Reed valve
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Reed valves are a type of
carbon fiber
).
Applications
Traditional
Reed valves, normally a
church organs and accordions. In nature, heart valves
operate in a somewhat similar fashion.
Pumps
Reed valves are used in some reciprocating compressor designs, and in the pumping element of some musical instruments, large and small.
Two-stroke engines
carbon fibre
Reed valves are commonly used in high-performance versions of the
two-stroke engine, where they control the fuel-air mixture admitted to the cylinder. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. The resulting pressure differential opens the valve and the fuel-air mixture flows into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber.[1] The Swedish motorcycle company Husqvarna
produced a two-stroke, 500 cc displacement single cylinder engine with a reed-valve controlled intake, one of the biggest in using this arrangement. Reed valves in two-stroke engines have been placed in the intake ports and also in controlling the intake to the crankshaft space.
Composite materials are preferred in racing engines, especially in
fatigue. The physical inertia of reed valves means that they are not as entirely precise in action as rotary valves
, a rotary valve engine may run better than a reed valve engine at a small rpm range but the reed valve engine often runs better over a wider rpm range. More sophisticated designs partly address this by creating multi-stage reeds with smaller, more responsive reeds within larger ones that provide more volume later in the cycle. Nevertheless, current technology favors reed valves almost to the exclusion of rotary valves due to their simplicity and low implementation costs and less rotational mass.
Wankel rotary combustion engines
Stratified Charge
Rotary Engine). However, this kind of intake port arrangement never reached the production line for automobile size RCEs. According to David W. Garside, who developed the Norton line of Wankel-powered motorcycles, data from other RCE producers pointed that reed valves do improve performances at low rpm and under partial load, but reduce the high speed power output of the engine, a feature considered inconvenient for motorcycle engines.
Pulse jets
Reed valves are used in the cheap but inefficient
ram-air
pressure due to forward motion helps scavenging and filling the combustion chamber with the new, fresh air charge, thus improving the power of the engine at higher speeds.
Design and modelling
Reed valves are designed considering the
eigenvalue
that is compared with exciting frequency.
Design of reed valves can be refined using simulations. The dynamic of petals[3] can be studied neglecting the coupling between fluid and structure: in this case the evolution of the structural part are simulated using lumped parameters models or FEM models, discharge coefficients at various valve lift are evaluated with experiments or CFD simulations.
The study of the complete system needs an integrated Fluid-structure interaction
model.
See also
References
- ISBN 0-13-160549-6
- ISBN 1-56091-008-9
- .
Further reading
- Irving, P E (1967). Two Stroke Power Units. London: George Newnes.