[Vwdiesel] diesel love

[Dan Sloan]

Had a friend of mine send me this...it apparently came from here:
http://www.edmunds.com/insideline/do/Features/articleId=108977
 
I would dearly love an Audi TDI.....
 
-- Dan
 
 

Why Americans should fall in love with the diesel 

Date posted: 01-23-2006 

Here are some figures to conjure with:


  

Audi A8 4.2 TDI quattro

Audi A8 4.2 quattro


Engine

326 - horsepower V8

335 - horsepower V8


Torque
(lb-ft)

479

317


0-100 km/h
(0-62 mph) 

5.9

6.2


Top speed
(mpg)

155

155


Average consumption (mpg)

30.0

23.7


Range 
(miles)

594

469


Emissions (CO2 g/km)

253

286


Consider those for a moment. The diesel-powered Audi A8 4.2 TDI is not only
more economical than the gasoline-powered A8 4.2, it also produces fewer
greenhouse gases and, most importantly for readers of this Web site, it's
also significantly quicker. 

For the past few years, while the U.S. has been bemoaning ever increasing
gas prices, the Europeans have been experiencing a quiet, bloodless diesel
revolution. The introduction of multivalve, common-rail direct-injection and
pre-ignition technology has transformed the diesel engine from a noisy
agricultural workhorse into an ultrarefined, economical powerhouse worthy of
the finest performance and luxury cars. Across Europe, more than a third of
new cars now stop at the black pump and in some countries, diesel cars
outsell petrol. 

It's a staggering transformation, and one from which the U.S. could learn
some important lessons. 

The techie bit 
The diesel revolution in Europe has been driven by new technology. Here are
some of the headlining acts:

Multivalve technology - Most modern turbodiesels, such as the Audi V8,
feature four valves per cylinder - two inlet and two exhaust. This allows
the fuel-injection nozzle to be positioned in the center of the combustion
chamber, producing more efficient, symmetrical combustion. Power is
increased, while harmful emissions are reduced. 

Computer-controlled direct injection - The car's onboard computer takes
readings from a range of sensors, such as the throttle position and engine
speed, and carefully regulates the fuel supply, which is injected directly
into the combustion chamber. Diesels do not require spark plugs; the fuel
ignites automatically when mixed with hot air.

The Audi V8 TDI is one of the first engines to use Piezo injectors. These
are capable of five separate injections of fuel during each engine stroke -
at 4,000 rpm that's 20,000 injections per minute or 333 per second. The
efficiency of the combustion is greatly improved. 

Common-rail technology - Diesels of old had separate fuel lines from the
pump to each injector. The pressure and injection timing were dependant on
the engine speed. Modern common-rail systems, by contrast, unite all the
injectors on a single feed line and operate independently of engine speed.
The fuel supply can therefore be precisely managed by the onboard computers.
Common-rail systems also operate at much higher injection pressures, which
helps optimize the fuel-air mix and the efficiency of the combustion
process. 

Pilot injection - Sometimes called "pre-ignition," pilot injection
eliminates the combustion spikes that cause the "rattle" traditionally
associated with diesel engines, especially at idling speeds. Pilot injection
introduces a small quantity of fuel into the combustion chamber prior to the
main power-inducing explosion. This injection takes place within a few
ten-thousandths of a second of the main explosion and results in a smoother
combustion cycle and reduced clatter. Even at a standstill, an Audi, BMW or
Mercedes-Benz diesel is now all but as refined as its gasoline sibling. 

Pilot injection has two other significant advantages. The system enhances
the engine's cold-start capability, so that diesels can now function at
temperatures as low as minus 40 degrees Fahrenheit. Pilot injection also
helps reduce nitrous-oxide emissions by lowering peak combustion
temperatures. 

Turbocharging - A turbodiesel is hardly a new concept, but the blowers used
are becoming increasingly sophisticated. The Audi V8 TDI features twin
turbochargers and twin intercoolers. BMW's new 535d, which is actually a
3.0-liter, is the first production diesel to use sequential turbos. A
smaller turbo operates from idle to low engine speeds - helping to generate
368 lb-ft at 1,500 rpm - before a second, larger turbo takes over at higher
engine speeds. The net result is 272 hp and 413 lb-ft of torque.

Emissions - Low-sulphur diesel, which becomes mandatory in the U.S. next
year, has been available in Europe for some time. As well as eliminating
unpleasant odors, low-sulphur fuel enables the use of catalytic converters
and particulate filter traps to dramatically reduce the nitrous oxides and
other harmful emissions produced by diesel engines. The Audi V8 combines
twin catalytic converters with a particular filter trap that requires no
additives and will therefore not need servicing during the car's lifespan.

The road to Damascus 
In years gone by, the case for diesel was made on rational, economic
grounds. Diesels might have been fractionally more expensive to buy, but the
additional outlay was soon offset by reduced running costs and higher
residual values. So what if it rattled a bit when cold, you could always
turn up the stereo.

Today, the economic rationale in favor of diesel is still relevant, but it's
been joined by more emotive impulses. In the U.K., for example, the BMW 530i
and 530d cost similar money. They have the same power output (231 hp), but
the diesel has dramatically more torque - 212 lb-ft vs. 384 lb-ft. The 530i
gets to 62 mph 1.3 seconds quicker than the 530d (which takes 7.8 seconds),
but in the midrange, when the torque becomes more relevant, the diesel car
pulverizes its petrol rival. That it's astonishingly refined, even at idle,
and achieves an average of 42.2 mpg to the 530i's 32.1 mpg (European
"combined" estimates for manual-transmission vehicles), is really the cherry
on top of the icing on top of the cake. The 530d is the enthusiast's choice,
pure and simple. 

The case for the opposition 
Some performance-car manufacturers argue that diesel power runs counter to
their brand values. Porsche, for example, reckons that the relatively
low-revving characteristics of a diesel engine are ill-suited to a
performance application. "A Porsche engine must be free revving," argues Jan
Roth, the project chief for the new Cayman S. "The Cayman engine's rev
limiter is set at 7,300 rpm; most diesels produce their peak power around
4,500 rpm." 

Porsche is also concerned about the noise of the engine. While the Audi V8
emits a throaty, deep growl, no diesel will match the sonorous roar of a
Porsche boxer. Instead of diesel, the Weissach boffins are trying to solve
the consumption/emissions conundrum by developing a hybrid version of the
Cayenne, which will be launched before the end of the decade.

Diesel engines also tend to be heavier than their petrol counterparts. In a
front-engine car, placing so much mass over the front wheels can compromise
the car's balance and handling. The Volkswagen Touareg 5.0 V10 TDI, for
example, suffers from excessive understeer. 

Final thoughts 
While diesel clearly isn't the answer to everyone's prayers, the U.S. market
is unquestionably missing out on the modern diesel phenomenon. Bountiful
torque, excellent refinement and a huge range are qualities well suited to
the American highway. It is surely time to put away the prejudices of the
1970s and embrace the modern diesel engine.