The Diesel Engines
The 3.0 TDI V6
A genuine power pack is being introduced for the new Audi A4 in the guise of the three-litre six-cylinder unit, an engine that recently made its debut in the larger Audi A8 and A6 saloons.
Compared with the competition, this engine offers more than impressive power and torque potential: 204 bhp and 450 Nm. Maximum torque is available just above idle speed, starting at a mere 1,400 rpm and giving the driver forceful acceleration at all speeds.
This means performance on the road that even many a sports car will find hard to match: acceleration to 100 km/h comes in just 7.2 seconds, top speed of the A4 3.0 TDI quattro is 235 km/h.
Further fortes are the engine's highly efficient noise management and fulfilment of the strict EU4 emissions standard.
Featuring turbocharger technology and map-controlled, cooled exhaust-gas recirculation, this V6 four-valve power unit is the first six-cylinder TDI in Audi's new family of V-configuration engines. Both the camshafts and the oil pump, incidentally, are driven by chains.
Like all engines in Audi's new V-generation, the V6 TDI has extremely compact dimensions, engine length, for example, measuring a mere 444 millimetres. This is also an important step in view of achieving an overall engine weight of just 219 kilos, making the 3.0 TDI one of the lightest V6 diesels in the world. This benefits not only the car's power-to-weight ratio, but also the weight distribution - two factors crucial to the superior driving dynamics of the new A4 3.0 TDI quattro.
Common Rail Technology with Piezo Inline Injectors
Mixture preparation is by means of a latest-generation common rail system. It features a high-pressure pump and one rail per cylinder bank. This increases maximum injection pressure to 1,600 bar, 250 bar more than with previous common rail systems.
This high injection pressure results in even finer atomisation of the fuel and therefore in better mixture preparation and more efficient combustion.
The piezo injectors are undoubtedly the most important innovation of the new common rail system. The injection process makes use of the piezo effect: a voltage is applied to ceramic which changes its crystal structures. The result is a minimal geometric change which - supported by a hydraulic element - mechanically triggers the opening of the injector needle.
The piezo injectors offer multiple advantages compared with conventional solenoid valves. The moving mass at the injector needle is for instance reduced by no less than 75 percent, from 16 to 4 grams in each case. This enables considerably smaller and more precisely metered injection quantities. At the same time, piezo technology allows a higher injector needle speed.
The number of injection processes per combustion cycle can thus be varied almost at will. Audi's TDI development engineers opted for up to five injection processes for the 3.0 V6: in addition to the main injection process, double pilot injection takes place at the lower end of the speed range and single pilot injection in the medium speed range.
This strategy produces both lower emissions and a smoother combustion process, the benefits of which are most immediately apparent in the engine's acoustic behaviour. The 3.0 TDI engine is not only much quieter and smoother running than its predecessor, it now unquestionably serves as the benchmark in its class.
Turbocharger with Two Intercoolers
For optimum charging of the combustion chamber in all operating conditions, the six-cylinder 3.0 TDI has a turbocharger accommodated inside the engine's "vee" to make optimum use of the available space. And to enhance efficiency to the highest level, the temperature of the intake air is reduced by two intercoolers running in parallel, any loss of pressure being kept to a minimum.
The exhaust gas is purified by a close-coupled primary catalytic converter - located close to the turbocharger - and the main converter under the floor. This enables the A4 3.0 TDI, as the first executive diesel of its kind, to clearly outperform the EU4 emission limits.
One feature of the new engine that is undoubtedly as welcome as its efficiency at reducing emissions is its impressive fuel economy. Its average consumption over 100 kilometres is just 7.5 litres of diesel. In practice this obviously means a very significant cruising range, the new A4 3.0 TDI quattro being able to cover almost 840 kilometres on one tank of fuel.
The Audi A4 3.0 TDI comes as standard with quattro permanent four-wheel drive and 6-speed manual gearbox or, as an option, a 6-speed automatic transmission with tiptronic function and sport program.
The 2.5 TDI V6
Audi's 120 kW (163 bhp) 2.5 V6 turbocharged diesel is further evidence of its expertise in TDI technology. This engine made its production debut in November 1999 as a fitting source of power for Audi's top model, the A8 saloon, and was offered shortly afterwards in the A4 model line. The V6 has since been fundamentally modified: the cylinder head with low-friction valve operation by roller cam followers ensures outstanding fuel efficiency and emission levels.
The high-torque engine - 350 Nm of torque are at the driver's disposal between 1,500 and 3,000 rpm - with four valves per cylinder, centrally located injectors, a turbocharger with electronically controlled variable turbine geometry (VTG) and an ultra-modern radial-piston distributor-type injection pump, represents a high level in TDI technology.
The V6 TDI's response to pressure on the throttle, even at very low engine speeds, is also quite amazing. A substantial and immediately usable amount of torque is available even at only 1,000 rpm.
Performance on the road speaks for itself: it takes the A4 2.5 TDI (163 bhp) with 6-speed manual gearbox 8.8 seconds to accelerate from a standstill to 100 km/h. It then continues briskly up to its maximum speed of 227 km/h.
This contrasts starkly with extreme modesty when it comes to fuel consumption: the Audi A4 2.5 TDI consumes just 6.8 litres of fuel per 100 kilometres. Another positive factor is that the Audi A4 TDI 2.5 V6 complies with the EU4 emissions standard.
The 2.0 TDI
Driving pleasure and supreme economy, refinement and environmental care: the 2.0 TDI four-cylinder with unit injector, one of the most modern engines in its class, made its debut in the executive class as a very talented all-rounder. Again, the particular strength of this engine is its outstanding output and torque combined with equally impressive all-round economy.
Maximum output of 103 kW (140 bhp) and peak torque of 320 Nm available all the way between 1,750 and 2,500 rpm make this the most powerful and dynamic four-cylinder diesel featured by Audi so far. Performance on the road is correspondingly impressive: the 2.0 TDI with 6-speed manual gearbox accelerates to 100 km/h in 9.7 seconds and continues on up rapidly to its top speed of
212 km/h.
Two other fortes of the 2.0 TDI four-cylinder engine are low fuel consumption - 5.7 litres of diesel fuel per 100 km - as well as compliance with the EU4 emissions standard.
The refinement of this four-cylinder unit in the new Audi A4 is equally outstanding. The balancing shaft module with two shafts rotating in opposite directions helps to reduce engine vibration to an absolute minimum particularly at high engine speeds, with second-order vibrations being reduced more than 80 percent.
With Optional Diesel Particulate Filter
Along with the launch of an optional particulate filter for the A4 2.0 TDI, Audi is now systematically building on its strategy of reducing emissions. A few months after their launch, the ultramodern V6 3.0 TDI and 2.0 TDI will be offered with a diesel particulate filter as an option.
This uses a system that also exploits the most advanced state of the art:
the "catalysed soot filter" (CSF for short), which has a dual-action filter coating containing precious metals.
The passive regeneration process involves the slow, environment-protecting breakdown of the particulates deposited in the filter into CO2. This takes place at a temperature of between 350 and 500 degrees and occurs continuously without any special measures being required, predominantly when the car is being driven at motorway speeds. The process of active regeneration, which goes unnoticed by the driver, is triggered automatically when the particulate filter has reached its maximum permitted degree of saturation. Depending on operating conditions, distances of up to 2,000 km can be covered before this takes place.
The 1.9 TDI
One of Audi's most successful and most-built engines is also to be found in the new A4: the four-cylinder 1.9-litre TDI with pump-injector direct injection. The latest version develops 85 kW (115 bhp) and produces an impressive 285 Nm of torque at just 1,900 rpm.
The A4 1.9 TDI takes just 11.2 seconds to pass the 100 km/h mark. And with a top speed of 201 km/h, the entry-level TDI model is the ideal car for long stretches on the motorway at high average speeds. Especially as the fuel consumption of around only 5.6 litres per 100 kilometres means that a distance of over 1,000 kilometres can be covered between stops for refuelling.
This once again demonstrates the superior maturity and efficiency of TDI technology in conjunction with the pump-injector unit. Indeed, this system is still able to provide the highest level of injection pressure of up to 2,050 bar - the weight of a car on an area as small as a fingernail.
This high pressure assures ultra-fine atomisation of fuel within the combustion chamber, thus providing excellent thermodynamic efficiency. On the road this means outstanding fuel economy and, at the same time, a high torque yield. And thanks to pilot-injection control, the performance spectrum of a pump-injector engine includes good engine acoustics and efficient emissions control. This likewise applies to the 1.9 TDI, which easily undercuts the EU4 emission limits.
The A4 1.9 TDI is available in combination with a 5-speed manual gearbox.
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