Clean Diesel vs. Gasoline: Introduction
Kudos to technology and good ol? creative thinking. Without you, we?d
live in a world devoid of pairings like vanilla ice cream and chocolate
chip cookie dough, or cell phones that allow us to access our email or
browse the hardware store?s assortment of hammers. There are countless
such examples of matches painfully obvious with the benefit of
hindsight, but on the flip side are marriages that will be forever
puzzling. That?s especially true with words. In fact, until recently the
words ?clean? and ?diesel? were not normally paired together. That
changed with the debut of a new generation of so-called oil burners,
including Volkswagen's Jetta TDI, Jetta SportWagen TDI and Touareg TDI.
Not only do these models run on cleaner fuel, they also deliver more
torque and superior fuel economy* while providing what many classify as a
fun driving experience. Best of all, VW?s TDI engine-equipped vehicles meet the same strict emissions standards set for gasoline-powered vehicles.
Clean Diesel vs. Gasoline: Engines
Drive down any U.S. highway and you?re apt to encounter more diesel
engines than you can shake a sustainably-harvested stick at, but chances
are the vast majority will be powering big rigs delivering goods. In
contrast, diesel-powered passenger cars have accounted for only 3.6
percent of all vehicles registered in the U.S.,** though that just might
change with the nationwide availability of clean diesel fuel and Volkswagen's TDI models.
Today?s diesel engine can trace its roots back to the early 1890s, at
which time Rudolf Diesel engineered and patented a more efficient
version of the gasoline-powered internal combustion engine (ICE). Both
diesel and gasoline engines are technically ICEs, meaning their inner
workings consist of a crankshaft, connecting rods, pistons, and intake
and exhaust valves. And both require the introduction of a volatile fuel
to operate, but that?s where the similarities end. Inside a gas engine,
a precise air/fuel mixture is pumped directly into a cylinder, at which
time a spark plug ignites the mixture, causing a mini explosion that
creates power by pushing down on the piston and rotating the crankshaft.
A diesel engine, on the other hand, lacks spark plugs, a distributor,
and an electronic ignition system. Instead, air is pumped into the
cylinder, compressed to a much greater degree, and as a result, gets
very hot. When the hot air is at maximum compression, fuel is sprayed
into the cylinder, causing a mini explosion without the need for a
spark.
That high-compression detonation is what caused the clatter sound often
associated with old diesels, used in everything from Mercedes-Benz
sedans to the Volkswagen Dasher and boasting not-so-memorable statistics
like 0-60 mph runs of more than 15 seconds. Modern engine designs have
eliminated much of the clatter, and the introduction of turbochargers
offered a big boost in terms of performance. But diesels still must deal
with tremendous internal pressure relative to their gas competitors. As
an example, the Volkswagen Jetta uses a cast iron engine block and
alloy cylinder heads in gas and TDI models.
With that in mind, diesels are typically built with stronger blocks and
parts, but in the case of the Jetta TDI, engineers were able to keep the
car?s overall curb weight in line with the gas-powered variant. Thanks
to the turbocharger, Volkswagen?s 2.0-liter four-cylinder TDI engine
generates a respectable 140 horsepower at 4,000 rpm and 236 lb.-ft. of
lively torque at only 1,750 rpm. Compare that to the Toyota Corolla?s
1.8-liter four-cylinder engine with 132 horsepower and 128 lb.-ft. of
torque, and the Honda Civic?s 1.8-liter four-cylinder that?s good for
140 horses and 128 lb.-ft. of twist.
One final issue focuses on difficult starts in cold weather, a result of
a need for hot air in the diesel?s combustion process. This situation
has been addressed by direct injection and the use of advanced engine
computers.
As a matter of fact, see the movie below about TDI in cold weather.