By Todd KahoA long-held view for some is that diesels and the environment are singularly incompatible. In short, diesels are viewed as ancient agrarian society technology…noisy, smelly, underpowered engines spewing clouds of black smoke that block the sun.
In some ways that mental image is well-earned, as anyone who has driven behind old diesel trucks and buses can attest. However, those who follow the latest advances in clean diesel technology know that diesel’s future is cleaner, and better. Still, impressions of old are difficult to overcome.
Volkswagen, the world leader in diesel engine production, is betting heavily that clean diesels are a valid and appropriate answer to many of the energy and environmental questions facing America and the world today. Acceptance of diesel powered passenger cars and SUVs in the U.S. would have a huge impact on our energy independence, particularly with a potential infusion of domestically produced biodiesel from renewable sources.
On average, a diesel engine delivers a 30 percent increase in fuel economy compared to a gasoline engine and a commensurate reduction in greenhouse gas emissions. Diesels are the most efficient internal combustion engines, firing on compression rather than an induced spark. Diesel fuel also delivers significantly higher energy content than gasoline yet is less flammable and explosive, making it a safer fuel. If new technology could allow diesels to fully meet stringent clean air standards, then diesels may well hold a clear advantage in both short- and long-term environmental strategies.
Unlike alternative fuels like hydrogen, the infrastructure to support clean diesel vehicles is already in place. The popularity of turbodiesel engines in light-duty pickup trucks – Dodge Cummins, Ford Powerstroke, and GM Duramax – has made diesel fuel more accessible than ever. No longer is it necessary to search out a truck stop to fuel up. A growing number of service stations have diesel right on the main fueling island.
Recently we had the opportunity to test drive a variety of Volkswagen’s TDI (Turbocharged Direct Injection) powered vehicles in the U.S. and Germany, and tour the automaker’s diesel research and development facilities in Wolfsburg. In Europe, Volkswagen offers a wide array of TDI powertrains ranging from a three-cylinder in its Lupo model on up to four, five, six, and 10 cylinder configurations. Driven by significantly higher fuel prices, diesel engines account for nearly half of VW’s sales in Europe.
Even though VW is only one of two automakers (along with Mercedes-Benz) currently offering diesel passenger cars in the U.S. market, TDI acceptance provides plenty of room for increasing diesel market share. The U.S.-spec “45-state” 1.9-liter TDI-PD (“Pumpe Duse”) engine offered in the Golf, Jetta, and New Beetle in most states represents 10 percent of the 320,000 VWs sold in the U.S. This is a highly loyal, dedicated owner base – many have multiple diesel VWs in their household. More TDI converts are likely with VW’s recent introduction of the 2.0-liter TDI Passat and 4.9-liter V-10 TDI powered Touareg luxury SUV to the American market. Considering that VW advertising campaigns in this country traditionally do not even mention the TDI, there’s certainly plenty of room for growth.
The most effective tool VW has for changing the diesel’s image is putting potential drivers behind the wheel for a test drive. The experience can quickly dispel the assumption that all diesels are underpowered. While horsepower figures may be lower than comparable gasoline internal combustion vehicles, torque figures are considerably higher… and torque is what you feel while driving. That torque delivers a sporty, fun feel, partly because maximum torque is produced at very low rpm, allowing you to feel the torque right off idle.
Driving the V-10 TDI in both the VW Touareg and Phaeton sedan on a variety of roads, including the Autobahn in and around Wolfsburg, was an enlightening and satisfying experience. The twin turbo 5.0-liter V-10 TDI produces an impressive 310 horsepower and 552 lbs-ft of torque at just 2,000 rpm. Coupled to a six-speed automatic, we found the V-10 to pull extremely well and drive the fun factor off the charts.
Comparing a European Passat 2.0-liter VW gasoline engine to a 2.0-liter TDI – the latter coming as a mid-2004 model year introduction in the U.S – is instructive. Both produce 130 horsepower, but while the gasoline engine makes 144 lbs-ft of torque at 3,300 rpm, the TDI produces a whopping 228 lbs-ft at just 1,900 rpm. Accel-eration figures from 0 to 60 mph are similar, with the TDI providing more torque-driven passing power evidenced by a two second quicker 50-75 mph time. Importantly, while the gasoline Passat offers a 30 mpg average, the TDI delivers a significantly higher 42 mpg. A U.S.-spec TDI powered Jetta sedan or wagon with manual transmission can manage 50 mpg on the highway, nipping at the heels of the new-tech gasoline-electric hybrids. The diminutive European 1.2-liter 3-cylinder TDI Lupo has achieved an amazing 78 mpg and meets year 2005 Euro 4 emission standards. Currently, 65 percent of all new VW diesels comply with this Euro 4 standard.
One of the missing elements of clean diesel in the U.S. is a lack of the low sulfur fuel that Europe has enjoyed for years. However, that will change as low sulfur diesel becomes widely available in 2006 when emissions laws mandate its use. In the meantime, low sulfur diesel is being test marketed in certain regions by such energy suppliers as ChevronTexaco, ConocoPhillips, and ARCO.
The first big step toward the modern clean diesel was taken over a decade ago with the introduction of direct injection technology in a turbocharged engine. Engineers have since refined the diesel with continuing advances in fuel delivery and injector design. The result is smoother and quieter diesel engines that produce more power. One of the tricks employed is delivering a small pre-injection of fuel at just the right moment prior to the main injection – a technique that noticeably quiets diesel operation. Modern unit-injector designs with strictly-controlled high pressure systems and tight tolerances, coupled with highly-efficient valve and combustion chamber designs, have cleaned up diesel emissions significantly while improving power and drivability. Significantly, particulate emissions have been reduced by over 90 percent in the past 15 years.
Exhaust aftertreatment systems are the final pieces of the clean diesel puzzle. Like catalytic converter technology in the 1970s, diesel aftertreatment technology (shown at left) is providing significant gains toward lowering tailpipe emissions. Current hardware includes an oxidating catalytic converter just behind the turbo exhaust outlet. Some applications also feature a NOx (oxides of nitrogen) catalytic converter behind this first catalytic converter. Removing particulates from the pretreated exhaust gas is handled by a diesel particulate filter, or trap, that separates particulates from exhaust gas and temporarily stores them. When particulate saturation reaches a predetermined level, a sensor raises exhaust temperature to incinerate the particulates and effectively regenerate the filter. All this is done seamlessly, completely unnoticeable by the driver.
Certainly, there is much work yet to be done before diesels will pass this country’s stringent LEV 2/BIN 5 emissions standards coming later this decade. Optimizing fuel injection, combustion, and aftertreatment systems holds promise, and the view from Wolfsburg is that it will happen, and on time. From Volkswagen chairman Bernd Pischets-rieder on down, there is a resolute belief at VW that clean diesel is not just a short-term solution, but a viable powertrain for decades to come.
That said, VW isn’t counting hybrid technology out either. Can you imagine the fuel economy possible with a diesel-electric VW hybrid?
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