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Audi introduces new high-efficiency 2.0L TFSI based on Miller cycle; 190 hp, 47 mpg

8 May 2015

Audi introduced its new series-production 2.0 TFSI gasoline turbocharged direct injection engine for the first time at the Vienna Motor Symposium this week. The engine, which features a new combustion method, will be used for the first time in the next generation of the A4.

The four-cylinder engine delivers 140 kW (190 hp) and 320 N·m (236.0 lb-ft) from a displacement of 1,984 cc; the high torque is applied in a broad range of 1,450 to 4,400 rpm. The engine also features low fuel consumption levels of less than 5.0 l/100 km (47.0 mpg US) in the NEDC, clearly undercutting both its predecessor and comparable competitors. Enabling the performance of the new 2.0 TFSI is a new combustion method, according to Audi. At its core, its principle is comparable to the Miller cycle.

AT150282_medium
2.0 TFSI with 140 kW (190 hp). Click to enlarge.

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.

One effect of the Miller cycle is to reduce pumping losses, improving the thermal efficiency of the engine. The Miller cycle can also deliver hefty torque for a given displacement. Yet another effect is that it can be used to mitigate the propensity for knock in highly boosted engines.

Audi engineers have further developed the Miller cycle approach in crucial ways, the company said. Audi attributed the increase in efficiency in the new 2.0L TFSI to the following factors:

  • The intake time has been significantly shortened (140° crank angle (CA) rather than 190 to 200° CA).

  • Owing to a higher boost pressure on the inlet side, the engine attains optimal cylinder charges despite the shorter intake time.

  • Early intake valve closing—well before the bottom dead center is reached—lowers the pressure, allowing a high, efficiency-boosting compression ratio.

  • The Audi engine features, as do other engines in the current Audi lineup, a dual injection system that combines direct injection with indirect injection into the intake manifold. (Earlier post.) In the partial load range, an additional injection upstream from the intake valve yields an efficient mixture formation that is already complemented by the direct injection in the intake manifold and in the combustion chamber. This also addresses particulates from gasoline direct injection.

  • The Audi Valvelift System (AVS) on the inlet side allows a short intake time at partial load and a longer time at higher loads (full load: 170° CA).

Thanks to this rightsizing approach, the new engine enjoys the consumption benefits of a downsizing engine in partial load operation, while at higher loads it has the advantages of a large-displacement engine. The result is optimal efficiency and performance characteristics across the entire engine speed range.

—Dr. Stefan Knirsch, Head of Engine Development at Audi

Beyond the new combustion method, the new engine, with a weight of only about 140 kg (308.6 lb), avails itself of other efficiency technologies. For example, the coolant flow is controlled so as to greatly shorten the engine warm-up time. Contributing to this benefit is also the exhaust manifold, integrated in the cylinder head.

The consistent reduction of friction as well as the use of low-friction engine oil (0W-20) also increases efficiency.

Resources

  • Li, Y., Zhao, H., Stansfield, P., and Freeland, P. (2015) “Synergy between Boost and Valve Timings in a Highly Boosted Direct Injection Gasoline Engine Operating with Miller Cycle,” SAE Technical Paper 2015-01-1262 doi: 10.4271/2015-01-1262

  • Luisi, S., Doria, V., Stroppiana, A., Millo, F. et al. (2015) “Experimental Investigation on Early and Late Intake Valve Closures for Knock Mitigation through Miller Cycle in a Downsized Turbocharged Engine,” SAE Technical Paper 2015-01-0760, doi: 10.4271/2015-01-0760

  • Tie Li, Yi Gao, Jiasheng Wang, Ziqian Chen (2014) “The Miller cycle effects on improvement of fuel economy in a highly boosted, high compression ratio, direct-injection gasoline engine: EIVC vs. LIVC,” Energy Conversion and Management, Volume 79, Pages 59-65 doi: 10.1016/j.enconman.2013.12.022

May 8, 2015 in Engines, Fuel Efficiency | Permalink | Comments (11) | TrackBack (0)

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Comments

This sounds very good - 47 mpg (us) in a petrol A4.

This car could do 60+ mpg with light weight body, lower resistance tires +++++ ?????

"The Audi Valvelift System (AVS) on the inlet side allows a short intake time at partial load and a longer time at higher loads (full load: 170° CA)."

smart

"The intake valve also closes earlier – well before the bottom dead center is reached. This lowers the medium pressure, allowing a high, efficiency-boosting compression ratio."

https://www.audi-mediaservices.com/publish/ms/content/en/public/pressemitteilungen/2015/05/07/world_premiere_at.html

kewl

I have two problems here :

Miller cycle is usually for diesel so let's call it an Atkison cycle, right ?

Why the Miller cycle reduce pumping losses ? I don't get it, the better efficiency comes from additional expansion not from less pumping losses

Usually turbo don't work well with Atkison cycle because the exhaust pressure is too low to power efficiently the turbo.

Any comments ?

Rather than leave the intake open longer, they close it sooner to provide a sort of "variable compression ratio". This allows efficient operation at low loads while still having power when needed.

Miller has forced induction, Atkinson does not. I like this idea and the numbers show that Audi is on the right track. 45+ MPG without hybrid is significant.

Without electric motor drive, even very fuel efficient standard drivetrains like Miller fall short of fuel economy by half, ie, a plug-in hybrid achieves an effective 110mpg. Miller cycle alone is obsolete.

The 100 MPGe figure for a PHEV is misleading, it does NOT take into account the energy required to produce the electricity. A 100 MPGe BEV is more like 40 MPGe when you consider 40% efficient power plants, minus transmission losses, charger loses and round trip battery loses.

Treehugger,

The Miller cycle is essentially an Atkinson cycle with supercharging.
Supercharging reduces pumping losses (turbocharging is a type of supercharging), as does throttling using valve timing instead of a conventional throttle.

The reason why Audi (and others) do this now is that variable valve technology has improved. Previous systems didn't have the flexibility to switch between Otto and Miller cycles.
Both the Miller and Atkinson cycles work by cutting-off air intake early. This gives the engine the effective displacement of a smaller engine, while recovering more expansion energy using a disproportionally longer stroke. The problem with that (as any Prius owner will know) is that it creates a very weak, low-rev engine that needs some form of augmentation in automotive applications (battery-electric power in the case of the Prius). These new multi-cycle VVT engines allow you to retain maximum power by using the Otto cycle when you need it, and still have the efficiency of the Atkinson/Miller cycle during the 95% of the time that you don't.

This is different, Miller and Atkinson leave the intake open past bottom dead center on the intake stroke. This closes the intake before BDC on the intake stroke, so it is effectively variable displacement and/or variable compression ratio.

Whoopee. My civic hybrid currently gets 55 mpg.

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