Why won't diesels catch on? Part 2

January 1, 11:52 PMOrlando Auto ExaminerMichael Block

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Honda i-CTDi clean diesel engine/courtesy of edmunds.com

My last article discussed some of a diesel engine's advantages over a gasoline engine, such as the fuel economy improvement thanks to significantly more efficient operation. Also, because of its sturdier engine design and its impervious resistance to preignition, a diesel engine will likely outlast a gasoline engine.

I left the best for last, however, and teased about the edge in performance potential a diesel engine can have over a gasoline engine.

So, without further ado, here is part 2 of my exploration of the diesel engine and its advantages.

Because a diesel engine has such a high compression ratio, it moves a lot more air a lot sooner than a gasoline engine does. Thus, diesels' most notorious claim-to-fame for speed is their immense torque. A normal 2.0L 4cyl gasoline engine will make anywhere from 90 to 120ft-lbs of torque, while a nearly identical 2.0L 4cyl diesel engine can make somewhere around 220ft-lbs of torque. Furthermore, while that gas engine likely makes its small torque around 4000rpm, the diesel can produce its large torque figure at around 1500rpm. For a diesel, this translates into a fantastic launch from a stop, where it can be putting down nearly three times the torque a gasoline engine can. Low-RPM torque is essential in racing as well, where a car that comes out of a corner on full-steam can edge in front of a car that is stumbling to get its RPMs up higher to make power.

The other distinct advantage is a byproduct of the aforementioned premise that diesels are much more resistant to knocking. What's most surprising about it, though, is that this characteristic makes a diesel ideal over a gasoline engine for producing ridiculous amounts of power.

As noted before, internal combustion engines are made to produce large amounts of horsepower on one basic law: the more air they can move, the more power they can make. A gasoline engine, if tuned exactly right, with very close monitoring of the air-fuel ratio and ignition timing, can produce a lot of horsepower... until it starts knocking. A diesel engine, however, is prone from knocking as long as it receives enough fuel to match the incoming air. So a diesel engine with an unlimited amount of air and fuel is then only limited by its own inherent design; if the internal engine components (crankshaft, pistons, rods, etc.) can handle it, a diesel engine can essentially make unlimited power.

That unlimited amount of air usually comes from a device that is so compatible and receptive to a diesel engine, that virtually all diesel engines sold in the world now come with them as standard equipment: turbochargers. Turbos work so well with diesel engines because, as mentioned, diesels are inherently more prepared than gasoline engines to handle an artifically forced intake charge, and also because a diesel engine does not have a throttle body for a turbo to work against (to answer another lingering question, no, a turbodiesel engine does not need a recirculating bypass, a.k.a. "blow-off", valve).

So... where do we stand? We've stated that diesel engines are more efficient by design, more durable and reliable, and now we have even shown that a diesel can perform with, and even above, a gasoline engine in motorsport applications. For a real-world example of diesel engines' successes in racing, simply read up on the statistics and track records of Audi's and Peugeot's Le-Mans prototype diesel race cars, the R10 TDi and 908 HDi FAP, respectively.

But. as I said in the previous article... diesels have failed to win over American buyers for decades. In fact, for the 2009 model year, only two manufacturers offer diesel automobiles (aside from trucks) to the general public: Mercedes and Volkswagen.

Americans have largely turned their noses up at diesels for several reasons. However, with the advent of new technology and stricter standards, those reasons have essentially been rendered obsolete.

Old diesels were noisy. Because the more advanced direct-injection systems that most diesels utilize today hadn't been developed yet, diesels of yesteryear essentially threw one big splash of fuel at the awaiting compressed air. That one big ignition of fuel got the job done, but it produced a loud tap, which made a running diesel engine sound like it had "a bunch of bottle caps rattling around inside the engine." But with direct-injection and more accurate fuel metering systems, a fuel injector can actually deposit several smaller, sequential squirts of fuel into the cylinder during one combustion cycle. This allows the fuel to burn more slowly and uniformly, thus greatly reducing the diesel's famous "bottle-cap" tapping.

Diesel engines, due to their higher combustion temperatures, have actually always emitted less carbon-monoxide than gasoline engines. However, in the past, diesel fuel had high sulfur content, which is emitted from the engine as black soot, also known as particulate emissions. Trucks and buses of days gone by were frequently seen bellowing out plumes of black smoke from their tailpipes. But in 2006, fueling stations began to sell ultra-low-sulfur diesel fuel, or ULSD, which contains 15ppm (parts per million) sulfur, 97% less sulfur than the old 500ppm diesel fuel. Now, most fueling stations nationwide sell ULSD, and ULSD will be required nationwide by December 2010. This drastic reduction in sulfur particulates in diesel fuel mean that the pollution complaints and environmental concerns of yore, now no longer apply.

Now, the inconvenience factor; this is still unfortunately a viable concern.

Diesel fuel is not available at every fueling station in America, so an extra bit of anticipation and planning is involved in operating a diesel vehicle to ensure that a fueling station that carries diesel is nearby when it's time to refuel. While diesel is cheaper in Europe, it is more expensive in America, so some of the potential savings of the increase in fuel economy are undermined by the higher fuel price. Finally, while diesels are more durable and reliable, they are inherently more costly to maintain. For example, oil changes are rarely less than $60 for a diesel. Repairs can also get quite costly, as some of the precision instruments that a diesel engine utilizes are expensive to replace, such as turbochargers, direct-injection components, etc.

Unfortunately, as the world economy tightens up and people are cutting costs anywhere they can, the initial investment of buying and maintaning a vehicle with a diesel engine appeals to only a few people who are willing to wait for the return of a long-lasting vehicle they can count on that also, over time, saves them money with better fuel economy.

But for those who do their research on diesel engines, understand their significant and distinct advantages over gasoline engines, and are willing to put up a few extra bucks up front, they will be richly rewarded with a vehicle that can go the extra distance, that can sip fuel, be immensely fun-to-drive along the way, and that makes good use of what is ultimately the superior design of the internal-combustion engine...

... the diesel.