[BillK]

Anyone subscribe to R&T? There was a pro-diesel article this month. You can view the whole article here:

http://www.roadandtrack.com/article.asp?section_id=36&article_id=6665

With a significant battle for an environmentally safe and foreign-policy-friendly fuel source brewing among the major automobile manufacturers, diesel stands above all others in the areas of infrastructure, availability and future development capability. Due to a tumultuous history, however, this fuel often seems to get overlooked.

The Cars
Diesels get no respect. Case in point, a recent marketing survey done by Kelley Blue Book indicated that most consumers would not consider a diesel-fueled vehicle for future car purchases. We believe there is ample evidence to turn the consensus around.

While it may not seem like it, all the major auto manufacturers are aboard the diesel wagon, and most of them have been for many years — just not here. The American consumers' reluctance to purchase diesel-powered cars stems from the unreliable incarnations manufactured during the late 1970s and mid 1980s. Reliability was so bad, a class-action lawsuit ensued and a bad taste was left in the mouths of many buyers. Even the diesel cars that worked well were noisy, smelly and sooty. This meant, no matter how you looked at it, that an entire generation of drivers felt disdain for the fuel. Diesel power did not inspire passion, except for those who liked trucks.

Cut to today. Many years of development abroad have made diesels palatable, environmentally friendly (the same or less emissions per mile as a comparable gasoline-fueled machine), and, dare we say it, downright fun. Let's explore a diesel car that we'll be getting soon, another that's available now, and a concept that we definitely want.

BMW has a well-earned reputation for producing powerful cars that are fun to drive. Thanks to diesel engines, BMW can add fuel-efficient to the list. To see how far diesels have come, we got behind the wheel of a European-spec BMW 330d sedan. While the 330d is the "previous" generation of the 335d we're slated to get later this year, our experience with the sedan proved to be eye-opening in just how performance-oriented today's diesels can be. The diesel- and gasoline-fueled 3 Series models utilize the same chassis and accouterments, but the 330d features a turbo-charged inline-6 engine producing 228 horsepower at 4000 rpm and 369 lb.-ft. of torque from 1750 to 3000 rpm. In simple terms, the 330d is a torque monster.

Our test car came equipped with a clean-shifting 6-speed transmission and optional M parts that included wheels, steering wheel and body kit. Wider than those on a stock 3 Series, the sportier wheels and tires were still no match for aggressive DSC-off, full-throttle shenanigans. The most surprising aspect was how controllable the midrange power was. Some would say the engine dynamics are boring, but in actuality, they're just a little different. Unlike a gasoline engine that, generally speaking, makes more power the faster you spin it, the diesel engine makes all of its mojo right in the thick of the powerband. Just keep the rev counter needle in the middle and you'll do no wrong. Aside from the inherently low redline of 4800 rpm and relatively bland engine tone, you'd never know you were driving a diesel.

Until it's time to fill up the tank, that is. We were able to achieve a real-world combined value of 31 mpg. What's more, since carbon dioxide, CO2, output is directly related to fuel consumption, according to BMW the 330d emits less CO2 per kilometer than the gasoline-fired 330i, at 163 grams per kilometer versus 173 g/km. Note, this is despite the fact that diesels produce a tad more CO2 per gallon consumed.

With the 330d already achieving such milestones, we can't wait to try the 335d. Thanks to a serial twin-turbo setup — a small turbo reduces low-rpm lag, while a larger turbo, mounted in-line, or in series, takes care of maximum power — the engine produces an additional 54 bhp (282 bhp) and 59 lb.-ft. of torque (428 lb.-ft. between 1750 and 2250 rpm). Needless to say, this should make the new car positively tire-shredding. Of course, with an increase in power comes an increase in consumption and CO2. Producing 178 g/km of CO2, it still emits much less than a current-spec 335i (222 g/km). On paper, the only fault we could find is the lack of a manual transmission for the new car.

We also had a chance to try the Mercedes-Benz E320 Bluetec sedan. Like the BMW, the E320 Bluetec features the same chassis and trim as its standard gasoline-powered stablemate. And again, just like the BMW, the use of a diesel engine ups the torque and mpg figures very nicely: 210 bhp and 400 lb.-ft. of torque for the diesel compared to 268 bhp and 258 lb.-ft. of torque for the comparable gasoline-powered E350, and 23 mpg city and 32 mpg highway for the Bluetec compared with a comparable gasoline-powered E350's 17/24 mpg, respectively.

Because of the inherently more dignified nature of the Mercedes (no casual drifting here), the driving experience of the two cars was nearly identical. An MSRP price point that's separated by just $1000 ($53,025 Bluetec versus $52,025 E350) really adds the proverbial fuel to the fire to promote the diesel powerplant. With the cost difference between diesel and premium fuel (the E350 requires premium) being fairly close, the increased mileage will be immediately felt in the pocketbook.

While the E320 is available now and the 335d will be available later this year, the one diesel-powered car that has the auto industry in a tizzy is the Audi R8 TDI concept. Equipped with a turbocharged 6.0-liter V-12, this midship-mounted engine is claimed to produce a whopping 500 bhp and an even more ridiculous 738 lb.-ft. of torque. All of this power will be transmitted to all four wheels via a 6-speed manual transmission. It's enough to bring grown men to their knees.

The Emissions
What's so different about emissions-control systems for diesel engines and just how do they work?

First, a quick background on diesel engines: Yes, they do cost more than gasoline engines, but this can be attributed to two factors. Diesel engines operate with higher compression ratios, so just about every part of the engine (the block, cylinder head, bearings, crankshaft, etc.) all need to be stronger than their gasoline counterparts. Diesel engines also require much more extensive exhaust after-treatment, which also adds to the cost.

They do, however, posses a greater ability to liberate power from fuel, thanks to the aforementioned high compression ratio and diesel fuel's naturally higher energy density per given volume. While a diesel's consumption advantage allows it to surpass gasoline in terms of CO2, it still lags behind in the critical soot and oxides of nitrogen, NOX, area. Costly after-treatment is currently the only alternative.

The E320 Bluetec and 335d feature two technologies to make these emissions much more manageable: urea injection to mitigate harmful NOX, and particulate filters to reduce dirty soot. Mercedes calls its system Bluetec, while BMW calls its system AdBlue.

After combustion, the exhaust flows into a catalytic converter that converts carbon monoxide and nitrogen monoxide into nitrogen dioxide and hydrocarbons. After that, an injector atomizes urea where the heat converts it into ammonia. This mixture then reacts in a second catalytic converter where the ammonia converts the exhaust into nitrogen (N2) and water.

Particulate filtration allows the once visibly dirty diesel engine to operate in today's clean tailpipe emissions society. As its name implies, the filter separates out particulate matter from the exhaust stream and holds it within its matrix. After a while, the matrix will become clogged with soot, at which point filter regeneration takes place. There are a few different solutions to filter regeneration, but the one commonality is that intense temperature, via the exhaust stream, is used to literally burn the soot off the filter matrix. High exhaust temperatures can be generated through either an engine-computer-commanded setting or the use of a dedicated fuel injector in the filter itself.

Both urea injection and particulate filtration technology have been designed to operate with minimal intervention by the driver. BMW's AdBlue supply, for example, can last as long as the car can go between routine service inspections, thereby ensuring a dealer-chaperoned urea refill at regular intervals.

Other Technology
Diesel engines operate under a property called controlled auto ignition (CAI). That is, they ignite themselves. Typically, when a piston of a diesel engine is going up in the cylinder on its compression stroke, a small amount of diesel fuel will be injected into the combustion chamber. This super-lean mixture lights off much easier than if the full amount of fuel was injected. After the preliminary injection, the full, power-producing injection event occurs. After this combustion, another injection event may occur to facilitate exhaust temperature heating for turbo operation, particulate filtration regeneration, or to "add fuel to the fire," so to speak, and help burn off any remaining fuel in the combustion chamber. Of course, the duration, timing and quantity of the fuel injected will vary due to load, atmospheric conditions and phase of the drive cycle (startup, idle, cruise and shutdown, for example).

The kicker is that all of this occurs without the diesel fuel actually mixing with the intake air the way gasoline engines operate. The fuel and air mixture stays separate, or stratified, until the moment of combustion. Therefore, the diesel fuel combustion process is called stratified charge compression ignition (SCCI). The super-heated and compressed air ignites the fuel when it's injected into the combustion chamber.

Another way of igniting a fuel-air mixture is through a process called homogenous charge compression ignition (HCCI). This process mixes the fuel and air into a homogeneous charge before compression, just like a traditional gasoline engine. And just like a traditional gasoline engine, gasoline is the fuel for this process!

By its very nature, HCCI is more volatile and difficult to work with than SCCI. "Engine knock," or the phenomenon in which the fuel-air mixture will ignite and burn due to a hot-spot in the combustion chamber, demonstrates that auto-ignition already exists in today's engine. If only the ignition events could be controlled...

As engine-control technology continues to evolve, the tools that allow an engine to operate under a controlled auto-ignition mode are slowly coming to pass. Variable cam timing and lift and direct injection are two such technologies. Currently, cylinder-pressure sensor technology is what most manufacturers cite as being the hold-up behind widespread implementation of this ignition mode.

Mercedes-Benz currently has a working prototype engine called the DiesOtto (combination of Diesel and Otto) that utilizes numerous technologies to control the HCCI process. Variable compression ratio, variable valve timing and lift and multiple turbochargers are some of the main components that are needed by the DiesOtto engine to initiate and maintain HCCI during the cruise phase of the drive cycle. Under startup and heavy load, the engine reverts to standard spark-actuated ignition.

The benefit to HCCI is obvious, offering all the power of a diesel-fueled engine with none of the ancillary (heavy and expensive) after-treatment systems of diesel.

While HCCI could very easily be the wave of the future, diesel fuel is here now. And with continuing advancements in pollution control, driveability and efficiency, it might just be the purist's next choice for fuel.

 

[Guest]

thanks, nice read.

 

[chittychittybangbang]

I found another diesel article in their archives from 2003, it's kind of fun comparing the old and new. We now have common rail pretty much standard in passenger cars and urea injection.

http://www.roadandtrack.com/article.asp?section_id=20&article_id=564

it's pretty long but i'll list it here anyways

Diesels made up 35 percent of Europe's 2002 new-car fleet; they're expected to surpass 50 percent by 2010. Yet the diesel's market share in the U.S. is a minuscule 0.26 percent. What do Europeans know that we don't?

Or what do we know that they don't?
As a concept, Rudolf Diesel's compression ignition has been around since 1893. This was 15 years after Nikolaus Otto demonstrated the efficacy of a spark-ignited 4-stroke powerplant (and 54 years after Sir William Grove came up with the idea of a fuel cell). And, in fact, after years of relative neglect, diesel research and development activities have become front-burner at automakers and suppliers around the world. As a result, today's high-performance diesel is a far cry from those black-smoke belching clatterers of yore.
But are we Americans ready for them? And are today's diesels up to the realities of tomorrow's environmental issues, both here and elsewhere around the world?
Let's delve into fundamentals. Then we'll examine why so many Europeans favor diesels, why few in the U.S. share this enthusiasm, and how things are likely to change for both over the next five years.

Compression? Or Spark?
Fundamentals separating the two types of automotive engines are their means of ignition and their control of power. As its name implies, a spark-ignition engine uses a sparkplug to initiate combustion of its compressed gasoline/air mixture. By contrast, with a diesel, intake air is compressed, fuel is sprayed in, and ignition occurs through the heat of compression alone; thus, the term compression ignition, CI, versus spark ignition, SI.
Output of a spark-ignition engine is controlled by throttling the intake air while precisely balancing the amount of fuel. In a sense, an SI engine gets strangled at light load; it breathes most freely at wide-open-throttle (a relatively rare condition, even with us enthusiasts).
By contrast, output of a CI engine is determined solely by the amount of fuel entering the combustion chamber; the air enters utterly unthrottled. Thus, a diesel has no added pumping losses at light load, and this is a fundamental reason for its frugality with fuel.
An SI engine's fuel/air mixture is compressed to around 1/10 of its intake volume; i.e., a compression ratio around 10:1. A typical CI engine's compression ratio is 20:1 or beyond. This higher compression enhances CI thermal efficiency; it also requires heavier components capable of withstanding greater combustion pressures.
With SI, the balancing act of air and fuel is important, because its combustion occurs ideally at a single particular air/fuel ratio, the stoichiometric one of 14:1 by weight. It can be finessed to run leaner; i.e., in lean-burn regimes of perhaps 30:1, but not without the complexities of direct injection and other tradeoffs. By contrast, in controlling output from full power to idle, a CI air/fuel mixture continues to ignite at 100:1 and leaner, another reason for a diesel's light-load efficiency.
In general, it's estimated that a diesel offers a fuel-economy benefit of perhaps 25-30 percent compared with an SI engine of similar displacement.

High End? Or Middle of the Barrel?
Both gasoline and diesel fuel are primarily petroleum products. There are biofuels of each type, but none has proven feasible in the large scale. Diesel fuel, like kerosene and jet fuel, is a middle distillate; gasoline, a lighter, high-end product.
Distressingly enough, in the old days when lamp and lubricating oils were the petroleum products in demand, high-end distillates were dumped into rivers and streams! Today, refineries are optimized for output, but still not without tradeoffs. The Europeans, for instance, refine so much diesel fuel that they end up with a glut of high-end product, some of this gasoline actually being sent our way. U.S. refineries favor cracking techniques that get more high-end out of the entire barrel. Ironically, one byproduct of this is an overproduction of diesel — but it's the wrong kind of diesel, with indifferent cetane and too much sulfur.
Just as octane measures the goodness of gasoline (actually, its knock resistance), cetane is the diesel's measure of quality. Briefly, cetane is inversely related to ignition lag; the higher the cetane, the less lag, the better the fuel. European diesel fuel is around 55 cetane; ours, more like 42-44.
Sulfur is the real problem, though, now and with future emissions controls, here and in Europe. Petroleum crudes vary from source to source. Benchmark Arab Light, for example, is a sweet crude (i.e., low in sulfur). Mayan and other Central American sources are considerably more sour. Refineries can finesse costs of crude supplies and sulfur removal, but only so far.
Sulfur in U.S. diesel fuel averages around 350 parts per million, 500 ppm being not unknown. In Europe, the absolute cap is 300 ppm; average levels are perhaps 175. In fact, Europeans already have low-sulfur diesel available with a maximum of 50 ppm, phasing down to 10 by 2005. We have low-sulfur diesel as well, but only in California. We also have similar national goals seen as crucial in meeting increasingly stringent (and immensely complex!) emissions-control standards phasing in between now and 2007. For example, by June 2006, 80 percent of U.S. diesel fuel sold by major refineries has a 15-ppm limit; this, rising to 100 percent by 2010.

HC, CO and CO2? Or NOx and Soot?
SI and CI powerplants differ radically in their engine-out (i.e., inherent) emissions. In particular, a diesel's hydrocarbon and carbon moNOxide emissions are much lower. And, as CO2 output is essentially proportional to fuel consumption, a diesel exhibits a marked advantage in this regard as well. However, its exhaust still requires aftertreatment. And exhaust-stream differences complicate its downstream controls.
Diesel combustion is hotter than an SI's; thus it produces more oxides of nitrogen, NOx. Yet its exhaust temperatures are considerably cooler, especially so if the engine is turbocharged (and thus extracting heat to drive the turbo). In fact, depending on load, diesel exhaust temperatures can be cooler by some 150 to 300 degrees Fahrenheit. Plus, as a diesel always operates with an excess of air (recall its unthrottled nature), there's always an overabundance of oxygen in its exhaust.
Lack of heat is bad news for just about any form of catalytic conversion. And a glut of oxygen is entirely the wrong condition for reducing NOx. Ironically, even though a diesel's emissions characteristics are not unfavorable, its exhaust stream is not particularly amenable to downstream treatment.
And there's soot. Particulates, to give them their proper name, are an inherent byproduct of diesel combustion. And, note, I'm not talking about the black smoke of an ill-maintained diesel. Particulates are micro-sized, all the more injurious to our lungs and all the more difficult to trap. What's more, diesels generate an elemental quandary of particulates and NOx: The hotter the combustion, the less particulates — but the more NOx. There's excellent argument that diesel particulates — and not CO2 — constitute the most hazardous byproduct of automotive transportation.

Why Europeans Like Their Diesels
Part of the European love affair with the diesel makes a lot of sense. Part is what I perceive as Eurocentric posturing on environmental issues.
Largely because of taxation, motor fuels have always been exceptionally expensive over there. Thus, a diesel's inherently better fuel economy is a real attraction. Also, in many European countries, there are tax-invoked differences between diesel and gasoline prices. Belgium is the most striking case, with diesel going for the equivalent of $2.98/gal. versus gasoline priced at $4.02/gal. Curiously, though U.K. taxation is absolutely throttling, the situation there is similar to ours: gasoline is $4.71/gal.; diesel, $4.80/gal.
A Brit might consider a diesel for its fuel economy. A Belgian motorist would be most profligate not to buy a diesel.
Also, there's the larger issue of environmentalism — particularly CO2 and its effect on global warming. I'll rant another time and place (this, after all, is what my Tech Tidbits column is for), but suffice to say the European Community has really bought into automotive CO2 as a significant contributor to global warming. Governments offer incentives beyond fuel taxation for buying diesels. Also, in many countries, registration costs are keyed to engine size, and small-displacement turbodiesels provide what customers want — namely, torque.

Common Rails, Unit Injectors and Multiple Squirts
The modern diesel engine has evolved into quite the engineering marvel. Diesel technology was slow to adopt electronic engine management, but today's designs have evolved quickly and continue to exhibit a great deal of potential.
A common-rail diesel injection, for instance, operates at extremely high pressure, as high as 24,000 psi. This common rail is an accumulator as well as distributor, thus decoupling fuel pressure from engine rpm. Volkswagen opts for the same high-pressure decoupling, but with a different strategy. Its unit injectors combine pumping and injection in single assemblies, one per cylinder. With either approach, fuel injection can occur when and how engineers deem optimal.
As an example of its benefit, common-rail injection all but eliminates diesel clatter. With traditional CI, this ringing of the cylinder block is a response to irregular combustion in unexpected regions of the chamber (the diesel's equivalent of knock). Today's systems pre-condition the combustion through multiple-injection strategies, with one or two pilot injections at precise time and location. These pilot events are of extremely short duration, 40 microseconds, and involve tiny amounts of fuel, on the order of 1 mm3.
Nor is the main injection a simple squirt. Piezoelectric injectors vary their nozzle geometry for super-fine, high-speed metering (see Tech Tidbits, August 2002). Arcane modeling techniques like genetic algorithms have suggested multiple events in this phase as well (see Tech Tidbits, February 2001).
What's more, post injections are used, one to complete the burn for reduced engine-out emissions, a second used intermittently to spike downstream HC, increasing temperatures for enhanced aftertreatment.
In the old days (10 years ago!), for each liter of displacement, diesels produced perhaps 45 bhp and around 70-80 lb.-ft. of torque. Today, figures are 75 bhp/liter and 110-120 lb.-ft./liter. It's no wonder that Europeans enjoy their diesels — so far.

Why Don't We Like Diesels?
The American experience with diesels has been, at best, a mixed one. Mercedes-Benz, Volkswagen and others have been in and out of the diesel market over the years. Oldsmobile soured the well in 1978 by coming to market with what turned out to be, in retrospect, a poorly-dieselized version of GM's 350-cu.-in. V-8. There never has been a price differential in favor of diesel fuel in this country. Last, heavy trucks — and truck stops — hardly added to diesel's passenger-car appeal.
Our emissions regulations haven't favored them (unlike in Europe, where standards are diesel- and gasoline-specific). As an example, California's South Coast Air Quality Management District has banned diesels from public vehicle fleets, and as recently as October 2002 a U.S. Circuit Court upheld this ban.

But Things Are Changing
Ironically enough, this court action was about the same time that the chairman of the California Air Resources Board spoke favorably of diesels in achieving the state's air quality objectives. And there has always been a dedicated band of knowledgeable diesel enthusiasts.
At the moment, Volkswagen's Golf, Jetta and New Beetle 1.9 TDIs are the only diesel-powered cars available here. In 2002, these turbocharged direct-injected VW diesels hardly dominated with only 15 percent of Golf, Jetta and New Beetle sales. However, whenever gasoline prices soar (as they inherently do from time to time), VW wishes it had scads more to sell. With this in mind, its Passat is getting a diesel later this year and the Touareg SUV will have a 5.0-liter V-10 TDI diesel in summer 2004.
Mercedes will bring us its E320 CDI (as in common-rail diesel injection) in 2004. Also in 2004, Jeep will offer its diesel Liberty already available outside North America. (By the way, there are also diesel PT Cruisers, built in Mexico but for Europe only. California-spec diesel fuel has to be trucked to the plant to fuel them; Mexican diesel would poison them with sulfur.)
Ford is studying plans for offering a diesel Focus within the next five years. Other U.S.-available diesels are concentrated toward the large end of the light-truck segment. Fully two out of three Ford F-Series Super Duty trucks, for instance, are diesel.

Diesel Clouds Ahead?
A lot of U.S. diesel activity is based on proposed hikes in the light-truck Corporate Average Fuel Economy standard phased in over 2005-2007. The class (which includes many pickups, minivans and SUVs) will likely face a 7.2-percent increase in mpg. Automakers are scrambling for SUV fuel efficiency, and dieselization is a straightforward 25-30-percent improvement.

 

[chittychittybangbang]

rest of the article

There's a downside, though, both here and in Europe. Increasingly stringent emissions-control regulations challenge the diesel even more than its spark-ignition counterpart. In a sense, it's like the SI engine back in the 1970s, at the beginning of 3-way catalysis. Even with ultra-low-sulfur fuel, it's not clear that our coming NOx and particulate regulations can be met.
And some pretty bizarre technology has been proposed. In response to Europe's Stage IV regulations, for instance, the PSA Peugeot Citroën HDI series has a silicon-carbide particulate filter that traps soot for some 250 miles, then requires a minute dose of rare-earth-derived compound to regenerate the device through superheating (around 850 degrees Fahrenheit!). A separate 1.3-gal. tank of this cerium-based Eolys additive needs replenishment every 50,000 miles or so.
Others are studying NOx reduction in a catalytic converter fed a combination of diesel exhaust and urea, an ammonia-based compound.

CSI's Catalyzed Trap
Oxnard, California-based Catalytic Solutions Inc. has teamed up with Japan's Asahi Glass Co., Ltd. to develop a catalyzed particulate filter for meeting Europe's Stage IV and Stage V regulations. Asahi's silicon-nitride honeycomb has very small particle size, all the better for high surface area and optimal catalyst coating. The CSI catalyst coating uses relatively low levels of precious metals; this, to improve light-off temperature yet reduce cost.
Its duty cycle depends on soot accumulation within the honeycomb's tiny passages. Periodically, a backpressure sensor recognizes the need for eliminating the accumulated soot. Subtle changes in fuel injection enhance catalytic activity and cause a temperature rise in the catalyst, thus promoting this downstream soot combustion. CSI's catalyst enables rapid soot combustion during this regeneration event. Most important, this action is imperceptible to the driver.
I've written about CSI before (see "Technology Update: Clean the Sky! Wash the Wind!" April 2001; and Tech Tidbits, June 2001). This current research and development may once more "clean the sky and wash the wind," only this time, to the benefit of Rudolf Diesel's compression-ignition concept.

 

[Guest]

A lot of U.S. diesel activity is based on proposed hikes in the light-truck Corporate Average Fuel Economy standard phased in over 2005-2007

Lol, written in 2003, has this happened yet? I think CAFE passenger car standards were just raised. I remember reading about zero emissions cars in CA back in the early 90s. That didn't happen either.