Turbocharged direct injection

Turbocharged direct injection or TDI[1] is a design of turbodiesel engines featuring turbocharging and cylinder-direct fuel injection[1] that was developed and produced by the Volkswagen Group (VW AG).[2] These TDI engines are widely used in all mainstream Volkswagen Group marquesof passenger cars and light commercial vehicles made by the company[3] (particularly those sold in Europe). They are also used as marine enginesin Volkswagen Marine[4][5][6] and Volkswagen Industrial Motor[7] applications.

TDI engines installed in 2009 to 2015 model year Volkswagen Group cars sold through 18 September 2015 had an emissions defeat device,[8][9]which activated emissions controls only during emissions testing. The emissions controls were suppressed otherwise, allowing the TDI engines to exceed legal limits on emissions.[10] VW has admitted to using the illegal device in its TDI diesel cars.[11]

In many countries, TDI is a registered trademark of Volkswagen AG.[2]

The TDI designation has also been used on vehicles powered by Land Rover-designed diesel engines. These are unrelated to Volkswagen Group engines.

TDI badge

TDI embossed on the engine cover

Volkswagen Marine 3.0-litre V6 TDI 265-6 marine engine

Volkswagen Group products which feature a TDI engine display a TDI badge


The TDI engine uses direct injection,[1][2] where a fuel injector sprays atomised fuel directly into the main combustion chamber of each cylinder,[1][2] 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[1][2] to increase the amount of air which is able to enter the engine cylinders,[2] 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.[1][12] These, in combination, allow for greater engine efficiency, and therefore greater power outputs[2] (from a more complete combustion process compared to indirect injection), while also decreasing emissions and providing more torque[2] 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,[13] 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.


The Fiat Croma

The first passenger car to be powered by direct injection was the 1986 Fiat Croma 2.0 TD i.d. (The Turbo Diesel iniezione diretta pump was developed by Bosch in accordance with Fiat’s engineering specifications).

Rover introduced its MDI turbocharged direct injection diesel developed with Perkins, (also known as the Perkins Prima) in 1988 in the Rover Montego. It was also sold in marine form by Volvo. It used a Bosch VE injection pump. The engine had been launched in naturally aspirated form for commercial vehicles in 1986.

The first Volkswagen Group TDI engine was the Audi-developed 2.5-litre R5 TDI – an inline five-cylinder engine (R5), introduced in the Audi 100 in 1989  – and this variant is still used today in Volkswagen Marine applications. The TDI arrangement has been enhanced through various stages of development – 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”, and “VP” (German: VerteilerPumpe) engines,  which use a distributor-type injection pump. In 2000, the Pumpe Düse (PD, variously translated “pump nozzle”, “unit injector”, “pump injector”) TDI engine[1] began to appear in Europe, eventually coming to North America a few years later.

The Pumpe Düse design was a reaction to the development of high-pressure common rail fuel injection systems by competitors – an attempt by Volkswagen Group 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 are slightly less refined when compared to the very latest common rail  and, with the original solenoid-operated unit injectors, were not able to control injection timing as precisely (a major factor in improving emissions).  Some current PD TDI engines now use piezoelectric unit injectors, allowing far greater control of injection timing and fuel delivery.

From the 2009 model year onwards, TDI engines using the common rail (CR) technique, again with piezoelectric injectors, are now used in various Volkswagen Group models.[1] The CR engines are available in many sizes, including 1.2, 1.6, 2.0, 2.7, 3.0, 4.2 and 6.0 litres, with outputs from 55 to 368 kW (75 to 500 PS) from these engines.

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.[8][9] 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.[10] 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.[11]

Audi R10 TDI LMP race car

SEAT León Mk2 TDI race car

Motor racing

A motor racing version of the common rail TDI engine made an impact in March 2006 when it was used in the Le Mans Prototype (LMP) Audi R10 TDI, and made its debut win in the 12 Hours of Sebring race.[14][15][16] This victory was followed three months later by another one in the 24 Hours of Le Mans race, becoming the first diesel-powered car to win these prestigious endurance races.[17][18][19] Fuel economy was a significant factor, as the car did not have to refuel as often as petrol engined race cars in the race.[20] The car was fueled with a special synthetic V-Power diesel from Shell.[21] The Audi R10, R15 and R18 TDIs have won at Le Mans seven times in eight years, from 2006 to 2011, with only the 2009 race being won by Peugeot’s 908 HDi FAP, which is also a diesel powered car.

In 2007, SEAT—with the León Mk2 TDI at the Motorsport Arena Oschersleben in Germany—became the first manufacturer to win a round of the World Touring Car Championship (WTCC) series in a diesel car,[22][23] only a month after announcing it will enter the FIA World Touring Car Championship with the León TDI. SEAT’s success with the León TDI was continued, and resulted in winning consecutively 2008 World Touring Car Championship and 2009 World Touring Car Championship both titles (for drivers as well as for manufacturers).[24][25]

In 2008, SEAT – with the León Mk2 TDI at Donington Park in England – became the first manufacturer to win a round of the British Touring Car Championship (BTCC) in a diesel-powered car. Jason Plato won race 1 of the weekend and Darren Turner won race 3.[26]


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 (a 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).[27]

Newer TDI engines, with higher injection pressures, are less forgiving of 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.[28]

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,[29] 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.


  1.  b c d e f g h “Technology – TDI – Super-efficient diesel engines for power with economy”. Volkswagen.co.uk. Volkswagen UK. 2010. Retrieved 4 March 2010.
  2.  b c d e f g h “Volkswagen AG – TDI Technical Glossary”. Volkswagen.com. Volkswagen AG. Retrieved 5 November 2009.
  3.  “TB 20 addendum – Technical Bulletin for Volkswagen Group timing belt renewal intervals” (PDF). Gates.com. Retrieved 4 November 2009.
  4.  “Volkswagen Marine > Engines <“. www.vw-m.de. Volkswagen Group. 2009. Archived from the original on 19 July 2011. Retrieved 4 November 2009.
  5.  “Boat engines from Volkswagen Marine – Self-study programme M001 – Design and function” (PDF). www.vw-m.de. Volkswagen Marine. April 2001. Archived from the original (PDF) on 19 July 2011. Retrieved 18 February 2010.
  6.  “Boat engines from Volkswagen Marine – Self-study programme M002 – Design and Operation” (PDF). www.vw-m.de. Volkswagen Marine. August 2006. Archived from the original (PDF) on 19 July 2011. Retrieved 18 February 2010.
  7.  “The SDI 1.9 Industrial Engine” (PDF), www.mi-uk.com, Volkswagen AG, March 2005, archived from the original (PDF) on 14 July 2011, retrieved 4 November 2009
  8.  b Phillip A. Brooks (18 September 2015). “VW Notice of Violation, Clean Air Act (18 September 2015)” (PDF). US Environmental Protection Agency. Retrieved 20 September2015.
  9.  b “EPA, California Notify Volkswagen of Clean Air Act Violations”. US Environmental Protection Agency. 18 September 2015. Retrieved 20 September 2015.
  10.  b Jack Ewing and Coral Davenport (20 September 2015). “Volkswagen to Stop Sales of Diesel Cars Involved in Recall”. New York Times. Retrieved 21 September 2015.
  11.  b “Volkswagen Says 11 Million Cars Worldwide Are Affected in Diesel Deception”. The New York Times. 22 September 2015. Retrieved 22 September 2015.
  12.  TDI engines – Operation of these engines.
  13.  “Self-study programme 316 The 2.0 ltr. [sic] TDI engine” (PDF). Volkswagen AG.
  14.  “12 Hours of Sebring”. Audi Canada website. Audi Canada. Retrieved 11 January 2013.
  15.  “2006 Audi R10”. topspeed.com car reviewsTopSpeed.com. Retrieved 11 January2013.
  16.  “Bosch Clean Diesel Helps Audi Dominate American Le Mans Series”. Bosch website. Bosch NA. Retrieved 11 January 2013.
  17.  Richards, Giles (17 June 2012). “Audi is first manufacturer to take Le Mans 24 Hours race with hybrid”. guardian.co.uk website. London: The guardian. Retrieved 11 January 2013.
  18.  “Audi R10 TDI – a history maker”. Audi UK website. audi.co.uk. Retrieved 11 January2013.
  19.  “Audi on course for a 10th victory ?”. Auto News – Site officiel du MansLemans.org. Retrieved 11 January 2013.
  20.  “2006 Audi R10”. Stories by Audi, edited by Supercars.net. Supercars.net. Retrieved 11 January 2013.
  21.  “Shell V-Power Diesel race fuel takes Audi R10 TDI to historic victory at Sebring”. Shell website. Shell. Retrieved 11 January 2013.
  22.  “ROUNDS 15 & 16 – OSCHERSLEBEN, GERMANY RACE 1 REPORT” (PDF). WTCC Beru Race of Germany – Motorsport Arena, Oschersleben – 25 / 26 August 2007. FIA World Touring Car Championship. Retrieved 12 January 2013.
  23.  “First victory for SEAT León TDI”. SEAT motorsport. www.volkswagen-group-motorsport.info. Retrieved 12 January 2013.
  24.  “SEAT Leon TDI: A double-double world champion”. WTCC season review. London: The guardian. 18 December 2009. Retrieved 12 January 2013.
  25.  “Year by year SEAT’s racing history”. SEAT sport website. SEAT sport. Archived from the original on 13 March 2012. Retrieved 12 January 2013.
  26.  “BTCC race reports 04/May/2008”. BTCC Donington Park. BTCC. Retrieved 12 January2013.
  27.  “Jetta engines”. Volkswagen Passenger Cars. Retrieved 2007-06-04.[dead link]
  28.  “Biodiesel FAQ”. Retrieved 2008-01-28.
  29.  Chevron paper Archived February 29, 2008, at the Wayback Machine.
Twincharger Twincharger refers to a compound forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and an engine-driven supercharger, each mitigating the weaknesses of the other. A belt-driven or shaft-driven supercharger offers exceptional response and low-rpm performance as it has no lag time between the application of throttle and pressurization of the manifold (assuming that it is a positive-displacement supercharger such as a Roots type or twin-screw and not a Centrifugal compressor supercharger, which does not provide boost until the engine has reached higher RPMs). When combined with a large turbocharger — if the "turbo" was used by itself, it would offer unacceptable lag and poor response in the low-rpm range — the proper combination of the two can offer a zero-lag powerband with high torque at lower engine speeds and increased power at the higher end. Twincharging is therefore desirable for small-displacement mo...
Fuel pump A fuel pump is a frequently (but not always) essential component on a car or other internal combustion engined device. Many engines (older motorcycle engines in particular) do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank or under high pressure to the fuel injection system. Often, carbureted engines use low pressure mechanical pumps that are mounted outside the fuel tank, whereas fuel injected engines often use electric fuel pumps that are mounted inside the fuel tank (and some fuel injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine). Fuel pressure needs to be within certain specifications for the engine to run correctly. If the fuel pressure is too high, the engine will run rough and rich, not combusting all of the fuel being pumped making the engine inefficient and a pollutant. If the pressure is too low, the engine may run lean, misfire, or s...
Turbo-diesel Turbo-diesel, also written as turbodiesel and turbo diesel, refers to any diesel engine equipped with a turbocharger. Turbocharging is common in modern car and truck diesel engines to produce higher power outputs, lower emissions levels, and improved efficiency from a similar capacity of engine. Turbo-diesels in automobiles offer a higher refinement level than their naturally aspirated counterparts. A diesel engine turbocharger History The turbocharger was invented in the early 20th century by Alfred Büchi, a Swiss engineer and the head of diesel engine research at Gebruder Sulzer engine manufacturing company in Winterthur. Büchi specifically intended his device to be used on diesel engines. His patent of 1905 noted the efficiency improvements that a turbocharger could bring to diesel engines  which in 1922 had first been developed for use in road transportation. At the time, metal and bearing technology was not sufficiently advanced to allow a practical turbocharger to be ...
Variable-geometry turbocharger Variable-geometry turbochargers (VGTs), (also known as variable nozzle turbines/VNTs), are a family of turbochargers, usually designed to allow the effective aspect ratio (A:R) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs do not require a wastegate. VGTs tend to be much more common on diesel engines as the lower exhaust temperatures mean they ...
Turbocharger A turbocharger, or colloquially turbo, is a turbine-driven forced induction device that increases an internal combustion engine's efficiency and power output by forcing extra air into the combustion chamber. This improvement over a naturally aspirated engine's power output is due to the fact that the compressor can force more air—and proportionately more fuel—into the combustion chamber than atmospheric pressure (and for that matter, ram air intakes) alone. Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Today the term "supercharger" is typically applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared with a mechanically driven ...