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2017 Audi A4 ultra with Millerized 2.0 TFSI offers 31 mpg combined; highest EPA-estimated fuel economy in competitive segment

Audi’s 2017 A4 ultra leverages the Millerized 2.0-liter TFSI engine (earlier post) to achieve 27 mpg (8.7 l/100 km) city, 37 mpg (6.35 l/100 km) highway, and 31 mpg (7.58 l/100 km) combined EPA-estimated fuel economy. No other luxury sedan in its non-hybrid competitive segment offers higher EPA-estimated city or highway mileage.

The efficiency of the 2.0 TFSI is the result of Audi’s Millerized combustion method with shorter compression and longer expansion phases as well as increased compression. The Miller cycle uses a higher expansion ratio than compression ratio (i.e., over-expansion) obtained by either early or late closing of the intake valves (EIVC and LIVC, respectively), and results in a smaller effective compression stroke; combustion and expansion proceed normally.

Audi’s Millerized combustion method uses shorter compression and longer expansion phases as well as increased compression. The Miller cycle uses a higher expansion ratio than compression ratio (i.e., over-expansion) obtained by either early or late closing of the intake valves (EIVC and LIVC, respectively), and results in a smaller effective compression stroke; combustion and expansion proceed normally.

The Audi TFSI intake valves close much earlier than usual; in connection with increased pressure in the intake manifold, this reduces throttling losses. With the shortened compression phase, Audi engineers increased the compression ratio from 9.6:1 to 11.7:1.

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This means that in the compression phase, the engine only has to compress as much gas as a 1.4 TFSI. Also in the expansion phase, in which it fully utilizes its two liters of displacement, it profits from the high compression ratio; the resulting higher level of pressure during combustion further increases the engine’s efficiency.

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In order for the fuel-air mixture to swirl sufficiently despite the short intake time, the combustion chambers, piston recesses, intake ducts and turbocharging of the new 2.0 TFSI are specially adapted to the new combustion method. Under higher loads, the Audi valvelift system opens the intake valves later, resulting in a higher charge, which ensures good power and torque delivery. Injection pressure has been increased to 250 bar.

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The 2.0L engine is mated to a seven-speed S tronic dual clutch transmission.

Standard driver assistance features including Audi pre sense city and benchmark technologies such as the available Audi virtual cockpit are other highlights of the A4 ultra, on sale Fall 2016.

The A4 ultra also integrates benchmark technologies including the available Audi virtual cockpit, optional MMI all-in-touch (MMI Navigation plus package) and newly available in-car Audi connect infotainment and security features, supported by 4G LTE connectivity (where available from provider).

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