Heron cylinder head

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A Heron cylinder head, or simply Heron head, is a design for the combustion chambers of the cylinder head on an internal combustion piston engine. The head is machined flat, with recesses only for inlet and exhaust valves, spark plugs, injectors and so on. The combustion chamber itself is contained within a dished depression in the top of the piston. The Heron head is suitable for petrol and diesel engines, for ohv and ohc valve-gear, and for small and large engine displacement capacities.

While it is possible for a flat cylinder head to be combined with simple flat-top pistons, that option ignores the reasons for having a depression in the top of each piston, namely: (i) it provides a compact space for combustion to begin, allowing an optimal flame front; and (ii) it creates significant squish. ("Squish" is an effect in internal combustion engines whereby turbulence is created when the compressed charge is "squished" as the piston reaches TDC. Such turbulence is desirable as it promotes more extensive mixing of the fuel/air mixture: cf: cf1, cf2, cf3).

The design, also known as the Gibson-Heron head, takes its name from the engineers who developed it at the Royal Aircraft Factory, Prof. A.H. Gibson and Samuel Dalziel Heron.[1]

Pros & Cons[edit]

  • Advantages include: simplicity of manufacture; compact dimensions; accuracy of the flat machined surface; simplified valve-gear; efficient combustion with good fuel economy.
  • Disadvantages include: the greater size and weight of each piston; volumetric efficiency poorer than conventional cylinder heads.