New Engines for the Audi A6
Audi A6 2.7 TDI
The second representative of the latest generation of V6 TDI engines with common rail system and piezo inline injectors is set to be launched from November 2004.
Like its big brother, which has a capacity of three litres, it makes use of the latest injection technology and consequently already undercuts the demanding EU4 emission limits, even without a diesel particulate filter.
A new crankshaft with the stroke reduced by 8.3 millimetres, new connecting rods and different pistons result in a total capacity of 2698 cc. This engine's key performance data are a power output of 132 kW (180 bhp) in a speed range of between 3,300 and 4,250 rpm and a peak torque of 380 Nm which is available from 1,400 rpm and remains at this high level all the way up to 3,300 rpm.
The results are a spontaneous response and tremendous pulling power even from the lowest revs. The 100 km/h mark is passed after just 8.9 seconds on the way up to a top speed of 227 km/h. But it is the mid-range sprints that are the outstanding discipline of this new high-performance engine.
The pioneering common rail injection system with piezo inline injectors permits up to five separate amounts of fuel to be injected per working cycle, at an injection pressure of 1600 bar. Piezo technology enables considerably smaller and more precisely metered injection quantities. At the same time, the system reacts twice as fast as existing solenoid-valve injectors thanks to the higher speed of the injector needle.
This effect is particularly important for the brief intervals between the - up to five - separate multiple injection processes. The fuel is injected into the combustion chamber via eight-hole nozzles. In conjunction with the combustion chamber recess, this results in excellent fuel preparation and consequently in particularly efficient combustion with extremely low emissions.
The 2.7-litre V6 TDI is also part of Audi's new range of V engines and has a chain drive for camshafts and oil pump. The cylinder spacing in the new engine block is now 90 millimetres. This gives the engine a compact length of just 444 millimetres. The engine block is made from vermicular graphite cast iron, a successful combination of low total engine weight, high strength and good acoustic properties. 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 A6 2.7 TDI.
Other key features of the engine include four-valve-per-cylinder technology with low-friction roller cam followers, turbocharging with two intercoolers and electrical control of the variable turbine geometry. The electrical adjustment of the guide vanes is more spontaneous and more exact. Particularly at low engine speeds, this builds up the boost pressure faster and thus achieves a significantly better response.
Variable swirl flaps are likewise integrated into the intake tract. These can be used to adjust the air movement according to the prevailing engine speed and load.
All these measures result not only in high performance and an enormous torque plateau, but also in low fuel consumption, extremely low emissions and outstanding acoustics. It is especially in this latter area that the new engine undoubtedly represents the new benchmark in its class.
And thanks to its controlled and cooled exhaust-gas recirculation, the new A6 2.7 TDI remains within the limits of the strict EU4 emissions standard, which is not due to become law until 2006.
The engine's economic superiority is at least as positive as its high standard of efficiency in the reduction of emissions: overall fuel consumption is a mere 6.8 litres of diesel per 100 kilometres.
Audi A6 3.0 TDI quattro with optional diesel particulate filter
As on the Audi A8 flagship model with 3.0-litre V6 TDI, a version with the option of a diesel particulate filter is to be added to the Audi A6 range from the autumn. This version reduces particulate emissions still further. Both with and without filter, the A6 3.0 TDI quattro with 225 bhp engine not only satisfies EU4, currently the strictest emission standard in force; it is also outstanding for its combination of dynamic performance and economical fuel consumption, while displaying all the characteristics of a comfortable long-distance luxury saloon.
The "catalysed soot filter" (CSF for short) has a filter coating containing precious metals and acting in two ways: the passive regeneration process involves the slow, environment-protecting breakdown of the particulates deposited in the filter. This process takes place within a temperature range of 300 - 500 degrees and occurs continuously without any special measures being required, predominantly when the car is being driven overland and at motorway speeds. The process of active regeneration is triggered 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. A decisive advantage: due to the fact that regeneration phases are rare as a result of the generally low level of untreated emissions, the average additional fuel consumption is very low at 0.1 litres per 100 kilometres. The system requires no fuel additives at all and lasts the lifetime of the vehicle itself.
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