Miller cycle

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The Miller cycle (also Miller cycle ) for internal combustion engines is named after the inventor Ralph Miller , who patented a valve train in 1957 in which the intake valve closes very early , even during the intake stroke. The filling and the final compression pressure are thereby reduced, but the compression and thus the expansion ratio remains the same. With the Miller engine, this causes an increase in the thermodynamic efficiency through better utilization of the expansion energy in the work cycle. The Miller cycle is an adaptation of the Atkinson cycle for engines with a simple crank drive .

Basics

Four-stroke cycle of an ideal-typical slow-running gasoline engine : 1: "Prime" ➝ 2: "compacting" ➝ 3: "Expand" ➝ 4: "pushing" real remains running fast on the cycle 1 inlet on the UT also opened to more time to let the fresh charge flow in while the piston is already starting to compress. ➯ With the Miller engine , you have to imagine the inlet end (Es) at around 45–90 °  crank angle before BDC, which results in the reduced degree of delivery .

In the Miller cycle, the intake valve is closed well before bottom dead center ( BDC) is reached on the intake stroke , so that even without throttling, only a relatively small amount of fresh charge (mixture or, with direct injection, air) enters the cylinder and bottom dead center is passed through with negative pressure (reduced Degree of delivery ). Depending on the concept, the geometric compression ratio is retained (reduced knocking tendency , less nitrogen oxide formation ) or increased (further increase in efficiency ).

Compression ratio & efficiency

If the compression ratio is selected correspondingly higher, the lower fresh charge after the compression stroke (at top dead center TDC) results in the same pressure as otherwise with a full charge: Without changing the critical final compression pressure, less mixture is burned and its geometric expansion ratio is increased. so that the working stroke can make better use of the expansion energy: Less unused energy (residual pressure) is released at the outlet and the reduced exhaust gas temperature technically facilitates the use of a turbocharger , which can compensate for the power loss of the reduced cylinder charge by charging with charge air cooling by Cycle provides additional torque where suction work would otherwise have to be done.

In principle , however, the same engine output requires a larger displacement with the Miller engine , because the higher efficiency is associated with a lower specific displacement .

Engine control

In order to enable a quantity control of the torque for vehicle engines over a wide speed range, the Miller cycle process is mostly implemented today with variable valve control , since the lossy classic control with throttle valve contradicts the goal of increasing efficiency anyway. In a Miller engine with fixed valve control (unlike in the Atkinson engine ), the degree of delivery and torque decrease sharply with increasing speed , which limits the range of application, but causes simple self-regulation as a pump motor, for example.

application
  • In 2010, Nissan presented a 1.2-liter three-cylinder engine with the designation HR12DDR , which developed 72 kW (98 hp) with an Eaton TVS compressor and Miller cycle. He reaches the cycle via his variable valve control; further efficiency measures include direct injection and a start-stop system . The engine was still in the testing phase in the summer of 2010.
  • The new Audi A4 presented in 2015 uses the Miller cycle in its 2.0-l TFSI gasoline engine with 140 kW (190 hp) in certain operating states, especially at partial load. The engine is now also offered in other model series from the manufacturer.

Comparison of Miller cycle and (modified) Atkinson cycle

In modern engines (gasoline and diesel), the modified Atkinson process is understood to mean the very late closing of the intake valve, i.e. well after bottom dead center (BDC), while in the Miller cycle the intake valve is closed well before BDC. The effect of the reduced fresh charge is the same; In contrast to the Miller cycle, the Atkinson cycle uses the gas dynamics of the intake process: In contrast to the Miller cycle, the Atkinson cycle increases the degree of delivery and thus the torque even with fixed valve control with increasing speed, so that it can also be adjusted without camshaft adjustment can be used well. With a little extra effort for variable valve timing , however, the Miller cycle is more efficient.

See also

literature

  • Patent US2817322 : Supercharged engine. Filed April 30, 1956 , published December 24, 1957 , inventor: Ralph Miller. ‌

Web links

Individual evidence

  1. ↑ a b Richard van Basshuysen, Fred Schäfer (ed.): Handbook internal combustion engine . 8th edition 2017, Springer Fachmedien Wiesbaden GmbH, Section 7.10.1.5 Variable valve trains . ISBN 978-3-658-10901-1 .
  2. ^ Günter P. Merker; Rüdiger Teichmann (Ed.): Fundamentals of Internal Combustion Engines , 7th edition, Springer Fachmedien Wiesbaden 2014, section 7.2 Internal engine pollutant formation and reduction . ISBN 978-3-658-03194-7 .
  3. ↑ The new 2.0-liter R4 TFSI engine from Audi. MTZ 05/2016, pp. 16-23. ISSN  0024-8525 10814.
  4. ↑ S 400 HYBRID: CO2 champion with efficient hybrid drive. In: daimler.com. Daimler AG , May 11, 2009, archived from the original on July 12, 2012 ; accessed on October 27, 2019 .
  5. ↑ New three-cylinder petrol engine for the Nissan Micra. In: micrafanpage.de . August 3, 2010, accessed September 20, 2010.
  6. ↑ Audi's new 2.0 TFSI - even more economical thanks to a new combustion process. In: automobil-produktion.de . May 7, 2015, accessed February 19, 2017.
  7. ↑ a b The new six-cylinder marine engine from MAN for yachts and work boats. MTZ 06/2016, pp. 50-55, ISSN  0024-8525 10814.
  8. ↑ a b Konrad Reif (ed.): Otto engine management at a glance . Springer Fachmedien Wiesbaden 2015, section cylinder filling . ISBN 978-3-658-09523-9 .