Audi has introduced a new low-displacement turbocharged gasoline engine in the A3 model line. (Earlier post.) The 1.2L TFSI engine generates 77 kW (105 hp), with fuel consumption of 5.5 L/100km (42.8 mpg US); CO2 emissions are 127 g/km (204 g/mile).
Downsizing entails the replacement of engine displacement with turbocharging. The wholly redesigned 1.2 TFSI—which produces a specific power output of 87.7 hp per liter from 1,197 cc (73.05 cu. in.) of displacement—uses the same technologies as its siblings with 1.8 and 2.0 liters displacement.
Turbocharging and direct gasoline injection facilitate a compression ratio of 10.0:1. This high value benefits the vehicle’s thermodynamics, and boosts performance as well as economic efficiency.
This engine’s low weight of 89.5 kilograms (197.3 lbs) not only enhances the efficiency of this four-cylinder unit, but also improves the axle load distribution of the Audi A3. The crankcase is made of cast aluminum and integrates reinforcing cylinder liners made of cast gray iron and a cutting-edge oil separator. The split timing cover consists of ultralight die-cast magnesium and plastic.
The undersquare 1.2 TFSI (bore x stroke 71.0 x 75.6 millimeters [2.80 x 2.98 inches]) has been optimized to minimize friction; this applies to the piston rings and the compact oil pump alike. The crankshaft’s main bearings and connecting-rod bearings are 42 mm (1.65 inches) in diameter; the eight slanted valves are actuated by a single camshaft driven via a chain.
Due to the valves’ design and complex dimensional characteristics, swirling arises in the intake ports, which facilitates good charging efficiency in the combustion chambers.
A common-rail system injects the fuel; up to 3,000 rpm, many instances allow for dual injection, which also optimizes combustion. Behind the turbocharger, which generates up to 0.9 bar of relative boost pressure, a water-cooled intercooler reduces the temperature of the intake air.
An electric control valve operates the turbocharger’s wastegate valve precisely, powerfully, and quickly; boost pressure builds up spontaneously and scavenging losses drop.
A typical turbocharged engine, this small four-cylinder unit operates at low rpms. Its 175 Nm (129 lb-ft) of torque are readily available between 1,500 and 3,500 rpm; 77 kW (105 hp) of output are available at 5,000 rpm, allowing smooth and efficient driving.
The three-door Audi A3 1.2 TFSI accelerates from 0 to 100 km/h in 11.1 seconds (A3 Sportback: 11.3 seconds). The A3 and the A3 Sportback reach a top speed of 190 km/h (118 mph). Compared with the predecessor engine generating 75 kW (102 hp), fuel consumption has dropped by more than 1 liter per 100 kilometers.
Sales of the A3 and A3 Sportback 1.2 TFSI will begin in the first quarter of 2010. The new four-cylinder engine will initially be paired with front-wheel drive and a six-speed manual transmission.