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Diesel’s second coming
Apr 4th 2008
From Economist.com

Will Americans finally warm to diesel cars?

EARLY last year, this column predicted that a new generation of lean and clean diesel cars would soon be heading for American shores (“Rudolf’s revenge”, February 9th, 2007). On cue, Mercedes-Benz, BMW and Volkswagen have started to introduce American versions of their latest diesel models that are clean enough to be sold even in environmentally conscious California. Japanese and American carmakers aren’t far behind.

Diesels are seen as an answer to soaring oil prices. While ludicrously low by European and Japanese standards, pump prices across America have risen by a breathtaking 60% over the past year. The average price for regular gasoline is now $3.30 a gallon; in California, it’s over $3.70 a gallon.

Diesel cars get around 35% more miles per gallon than their petrol equivalents. Diesel fuel is 15% heavier than petrol, and packs a bigger energy punch to start with.

Better still, a diesel engine has none of its petrol cousin's “pumping losses”. These come with throttling the air-fuel supply, which allows the engine to run at speeds less than flat out. Instead, the diesel engine varies the amount of fuel squirted into its cylinders depending on the work load placed on it. Unrestricted by pumping losses, diesels can achieve efficiencies of around 40%.

The best petrol engines can manage is around 30%, provided the throttle is wide open and the air flowing into the cylinders unrestricted. As that happens only when the car is being driven flat out, a petrol engine’s overall efficiency turns out to be a dismal 17%.

In Europe, where petrol costs around $7 per gallon, lower taxes on diesel fuel—along with better mileage—have encouraged motorists to ditch their gas guzzlers for diesel sippers. Diesels now account for half of all new cars bought in Europe, and more than 30% of all cars on the road. In America, fewer than 3% of passenger vehicles are diesel powered.

That’s because earlier diesels left such a bad impression on Americans. In their haste to rush them into showrooms in the wake of the oil shocks of the 1970s, carmakers simply “dieselised” existing petrol engines, hoping they would be up to the job.

Few were. Unlike petrol engines, which use spark plugs to ignite their air-fuel mixture, diesels set fire to their fuel spontaneously by squeezing the gases in the cylinders to much higher pressures—and thus higher temperatures—than petrol engines can endure.

As a consequence, the components used have to be beefier all round. And not only within the engine. Diesel cars also need stouter brakes and springs and tougher transmissions.

Unfortunately, first-generation diesels used in America were poorly designed. Most were not only smoky, smelly and noisy clunkers, but difficult to start and prone to breaking down.

Over the past couple of decades, diesel engines in Europe have been refined past all recognition. With their high-pressure fuel injection, variable injection-timing, more advanced combustion-chamber designs and lightweight turbo-chargers, modern diesels are now indistinguishable from petrol-engine cars—save for their fewer trips to the gas station.

And now they are squeaky clean as well. For a long time, the diesel’s downside was the eye-watering oxides of nitrogen (NOx) emitted from its tailpipe—a consequence of the higher temperatures inside the engine.

Also, because spontaneous ignition usually occurred before the air and diesel were completely mixed, any unburned fuel left in cooler parts of the cylinders finished up as smoky soot being pumped out at the rear. On the plus side, the diesel’s better fuel efficiency meant it produced a lot less carbon dioxide per mile.

To meet California’s tough emission standards, carmakers have had to find ways to mop up the diesel’s unwanted NOx and trap its soot. The answer is to inject urea into a catalytic converter in the exhaust. The heat turns the atomised urea into ammonia, which, in turn, converts the hot exhaust gases into nitrogen and water. The soot is trapped by a fine mesh in a particulate filter added to the tailpipe.

Sounds complicated, but the diesel’s extra requirements cost less than you might think. For instance, Mercedes-Benz’s big new diesel sedan (the E320 Bluetec) has a sticker price of $53,025, while the petrol version of the same car costs $52,025. The Mercedes diesel gets 23 miles per gallon in the city and 32 on the highway, compared with 17 and 24 for the petrol version.

So, two decades after vanishing in a puff of smoke, diesels seem poised to reappear on the American landscape. Your correspondent will be among the first to plonk down his cash the moment diesel versions of family runabouts arrive. But he wonders where all the fuel will come from if Americans take to diesels as much as they’ve embraced hybrids.

Fact is, there’s a global shortage of the stuff. That’s why, shorn of tax breaks, diesel costs so much more than petrol. Over the past year, the average price of diesel in America has risen by 117%—twice as fast as petrol. While both carry the same taxes in America, diesel now costs 60 to 70 cents a gallon more than regular gas.

With spring in the air, factories, office, stores and homes in the chillier northern half of America will have started to turn down their oil-fired heating systems. Meanwhile, farmers and truckers (big users both of diesel fuel) are in the midst of their slackest season of the year. Couple that with an economy that’s lurching towards recession, and you would be excused for thinking the price of diesel—which comes from the same part of the barrel as heating oil—would now be falling.

Actually, if anything, it’s continuing to rise. That’s because of the burgeoning demand from Europe, China and India.

It doesn’t help that the catalytic crackers used by oil refineries in America are optimised to produce as much petrol as possible—typically about 50% of every barrel. Diesel accounts for only 15% of the rest, with the balance used to produce heating oil, jet fuel, heavy fuel, liquid petroleum gas, asphalt and other products.

Refineries in Europe and elsewhere tend to use hydrocrackers that produce 25% petrol and 25% diesel. They would like to produce more diesel than they currently do, but that would mean producing even more petrol than they need. At present, they export their surplus to America.

So, if America switched to diesel cars in a big way, the Europeans would be even more awash in unwanted petrol than they are today, and might have to dump it elsewhere or even idle some refinery capacity. Either way, the global price of diesel would soar still further.

Meanwhile, back at the pump in America, diesel currently costs 20% more per gallon than regular petrol. When that premium reaches 35%, the difference in fuel efficiency will equal the difference in price—and there will be no economic reason to make the switch. Some reckon that day is only a few years away.

Copyright © 2008 The Economist Newspaper and The Economist Group. All rights reserved.

TV550

Interesting article on Diesel. I think when Diesel prices hit 30% more than Gas prices it really would void the benefits of diesel engines. I hope that does not happen but according to the article it looks like it will.

scottybdiving

True ................ if the cost savings at the pump were the only benefit. The diesels that were available in the US (largely in pickups) until recently, have always cost a huge premium over gas engines. In the early 80's, that premium was around$ 2500 and has steadily increased to over $9000 in todays Duramax, Powerstroke, and Cummins diesels. They are more expensive to maintain, often requiring 15 qts of oil with very expensive fuel and air filters. Therefore, we have never been able to justify the difference in cost merely by the fuel savings. Yet, they sold them in droves. I was told around Y2K that International was building 250,000 engines / year, for Ford pickups alone.

So if the cost premium washed out any savings at the pump, why do you think all those people and companies and agencies paid the premium for the diesel engines? Longevity, durability, and resale.

Quicks

...don't forget Torque

lkchris

Assuming people buying hybrids will keep them long enough and be willing to pay for replacement batteries, it really can be said that folks will pay to be green.

Could be same for diesels.

StevethePilot

+1

Danno4x4

My last diesel Mercedes was a 1985 300D Turbo... When I bought it, it had 290K miles on it... When I sold it, it had 425K miles... Ran just as good as the day I bought it...

I'd really like to see a hybrid, or even a gasoline engined vehicle last that long... How many battery/engine replacements would be needed? I would think probably more than one.

The diesel fuel debate economics debate is a valid one, but I recall just about a year ago that diesel cost the same (around me anyway) as regular unleaded... I am willing to bet that come this summer... We may see a reduction of price relative to gasoline again.

oinick

My GL 320 is the first diesel I have ever owned and frankly I love it. Even if diesel goes up another twenty cents a gallon over premium unleaded it is still more economical to run than a gasoline GL. And don't forget the initial $2500 price break when you buy the GL 320 instead of the GL 450.

Diesel is like everything else. The price goes up when demand goes up, or more accurately when demand outstrips supply. When the "split" from a barrel of oil no longer needs to make so much fuel oil for the cold areas of the country there will be more raw product to make diesel. The price in the summer has historically gone down because of this.

Greul

I just got 27.8 mpg on a 225 mile trip (25% city / 75% hwy) last weekend (and without a tail wind for those of you who'd speculate) . Although diesel here is just under $4.00 still a lot more economical over my '01 BMW X5 4.4 which rarely got better than 16.5 mpg. Chalk another advantate up for diesel.

StevethePilot

http://editorial.autos.msn.com/artic...topart=hybrids

Not a bad article on diesel, again.

STP

Comfy_Couch

Mercedes-Benz 300D

BMW Works to Clean Up Diesel's Rep

scottybdiving

This morning Premium 2.19, Diesel 2.19. Diesel had been 2.09 until the threat of the refinery strike.

lkchris

Just thought I'd mention that there is plenty of throttle-less gasoline engine technology out there.

BMW may be the leader, and its engines' speed is controlled by varying intake valve lift rather than by any throttle(s) in the intake tract.

http://www.bmwusa.com/Standard/Conte...lvetronic.aspx

Of course a partially-opened intake valve is indeed a form of restriction and throttling, but then again so is a completely opened intake valve and there's no such thing as unrestricted intake flow.

Still, 40% is better than 30% and for sure 17%, but much of the benefit comes from the fact a diesel can run at varying fuel/air ratios and a spark-ignition gasoline engine apparently must always run at stoichiometric.

Article probably doesn't show awareness of Mercedes' "diesotto" concepts, either.
http://en.wikipedia.org/wiki/DiesOtto

Also
http://www.viewegteubner.de/index.ph...09869b01fb471c