Diesels are very popular these days. They perform well, with stump-pulling torque, and are vastly more efficient than their gasoline-powered counterparts. Whereas a few decades ago a diesel engine would be written off as a smokey, slow oil-burners, these days the demand is very high, and former negative diesel traits have all been eliminated due to the advanced technology of today.
Perhaps the most impressive diesel offerings come from the German manufacturers. BMW , Audi , and Mercedes all offer several diesel engines that are every bit as desirable — if not more — as their respective gasoline versions.
Audi has an innovative new spin on the turbo-diesel with itsA6 . It is still a mono-turbo setup, but with an electric turbo chiming in to help out at lower revs. This innovative design will virtually eliminate turbo lag and provide even more oomph off the line than diesels are already famous for.
How does it work?
Click past the jump to read more about the 2014 Audi A6 TDI Concept.
Audi A6 TDI Concept in detail
The new, innovative mono-turbo design combines a regular, exhaust-gas-driven conventional turbocharger with a small electric compressor to aid in producing off-idle, low-end torque. Because exhaust gas is at a lower temperature in a diesel application, less energy is available to drive a turbocharger at low engine speeds. This is the reason diesels suffer turbo lag. While diesel torque is plentiful, there is usually a noticeable — albeit short — interval before the power kicks in. Audi’s goal is to eliminate this.
The small, electric turbo is nestled between the regular turbocharger and the air intake system, and normally remains idle. However, when the car’s ECU detects low exhaust gas energy at low engine speeds, the electric compressor kicks in immediately. While diesels are low-revers, with torque peaks beginning usually around 1,500 rpm, the electric turbocharger will provide instant response below this range.
Capable of 7 kW, the electric motor will accelerate the conventional turbo’s compressor wheel to maximum speed in a lightning-quick 250 milliseconds, virtually eliminating turbo lag from idle. Audi is very adamant about the way these two turbos work together in harmony, and we have no reason to doubt its engineers.
Response isn’t the only benefit of this new design; Audi asserts that this new turbo system will deliver improved fuel economy as well. Because this system will provide instant response, there is less downshifting, thus reducing engine speed and improving efficiency. Audi claims a huge increase in top-gear acceleration as well.
We can’t wait to drive one. The U.S.-spec 3.0-liter Audi A6 TDI produces a hefty 240 horsepower between 3,500 and 3,750 rpm and a crazy 428 pound-feet of torque between 1,400 and 5,200 rpm; expect torque to kick in around 1,150-rpm mark, and expect to see a slight upswing in both torque and horsepower. The modified numbers are sheer speculation for now, as Audi only revealed the specifications on the RS5 with this technology.
What do you think about this exciting new technology? Let us know in the comments section!
Gallery Audi A6 TDI Concept
The TDI engine gets its power from the boost pressure developed by the turbocharger, which is dependent on the energy of the exhaust. The electric biturbo breaks this dependency. Its supplemental electric compressor enables a rapid buildup of boost pressure and high torque even at low engine speeds. 25 years after the invention of the TDI, Audi is now taking the next big step and making the diesel engine even more emotional and sporty.
In addition to the classic exhaust gas turbocharger, the electric biturbo has a second charger arranged in series. Instead of a turbine wheel, it contains a small electric motor that applies a maximum drive power of seven kW to accelerate the compressor wheel to maximum speed within 250 milliseconds.
The electric compressor is downstream of the intercooler. At very low engine speeds and thus correspondingly low exhaust gas energy at the turbocharger, the bypass valve closes and the air is routed to the electric compressor. This can be flexibly and compactly integrated into a variety of forced induction concepts.
Audi has built two technology studies with the electric biturbo: The Audi A6 TDI concept is equipped with the new 3.0 TDI monoturbo; the Audi RS 5 TDI concept with the 3.0 TDI biturbo. In steady-state – no additional impetus – the monoturbo produces a constant 240 kW (326 hp) and 650 Nm (479.4 lb-ft) of torque, the latter between 1,500 and 3,500 rpm. The electric compressor fills the gap in the torque curve below this range and provides for fast response and excellent elasticity. Acceleration from 60 to 120 km/h (37.3 to 74.6 mph) in sixth gear is reduced from 13.7 to 8.3 seconds.
The modified V6 biturbo in the Audi RS 5 TDI concept is even more impressive. It produces 283 kW (385 hp), and peak torque of 750 Nm (553.2 lb-ft) is available between 1,250 and 2,000 rpm. The electric compressor provides for tremendous power when starting off. If the driver stays on the accelerator, 100 km/h (62.1 mph) is reached in roughly four seconds. Boost pressure is available immediately after each change of gears thanks to the intelligent interplay between the two turbochargers.
The most impressive aspect of both technology studies, however, is the rapid, nearly seamless development of power even at low engine speeds. The strengths of the electric biturbo lie exactly where they make the most sense in everyday driving. It eliminates the need for constant downshifting, keeping engine speeds low. Sporty drivers will really appreciate the passing power and immediate delivery of power when exiting a curve. The electric biturbo is suitable for use in many Audi model series as well as with gasoline engines, in principle. It will soon enter series production in the TDI sector.
The energy required to drive the electric compressor is largely generated by recuperation during coasting phases, so that the end effect is essentially neutral with regard to energy consumption. It is supplied with power via a separate 48-volt electrical system, complete with its own compact lithium-ion battery in the trunk and power electronics. A DC/DC converter provides the connection to the 12-volt electrical system.
The new 48-volt subsystem offers major advantages. It can supply the high-performance electrical consumers of the future – thermoelectric heating elements, electromechanical rear brakes or engine auxiliaries such as oil and water pumps – with more energy than the 12-volt electrical system. Higher voltage means lower currents, allowing for smaller cable cross-sections and thus reduced weight. Audi plans to introduce the 48-volt electrical subsystem to multiple model series shortly.
In parallel to this, the Audi engineers are also working to electrify the drivetrain. There will be a tailored solution for each customer. The hybrid platform offers numerous solutions, from the electric biturbo to the TDI with plug-in technology. The combination with the electric motor opens up new possibilities. It enables targeted shifting of the load points to the benefit of both fuel consumption and emissions behavior. In urban traffic, the electric motor provides for zero-emissions power.
Another interesting electrification option is the electric quattro drive, the e-quattro. Audi has shown this in many of its show cars. The TDI and an electric motor drive the front wheels, while a second electric motor in the rear drives the rear wheels. The battery can be installed in part in the floor tunnel.