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Deltoid muscle
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"Delts" redirects here. For the fraternity, see Delta Tau Delta.
Deltoid muscle
Deltoid muscle
Muscles connecting the upper extremity to the vertebral column (not all are labeled)
Details
Origin
the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula
Insertion
deltoid tuberosity of humerus
Artery
thoracoacromial artery, anterior and posterior humeral circumflex artery
Nerve
Axillary nerve
Actions
shoulder abduction, flexion and extension
Antagonist
Latissimus dorsi
Identifiers
Latin
musculus deltoideus
MeSH
D057645
TA
A04.6.02.002
FMA
32521
Anatomical terms of muscle
[edit on Wikidata]
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the common shoulder muscle, particularly in other animals such as the domestic cat. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.[1]
It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). Deltoid is also further shortened in slang as "delt".
A study of 30 shoulders revealed an average mass of 191.9 grams (6.77 oz) in humans, ranging from 84 grams (3.0 oz) to 366 grams (12.9 oz).[2]
Contents
1 Structure
1.1 Insertion
1.2 Blood supply
1.3 Nerve supply
2 Function
3 Clinical significance
4 Other animals
5 References
6 See also
Structure[edit]
Previous studies showed that the insertion of the intramuscular tendons of the deltoid muscle formed three discrete sets of fibers, often referred to as "heads":[3]
The anterior or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle.[4] The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.[5]
The anterior deltoids[6] are commonly called front delts[7] for short.
Lateral or acromial fibers arise from the superior surface of the acromion process of the scapula.[4]
They are commonly called lateral deltoid.[8] This muscle is also called middle delts,[7] outer delts,[9] or side delts[8] for short.
They are also mistakenly called medial deltoid,[10] which is wrong, as their origin is the least medial portion of the deltoid.
Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula.[4]
They are commonly called posterior deltoid[11] or rear deltoid[12] (rear delts for short[13]).
Fick[14] divided these three groups of fibers, often referred to as parts (Latin: pars) or bands, into seven functional components as did Kapandji and Sakoma Y et al. :[15][16] the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In standard anatomical position (with the upper limb hanging alongside the body), the central components (II, III, and IV) lie lateral to the axis of abduction and therefore contribute to abduction from the start of the movement while the other components (I, V, VI, and VII) then act as adductors. During abduction most of these latter components (except VI and VII which always act as adductors) are displaced laterally and progressively start to abduct.[15]
Side.
Front.
Back.
Animation.
Deltoid muscle.
Anterior part of deltoid (arises from most of the anterior border and upper surface of the lateral third of the clavicle.)
Lateral part of deltoid (arises from the superior surface of the acromion process.)
Posterior part of deltoid (arises from the lower lip of the posterior border of the spine of the scapula.)
Insertion[edit]
From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the middle fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.
Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally gives off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the medial and lateral intermuscular septa. [17]
Blood supply[edit]
The deltoid is supplied by the posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery which branches from the axillary artery.[18]
Nerve supply[edit]
The deltoid is innervated by the axillary nerve.[18] The axillary nerve originates from the anterior rami of the cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.[citation needed]
The axillary nerve is sometimes damaged during surgical procedures of the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus.[citation needed]
Function[edit]
When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect.[19] This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction.
The anterior fibers assist Pectoralis Major to flex the shoulder. The anterior deltoid also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus.[20]
The lateral fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers.[21]
Deltoid muscle with superior limb in abduction
The posterior fibers assist the latissimus dorsi to extend the shoulder. Other transverse extensors, the infraspinatus and teres minor, also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats.[22]
An important function of the deltoid in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation.[2] The lateral fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers.[23]
The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.[2]
Clinical significance[edit]
The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy is the result of various causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoideal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation.[24]
Other animals[edit]
The deltoid is also found in members of the great ape family other than humans. The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan, which engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders. In other apes, like the common chimpanzee, the deltoid is much larger than in humans, weighing an average of 383.3g compared to 191.9g in humans. This reflects the need to strengthen the shoulders, particularly the rotatory cuff, in knuckle walking apes for the purpose of supporting the entire body weight.[2]
References[edit]
Jump up ^ Brown JM, Wickham JB, McAndrew DJ, Huang XF. (2007). Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. J Electromyogr Kinesiol. 17(1):57-73. PMID 16458022 doi:10.1016/j.jelekin.2005.10.007
^ Jump up to: a b c d Potau JM, Bardina X, Ciurana N, Camprubí D. Pastor JF, de Paz F. Barbosa M. (2009). Quantitative Analysis of the Deltoid and Rotator Cuff Muscles in Humans and Great Apes. Int J Primatol 30:697–708. doi:10.1007/s10764-009-9368-8
Jump up ^ The Anatomy of the Shoulder Muscles: "The Deltoid is a three-headed muscle that caps the shoulder. The three heads of the Deltoid are the Anterior, Lateral, and Posterior."
^ Jump up to: a b c "Deltoid Muscle". Wheeless' Textbook of Orthopaedics. December 2011. Retrieved January 2012. Check date values in: |accessdate= (help)
Jump up ^ Leijnse, J N A L; Han, S-H; Kwon, Y H (December 2008). "Morphology of deltoid origin and end tendons – a generic model" (PDF). J Anat. 213 (6): 733–742. doi:10.1111/j.1469-7580.2008.01000.x. PMC 2666142  . PMID 19094189. Retrieved January 2012. Check date values in: |accessdate= (help)
Jump up ^ Anterior Deltoid
^ Jump up to: a b Pick up your delts from Muscle and Fitness: "target point: front/middle delts"
^ Jump up to: a b Lateral deltoid
Jump up ^ The Best Exercise for Outer Delts on LiveStrong.com in 2011
Jump up ^ Shoulders Anatomy by Yu Yevon
Jump up ^ Posterior Deltoid
Jump up ^ Rear Deltoid Stretch
Jump up ^ Lee Hayward - Rear delts
Jump up ^ Fick, R. (1911). Handbuch der Anatomie und Mekanik der Gelenke. Jena: Gustav Fischer.
^ Jump up to: a b Kapandji, Ibrahim Adalbert (1982). The Physiology of the Joints: Volume One Upper Limb (5th ed.). New York: Churchill Livingstone.
Jump up ^ [Anatomical and functional segments of the deltoid muscle. J Anat. 2011 Feb;218(2):185-90. doi: 10.1111/j.1469-7580.2010.01325.x. Epub 2010 Nov 30. ]: "
Jump up ^ Rispoli, Damian M.; Athwal, George S.; Sperling, John W.; Cofield, Robert H. (2009). "The anatomy of the deltoid insertion" (PDF). J Shoulder Elbow Surg. 18: 386–390. doi:10.1016/j.jse.2008.10.012. Archived from the original (PDF) on 2012-09-04.
^ Jump up to: a b Anatomy photo:03:03-0103 at the SUNY Downstate Medical Center
Jump up ^ Radiography of the Upper Extremities: 24 ARRT Category A. CE4RT, 2014. 201. Print.
Jump up ^ Muscles/DeltoidAnterior at exrx.net
Jump up ^ Muscles/DeltoidLateral at exrx.net
Jump up ^ Muscles/DeltoidPosterior at exrx.net
Jump up ^ http://muscleguide.co.uk/exercises/lateral-deltoid-raise.html
Jump up ^ Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Chapter on deltoideal enthesopathy available at ShoulderUS.com
See also[edit]
Wikimedia Commons has media related to Deltoid muscles.
This article uses anatomical terminology; for an overview, see Anatomical terminology.
hide
v
t
e
Muscles of the arm
Shoulder
deltoid
rotator cuff
supraspinatus
infraspinatus
teres minor
subscapularis
teres major
fascia:
deltoid fascia
supraspinous fascia
infraspinous fascia
Arm
(compartments)
anterior
coracobrachialis
biceps
brachialis
posterior
triceps brachii
anconeus
articularis cubiti
fascia
axillary sheath
axillary fascia
brachial fascia
intermuscular septa
lateral
medial
other
spaces
quadrangular space
triangular space
triangular interval
Forearm
anterior
superficial:
pronator teres
palmaris longus
flexor carpi radialis
flexor carpi ulnaris
flexor digitorum superficialis
deep:
pronator quadratus
flexor digitorum profundus
flexor pollicis longus
posterior
superficial:
mobile wad
brachioradialis
extensor carpi radialis longus and brevis
extensor digitorum
extensor digiti minimi
extensor carpi ulnaris
deep:
supinator
anatomical snuff box
abductor pollicis longus
extensor pollicis brevis
extensor pollicis longus
extensor indicis
fascia
bicipital aponeurosis
common tendons
extensor
flexor
antebrachial fascia
other
cubital tunnel
Hand
lateral volar
thenar
opponens pollicis
flexor pollicis brevis
abductor pollicis brevis
adductor pollicis
medial volar
hypothenar
opponens digiti minimi
flexor digiti minimi brevis
abductor digiti minimi
palmaris brevis
intermediate
lumbrical
interossei
dorsal
palmar
fascia
posterior:
extensor retinaculum
extensor expansion
anterior:
flexor retinaculum
palmar aponeurosis
Retrieved from "https://en.wikipedia.org/w/index.php?title=Deltoid_muscle&oldid=855260212"
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Squib (explosive)
From Wikipedia, the free encyclopedia
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For the firearms malfunction, see squib load.
A typical Chinese Squib
A squib is a miniature explosive device used in a wide range of industries, from special effects to military applications. It resembles a tiny stick of dynamite, both in appearance and construction, although with considerably less explosive power. Squibs consist of two electrical leads which are separated by a plug of insulating material, a small bridge wire or electrical resistance heater, and a bead of heat-sensitive chemical composition in which the bridge wire is embedded.[1] Squibs can be used for generating mechanical force, or to provide pyrotechnic effects for both film and live theatrics. Squibs can be used for shattering or propelling a variety of materials.[2]
A squib generally consists of a small tube filled with an explosive substance, with a detonator running through the length of its core, similar to a stick of dynamite. Also similar to dynamite, the detonator can be a slow-burning fuse, or as is more common today, a wire connected to a remote electronic trigger.[3] Squibs range in size, anywhere from .08" up to 6/10" (~2 to 15 millimeters) in diameter.[2]
In the North American film industry, the term squib is often used to refer variously to: electric matches and detonators (used as initiators to trigger larger pyrotechnics). Squibs are generally (but not always) the main explosive element in an effect, and as such are regularly used as “bullet hits”.[2] Conventional squibs fire once, with the exception of eSquibs, which fire 200 or more times before depletion. [4]
Contents
[hide]
1 Uses
2 History
2.1 The famous "Squib Case"
2.2 Squibs in film
2.3 Origin of the phrase "damp squib"
3 See also
4 References
Uses[edit]
Squibs were once used in coal mining to break coal away from rock. In the 1870s, some versions of the device were patented and mass-produced as "Miners' Safety Squibs".[5]
Today, squibs are widely used in the motion picture special effects industry to simulate bullet impacts on inanimate objects. Items such as sand, soil or wood splinters may be attached to the squib to simulate the "splash" that occurs when bullets pierce different materials.[2]
Although squibs were once used even for the simulation of bullet hits on live actors, such use has been largely phased out in favor of more advanced devices that are safer for the actor, such as miniature compressed gas packs. These alternate devices are often still referred to as "squibs" even though they do not use explosive substances. The devices (whether explosive or not) are coupled with small balloons filled with fake blood (blood squibs) and often other materials to simulate shattered bone and tissue.[6]
Squibs are used in emergency mechanisms where gas pressure needs to be generated quickly in confined spaces, while not harming any surrounding persons or mechanical parts. In this form, squibs may be called gas generators. One such mechanism is the inflation of automobile air bags. In military aircraft, squibs are used to deploy countermeasures, and are also implemented during ejection to propel the canopy and ejection seat away from a crippled aircraft. They are also used to deploy parachutes.[3] Squibs are also used in automatic fire extinguishers, to pierce seals that retain liquids such as halon, fluorocarbon, or liquid nitrogen.
History[edit]
Squibs were originally made from parchment tubes, or the shaft of a feather, and filled with fine black powder. They were then sealed at the ends with wax. They were sometimes used to ignite the main propellant charge in cannon.[7]
The famous "Squib Case"[edit]
Squibs are mentioned in the prominent tort case from eighteenth-century England, Scott v. Shepherd, 96 Eng. Rep. 525 (K.B. 1773). A lit squib was thrown into a crowded market by Shepherd, and landed on the table of a gingerbread merchant. A bystander, to protect himself and the gingerbread, threw the squib across the market, where it landed in the goods of another merchant. The merchant grabbed the squib and tossed it away, accidentally hitting Scott in the face, putting out one of his eyes.
Squibs in film[edit]
The first documented use of squibs to simulate bullet impacts in movies was in the 1955 Polish film Pokolenie by Andrzej Wajda, where for the first time audiences were presented with a realistic representation of a bullet impacting on an on-camera human being, complete with blood spatter. The creator of the effect, Kazimierz Kutz, used a condom with fake blood and dynamite. [8]
Origin of the phrase "damp squib"[edit]
Look up damp squib in Wiktionary, the free dictionary.
While most modern squibs used by professionals are insulated from moisture, older uninsulated squibs needed to be kept dry in order to ignite, thus a "damp squib" was literally one that failed to perform because it got wet. Often misheard as "damp squid",[9] the phrase "damp squib" has since come into general use to mean anything that fails to meet expectations.[10] The word "squib" has come to take on a similar meaning even when used alone, as a diminutive comparison to a full explosive.[11]
See also[edit]
Pyrotechnics portal
Firecracker
Squib load
References[edit]
Jump up ^ Thibodaux, J.G. "Special Rockets and Pyrotechnics Problems". Langley Research Center. NTRS. Retrieved July 1, 1961. Check date values in: |access-date= (help)
^ Jump up to: a b c d "Top 10 Frequently Asked Questions". Fantasy Creations FX.
^ Jump up to: a b US 5411225 “Reusable non-pyrotechnic countermeasure dispenser cartridge for aircraft.”
Jump up ^ http://livedesignonline.com/news/ldi-2014-award-winners-announced
Jump up ^ Wallace, Anthony F. C. (1988). St. Clair, a nineteenth-century coal town's experience with a disaster-prone industry. Cornell University Press. p. 50. ISBN 978-0-8014-9900-5.
Jump up ^ Grossman, Andrew. "Bleeding Realism Dry". Bright Lights Film Journal. p. 2.
Jump up ^ Calvert, James B. "Cannons and Gunpowder". University of Denver.
Jump up ^ J.Sz., Gazeta Wyborcza, 2008
Jump up ^ "Damp Squid: The top 10 misquoted phrases in Britain". The Daily Telegraph. London. 24 February 2009.
Jump up ^ "Definition of damp squib". Allwords.com.
Jump up ^ "squib: Definitions, Synonyms". Answers.com.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Squib_(explosive)&oldid=808772015"
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List of Scottish cricket and football players
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This is a list of sportsmen who have played both first-class cricket and professional football in Scotland or England. The list includes four sportsmen who are dual internationals, having represented Scotland's national team at both sports.
Contents
[hide]
1 List of Scottish cricket and football players
1.1 Dual internationals
1.2 Scotland cricket team / Professional football
2 See also
3 References
List of Scottish cricket and football players[edit]
This list is incomplete; you can help by expanding it.
Dual internationals[edit]
Name
Cricket club/team
Football club/team
Ref
Notes
Macdonald, JohnJohn Macdonald
Scotland
Scotland
[1] The first sportsman to represent Scotland at both sports. Won his cricket cap first.
Symon, ScotScot Symon
Scotland
Dundee
Portsmouth
Rangers
Scotland
[1] Won his cricket cap first
Ford, DonaldDonald Ford
Scotland
Heart of Midlothian
Falkirk
Scotland
[1] Won his football cap first
Goram, AndyAndy Goram
Scotland
Oldham Athletic
Hibernian
Rangers
Notts County
Sheffield United
Motherwell
Manchester United
Hamilton Academical
Coventry City
Queen of the South
Elgin City
Scotland
[1][2] Won his football cap first
Scotland cricket team / Professional football[edit]
Name
Cricket club/team
Football club/team
Ref
Notes
Souness, JimJim Souness
Scotland
Hibernian
Falkirk
Heart of Midlothian
Dudman, LenLen Dudman
Scotland
Falkirk
Forfar Athletic
See also[edit]
List of English cricket and football players
References[edit]
^ Jump up to: a b c d David Gordon (26 February 2014). "FORGOTTEN CRICKET/FOOTBALL INTERNATIONAL REDISCOVERED". Cricket Scotland. Retrieved 11 May 2015.
Jump up ^ Martin Williamson. "Andy Goram profile". ESPNcricinfo. Retrieved 11 May 2015.
[show]
v
t
e
Cricketers who played other sports
Association football (England)
Association football (Scotland)
Australian rules football
Rugby league
Rugby union
Retrieved from "https://en.wikipedia.org/w/index.php?title=List_of_Scottish_cricket_and_football_players&oldid=757130486"
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Compression ratio
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For compression ratio in data compression, see data compression ratio.
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2009) (Learn how and when to remove this template message)
A four-stroke engine showing the stroke of the piston.
The static compression ratio of an internal combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.
In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.[1]
For example, a cylinder and its combustion chamber with the piston at the bottom of its stroke may contain 1000 cc of air (900 cc in the cylinder plus 100 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio.
A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher efficiency is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. It may be more helpful to think of it as an "expansion ratio", since more expansion reduces the temperature of the exhaust gases, and therefore the energy wasted to the atmosphere. Diesel engines actually have a higher peak combustion temperature than petrol engines, but the greater expansion means they reject less heat in their cooler exhaust.
Higher compression ratios will however make gasoline engines subject to engine knocking (also known as detonation) if lower octane-rated fuel is used. This can reduce efficiency or damage the engine if knock sensors are not present to modify the ignition timing.
On the other hand, Diesel engines operate on the principle of compression ignition, so that a fuel which resists autoignition will cause late ignition, which will also lead to engine knock.
Contents
1 Formula
2 Typical compression ratios
2.1 Gasoline (petrol) engine
2.2 Petrol/gasoline engine with pressure-charging
2.3 Petrol/gasoline engine for racing
2.4 Ethanol and methanol engines
2.5 Gas-fueled engine
2.6 Diesel engine
2.7 Kerosene engine
3 Fault finding and diagnosis
4 Variable Compression Ratio (VCR) engines
5 Dynamic compression ratio
6 Compression ratio versus overall pressure ratio
7 See also
8 Notes
9 External links
Formula[edit]
Static compression ratio ( C R {\displaystyle CR} ) is calculated by the formula
C R = V d + V c V c {\displaystyle {CR}={\frac {V_{d}+V_{c}}{V_{c}}}}
Where:
V d {\displaystyle V_{d}} = displacement volume. This is the volume inside the cylinder displaced by the piston from the beginning of the compression stroke to the end of the stroke.
V c {\displaystyle V_{c}} = clearance volume. This is the volume of the space in the cylinder left at the end of the compression stroke.
V d {\displaystyle V_{d}} can be estimated by the cylinder volume formula
V d = π 4 b 2 s {\displaystyle V_{d}={\tfrac {\pi }{4}}b^{2}s}
Where:
b {\displaystyle b} = cylinder bore (diameter)
s {\displaystyle s} = piston stroke length
Because of the complex shape of V c {\displaystyle V_{c}} it is usually measured directly. This is often done by filling the cylinder with liquid and then measuring the volume of the used liquid.
Typical compression ratios[edit]
Gasoline (petrol) engine[edit]
The compression ratio in a gasoline (petrol)-powered engine will usually not be much higher than 10:1 due to potential engine knocking (detonation) and not lower than 6:1. Some production automotive engines built for high performance from 1955–1972, used high-octane leaded gasoline or '5 star' to allow compression ratios as high as 13.0:1.
A technique used to prevent the onset of knock is the high "swirl" engine that forces the intake charge to adopt a fast circular rotation in the cylinder during compression that provides quicker and more complete combustion. It is possible to manufacture gasoline engines with compression ratios of over 11:1 that can use 87 (MON + RON)/2 (octane rating) fuel with the addition of variable valve timing and knock sensors to delay ignition timing. Such engines may not produce their full rated power using 87 octane gasoline under all circumstances, due to the delayed ignition timing. Direct fuel injection, which can inject fuel only at the time of fuel ignition (similar to a diesel engine), is another recent development which also allows for higher compression ratios on gasoline engines.
The compression ratio can be as high as 14:1 (2014 Ferrari 458 Speciale) in engines with a 'ping' or 'knock' sensor and an electronic control unit. In 1981, Jaguar released a cylinder head that allowed up to 14:1 compression; but settled for 12.5:1 in production cars. The cylinder head design was known as the "May Fireball" head; it was developed by a Swiss engineer Michael May.
In 2012, Mazda released new petrol engines under the brand name SkyActiv with a 14:1 compression ratio (U.S. models have a 13:1 compression ratio to allow for 87 AKI octane), to be used in all Mazda vehicles by 2015.[2][3][4]
Petrol/gasoline engine with pressure-charging[edit]
In a turbocharged or supercharged gasoline engine, the CR is customarily built at 10.5:1 or lower. This is due to the turbocharger/supercharger already having compressed the air before it enters the cylinders. Port fuel injected engines typically run lower boost than direct fuel injected engines because port fuel injection allows the air/fuel mixture to be heated together which leads to detonation. Conversely, directly injected engines can run higher boost because heated air will not detonate without a fuel being present. In this instance fuel is injected as late as 60 degrees before top dead center to avoid heating the mixture to the point of compression ignition.
Petrol/gasoline engine for racing[edit]
Motorcycle racing engines can use compression ratios as high as 14.7:1, and it is common to find motorcycles with compression ratios above 12.0:1 designed for 86 or 87 octane fuel. F1 engines come closer to 17:1, which is critical for maximizing volumetric/fuel efficiency at around 18,000 RPM.[citation needed]
Ethanol and methanol engines[edit]
Ethanol and methanol can take significantly higher compression ratios than gasoline. Racing engines burning methanol and ethanol fuel often incorporate a CR of 14.5-16:1.
Gas-fueled engine[edit]
The CR may be higher in engines running exclusively on LPG or CNG, due to the higher octane rating of these fuels.
Diesel engine[edit]
There is no spark plug in an auto-ignition diesel engine; the heat of compression raises the temperature of the air in the cylinder sufficiently to ignite the diesel when this is injected into the cylinder; after the compression stroke. The CR will customarily exceed 14:1 and ratios over 22:1 are common. The appropriate compression ratio depends on the design of the cylinder head. The figure is usually between 14:1 and 23:1 for direct injection engines, and between 18:1 and 23:1 for indirect injection.And also in crdi injection.
Kerosene engine[edit]
A compression ratio of 6.5 or lower is desired for operation on kerosene. The petrol-paraffin engine version of the Ferguson TE20 tractor had a compression ratio of 4.5:1 for operation on tractor vaporising oil with an octane rating between 55 and 70.[5]
Fault finding and diagnosis[edit]
Measuring the compression pressure of an engine, with a pressure gauge connected to the spark plug opening, gives an indication of the engine's state and quality. There is, however, no formula to calculate compression ratio based on cylinder pressure.
If the nominal compression ratio of an engine is given, the pre-ignition cylinder pressure can be estimated using the following relationship:
p = p 0 × CR γ {\displaystyle p=p_{0}\times {\text{CR}}^{\gamma }}
where p 0 {\displaystyle p_{0}\;} is the cylinder pressure at bottom dead center which is usually at 1 atm, CR {\displaystyle {\text{CR}}} is the compression ratio, and γ {\displaystyle \gamma \;} is the specific heat ratio for the working fluid, which is about 1.4 for air, and 1.3 for methane-air mixture.
For example, if an engine running on gasoline has a compression ratio of 10:1, the cylinder pressure at top dead center is
p TDC = 1 bar × 10 1.4 = 25.1 bar {\displaystyle p_{\text{TDC}}=1{\text{ bar}}\times 10^{1.4}=25.1{\text{ bar}}}
This figure, however, will also depend on cam (i.e. valve) timing. Generally, cylinder pressure for common automotive designs should at least equal 10 bar, or, roughly estimated in pounds per square inch (psi) as between 15 and 20 times the compression ratio, or in this case between 150 psi and 200 psi, depending on cam timing. Purpose-built racing engines, stationary engines etc. will return figures outside this range.
Factors including late intake valve closure (relatively speaking for camshaft profiles outside of typical production-car range, but not necessarily into the realm of competition engines) can produce a misleadingly low figure from this test. Excessive connecting rod clearance, combined with extremely high oil pump output (rare but not impossible) can sling enough oil to coat the cylinder walls with sufficient oil to facilitate reasonable piston ring sealing. In engines with compromised ring seals, this can artificially give a misleadingly high compression figure.
This phenomenon can actually be used to some slight advantage. If a compression test does give a low figure, and it has been determined it is not due to intake valve closure/camshaft characteristics, then one can differentiate between the cause being valve/seat seal issues and ring seal by squirting engine oil into the spark plug orifice, in a quantity sufficient to disperse across the piston crown and the circumference of the top ring land, and thereby affect the mentioned seal. If a second compression test is performed shortly thereafter, and the new reading is much higher, it would be the ring seal that is problematic, whereas if the compression test pressure observed remains low, it is a valve sealing (or more rarely head gasket, or breakthrough piston or, rarer still, cylinder-wall damage) issue.
If there is a significant (greater than 10%) difference between cylinders, that may be an indication that valves or cylinder head gaskets are leaking, piston rings are worn, or that the block is cracked.
If a problem is suspected, then a more comprehensive test using a leak-down tester can locate the leak.
Variable Compression Ratio (VCR) engines[edit]
Because cylinder-bore diameter, piston-stroke length and combustion-chamber volume are almost always constant, the compression ratio for a given engine is almost always constant, until engine wear takes its toll.
One exception is the experimental Saab Variable Compression engine (SVC). This engine, designed by Saab Automobile, uses a technique that dynamically alters the volume of the combustion chamber (Vc), which, via the above equation, changes the compression ratio (CR).
The Atkinson cycle engine was one of the first attempts at variable compression. Since the compression ratio is the ratio between dynamic and static volumes of the combustion chamber, the Atkinson cycle's method of increasing the length of the power stroke compared to the intake stroke ultimately altered the compression ratio at different stages of the cycle.
On August 15, 2016 Nissan Motor Company announced a new variable compression engine that can choose an optimal compression ratio variably between 8:1 and 14:1. That lets the engine adjust moment by moment to torque demands, always maintaining top efficiency. Nissan says that the turbo-charged, 2-liter, four-cylinder VC-T engine averages 27 percent better fuel economy than the 3.5-liter V6 engine it replaces, with comparable power and torque.[6]
Dynamic compression ratio[edit]
The calculated compression ratio, as given above, presumes that the cylinder is sealed at the bottom of the stroke, and that the volume compressed is the actual volume.
However: intake valve closure (sealing the cylinder) always takes place after BDC, which may cause some of the intake charge to be compressed backwards out of the cylinder by the rising piston at very low speeds; only the percentage of the stroke after intake valve closure is compressed. Intake port tuning and scavenging may allow a greater mass of charge (at a higher than atmospheric pressure) to be trapped in the cylinder than the static volume would suggest ( This "corrected" compression ratio is commonly called the "dynamic compression ratio".
This ratio is higher with more conservative (i.e., earlier, soon after BDC) intake cam timing, and lower with more radical (i.e., later, long after BDC) intake cam timing, but always lower than the static or "nominal" compression ratio.
The actual position of the piston can be determined by trigonometry, using the stroke length and the connecting rod length (measured between centers). The absolute cylinder pressure is the result of an exponent of the dynamic compression ratio. This exponent is a polytropic value for the ratio of variable heats for air and similar gases at the temperatures present. This compensates for the temperature rise caused by compression, as well as heat lost to the cylinder. Under ideal (adiabatic) conditions, the exponent would be 1.4, but a lower value, generally between 1.2 and 1.3 is used, since the amount of heat lost will vary among engines based on design, size and materials used, but provides useful results for purposes of comparison. For example, if the static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be (7.5)^1.3 × atmospheric pressure, or 13.7 bar. (× 14.7 psi at sea level = 201.8 psi. The pressure shown on a gauge would be the absolute pressure less atmospheric pressure, or 187.1 psi.)
The two corrections for dynamic compression ratio affect cylinder pressure in opposite directions, but not in equal strength. An engine with high static compression ratio and late intake valve closure will have a DCR similar to an engine with lower compression but earlier intake valve closure.
Additionally, the cylinder pressure developed when an engine is running will be higher than that shown in a compression test for several reasons.
The much higher velocity of a piston when an engine is running versus cranking allows less time for pressure to bleed past the piston rings into the crankcase.
a running engine is coating the cylinder walls with much more oil than an engine that is being cranked at low RPM, which helps the seal.
the higher temperature of the cylinder will create higher pressures when running vs. a static test, even a test performed with the engine near operating temperature.
A running engine does not stop taking air & fuel into the cylinder when the piston reaches BDC; The mixture that is rushing into the cylinder during the downstroke develops momentum and continues briefly after the vacuum ceases (in the same respect that rapidly opening a door will create a draft that continues after movement of the door ceases). This is called scavenging. Intake tuning, cylinder head design, valve timing and exhaust tuning determine how effectively an engine scavenges.
Compression ratio versus overall pressure ratio[edit]
Compression ratio versus pressure ratio
Compression ratio and overall pressure ratio are interrelated as follows:
Compression ratio
2:1 3:1 5:1 10:1 15:1 20:1 25:1 35:1
Pressure ratio
2.64:1 4.66:1 9.52:1 25.12:1 44.31:1 66.29:1 90.60:1 145.11:1
The reason for this difference is that compression ratio is defined via the volume reduction:
CR = V 1 V 2 {\displaystyle {\text{CR}}={\frac {V_{1}}{V_{2}}}} ,
while pressure ratio is defined as the pressure increase:
PR = P 2 P 1 {\displaystyle {\text{PR}}={\frac {P_{2}}{P_{1}}}} .
In calculating the pressure ratio, we assume that an adiabatic compression is carried out (i.e. that no heat energy is supplied to the gas being compressed, and that any temperature rise is solely due to the compression). We also assume that air is a perfect gas. With these two assumptions, we can define the relationship between change of volume and change of pressure as follows:
P 1 V 1 γ = P 2 V 2 γ ⇒ P 2 P 1 = ( V 1 V 2 ) γ {\displaystyle P_{1}V_{1}^{\gamma }=P_{2}V_{2}^{\gamma }\Rightarrow {\frac {P_{2}}{P_{1}}}=\left({\frac {V_{1}}{V_{2}}}\right)^{\gamma }}
where γ {\displaystyle \gamma } is the ratio of specific heats (air: approximately 1.4). The values in the table above are derived using this formula. Note that in reality the ratio of specific heats changes with temperature and that significant deviations from adiabatic behavior will occur.
See also[edit]
Mean effective pressure
Overall pressure ratio - a closely related ratio for jet engines
Notes[edit]
Jump up ^ Encyclopædia Britannica, Compression ratio, retrieved 2009-07-21
Jump up ^ gSiteLife.Recommend("ExternalResource","110429942"); Tweet (2011-04-22). "2012 Mazda 3 gets 40-mpg SkyActiv engine option; diesel expected in 2014". Autoweek. Retrieved 2012-05-29. CS1 maint: Multiple names: authors list (link)
Jump up ^ [1] Archived March 12, 2012, at the Wayback Machine.
Jump up ^ VANDERWERP, DAVE (August 2010). "Mazda Engine News: Mazda Sky Gas and Diesel Details". Car and Driver. Retrieved 2012-05-29.
Jump up ^ "Tractor Vaporising Oil". Web.archive.org. 2005-04-18. Archived from the original on October 12, 2007. Retrieved 2014-08-10.
Jump up ^ Blain, Loz. "Turbo power meets extreme efficiency: Infiniti unveils world's first production engine with variable compression ratios". newatlas.com. Archived from the original on 2017-10-12. Retrieved 2018-04-28.
External links[edit]
"Here Comes High Compression Engines " 1949 highly detailed article in Popular Science with photos and cutaway drawings
Variable compression engine
Cam Timing vs. Compression Ratio Analysis
Calculating Compression Ratio changes with engine modifications
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