The powertrain of the Audi A4 TDI concept e uses a 2.0-liter direct-injection TDI engine with an output of 88 kW (120 hp) and 290 Nm (214 lb-ft) of torque from 1,750 to 2,500 rpm. The piezo injectors in the common-rail system inject the extremely finely atomized fuel at a pressure of up to 1,800 bar, and the special piston geometry provides optimized thermodynamics in the combustion chambers.

The 2.0 TDI also features a comprehensive package of additional efficient technologies. The oil cooler, the oil nozzles for cooling the piston crowns, the oil pump and the water pump have been designed so that they can be switched off—when inactive they do not require any power. New piston rings resulted in lower tangential forces, the spring pressure on the intake valves was reduced slightly, and the vacuum pump for the brake booster received a new actuator. These measures as a whole reduce emissions by 5 grams of CO₂/km.

Other engine-related modifications include reduced internal friction, a new thermal management system during the warm-up phase and an electronically controlled fuel pump. Just as in the production version, Audi is using a thermostatically controlled cooling circuit with an internal heat exchanger for the automatic air conditioning system. It responds in a highly efficient manner—the system uses 20% less fuel than its predecessor. The A4 TDI concept e uses a new controller: the engine disconnects the air conditioning system’s compressor from its drive whenever possible.

Like other Audi production models, the A4 TDI concept e uses a recuperation system that converts the energy of motion during deceleration into usable electrical energy. In the deceleration and braking phases the A4 TDI concept e operates with increased secondary voltage. At this point, it is able to convert the kinetic energy into electrical energy; it is buffered in an absorbent glass mat battery. Whenever the sedan accelerates again, the battery feeds the energy back in, thus reducing the load on the alternator.

The 2.0 TDI transfers its power to a six-speed manual transmission with considerably reduced internal friction. It was specially customized to the high-torque TDI engine and has somewhat taller ratios for gears three through six. Most of the housing consists of ultra-light magnesium, which reduces weight by nearly 5 kg. A foam-packed skin serves as insulation, ensuring that the transmission oil heats up faster after the vehicle has been started. The drive shafts from the differential to the front wheels have also been redesigned.

The transmission is coupled to a start-stop system that switches the engine off whenever the sedan comes to a standstill. The TDI is deactivated whenever the A4 TDI concept e comes to a standstill, the shift lever is in the neutral position, and the driver’s foot is off the clutch pedal. It starts up again as soon as the driver steps on the clutch—a specially developed starter handles this in around two tenths of a second, which is faster and smoother than a traditional component. While the driver puts the vehicle in gear, the TDI speeds up; when the driver’s foot comes off the pedal, it drops down to idle speed.

An electro-mechanical part replaced the electro-hydraulic power steering. This yielded a further reduction of 4 grams of CO2/km. It does not have to circulate any hydraulic fluid, nor absorb any energy while the vehicle is traveling in a straight line—the electric motor which provides power assistance only kicks in if the driver turns the wheel.

Electrically actuated brakes are fitted at the rear. With active brake control, residual brake torque is almost non-existent. It only arises if the small air gap that is necessary for a stiff feel to the pedal and immediate brake response results in a slightly unevenly shaped disk rubbing on the lining. Using electrical rear-axle brakes will achieve the same effect on the front axle: here, an enlarged air gap is also possible since the power brake system only has to carry out the lining displacement for one axle.

Audi engineers further enhanced the aerodynamics of the concept e. A trunk lid with a restrained separating edge, the partially closed grid in the single-frame grille and sporty suspension tuning with optimized ride height contribute to the excellent drag coefficient of 0.25 (production model: 0.27).

The underbody of the technology study painted in Daytona Grey is faired much more extensively than the production model; the rear lights feature LED technology, which uses much less power than regular bulbs. Newly designed, dip-polished cast aluminum wheels, of the size 7.5 J x 17 improve the flow of air around the wheels and wheel housings. The tires are designed for smooth running, but also provide sporty grip due to their 225/50 R17 wide format.

The driver has two major aids in the A4 TDI to support eco-driving. An efficiency program that shows up on the instrument panel display acts like a trainer, pointing out open side windows or recommending rapid upshifting. The navigation system will always offer an especially fuel-saving route as an alternative whenever the driver enters a destination.

Audi has deployed a several ‘e’ models: the A3 1.9 TDI e and A3 Sportback 1.9 TDI e, the A6 2.0 TDI e and the A8 2.8 FSI e. Audi says it plans to expand its ‘e’ model line in the near future and start putting further technologies from its modular efficiency assembly into production.