TECHNICAL: DIESEL REDUX
by Bob Hagin
November 06, 1998
I've never been much of a fan of diesel engines in automobiles. I had the misfortune of having to work on an elderly diesel-powered Isuzu Bellil early in my career and I think it soured my psyche on the subject.
The reason for my current contemplation of the diesel as a powerplant in passenger cars is that the two German Giants, Volkswagen and Mercedes-Benz, are making tentative advertising sorties to promote their diesel cars. Volkswagen probably has the highest profile of the two in this area since it has had a diesel-powered New Beetle in production since the inception of that car and several of the "buff" magazines have done either extended road tests of the car or travelogues that feature the Diesel-Beetle as the prime mover. According to reports (we haven't been given one for evaluation), it goes along at a very good clip and avoids the traditional diesel image of being only slightly faster than a little old man on a bicycle. Actually, the folks at VW also offer the more conventional Jetta sedan and its upscale Passat (an Audi look-alike) with the same engine.
The Mercedes offering in the diesel world this year is its very classy E300 sedan. Mercedes promotional literature claims that with a 0- to-60 time of 8.5 seconds, the nimble four-door lays claim to the title of World's Quickest Diesel Car. Since we haven't had a Mercedes diesel either, I'll have to accept the statement as gospel. The Mercedes romance with the diesel engine goes back many decades and the company also claims to have been the first to install a diesel in a passenger car back in 1936.
Grammatically speaking, the word should be spelled with a capital "D" since its designer was Rudolph Diesel, a German PhD engineer who developed the system before World War I. Simplistically explained, a diesel engine operates by having air (sans fuel) admitted into its cylinders where the rising piston compresses it to a very high pressure. The air also gets very hot (check your high school physics text book for an explanation here) and at the top of the piston's stroke, diesel fuel (best described as high-class kerosene) is squirted into the combustion chamber where it explodes. No spark plugs; no ignition wires; no high-tension electricity - but it's these explosions that cause the characteristic diesel engine "rumble." An unattractive side effect of burning even high-quality kerosene in an auto is that the exhaust smells bad. No one likes to be stuck behind a diesel in traffic.
Unfortunately, the power-potential of kerosene is much lower than the much more volatile gasoline, so to achieve acceptable power output, both the VW and Mercedes diesel utilize a turbocharger to cram higher-than-normal amounts of air into the cylinders. Fortunately diesel engines are constructed to be much more sturdy and stout than their gas-powered stablemates. At least they should be.
Diesel-powered passenger cars have had an ongoing, albeit sporadic presence in the U.S car market for several decades. Mercedes leads the field by having offered a diesel car to Americans since 1949. These early versions weren't turbocharged - hence the diesel reputation for leisurely motoring.
Another attribute of the diesel design is that it will squeeze considerable mileage out of a gallon of fuel which made the design very attractive to auto makers in the days following the fuel crisis of the early '70s. Mercedes exploited this economical fuel mileage by cranking up its output of kerosene-burners and a plethora of other manufacturers jumped on that smelly bandwagon.
In '75 Volkswagen introduced its front-engined, front-drive Rabbit to phase-out its original Beetle. It was an instant success and two years later, it was made available with a non-turbocharged small diesel engine with claims of upwards of 50 miles per gallon.
Since then, many major manufacturers has offered a diesel at here at one time or another. Peugeot, Audi, Ford, Isuzu, Mazda, Nissan, Toyota and Volvo all gave diesel a whirl with varying degrees of success. Once the governmental push to conserve fossil-fuel subsided, the diesel engine diminished in importance.
General Motors also got into the game with disastrous results. In '78 Oldsmobile offered a 350 cubic-inch diesel engine that was a hasty-redesign of its highly respected V8 gasoline engine. In short order Pontiac, Chevrolet, Buick, Cadillac and even the GMC pickup all offered this faulty engine to the public. Its failure rate was astronomical. At its peak of unreliability, I know of several conversion shops that specialized in installing 350 Chevrolet gasoline engines in place of the diesel. This G.M. diesel fiasco soured thousands of American car owners on diesel power.
But with the advent of Volkswagen and Mercedes making strong bids to increase public acceptance of diesel-powered passenger car, the plight of that much-maligned powerplant may be brightening. Herr Professor Diesel would be proud.