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