The Resurgence of the Diesel Car
In the 1970s, half of all Mercedes-Benze’s sold in the U.S. were equipped with diesel engines. Other automakers took notice and released a range of diesels in their products in the early 1980s. However, poor fuel quality, crude designs and phenomenal failure of GM’s small block diesel V8 doomed the diesel here. Regardless of how fuel efficient they might be, diesels got a reputation for being too unreliable and too lethargic to suit American buyers.
In Europe, however, the story was different. Higher gas prices and less demanding driving conditions kept diesels on the market, and years of development made them a good choice for factors other than mileage. Today, over half of vehicles sold in Europe are diesels with oil burners in everything from the fuel-sipping VW Lupo to BMW’s high performance M line. Now, the diesel is posed for a comeback in America thanks to a combination of factors:
For a long time, diesel engines were simply too dirty to meet U.S. emissions regulations, limiting their use to more loosely regulated commercial trucks. The high heat conditions inside the combustion chamber fuses together nitrogen and oxygen in the air to form nitrous oxides (NOx.) Automakers had limited success combating NOx emissions by injecting more fuel into the engine: While it kept NOx from forming, it also reducing fuel economy and power
Diesels now combat this pollutant with urea injection. This chemical turns NOx from the exhaust into ammonia, which can be broken down by a catalyst into N2 and H2O, the same nitrogen and water already found in the air. This way the engine can run a leaner mix for better overall performance.
These technologies have been around for a while, but the last stumbling block was removed with the introduction of Ultra Low Sulfur Diesel. Not only is sulfur a direct pollutant, it also damages the catalyst used with urea injection systems. By offering this fuel mixture to customers, automakers could finally use the same technology they had been offering in Europe.
Hybrid Fuel Economy Without the Complexity
While the Passat TDI may match the fuel economy of its hybrid competitors, it costs thousands less. Automakers are taking notice, and are adapting their European motors for U.S. requirements.
Gasoline Engines are Nearing Diesel Complexity
Not too long ago, the direct injectors, thicker blocks, high pressure fuel pumps and turbochargers used in diesel engines made them far more expensive than their gasoline counterparts. Now that gas engines are adapting these parts, their prices have gone up. On the other hand, increased manufacturing of these parts has lowered the manufacturing costs of diesels, further eroding the price difference between these two engines.
Diesel engines have always made a lot of torque, especially at low RPM. This means they can move lots of weight and climb steep hills at low engine speeds, making them better performers on the highway than gas engines. Improvements in turbocharger technology has greatly improved high RPM performance, increasing horsepower and cutting acceleration times.
Meanwhile, American enthusiasts have come to realize the potential power of diesel-equipped consumer trucks, creating a niche for diesel drag racing. This has all but erased the diesel’s reputation for slowness.
Mercedes Benz now has a hybrid system that combines an electric motor with a four cylinder diesel, providing the power needed to move large vehicles and the fuel economy expected from small hybrids. Under European testing, an E Class wagon equipped with this combination can get 45 mpg on the highway, efficiency otherwise unheard of in a full size luxury car. This technology offers the best fuel efficiency possible outside of electric vehicles.