A Heron cylinder head, or simply Heron head, is a design for the

combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Interna ...

s of the

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...

on an

internal combustion An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...

piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...

, named for engine designer S.D.Heron. 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 A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...

. The Heron head is suitable for petrol and diesel engines, for

ohv An overhead valve (OHV) engine, sometimes called a ''pushrod engine'', is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with earlier flathead engines, where the valves were located bel ...

and

ohc An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

valve-gear, and for small and large engine displacement capacities. While a flat cylinder head could 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" as the piston reaches TDC. This causes turbulence, which is desirable because it promotes more extensive mixing of the fuel/air mixture: cf: cf1, cf2, cf3. Having no space available at the top of piston travel to maintain compression ratio would also mean that the air-fuel mixture would be compressed to zero volume (or close), which is far too high a compression ratio for any internal combustion engine to run on (due to detonation before the piston even reached top dead center) unless the stroke was carefully designed to leave a small gap between the top of the cylinder and the head when the piston is at TDC; in a normal engine the size of the combustion chamber dictates the compression ratio of the engine (i.e. the volume of the cylinder is compressed into the space of the chamber at TDC; a flat piston and flat head would leave no space for the air-fuel mixture, unless designed so the piston doesn't actually reach the top of the cylinder bore)

Pros and cons

* 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 with non parallel valves.

Applications

Alfa Romeo Alfasud The Alfa Romeo Alfasud (Type 901, 902 and 904) is a small family car manufactured and marketed from 1971 to 1989 by Alfa Romeo as a front-engine, four-door, five-passenger entry-level model over a single generation — with facelifts in 1977 a ...

boxer engine *

Audi F103 F103 is the internal designation for a series of car models produced by Auto Union GmbH (after merger with NSU Motorenwerke in 1969: Audi NSU Auto Union) in West Germany from 1965 to 1972, derived from the earlier DKW F102. To signify the change ...

pushrod four engine used in different Audi models of the 1960s and 1970s * Chevrolet 348-409 V8 engines, 1958-1965 * Ford 383-410-430-462 "MEL" V-8 engines, 1958-1968 * Ford 401-477-534 "Super Duty" V-8 engines, 1957-1982 * Ford Essex V4 engine * Ford Essex V6 engine *

Ford Kent engine The Ford Kent is an internal combustion engine from Ford of Europe. Originally developed in 1959 for the Ford Anglia, it is an in-line four-cylinder pushrod engine with a cast-iron cylinder head and block. The Kent family can be divided into t ...

Jaguar V12 engine The Jaguar V12 engine is a V12 internal combustion engine produced by Jaguar Cars. The engine was based on a prototype design by Claude Baily for an intended Le Mans car—the Jaguar XJ13. The XJ13 project was terminated in 1966 before the car wa ...

* Puma racing engines *

Moto Guzzi Moto Guzzi is an Italian motorcycle manufacturer and the oldest European manufacturer in continuous motorcycle production. Established in 1921 in Mandello del Lario, Italy, the company is noted for its historic role in Italy's motorcycling ma ...

Moto Morini Moto Morini is an Italian motorcycle manufacturer founded by Alfonso Morini in Bologna, in 1937. Earlier, Morini had also manufactured motorcycles together with Mario Mazzetti under the name MM. Moto Morini came under Cagiva control in 1987, t ...

3½ & 500 *

Renault F-Type engine F Renault engine (F for ''fonte'', French for cast iron) is an automotive internal combustion engine, four-stroke, inline-four engine bored directly into the iron block, water cooled, with overhead camshaft driven by a timing belt, and with an a ...

also named B18E/B18F/B18FT by

Volvo The Volvo Group ( sv, Volvokoncernen; legally Aktiebolaget Volvo, shortened to AB Volvo, stylized as VOLVO) is a Swedish multinational manufacturing corporation headquartered in Gothenburg. While its core activity is the production, distributio ...

applied to the

Volvo 440/460 The Volvo 440 and 460 are versions of a small family car produced by the Swedish manufacturer Volvo between June 1988 and September 1996. The 440 was a five-door hatchback and the 460 a four-door saloon which followed in 1989. They were built at ...

and

Volvo 480 The Volvo 480 is a sporty compact car that was produced in Born, Netherlands, by Volvo from 1986 to 1995. It was the first front-wheel drive car made by Volvo and the only Volvo featuring pop-up headlights. The 480 was available in only one body ...

. * Rover 2000 P6 * Standard Wetliner I4 engine as used in Standard 2000 which is a licensed

Rover SD1 The Rover SD1 is both the code name and eventual production name given to a series of executive cars built by the Specialist Division (later the ''Jaguar-Rover-Triumph'' division) of British Leyland (BL), under the Rover marque. It was produced ...

Volkswagen EA827 engine The EA827 family of petrol engines was initially developed by Audi under Ludwig Kraus leadership and introduced in 1972 by the B1-series Audi 80, and went on to power many Volkswagen Group models. This is a very robust water-cooled engine configur ...

(e.g. the 1600cc 100 bhp engine of Audi 80 GT) * Volkswagen EA831 engine also used in

Porsche 924 The Porsche 924 is a sports car produced by Porsche in Neckarsulm, Germany,from 1976 until 1988. A two-door, 2+2 (car body style), 2+2 coupé, the 924 replaced the Porsche 912, 912E and Porsche 914, 914 as the company's entry-level model. Altho ...

* Volkswagen

Wasserboxer The Volkswagen wasserboxer is a four cylinder horizontally opposed pushrod overhead-valve (OHV) petrol engine developed by Volkswagen. The engine is water-cooled, and takes its name from the german: "wasserboxer" ("Water-boxer"); with "boxer" b ...

Vanagon engines * Volvo B200K/B230K engine applied to the

Volvo 200 The Volvo 200 Series (or 240 and 260 Series) is a range of mid-size cars produced by Swedish company Volvo Cars from 1974 until 1993, with more than 2.8 million total units sold worldwide. Like the Volvo 140 Series (1966 to 1974), from which it ...

360 360 may refer to: * 360 (number) * 360 AD, a year * 360 BC, a year * 360 degrees, a circle Businesses and organizations * 360 Architecture, an American architectural design firm * Ngong Ping 360, a tourism project in Lantau Island, Hong Kong * Q ...

740 __NOTOC__ Year 740 ( DCCXL) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar, the 740th year of the Common Era (CE) and ''Anno Domini'' (AD) designations, the 740th year of the 1st millennium, th ...

and

940 Year 940 ( CMXL) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. Events By place Europe * The tribe of the Polans begins the construction of the following fortified settlements (Gi ...

in some markets.

References

{{Reflist Piston engine combustion chambers Cylinder head