Audi reduces fuel consumption 21% in new direct injection 1.8L TFSI; indirect injection in part-load range
|Audi A5 1.8 liter TFSI engine. Click to enlarge.|
Audi’s base gasoline engine in the updated A5 family—the 1.8 liter TFSI—incorporates new solutions in fuel injection and other technologies to deliver its 125 kW (170 hp) and 320 N·m (236 lb-ft) torque, with 5.7 liters per 100 km fuel consumption (41 mpg US), corresponding to 134 grams of CO2/km (215.65 g/mile).
Fuel consumption in the new 1.8 TFSI has been reduced by 21% compared with the previous model engine.
The four-cylinder engine displaces 1,798 cm3 and delivers its 320 N·m torque between 1,400 and 3,700 rpm. Peak output of 125 kW is achieved at 3,800 rpm. With a manual transmission, the 1.8 TFSI accelerates the Audi A5 Coupé from zero to 100 km/h; top speed is 230 km/h (142.92 mph).
Combustion behavior was a particular focus of the development work. In addition to FSI direct injection, the 1.8 TFSI also uses indirect injection in the part-load range. This system injects the fuel at the end of the intake manifold near the tumble valves, where it is swirled intensively with the air.
The rail pressure of the FSI system has been increased from 150 to 200 bar. The direct injection system is active when starting off and at higher loads. It can perform two or three individual injection operations per work cycle.
The injection system reduces fuel consumption and particulate emissions to such an extent that the four-cylinder engine complies with the limits of the future Euro 6 standard.
To further optimize gas exchange, the valve control system has been given greater operating freedom. The Audi valvelift system, which adjusts the lift of the valves in two stages, is active on the exhaust side. The two camshafts can be adjusted through 30 or 60 degrees of crankshaft angle.
The thermal management of the four-cylinder engine features a new fully electronic coolant regulation system. Two fast-switching, rotating cores, which are consolidated in a module and driven by an electric motor via a screw drive, control the flow of coolant. One of their primary objectives is to bring the motor oil up to operating temperature as quickly as possible following a cold start. This is done by keeping the coolant in the crankcase for a relatively long time.
The cabin heating runs off of a separate loop in the cylinder head. The main radiator, which dissipates the heat to the environment, does not come into play until the latest possible moment.
The new rotating core module can set the water temperature between 85 and 107 °C as a function of load and rpm to always achieve the best compromise between minimal internal friction and thermodynamic efficiency. Switchable valves throughout the cooling system manage heat flows between the engine, the heat exchanger for the transmission and the cabin. All together, the thermal management system reduces the CO2 emissions of the 1.8 TFSI by around 2.5 g per 100 km (4 g/mile).
This concept benefited from the integration of the exhaust manifold into the water-cooled cylinder head. Because this also reduces the exhaust gas temperature, it is not necessary with the 1.8 TFSI to enrich the mixture at full load, which reduces fuel consumption significantly when driving sportily.
The turbocharger in the 1.8 TFSI is also an all-new design that develops the high relative boost pressure of up to 1.3 bar very systematically. Key features include a turbine wheel made from a new alloy that can withstand exhaust temperatures of up to 980 °C, the oxygen sensor mounted directly upstream of the turbine wheel, a pulsation damper, a compressor wheel machined from a solid blank and an electric wastegate actuator that adjusts the boost pressure particularly quickly and precisely to further reduce fuel consumption.
Engine weight has been reduced from 135 to 131.5 kilograms (298 to 290 lb). The new turbocharger/cylinder head module, a new casting process for the gray cast iron crankcase that reduces wall thickness to roughly three millimeters (0.12 in) and the crankshaft with four rather than eight counterweights and reduced main bearing diameters all contributed to this weight reduction. The pistons are made of new, high-strength alloy. Lightweight polymers are used for the oil pan, and many screws are made of aluminum.
Internal friction has also been significantly reduced by the use of an novel coating on the piston skirts and by mounting the two balance shafts that counteract the second-order inertial forces in roller bearings. The regulated oil pump requires little energy itself, and the oil-jet cooling for the piston heads is controlled via a high-precision electric system.