasoline, but something has driven diesel prices consistently higher than gasoline since about 2004. Diesel engines convert about 45% of the energy into work while  gasoline engines only convert about 30%—though with recent efforts that may be changing. And good diesel engines can last twice as long as gasoline engines.

But PetroDiesel fuel—made from petroleum—is nasty stuff. It sticks to your hands, face and clothing rather than evaporating. Its high particulate exhaust is difficult to trap and carcinogenic. But for every guy raving about his hybrid's fuel economy, there's a guy saying, "I've been getting close to that on my VeeDub diesel for decades."

To avoid the toxic exhaust, one can look for B100, 100% cleaner biodiesel, but you'll need a specially-modified diesel engine, and a map or a website to find suppliers. There is also B20, which is only 20% biodiesel, which doesn't sound like much of an improvement, and B5 and B2, which sound negligible, but are approved for most unmodified diesels.

As seen in the 30 Days episode about the ecovillage, one can also modify a diesel to use heated vegetable oil. Vegetable oil is not biodiesel, and biodiesel is not vegetable oil. Biodiesel may be made from vegetable oil, but vegetable oil fuel is actually frowned upon by the feds. Drivers have been harassed for using vegetable oil, and the feds have tried to collect taxes on free waste oil that some use.

But it's kind of amazing to think that waste fryer oil will run your car. If you can find a willing restaurant manager, you might get their waste vegetable oil for free. Conversions use either prefiltered straight vegetable oil (SVO) or waste vegetable oil (WVO) which will make your exhaust smell like french fries. Vegetable oil isn't perfect but it contains no sulfur and is carbon neutral. Opinions vary but CO, CO2, HC and TPM (total particulate matter) emissions seem to be lower. NOx (nitric oxide and nitrogen dioxide) seem to be higher but can be brought to baseline with timing adjustments.

A conversion will cost a thousand dollars or two, though, and the vegetable oil tank will take up space in your trunk, and with WVO you will have to invest time collecting and filtering the oil. You can buy converted cars from specialists like Frybrid or Greasecar. Greasecar advises using pure oil but Frybrid says hydrogenated or partially hydrogenated vegetable oil (HVO) is also fine.

Green Car Congress just reported that researchers have gotten reduced emissions with HVO:

A team of researchers in Finland reports that by adjusting engine parameters for the use of hydrogenated vegetable oil (HVO) renewable diesel fuel across a range of loads (50%, 75%, and 100%), particulate matter and NOx emissions can both be reduced by more than 25% relative to the values from using HVO with standard engine conditions.

I suspect that ICE engines in general are going to get a lot more efficient, and maybe cleaner, from better tuning and start-stop technology, but as with hybrids, the general trend is towards more complexity, thus greater cost to achieve the utility we used to take for granted.

This Dagblog needs more manly articles like this. The diesel engine is so dam much more efficient than a gasoline engine. It operates at a very high compression rate. In fact, the fuel/air mixture is ignited by compression rather than by a spark (plug) as in a standard gas engine. They are often designed to maximize power, but when designed to maximize burning efficiency, can be the cleanest engines in the world.

According to hyperphysics: "In the diesel engine, air is compressed adiabatically with a compression ratio typically between 15 and 20. This compression raises the temperature to the ignition temperature of the fuel mixture which is formed by injecting fuel once the air is compressed.

The ideal air-standard cycle is modeled as a reversible adiabatic compression followed by a constant pressure combustion process, then an adiabatic expansion as a power stroke and an isovolumetric exhaust. A new air charge is taken in at the end of the exhaust..."

In Europe where fuel costs are much higher, about 50% of the cars run on diesel. They are about 1/3 more efficient than gasoline engines in converting fuel (explosive charge) energy into mechanical energy. Maybe even more important, refining diesel from petroleum occurs directly. The process of squeezing gasoline out of diesel through catalytic reforming adds steps and costs. The fact that diesel costs more than gas at the pump DOES NOT reflect the cost and environmental advantages of producing diesel, which are decidedly superior to gasoline. And I am the Decider.

 

by The Decider 5/22/2012 - 12:41 pm

Have not kept up with diesel technology, but will agree with your positive assertions relative to the subject.  I have considered diesel relative to choosing my future automobile purchases.  There are some negatives that should influence your decision to go to diesel propulsion:  Few auto mechanics are diesel qualified.   As stated the two systems are unique when it comes to ignition.  As diesel components are a rarity inside the States, expect long waits for replacement parts.   In areas of extremely cold temperatures, diesels can be very hard to start.  (I'm not certain now, but in the old days, diesel locomotives sat idling for days rather than being shut-down because of fear of inability to restart them.)  Once again, over time, these weaknesses may have been corrected, but in my experience. diesels had such wide tolerances,  you could have thrown a cat between the piston rings and the cylinder walls.

by chucktrotter 5/23/2012 - 7:41 pm

Good points. I walked past an old Benz 300D after swimming. The back half was filthy with exhaust and fume deposits.

by Donal 5/23/2012 - 8:04 pm (re: chucktrotter)

My anecdotal is that the slow transition (still not complete) of the NYC bus fleet from conventional diesel to diesel with more filters or natural gas or diesel/electric hybrids has made an incredible difference in the foul air stench of Manhattan (now you can actually smell the urine and rotting garbage in the summertime, before you couldn't because you were busy choking on the all the idling bus fumes! wink)

But you don't have to believe just my anecdotal, see here:

The study found that conventional diesel buses are comparatively fuel efficient, but produce nitrogen oxide pollutants that can contribute to photochemical smog as well as large amounts of fine soot and sulfate particles, which are suspected to contribute to heart disease and lung cancer

Yeah, we're talking good ole time plain vanilla air  pollution here, smog and soot, the stuff that makes you choke and your eyes smart, not any of that fancy greenhouse gas stuff. When the diesel is idling in traffic, and then when it accelerates up again, it's pretty damn noxious stuff. I believe you can also see this discussed on websites about why urban kids have so much asthma, though there's no definitive answer on that question.

by artappraiser 5/23/2012 - 11:15 pm (re: Donal)

W.H.O. Declares Diesel Fumes Cause Lung Cancer
By DONALD G. McNEIL Jr., New York Times, June 12, 2012

Diesel fumes cause lung cancer, the World Health Organization declared Tuesday, and experts said they were more carcinogenic than secondhand cigarette smoke.

The W.H.O. decision, the first to elevate diesel to the “known carcinogen” level, may eventually affect some American workers who are heavily exposed to exhaust. It is particularly relevant to poor countries, where trucks, generators, and farm and factory machinery routinely belch clouds of sooty smoke and fill the air with sulfurous particulates.

The United States and other wealthy nations have less of a problem because they require modern diesel engines to burn much cleaner than they did even a decade ago. Most industries, like mining, already have limits on the amount of diesel fumes to which workers may be exposed.

The medical director of the American Cancer Society praised the ruling by the W.H.O.’s International Agency for Research on Cancer, saying his group “has for a long time had concerns about diesel.”

The cancer society is likely to come to the same conclusion the next time its scientific committee meets, said the director, Dr. Otis W. Brawley.

“I don’t think it’s bad to have a diesel car,” Dr. Brawley added. “I don’t think it’s good to breathe its exhaust. I’m not concerned about people who walk past a diesel vehicle, I’m a little concerned about people like toll collectors, and I’m very concerned about people like miners, who work where exhaust is concentrated.” [....]

by artappraiser 6/13/2012 - 2:04 pm

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