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The Volkswagen TDI Biodiesel
Ask any American what comes to mind about a diesel vehicle and the first three things that will come out are: big trucks, noisy, slow, and dirty diesel fumes. The only problem is that description really applies to the archaic diesel engine. However, in all fairness, any diesel engine technically can run on biodiesel, thus eliminating the “dirty diesel fumes” that come from petrol diesel.
Just like its cousin, the gasoline engine, the diesel engine has benefited greatly from technological advances and one of the most enhanced diesel engines is the Volkswagen TDi. TDi stands for Turbo Direct Injection and is the technology used for modern diesel engines produced by Volkswagen Group. Unlike preceding diesel engines, the TDi runs more quietly and offers more power than typical diesels. The TDi engine is used in many of Volkswagen’s passenger vehicles, from the compact Golf hatchback to their new Touraeg SUV.
The engine uses direct injection where a fuel injector sprays directly into the engine cylinder rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine is coupled with a turbocharger and intercooler to increase the amount of air that can get into the engine cylinders, thereby increasing the amount of fuel that can be injected and combusted. In combination, these allow for greater engine performance while also decreasing harmful emissions.
The reduced material volume of the direct injection diesel engine reduces heat losses and thereby increases engine efficiency, at the expense of increased combustion noise. A direct injection engine is also easier to start when cold, due to the reduced heat loss of the design.
The first TDi engine was a 2.5L inline five-cylinder introduced in the Audi 100 in 1989. Over time, the TDI arrangement has been enhanced by improving the efficiency of the turbocharger, increasing the pressure at which fuel can be injected, and more precisely timing when the injection of fuel takes place. There have been a few major generations, starting with what are known as "VE" engines. In 2000, the Pumpe Düse (PD, variously translated "pump nozzle", "unit injector", "pump injector") engine began to appear in Europe, eventually coming to North America a few years later.
The PD design was a reaction to the development of common rail fuel injection by competitors; an attempt by Volkswagen to create an in-house technology of comparable performance that would not require any royalties to be paid. However, while Pumpe Düse engines had a significantly higher injection pressure than older engines, they couldn't keep up with common rail and weren't able to control injection timing as precisely (a major factor in improving emissions). PD technology was abandoned, and new engines appearing as of 2006 are using the common rail technique with piezo injectors.
These cars are the quietest, most fuel-efficient diesel passenger cars available in the U.S. market. They also have plenty of torque and power compared to the older diesel vehicles. The Jetta, Golf, and Beetle Tdis all share the same 1.9L Turbo Diesel Engines. Fuel economies vary depending on driving style, but the manual transmissions average 40-49mpg and automatic transmissions average 35-45 mpg. The Passat has a 2.0L Turbo Diesel engine. It is only available in an automatic transmission with a fuel economy of 32-37 mpg. The Touraeg has a 10 cylinder, 3.9L Turbo Diesel engine. Just like the Passat, it is only available in an automatic transmission, however with its significantly lower fuel economy of 17-22 mpg, we prefer to recommend the Passat wagon as a much “greener” alternative.
