In America, we have presumptions about diesel fuel that are based on two things: First, the diesel-powered cars many people drove in the 1970s. Second, the column of black smoke pouring from the exhaust stacks of a poorly running big rig. But in the last 20 years both diesel technology and the fuel itself have gone through incredible transformations that make them cleaner to utilize than their gasoline counterpart. Here's how:
The basics of diesel fuel
Diesel fuel — along with gasoline, kerosene, jet fuel and many other distillates — starts from the same base material: Crude oil. Petroleum-based diesel fuel is subjected to a process called "fractional distillation," during which crude oil is heated to between 392˚F and 662˚F.
Because diesel fuel is distilled at a higher boiling point than gasoline, diesel fuel is more dense than gasoline. It just plain weighs more: about 6.943 pounds per U.S. gallon of diesel, versus 6.217 pounds per US gallon of gasoline. That density translates into more energy — technically called "volumetric energy density" — by volume. Measured in British Thermal Units (BTUs), a gallon of diesel fuel contains about 147,000 BTUs, versus gasoline's 125,000 BTUs, so your Audi TDI® clean diesel simply takes less fuel to go further.1
The (former) diesel tradeoff
Diesel inherently offers better efficiency than gasoline.1 It's why heavy trucks around the world depend on it. But in years past, the tradeoff for using diesel fuel was higher emissions. The fuel was less refined and contained a lot of sulfur, which translated into some pretty nasty emissions.
But since 2006, the United States has enacted much more stringent rules for diesel fuel that have required refineries to dramatically reduce the sulfur it contains. Today's diesel fuel contains 97 percent less sulfur than the fuel produced as late as 2005. The transition to ultra-low sulfur diesel (ULSD) began in 2006 and became mandatory in 2010.
The benefits of ULSD
With the introduction of ULSD, Audi developed a series of technologies that enabled its array of TDI® clean diesel vehicles — the A6 and A7 sedans, the Q5 crossover, the Q7 SUV, and the flagship A8 L — to not only help capitalize on the power contained in a drop of diesel fuel, but to trap even more pollutants, helping Audi TDI® clean diesel vehicles produce lower CO2 emissions than gasoline-powered automobiles.1
A network of sensors on board each Audi TDI® clean diesel vehicle help monitor the soot level and emissions of the exhaust, filtering excess pollutants and particulate emissions at a rate of up to 95 percent. The diesel particulate filter catches particles to help clean the exhaust under normal driving conditions, but in city driving, when engine load is much lower, the system keeps exhaust temperature at an optimal range between 1,150˚F and 1,200˚F, helping to oxidize soot before it even reaches the filter.
Simultaneously, Audi TDI® clean diesel cars, crossovers, and SUVs employ an AdBlue® reducing agent that injects a mixture of 32 percent urea and water, helping to turn nitric oxide (NOx) emissions into nitrogen and oxygen. This additive is 50-state emissions-compliant and helps make diesel fuel even cleaner.
Audi is leading the way in developing these technologies, all to help you enjoy a performance-oriented driving experience, with much greater fuel efficiency and lower emissions. Audi brings 40 years of diesel experience. It's time to experience Audi TDI® clean diesel for yourself.
1 See www.fueleconomy.gov for EPA fuel economy estimates and emissions details. Your mileage and emissions will vary and depend on several factors including your driving habits and vehicle condition.