Air flow limiter

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Graphic representation of a NASCAR air flow limiter

The air volume limiter (also air mass limiter or air restrictor or restrictor plate ) can be used to reduce the amount of air that is fed to an internal combustion engine in order to limit the output to a limit specified by the regulations.

technology

The cross-section of the intake tract is technically narrowed, which means that less air gets into the combustion chamber. In order to maintain the optimal fuel-air ratio, the fuel supply must also be reduced accordingly. This reduces the converted energy per time, i.e. the performance. The maximum flow rate is reached when the flow velocity in the narrowest cross section reaches the speed of sound .

The resulting limitation of air mass can be described by the tailored size equation:

Air mass flow in [kg / s]
Narrowest cross-section in m²

Unless specified by the regulations, the inlet on the air mass limiter can have the shape of a Laval nozzle , with the narrowest cross-section complying with the regulations. Alternatively, a swirl venturi ( double cone , narrowest cross-section with a circumferential groove) is proposed.

An anti-lag system is used to reduce the effect of air mass restriction on supercharged engines .

application

In road traffic, mopeds and motorcycles are occasionally throttled in order to keep the performance within the respective driving license class or to achieve a cheaper insurance premium. While throttles on the exhaust gas side are common in two-stroke engines , four-stroke engines are usually reduced in performance on the intake side with an air flow limiter.

Air flow limiters are often found in racing cars so that a performance that complies with the regulations is achieved. For example, an air restrictor with a diameter of 33 mm is used in the turbochargers of the so-called World Rally Cars , which should limit the nominal output to 220 kW (300 PS). If one uses a largely equivalent top-of- the-range engine from the European Rallycross Championship, in which an air flow limiter with a 45 mm diameter helps the engine to generate over 400 kW (550 hp), it is easy to see how a relatively simple measure can achieve maximum output of a motor can be limited.

The DTM cars are also a prominent example . Likewise, the engines of the vehicles of the American Monster Energy NASCAR Cup Series, where the high-speed oval courses are common there , are increased by means of the restrictor plates from more than 590 kW (802 PS) to around 330 kW (449 PS), i.e. by almost half, throttled. In sports car races such as the GT3 group or the 24-hour race on the Nürburgring , air flow limiters are used as part of the Balance of Performance to ensure a comparable performance of the top teams every year.

Since 1971, all Formula 3 engines have had to be fitted with an air flow limiter with a diameter of 26 mm. This means that the engine output of the units from various manufacturers in 2012 was around 158 to 184 kW (215–250 PS).

literature

  • Gert Hack : make cars faster. 11th edition, Motorbuchverlag, Stuttgart, 1980, ISBN 3-87943-374-7
  • Hans-Hermann Braess, Ulrich Seiffert: Vieweg manual automotive technology. 2nd edition, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden, 2001, ISBN 3-528-13114-4

Individual evidence

  1. ↑ Michael Trzesniowski: drive . Springer Fachmedien GmbH, Wiesbaden 2017, ISBN 978-3-658-15534-6 , A.4 4 assembly modules, p. 96 .
  2. ^ According to H. Watson et al., Optimizing the Design of the Air Flow Orifice or Restrictor for Race Car Applications , SAE Paper 2007-01-3553
  3. ↑ Almost every model can be throttled. (No longer available online.) Motorradonline.de, August 17, 1998, archived from the original on May 20, 2013 ; Retrieved January 5, 2013 .
  4. ↑ Mark Aumann: Inside NASCAR: Fuel injection a 'really big step'. NASCAR.com, January 11, 2012, accessed on January 5, 2013 (illustration of the position of the “restrictor plate” air flow limiter in the two graphics).
  5. ↑ Walt Thurn: FIA GT3 Dubai Race - Desert Storm. vetteweb.com, June 30, 2008, accessed January 5, 2013 .
  6. ↑ Formula 3 Cup, the way to F1. MRT–Sport.de, March 1, 2010, accessed on January 7, 2013 .
  7. ↑ More performance, less costs. Formula 3 Cup - new ways from 2012. Motorsport-Magazin.com, accessed January 7, 2013 .