Atkinson cycle - Revision history

Red marquis: /* External links */

2010-03-02T05:01:42Z

External links

← Older revision		Revision as of 05:01, 2 March 2010
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	* [http://www.keveney.com/Atkinson.html Animation of Atkinson Cycle Engine] Note that this animation shows the true Atkinson engine, which uses a complex linkage that allows different stroke lengths for intake/compression and power/exhaust. However, the illustration shows the engine with the linkage laid out to generate 4 equal strokes. To alter the ratio of the strokes, the rightmost pivot point (the one that is attaching the horizontal green link to the frame) should be moved downwards along the frame. This will allow more angular movement as the link rotates up, giving a longer piston stroke for power and exhaust, and less angular movement as the link rotates down, giving a shorter piston stroke for intake and compression. In fact, a sliding pivot point at that location would allow the engine to dynamically change the stroke ratios.		* [http://www.keveney.com/Atkinson.html Animation of Atkinson Cycle Engine] Note that this animation shows the true Atkinson engine, which uses a complex linkage that allows different stroke lengths for intake/compression and power/exhaust. However, the illustration shows the engine with the linkage laid out to generate 4 equal strokes. To alter the ratio of the strokes, the rightmost pivot point (the one that is attaching the horizontal green link to the frame) should be moved downwards along the frame. This will allow more angular movement as the link rotates up, giving a longer piston stroke for power and exhaust, and less angular movement as the link rotates down, giving a shorter piston stroke for intake and compression. In fact, a sliding pivot point at that location would allow the engine to dynamically change the stroke ratios.
	* [http://modifiedatkinsoncycleengine.blogspot.com Modified Atkinson Cycle Engine:] alternative variable valve timing strategy increases low speed torque obtainable from Atkinson Cycle Engine.		* [http://modifiedatkinsoncycleengine.blogspot.com Modified Atkinson Cycle Engine:] alternative variable valve timing strategy increases low speed torque obtainable from Atkinson Cycle Engine.
	* [http://www.ornl.gov/~webworks/cpr/v823/rpt/106982.pdf COMPARISON OF PRIME MOVERS SUITABLE FOR USMC EXPEDITIONARY POWER SOURCES], [[Oak Ridge National Laboratory]]		* [http://www.ornl.gov/~webworks/cpr/v823/rpt/106982.pdf COMPARISON OF PRIME MOVERS SUITABLE FOR USMC EXPEDITIONARY POWER SOURCES], Oak Ridge National Laboratory
	* [http://libralato.co.uk Libralato Engines] Home page of the company developing the rotary Atkinson cycle engine		* [http://libralato.co.uk Libralato Engines] Home page of the company developing the rotary Atkinson cycle engine
	* [http://white-smoke.wetpaint.com/page/Rotary+Engine Rotary Atkinson cycle engine] A web page giving details of this engine and comparisons with conventional and Wankel engines.		* [http://white-smoke.wetpaint.com/page/Rotary+Engine Rotary Atkinson cycle engine] A web page giving details of this engine and comparisons with conventional and Wankel engines.

Red marquis at 04:57, 2 March 2010

2010-03-02T04:57:49Z

← Older revision		Revision as of 04:57, 2 March 2010
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	The '''Atkinson-cycle engine''' is a type of [[internal combustion engine]] invented by [[James Atkinson ~~(inventor)\|James Atkinson]]~~ in 1882. The Atkinson cycle is designed to provide efficiency at the expense of [[power density]] and is beginning to see use in modern [[hybrid electric]] applications.		The '''Atkinson-cycle engine''' is a type of [[internal combustion engine]] invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density and is beginning to see use in modern [[hybrid electric]] applications.

	==Design==		==Design==
	The original Atkinson-cycle [[Reciprocating engine\|piston engine]] allows the intake, compression, power, and exhaust [[Stroke ~~(engine)~~\|strokes]] of the [[four-stroke cycle]] to occur in a single turn of the [[crankshaft]] and was designed to bypass patents covering the existing [[Four-stroke cycle\|Otto cycle]] engines.<ref>{{US patent reference \| number =367496 \| y = 1887 \| m =08 \| d = 02 \| inventor =James Atkinson \| title =Gas-Engine}}</ref> Due to the unique [[crankshaft]] design of the Atkinson, the expansion ratio may differ from the [[compression ratio]]. By adjusting the linkage to allow a power stroke that is longer than the compression stroke, the engine can achieve greater efficiency than with the Otto cycle engine. While Atkinson's original engine design is no more than a historical curiosity, the Atkinson cycle, where the power stroke is longer than the compression stroke, is increasing in popularity due to the increase in fuel economy it provides.		The original Atkinson-cycle [[Reciprocating engine\|piston engine]] allows the intake, compression, power, and exhaust [[Stroke\|strokes]] of the [[four-stroke cycle]] to occur in a single turn of the [[crankshaft]] and was designed to bypass patents covering the existing [[Four-stroke cycle\|Otto cycle]] engines.<ref>{{US patent reference \| number =367496 \| y = 1887 \| m =08 \| d = 02 \| inventor =James Atkinson \| title =Gas-Engine}}</ref> Due to the unique [[crankshaft]] design of the Atkinson, the expansion ratio may differ from the compression ratio. By adjusting the linkage to allow a power stroke that is longer than the compression stroke, the engine can achieve greater efficiency than with the Otto cycle engine. While Atkinson's original engine design is no more than a historical curiosity, the Atkinson cycle, where the power stroke is longer than the compression stroke, is increasing in popularity due to the increase in fuel economy it provides.

	~~{{clear}}~~

	==Ideal thermodynamic cycle==		==Ideal thermodynamic cycle==
	~~[[Image:T cycle AtkinsonMiller.png\|thumb\|right\|250px\|'''Figure 1: Atkinson Gas Cycle''']]~~

	The ideal Atkinson cycle consists of following operations:		The ideal Atkinson cycle consists of following operations:

	# [[Isentropic ~~process\|Isentropic]]~~ or ~~[[Reversible process (thermodynamics)\|~~reversible~~]] [[Adiabatic process\|~~adiabatic]] compression.		# Isentropic or reversible adiabatic compression.
	# [[Isochoric]] heating.		# Isochoric heating.
	# Isentropic expansion.		# Isentropic expansion.
	# [[Isobaric]] cooling.		# Isobaric cooling.

	~~{{clear}}~~

	== Modern "Atkinson-cycle" engines ==		== Modern "Atkinson-cycle" engines ==
	~~[[Image:Atkinson-cycle engine.jpg\|thumb\|250px\|A small engine with Atkinson-style linkages between the piston and flywheel. Modern Atkinson-cycle engines do away with this complex energy path.]]~~
	Recently Atkinson cycle has been used to describe a modified [[Otto cycle]] engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This is more like a [[Miller cycle]] engine than an actual ''Atkinson cycle'' engine. The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed) but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio. Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.		Recently Atkinson cycle has been used to describe a modified [[Otto cycle]] engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This is more like a [[Miller cycle]] engine than an actual ''Atkinson cycle'' engine. The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed) but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio. Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.

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	Four-stroke engines of this type with this same type of intake valve motion but with a [[supercharger]] to make up for the loss of power density are known as [[Miller cycle]] engines.		Four-stroke engines of this type with this same type of intake valve motion but with a [[supercharger]] to make up for the loss of power density are known as [[Miller cycle]] engines.

	~~{{clear}}~~

	== Rotary Atkinson-cycle engine ==		== Rotary Atkinson-cycle engine ==
	~~[[Image:WikiDartEngine.gif\|right\|250px\|thumb\|Rotary Atkinson-cycle engine]]~~

	The Atkinson cycle can be used in a rotary engine. In this configuration an increase in both power and efficiency can be achieved when compared to the Otto cycle. This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle. Exhaust gases are expelled from the engine by compressed-air scavenging. This modification of the Atkinson cycle allows for the use of alternative fuels like Diesel and hydrogen. See External Links for more information.		The Atkinson cycle can be used in a rotary engine. In this configuration an increase in both power and efficiency can be achieved when compared to the Otto cycle. This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle. Exhaust gases are expelled from the engine by compressed-air scavenging. This modification of the Atkinson cycle allows for the use of alternative fuels like Diesel and hydrogen. See External Links for more information.

	~~{{clear}}~~

	==Vehicles using "Atkinson-cycle" engines==		==Vehicles using "Atkinson-cycle" engines==
	~~[[Image:Prius2004.JPG\|thumb\|225px\|[[Toyota Prius]] 2004 NHW20.]]~~
	~~[[File:2010 Ford Fusion Hybrid.jpg\|225px\|thumb\|right\|2009 [[Ford Fusion Hybrid]].]]~~

	While a modified [[Otto cycle]] engine using the "Atkinson cycle" provides good fuel economy, it is at the expense of a lower power-per-displacement as compared to a traditional four-stroke engine.<ref>John B Heywood 'Internal Combustion Engine Fundamentals' p184-186</ref> If demand for more power is intermittent, the power of the engine can be supplemented by an [[electric motor]] during times when more power is needed. This forms the basis of an Atkinson-cycle-based [[hybrid electric]] drivetrain. These electric motors can be used independently of, or in combination with, the Atkinson-cycle engine, to provide the most efficient means of producing the desired power.		While a modified [[Otto cycle]] engine using the "Atkinson cycle" provides good fuel economy, it is at the expense of a lower power-per-displacement as compared to a traditional four-stroke engine.<ref>John B Heywood 'Internal Combustion Engine Fundamentals' p184-186</ref> If demand for more power is intermittent, the power of the engine can be supplemented by an [[electric motor]] during times when more power is needed. This forms the basis of an Atkinson-cycle-based [[hybrid electric]] drivetrain. These electric motors can be used independently of, or in combination with, the Atkinson-cycle engine, to provide the most efficient means of producing the desired power.
Line 54:		Line 43:

	Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at [[Bottom dead centre]] and [[Top dead centre]]. The effective compression ratio of the air-fuel mixture in an "Atkinson-cycle" engine, with respect to atmospheric pressure, is lower due to the aforementioned delay in closing the intake valve.		Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at [[Bottom dead centre]] and [[Top dead centre]]. The effective compression ratio of the air-fuel mixture in an "Atkinson-cycle" engine, with respect to atmospheric pressure, is lower due to the aforementioned delay in closing the intake valve.

	~~{{Thermodynamic cycles\|state=uncollapsed}}~~

	~~{{clear}}~~

	==See also==		==See also==
	*[[History of the internal combustion engine]]		*[[History of the internal combustion engine]]

	~~==References==~~
	~~{{reflist}}~~

	== External links ==		== External links ==

Red marquis at 04:53, 2 March 2010

2010-03-02T04:53:41Z

← Older revision		Revision as of 04:53, 2 March 2010
Line 1:		Line 1:
	~~comment4~~, http://~~greisey~~.com/ ~~adipex~~, http://~~calculadoras~~.~~biz/ reductil,~~ http://~~godsavetherobots~~.~~net~~/ ~~adipex-p~~, http://~~da-riverside~~.~~org/ weight loss phentermine,~~ http://~~arborhouseproducts~~.com/ ~~cigarette winston,~~ http://~~littleboilers~~.com/ ~~levitra link,~~		The '''Atkinson-cycle engine''' is a type of [[internal combustion engine]] invented by [[James Atkinson (inventor)\|James Atkinson]] in 1882. The Atkinson cycle is designed to provide efficiency at the expense of [[power density]] and is beginning to see use in modern [[hybrid electric]] applications.

			==Design==
			The original Atkinson-cycle [[Reciprocating engine\|piston engine]] allows the intake, compression, power, and exhaust [[Stroke (engine)\|strokes]] of the [[four-stroke cycle]] to occur in a single turn of the [[crankshaft]] and was designed to bypass patents covering the existing [[Four-stroke cycle\|Otto cycle]] engines.<ref>{{US patent reference \| number =367496 \| y = 1887 \| m =08 \| d = 02 \| inventor =James Atkinson \| title =Gas-Engine}}</ref> Due to the unique [[crankshaft]] design of the Atkinson, the expansion ratio may differ from the [[compression ratio]]. By adjusting the linkage to allow a power stroke that is longer than the compression stroke, the engine can achieve greater efficiency than with the Otto cycle engine. While Atkinson's original engine design is no more than a historical curiosity, the Atkinson cycle, where the power stroke is longer than the compression stroke, is increasing in popularity due to the increase in fuel economy it provides.

			{{clear}}

			==Ideal thermodynamic cycle==
			[[Image:T cycle AtkinsonMiller.png\|thumb\|right\|250px\|'''Figure 1: Atkinson Gas Cycle''']]

			The ideal Atkinson cycle consists of following operations:

			# [[Isentropic process\|Isentropic]] or [[Reversible process (thermodynamics)\|reversible]] [[Adiabatic process\|adiabatic]] compression.
			# [[Isochoric]] heating.
			# Isentropic expansion.
			# [[Isobaric]] cooling.

			{{clear}}

			== Modern "Atkinson-cycle" engines ==
			[[Image:Atkinson-cycle engine.jpg\|thumb\|250px\|A small engine with Atkinson-style linkages between the piston and flywheel. Modern Atkinson-cycle engines do away with this complex energy path.]]
			Recently Atkinson cycle has been used to describe a modified [[Otto cycle]] engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This is more like a [[Miller cycle]] engine than an actual ''Atkinson cycle'' engine. The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed) but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio. Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure; when this occurs, all the available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.

			The disadvantage of the four-stroke Atkinson-cycle engine versus the more common Otto-cycle engine is reduced power density. Because a smaller portion of the compression stroke is devoted to compressing the intake air, an Atkinson-cycle engine does not take in as much air as would a similarly designed and sized Otto-cycle engine.

			Four-stroke engines of this type with this same type of intake valve motion but with a [[supercharger]] to make up for the loss of power density are known as [[Miller cycle]] engines.

			{{clear}}

			== Rotary Atkinson-cycle engine ==
			[[Image:WikiDartEngine.gif\|right\|250px\|thumb\|Rotary Atkinson-cycle engine]]

			The Atkinson cycle can be used in a rotary engine. In this configuration an increase in both power and efficiency can be achieved when compared to the Otto cycle. This type of engine retains the one power phase per revolution, together with the different compression and expansion volumes of the original Atkinson cycle. Exhaust gases are expelled from the engine by compressed-air scavenging. This modification of the Atkinson cycle allows for the use of alternative fuels like Diesel and hydrogen. See External Links for more information.

			{{clear}}

			==Vehicles using "Atkinson-cycle" engines==
			[[Image:Prius2004.JPG\|thumb\|225px\|[[Toyota Prius]] 2004 NHW20.]]
			[[File:2010 Ford Fusion Hybrid.jpg\|225px\|thumb\|right\|2009 [[Ford Fusion Hybrid]].]]

			While a modified [[Otto cycle]] engine using the "Atkinson cycle" provides good fuel economy, it is at the expense of a lower power-per-displacement as compared to a traditional four-stroke engine.<ref>John B Heywood 'Internal Combustion Engine Fundamentals' p184-186</ref> If demand for more power is intermittent, the power of the engine can be supplemented by an [[electric motor]] during times when more power is needed. This forms the basis of an Atkinson-cycle-based [[hybrid electric]] drivetrain. These electric motors can be used independently of, or in combination with, the Atkinson-cycle engine, to provide the most efficient means of producing the desired power.

			Several production vehicles use "Atkinson-cycle" engines:

			*[[Toyota Prius]] [[hybrid electric]] (front-wheel drive) with a (purely geometric) compression ratio of 13.0:1
			*[[Ford Escape Hybrid\|Ford Escape]]/[[Mercury Mariner]]/[[Mazda Tribute]] [[hybrid electric]] (front- and four-wheel drive) with a compression ratio of 12.4:1
			*[[Ford Fusion Hybrid]]/[[Mercury Milan Hybrid]] [[hybrid electric]] (front-wheel drive) with a compression ratio of 12.3:1
			*[[Toyota Camry Hybrid]] [[hybrid electric]] (front-wheel drive) with a compression ratio of 12.5:1
			*[[Chevrolet Tahoe Hybrid]] [[hybrid electric]] (four-wheel drive) with a compression ratio of 10.8:1
			*[[Lexus RX 450h]] [[hybrid electric]] (front-wheel drive)
			*[[Mercedes-Benz_M-Class#ML450_Hybrid\|Mercedes ML450 Hybrid]] [[hybrid electric]]
			*[[Mercedes-Benz_S-Class#S400_BlueHYBRID\|Mercedes S400 Blue Hybrid]] [[hybrid electric]]
			*[[Lexus HS250h]]

			Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at [[Bottom dead centre]] and [[Top dead centre]]. The effective compression ratio of the air-fuel mixture in an "Atkinson-cycle" engine, with respect to atmospheric pressure, is lower due to the aforementioned delay in closing the intake valve.

			{{Thermodynamic cycles\|state=uncollapsed}}

			{{clear}}

			==See also==
			*[[History of the internal combustion engine]]

			==References==
			{{reflist}}

			== External links ==
			* [http://www.keveney.com/Atkinson.html Animation of Atkinson Cycle Engine] Note that this animation shows the true Atkinson engine, which uses a complex linkage that allows different stroke lengths for intake/compression and power/exhaust. However, the illustration shows the engine with the linkage laid out to generate 4 equal strokes. To alter the ratio of the strokes, the rightmost pivot point (the one that is attaching the horizontal green link to the frame) should be moved downwards along the frame. This will allow more angular movement as the link rotates up, giving a longer piston stroke for power and exhaust, and less angular movement as the link rotates down, giving a shorter piston stroke for intake and compression. In fact, a sliding pivot point at that location would allow the engine to dynamically change the stroke ratios.
			* [http://modifiedatkinsoncycleengine.blogspot.com Modified Atkinson Cycle Engine:] alternative variable valve timing strategy increases low speed torque obtainable from Atkinson Cycle Engine.
			* [http://www.ornl.gov/~webworks/cpr/v823/rpt/106982.pdf COMPARISON OF PRIME MOVERS SUITABLE FOR USMC EXPEDITIONARY POWER SOURCES], [[Oak Ridge National Laboratory]]
			* [http://libralato.co.uk Libralato Engines] Home page of the company developing the rotary Atkinson cycle engine
			* [http://white-smoke.wetpaint.com/page/Rotary+Engine Rotary Atkinson cycle engine] A web page giving details of this engine and comparisons with conventional and Wankel engines.
			* [http://www.allaboutprius.com/tipsarticle/1014183_the-priuss-not-so-secret-gas-mileage-secrets The Prius's Not So Secret Gas-Mileage Secrets] A quick and easy take on how the Prius uses the Atkinson cycle to get better results than an Otto-cycle engine.

			[[Category:Engine technology]]
			[[Category:Hybrid vehicles]]
			[[Category:Engines]]

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