For Audi, the issue of fuel consumption has long been seen as a matter of elementary customer benefit and is a focus of technical development. Public discussions about the issue at the start of the year were frequently highly superficial and not especially objective. It is therefore logical for us to present the central facts and physical relationships. CO2 emissions in particular are a focus of such discussions.
While CO2 emissions in industry and in the energy sector have been increasing since 1999, the transport sector has reduce carbon dioxide emissions so much that it has actually compensated for the increases in other sectors. In Germany it has even achieved an overall reduction. German automobile manufacturers, first and foremost Audi, have employed technological innovations to achieve a lasting increase in efficiency.
A selection of statistics underline this achievement. Compared to 1990, 36 percent less fuel is required today to generate 1 kW of output. Hand in hand with this, fuel consumption per kilogram of vehicle weight has been reduced by 29 percent. Conversely, significantly more people can be transported for each litre of fuel – 68 percent more – than was possible in 1990.
German manufacturers have achieved significantly greater reductions than the importers from Europe and Asia. Today they achieve the lowest CO2 emissions in relation to output generated. Measured on this parameter, German manufacturers lead with an average of 1.8 g/km CO2 for each 1 kW of output, followed by Japanese manufacturers with 1.9 g/km CO2. French, Italian and Korean manufacturers still emit 2.1 g/km CO2 for the same result.
CO2 is not a classic emission like nitric oxides (NOx), hydrocarbons (HC) or carbon monoxide (CO). When we talk about CO2, we talk about fuel consumption. There is a fixed linear relationship between the two variables. Its higher energy content means that a diesel engine produces about 10% more CO2 than a petrol engine with the same nominal consumption, namely 26.5 grams of CO2 per km. On a spark-ignition engine, one litre of fuel burned over 100 km equates to 23.8 grams of CO2 per km.
Fundamentally, a mere 23 percent of the energy contained in the fuel can actually be converted into propulsive force. Even in ideal energy conversion, 31 percent is lost due to the thermodynamics of the combustion within the engine and a further 19 percent is lost due to friction, the combustion process and load changes within the engine. Another 19 percent is lost in the drive train – this includes the gearbox, the power steering servo pump, the wheel bearings and the tyres. And 8 percent is absorbed by the electrics, cooling system and the air conditioning.
So it is not enough to simply develop measures to reduce fuel consumption by looking at the engine, for the engine is only responsible for half the fuel consumption, and only a fraction of this can be optimised. This makes it important for every single vehicle component to be examined for its potential to reduce consumption and to be optimised wherever possible.
Different components have a different degree of influence on fuel consumption. Reducing the mass of the vehicle by 100 kilograms will save 0.3 litres/100 km. A 10 percent reduction in air resistance will improve fuel consumption by 0.15 litres/100 km. 200 watts of mechanical power has the same effect as 100 watts of electrical power: 0.1 litres/100 km. Add to this the power steering pump with a power draw of 2 kW, the air conditioning, which requires 1 litre / 100 km at an outside temperature of 35 degrees Celsius, and the rolling resistance of the tyres. At 120 km/h this amounts to 2 litres/100 km. Taken together, all these factors are too great to be ignored.
Audi working hard in the field of fuel consumption – the Audi e-models
The four new e-models – A3, A3 Sportback and A4 saloon and Avant estate – which Audi has produced within a very short period of time, demonstrate how seriously it takes the issues of reducing fuel consumption and saving resources, and the commitment with which it is dealing with them. Despite their special design, they uncompromisingly satisfy the customer's expectations with respect to drivability, just like any other car made by Audi.
The A3 1.9 TDI e with the 1.9 litre diesel engine generating 77 kW (105 bhp) not only reduces CO2 emissions by 10 g/km or 8 percent compared to the basic version, with 119 g/km it even undercuts the much talked about limit of 120 g/km – and it does so with an outstanding performance. In terms of customer-relevant CO2 emissions, the A3 1.9 TDI e is on a par with hybrid models, but in terms of dynamism it is far superior.
The Audi A3 has longer transmission ratios for 3rd to 5th gears. The two Audi A4 2.0 TFSI models have a manual gearbox with an additional long-ratio 6th gear. Add to this a whole series of weight-reduction modifications – for example, the bonnet of the A4 is made of aluminium. The alloy wheels, fitted as standard, are of 205/55 16 inch format. Various aerodynamic modifications such as the rear spoiler on the A4 saloon, which comes from the S line range, round off the package of modifications. Even the engine electronics on all the e-models have been tuned for optimum fuel economy.
The new Audi A4 2.0 TFSI, with its multiple-award-winning 2-litre TFSI with 125 kW/170 bhp, shows particularly clearly what this progress can achieve. On the one hand, the saloon has an impressive performance with a top speed of 30 km/h and accelerating from 0 to 100 km/h in 8.3 seconds. The Avant is hardly any slower. On the other hand, it has extremely low fuel consumption of just .1 l/100 km, giving it a range of up to 1000 kilometres on a single tank of fuel.
The Audi A3 and A3 Sportback 1.9 TDI have a spectacularly low 4.5 l/100 km. They each manage up to 1200 km between refuelling stops.
Intelligent technical details enable the customer to use his fuel even more efficiently. All four models have a gear shift indicator located in the instrument cluster, in the driver's direct field of vision. Depending on current engine load and speed, it tells the driver whether the next gear would be a better choice. When it comes to fuel consumption, it is essential for the driver to make full use of the vehicle's potential – the new gear shift indicator provides him with a valuable aid here.
Ultimately it is the driver himself who is responsible for his driving style – despite all technical advances. His individual style can reduce fuel consumption, and with it emissions, by up to 30 percent, without compromising on speed and dynamism. To inform customers in detail about this, Audi introduced efficiency training into its Driving Experience programme in the spring of 2007.
Audi will never rest on its laurels with what it has achieved – not even in the field of e-models. The brand is developing a number of technologies that will make all its models more efficient. This "integrated approach", that is the simultaneous optimisation of all vehicle components, will produce future proof and sustainable technological solutions.
Audi will have an e-model in each of its core model series in the foreseeable future.
Audi Tech: Maximum Efficiency in Everyday Operation – the Audi e-Models
