Audi is celebrating the 25th anniversary of the TDI engine this year. In the autumn of 1989, the brand presented the Audi 100 with a 2,5-liter TDI engine, a fully electronically controlled direct-injection turbo diesel engine at the IAA in Frankfurt.
Oil crisis argument for developing new diesel
Already in the mid-1970s, under the influence of the oil crisis, Audi began developing a new, fuel-efficient engine that would eventually become the TDI. In 1989, Audi presented the 2.5 TDI engine at the IAA in Frankfurt in an Audi 100, the Ingolstadt model that has since achieved young-timer status. The first TDI engine was a five-cylinder in-line turbo diesel engine with a cylinder capacity of 2.461 cm3, direct fuel injection and fully electronic engine management. The power of 88 kW (120 hp) and the torque (265 Nm) were the founders of new standards in diesel technology. Standards that showed that diesel-powered cars were able to keep pace in terms of performance with the counterpart that had a fast and powerful gasoline engine. Audi was not the first brand to provide a passenger car with such diesel technology. Fiat had the scoop by equipping the Croma with a directly injected turbo diesel.
More and more variants
In 1991, the 1.9 TDI engine debuted in the Audi 80, followed four years later by a more powerful variant in the A4. The increase in power was mainly due to a new turbocharger with variable turbine geometry. 1997 introduced the first V6 TDI engine with four valves per cylinder. The 2.5 TDI delivered 110 kW (150 hp) and a torque of 310 Nm. The next step was the V8 TDI engine with a displacement of 3.328 cm3, which was delivered in the Audi A1999 from October 8. Smaller TDI engines also followed, such as the 1.2 TDI in the Audi A2 in 2001, with which an average consumption of 2,99 liters per 100 km could be achieved. The V12 TDI, which appeared at the end of 2008 in the Q7, was the strongest diesel engine produced in series in a passenger car the crown on TDI technology from Audi. The V12 TDI engine achieved a power of 368 kW (500 hp) and a torque of 1.000 Nm from six liters. In response to increasingly stricter exhaust gas standards - especially in the US - Audi came up with the clean diesel technology in 2009. The 3.0 TDI clean diesel had a common rail system with new sensors in the combustion chambers. Fine atomization and precise combustion resulted in fewer emissions, while a selective reduction catalyst in the exhaust reduced the nitrogen oxides. In 2013, the diesel particulate filter with SCR layer followed. The Audi engineers are currently working on the electric bi-turbo, which makes the conventional compressor of the "normal TDI-s" superfluous. With the latter regular variant, the charge pressure of the turbocharger depends on the energy from the exhaust gases. In the new variant, an additional electric compressor provides loading pressure at low speeds.
Turbo compression, injection and exhaust gas cleaning are the most important factors
The TDI development has since 1989 contributed to the growing popularity of the diesel engine. The development proceeded in several steps, with turbo compression, injection and exhaust gas cleaning as the most important factors. In the course of the 25 year, the power and torque of the TDI engine in relation to the engine capacity more than doubled, while the emission of harmful substances decreased by 98 percent in the same period. Other tasks are based on changing legislation and economic questions, such as requirements with regard to emissions or the composition of diesel fuel. For example, in a number of US states, the new 3.0 TDI for the ULEV-II standard is already equipped with a double-cooled exhaust gas return. If China, a country where the quality of the fuel still shows strong fluctuations, becomes a diesel market, criteria such as height and thin air will also play a more important role.
Some 7,5 million Audis with TDI engines have already been produced
So far, Audi has produced around 7,5 million cars with a TDI engine. The best-selling engine is the 2.0 TDI. Three million Audis were equipped with it. Over the years, Audi's corporate brothers including VW, Skoda and Seat also realized excellent sales of variants with a TDI engine under the hood. The many variants with TDI engine supplied still have an important share in the sales figures of the Volkswagen Group to this day. With that they also contributed to a large extent to the popularity of the "VAG diesel new style", which made its sales debut in 1989 in the front of the Audi 100.