New Audi A8 4.2 TDI quattro

Press Release

Common rail technology with piezo injectors

The Bosch EDC16 CP system, with fuel delivery, trigger-start, boost pressure and exhaust-gas recirculation control, is responsible for engine management on the V8 TDI. As on the A8 with a petrol engine, this electronic system now means that it is possible to start the engine automatically at the push of a button.

Mixture preparation is by means of a latest-generation common rail system. It has a high-pressure pump – located inside the V of the engine – and one pressurized pipe or "rail" for each cylinder bank. The maximum injector pressure is now 1,600 bar, 250 bar more than with previous common-rail systems, a value that corresponds with the weight of a medium-sized saloon on the surface area of a fingernail.

This high injection pressure results in even finer atomisation of the fuel and therefore in better mixture preparation and more efficient combustion. The consequence is not merely extra power and torque, but also reduced fuel consumption and emissions.

The piezo inline injectors are undoubtedly the most important innovation of the new common rail system. Electrically excitable piezo crystals undertake the triggering of the injectors. As soon as a voltage is applied to the crystals, they contract and, assisted by a hydraulic element, mechanically trigger the opening of the injector needle.

The piezo injectors offer multiple advantages compared with conventional solenoid valves. The moving masses on the injector needles can, for instance, be reduced by no less than 75 percent, from sixteen to four grams in each case.

This enables considerably smaller and more precisely metered injection quantities. At the same time, piezo technology permits a higher injector needle speed. With a value of 1.3 metres per second, the piezo system responds twice as fast as other common rail injectors.

The number of injection processes per combustion cycle can thus be varied almost at will. In the case of the 4.2 V8, the Audi TDI development team decided on up to four injections. In the lower engine speed range there is a double injection in addition to the main injection, and a single pre-injection in the mid-range.

This strategy produces a smoother combustion process, the benefits of which are most immediately apparent in the engine's acoustic behaviour. The 4.2 TDI engine has once again become significantly quieter and smoother-running, even compared to its already highly cultivated predecessor, and without doubt it sets the benchmark for the class in this discipline.

The fuel is injected into the combustion chamber via eight-hole jets. They too play a major part in making the combustion process ultra-efficient, and thus improving the quality of emissions, by distributing the fuel homogeneously throughout the combustion chamber.

Highly effective exhaust emission control

The 4.2 TDI has a twin-pipe exhaust system with particulate filters as standard. In each exhaust pipe the cleaning of the exhaust gases is undertaken by an oxidising catalytic converter close to the engine and a catalytically coated particulate filter.

The catalytic converter close to the engine ensures adherence to the EU-4 limits by rapidly converting hydrocarbons and carbon monoxide.

The particulate filter, made of silicon carbide with thin-wall technology, is located in the under-floor area. The combination of thin-wall technology and catalytic coating enables controlled regeneration from temperatures of approx. 580 ºC, with simultaneously low exhaust back pressure. This is reflected in only marginally increased fuel consumption and enhanced regeneration efficiency.

The A8 4.2 can cover distances of up to 2,000 kilometres before the filter reaches its maximum charge level. The charge status of the filter is continuously checked by means of monitoring of the exhaust back pressure and parallel simulation calculation for both exhaust pipes separately.

When regeneration becomes necessary, the engine management system generates the required increase in temperature by means of measures taken within the engine and exothermic conversion of unburned hydrocarbons in the oxidising catalytic converter. Up to 5 injections are also possible with the common-rail injection system used at Audi.

Top performance and impressive fuel economy

The 4.2 TDI engine is currently the most powerful diesel engine to be found in any production saloon car. 240 kW (326 bhp) at 3,750 rpm are the new benchmark – an increase of no less than 51 bhp over its 275 bhp predecessor.

The A8 4.2 TDI quattro has the performance of a top athlete. This lightweight luxury saloon with its aluminium body takes only 5.9 seconds to sprint from a standstill to 100 km/h – making it quicker than any other diesel saloon on the international market. It is capable of a governed top speed of 250 km/h.

The torque gives the driver a feeling of pulling power in every speed range that is otherwise only to be experienced in a sports car. 650 Newton-metres between 1,600 and 3,500 rpm – this figure makes the A8 4.2 TDI quattro the Audi with the most torque of them all.

Despite the 51 bhp increase in engine output, the new Audi A8 4.2 TDI quattro consumes no more fuel than its predecessor – quite the opposite,in fact: Average consumption of just 9.4 litres / 100 km means a cut in fuel consumption of 0.2 litres – a figure that is nothing less than sensational!

Audi A8 4.2 TDI quattro: Supreme sportiness

All Audi A8 V8 TDI models are equipped with 6-speed tiptronic transmission with DSP dynamic gearshift programme and additional sports programme. The engine's output and torque are always unleashed with such precision that the conflicting requirements of spontaneous power flow, high performance and perfectly refined running are all achieved.

Quattro permanent four-wheel drive converts the engine's performance into superbly effective propulsion and cornering stability, effortlessly and safely converting its enormous torque onto the road. The aluminium Audi Space Frame (ASF) body provides the high-strength basis for low weight, dynamic performance and excellent handling.

The Audi A8 has an aluminium chassis with four-link front suspension and self-tracking trapezoidal-link rear suspension. Adaptive air suspension – an air suspension system with continuous damper control – provides the driving characteristics suitable for every driving situation. It simultaneously reduces body movement, thus optimizing road holding and comfort.

With its combination of a powerful TDI, highly developed lightweight construction and the dynamic qualities of its suspension, the Audi A8 4.2 TDI presents itself as a luxury saloon offering a new level of sporty dynamism and superiority.