Squish (piston engine)

Last updated
Squish band Squish band.svg
Squish band
Flathead with squish Side-valve engine v2.png
Flathead with squish

Squish is an effect in internal combustion engines which creates sudden turbulence of the air-fuel mixture as the piston approaches top dead centre (TDC). [1] [2]

Contents

In an engine designed to use the squish effect, at top dead centre the piston crown comes very close (typically less than 1 mm [2] ) to the cylinder head. The gases are suddenly "squished" out within the combustion chamber, creating turbulence which promotes thorough air-fuel mixing, a factor beneficial to efficient combustion. Squish effect may be found in side-valve, OHV and OHC engines, including engines with a Heron cylinder head. Squish effect may be found in any fuel type internal combustion piston engine. Squish piston engines are also found in both two stroke and four stroke engines.

Turbulence in the combustion chamber due to this squish helps with air-fuel mixing, cylinder wall heat transfer, thermal efficiency, and overall engine performance. Heat transfer is aided when the combustion gasses swirl around and heat the cylinder wall, allowing the cooling system to work more efficiently. [3] This efficiency and swirling can also reduce the amount of soot production. [4]

Design Types

Squish piston engines are achieved by modifying an engine's head, block, or the piston crown. Some engine designs include combinations of these different design types. These combinations are used when certain design parameters that attribute the shape and constraints of the combustion chamber.

Modified Head

Modified head squish piston engines utilise a space in the head to make an air pocket for squishing and combustion to occur. Depending on the shape of the pocket and what type of engine, the valve position must be skewed to ensure that both the intake and exhaust valve can fit in the pocket. Modified head squish piston engines can also be made to fit the application on a flathead engine as well as overhead camshaft and two stroke engines.

Modified Block

Modified block squish piston engines utilise a space in the block to create a pocket for squishing and combustion to occur. These squish piston engines are otherwise referred to as flat head engines. [5] These types of engines are not very common anymore because of the inherent issues with insufficient air flow into the engine which directly affects the compression ratio. This design is mostly used in small, low cost applications. [6]

Modified Piston

Modified piston squish piston engines utilise a space in the piston to create an air pocket for squishing and combustion to occur. This is the most common way to create a squish piston engine because it is the smallest and easiest part to manufacture. These pockets can be made by making a recess in the piston crown. This is called a deep bowl piston. [3] Others may use raised areas relative to the piston rings to create a different effect in the combustion chamber. This creates a different type of turbulence that goes down instead of up in the piston itself. To promote turbulence and mixing of the air–fuel mixture, the piston crown must have a recess parallel to the angle that the fuel is injected. It also requires a curve on the outer section of the piston crown. This design directs air from the squish area into the centre of the combustion chamber. This is where the squished air is mixed with the fuel from the injector creating a more evenly mixed air–fuel ratio. However this is only one design for a diesel engine. When looking at engines with more valves and different injector locations there are many different designs that increase the efficiency of the engine. [7] There are also ways to modify the piston and give it intake and exhaust squish areas. This affects how the whole engine runs and the intake and exhaust velocity that in produced.

Related Research Articles

<span class="mw-page-title-main">Compression ratio</span> Ratio of the volume of a combustion chamber from its largest capacity to its smallest capacity

The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.

<span class="mw-page-title-main">Two-stroke engine</span> Internal combustion engine type

A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during one power cycle, this power cycle being completed in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

<span class="mw-page-title-main">Exhaust gas recirculation</span> NOx reduction technique used in gasoline and diesel engines

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.

A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.

In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

<span class="mw-page-title-main">Hemispherical combustion chamber</span> Combustion chamber with a domed cylinder head

A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head notionally in the approximate shape of a hemisphere. An engine featuring this type of hemispherical chamber is known as a hemi engine.

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.

Indirect injection in an internal combustion engine is fuel injection where fuel is not directly injected into the combustion chamber.

<span class="mw-page-title-main">Inlet manifold</span> Automotive technology

An inlet manifold or intake manifold is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.

<span class="mw-page-title-main">Flathead engine</span> A type of four-stroke engine

A flathead engine, also known as a sidevalve engine or valve-in-block engine, is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine.

Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air–fuel ratio may be as lean as 65:1. The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.

<span class="mw-page-title-main">Gasoline direct injection</span> Mixture formation system

Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold.

<span class="mw-page-title-main">Ram-air intake</span> An intake design which uses air pressure from vehicle motion to increase static air pressure

A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle motion, or ram pressure, to increase the static air pressure inside of the intake manifold on an internal combustion engine, thus allowing a greater massflow through the engine and hence increasing engine power.

<span class="mw-page-title-main">Valvetrain</span> Mechanical system in an internal combustion engine

A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

<span class="mw-page-title-main">IOE engine</span> Type of combustion engines

The intake/inlet over exhaust, or "IOE" engine, known in the US as F-head, is a four-stroke internal combustion engine whose valvetrain comprises OHV inlet valves within the cylinder head and exhaust side-valves within the engine block.

The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity, and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes.

The inertial supercharging effect is the increase of volumetric efficiency in the cylinder of an engine.

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, 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. The Heron head is suitable for petrol and diesel engines, for ohv and ohc valve-gear, and for small and large engine displacement capacities.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

References

  1. ↑ "How to Measure Your Cylinder Head Squish Clearance..." Retrieved 16 June 2013.
  2. 1 2 "The Combustion Chamber" Retrieved 16 June 2013.
  3. 1 2 Wu, Horng-Wen; Perng, Shiang-Wuu (May 2002). "LES analysis of turbulent flow and heat transfer in motored engines with various SGS models". International Journal of Heat and Mass Transfer. 45 (11): 2315–2328. doi:10.1016/s0017-9310(01)00325-8.
  4. ↑ "Deere & company files patent application for internal combustion engine with high squish piston". Indian Patents News. 2010-09-08. ProQuest   749812113.
  5. ↑ Borgnakke, C.; Davis, G. C. (1982-02-01). "The Effect of In-Cylinder Flow Processes (Swirl, Squish and Turbulence Intensity) on Engine Efficiency — Model Predictions". SAE Technical Paper Series. Vol. 1. Warrendale, PA. doi:10.4271/820045.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ↑ McKelvie, Steve (2012-07-13). "A Critique of the "Flathead" or Side-Valve Engine Design" . Retrieved 2019-04-30.
  7. ↑ Fujimoto, M (July 2002). "Effect of combustion chamber shape on tumble flow, squish-generated flow and burn rate". JSAE Review. 23 (3): 291–296. doi:10.1016/S0389-4304(02)00201-1.

Bibliography

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.