Turbocharged direct injection


Turbocharged direct injection or TDI is a design of turbodiesel engines featuring turbocharging and cylinder-direct fuel injection that was developed and produced by the Volkswagen Group (VW AG). These TDI engines are widely used in all mainstream Volkswagen Group marquesof passenger cars and light commercial vehicles made by the company (particularly those sold in Europe). They are also used as marine enginesin Volkswagen Marine and Volkswagen Industrial Motor applications.
Some TDI engines installed in 2009 to 2015 model year Volkswagen Group cars sold through 18 September 2015 had an emissions defeat device, which activated emissions controls only during emissions testing. The emissions controls were suppressed otherwise, allowing the TDI engines to exceed legal limits on emissions. VW has admitted to using the illegal device in its TDI diesel cars.
In many countries, TDI is a registered trademark of Volkswagen AG.
The TDI designation has also been used on vehicles powered by Land Rover-designed diesel engines. These are unrelated to Volkswagen Group engines.
The TDI engine uses direct injection, where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder, rather than the pre-combustion chamber prevalent in older diesels which used indirect injection. The engine also uses forced induction by way of a turbocharger to increase the amount of air which is able to enter the engine cylinders, and most TDI engines also feature an intercooler to lower the temperature (and therefore increase the density) of the 'charged', or compressed air from the turbo, thereby increasing the amount of fuel that can be injected and combusted. These, in combination, allow for greater engine efficiency, and therefore greater power outputs (from a more complete combustion process compared to indirect injection), while also decreasing emissions and providing more torque than the non-turbo and non-direct injection petrol engined counterpart from VAG.
Similar technology has been used by other automotive companies, but "TDI" specifically refers to these Volkswagen Group engines. Naturally aspirated direct-injection diesel engines (those without a turbocharger) made by Volkswagen Group use the Suction Diesel Injection(SDI) label.
Because these engines are relatively low displacement and quite compact, they have a low surface area. The resulting reduced surface area of the direct injection diesel engine reduces heat losses, and thereby increases engine efficiency, at the expense of slightly increased combustion noise. A direct injection engine is also easier to start when cold, because of more efficient placing and usage of glowplugs.
Direct injection turbodiesel engines are frequent winners of various prizes in the International Engine of the Year Awards. In 1999 in particular, six out of twelve categories were won by direct injection engines: three were Volkswagen, two were BMW, and one Audi. Notably that year, the Volkswagen Group 1.2 TDI 3 L beat the Toyota Prius to win "Best Fuel Economy" in its class. The TDI engine has won "Green Car of the Year" award in the years 2009 (Volkswagen Jetta 2.0-litre common-rail TDI clean diesel) and 2010 (Audi A3 TDI clean diesel) beating other various electric cars.

Emissions testing falsification

On 18 September 2015 the US EPA and California Air Resources Board served notice to VW that approximately 480,000 VW and Audi automobiles equipped with 2.0 TDI engines sold in the US between 2009 and 2015 had an emissions compliance defeat device installed. The defeat device, in the form of specially crafted engine management unitfirmware, detects emissions testing conditions, and in such conditions will cause the vehicle to comply with emissions regulations by properly activating all emissions controls. However, under normal driving conditions, the emissions controls are suppressed, allowing the engine to produce more torque and get better fuel economy, at the expense of emitting up to 40 times more nitrogen oxides than allowed by law. Such NOx emission levels are not in compliance with US regulations. VW has since admitted to these allegations, and said that the illegal software was in use in its diesel cars worldwide, affecting some 11 million vehicles.


The fuels required for TDI engines include diesel fuel (also known as petrodiesel), or B5, B20, or B99 biodiesel, depending on emissions equipment, location dependent.
A 2007 Volkswagen Jetta Mk5 with a 1.9 TDI engine and a five-speed manual transmission achieves 5.2 litres per 100 kilometres (54 mpg‑imp; 45 mpg‑US) on the European combined-cycle test (an US EPA test of the same vehicle would achieve around 34 MPG), while a six-speed direct-shift gearbox (DSG) automatic version reaches 5.9 litres per 100 kilometres (48 mpg‑imp; 40 mpg‑US).
Newer TDI engines, with higher injection pressures, are less forgiving about poor-quality fuel than their 1980s ancestors. Volkswagen Group's warranty does not cover damage due to bad fuel (diesel or bio), and has in the past recommended that only mixtures up to 5% biodiesel (B5) be used. Volkswagen Group has recently permitted mixes up to B20, and has recommended B5 be used in place of 100% petroleum-based diesel because of biodiesel's improved lubricating properties.
In North America, 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, 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 may increase fuel economy.
New ultra low-sulphur petroleum-only diesels are known to cause some seals to shrink, and may cause fuel pump failures in TDI engines used in 2006 to 2009 models. TDI engines from 2009 on and before 2006 are designed to use ULSD exclusively; biodiesel blends are reported to prevent that failure


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