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Turbo Direct Injection (TDI) is the technology used for modern diesel engines produced by Volkswagen Group, and is widely used in passenger cars produced by the company (especially those sold in Europe).

Contents 1 Overview 2 History 3 Fuel 4 See also 5 References 6 External links

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. These, in combination, allow for greater engine performance while also decreasing harmful emissions and providing more torque than its gasoline counterpart.

Similar technology has been used by other companies but "TDI" refers to these Volkswagen Group engines. Normally-aspirated engines (those without a turbocharger) made by Volkswagen Group use the label "Suction Direct Injection" (SDI).

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. 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. While Pumpe Düse engines had a significantly higher injection pressure than older engines they could not 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 in 2008 are using the common rail technique with piezoelectric injectors.

A racing version of the common rail TDI engine made an impact in 2006 when it was used in the Audi R10, which won the 12 Hours of Sebring and 24 Hours of Le Mans, becoming the first diesel-powered car to win either of those races. Fuel economy was a significant factor as the car didn't have to refuel as often as others in the race. The car used a special synthetic diesel blend as fuel.

Direct injection turbodiesel engines are frequent winners of various prizes in the International Engine of the Year Awards. In 1999 in particular 6 out of 12 categories were won by direct injection engines: 3 were Volkswagen, 2 were BMW and 1 Audi. Notably that year the Volkswagen 1.2L TDI beat the Toyota Prius to win "Best Fuel Economy" in its class.

Like most diesel engines, TDI engines can run on petrodiesel or B5, B20, or B99 biodiesel.

In terms of fuel efficiency, and clean emissions when run on biodiesel or SVO/WVO, TDI engines are among the best on the market. This is often overlooked because they do not drive on gasoline. As an example, a 2007 Volkswagen Jetta 1.9L TDI with 5-speed manual achieves 5.2l/100km (54 mpg UK or 45 mpg US) on the European combined-cycle test while a DSG automatic reaches 5.9l/100km (48 mpg UK or 40 mpg US).^[1]

Newer TDI engines, with higher injection pressures, are less forgiving about poor-quality fuel than their 1980s ancestors. Since fuel quality can vary when using WVO/SVO or biodiesel, only mixtures up to B5 are officially allowed. Doing otherwise can void the TDI's warranty. No. 2 diesel fuel is recommended since it has a higher cetane number than No. 1 fuel and has lower viscosity (better ability to flow) than heavier fuel oils. Some owners in North America, where cetane levels are generally poor (as low as 40), use additives and/or premium diesel to get cetane numbers closer to the standard levels found in the European market (at least 51) where the engine is designed. Improved cetane reduces emissions while improving performance and potentially increasing fuel economy.

• List of Volkswagen TDI engines
• Diesel engine
• Turbodiesel
• Common rail

1. ^ Jetta engines. Volkswagen. Retrieved on 2007-06-04.

• myturbodiesel.com A turbodiesel technical forum and "how to" page for Volkswagens.
• TDI Club A comprehensive source for all TDI information.
• VW Golf TDI Review of Volkswagen Golf TDI automobile