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{{Short description|Type of internal combustion engine}}
The '''Bourke engine''' was designed by Russell Bourke in the late ], who endeavored to improve upon the ] engine. Despite finishing his redesign and building several working engines; bad luck (] breaking out), bad health and a know-best attitude compounded to prevent his engine from ever coming to market despite its claimed advantages. Well into the 2000's there are several small groups extolling the virtues of the design. The Bourke engine has two opposed cylinders with the pistons in a ] mechanism. Because the motion of the pistons is a perfect sine wave with regards to time vs displacement the fuel burns in a smaller volume, and so burns hotter. The Bourke engine also has a looser coupling with the output shaft, preventing excess vibration. The intake valves are replaced by ports, saving on parts.
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The '''Bourke engine''' was an attempt by Russell Bourke, in the 1920s, to improve the two-stroke ]. Despite finishing his design and building several working engines, the onset of ], lack of test results,<ref>{{Cite web |url=http://bourke-enginefiles.i8.com/146.htm |title=War Department |access-date=2008-01-13 |archive-url=https://web.archive.org/web/20071230052815/http://bourke-enginefiles.i8.com/146.htm |archive-date=2007-12-30 |url-status=dead }}</ref> and the poor health of his wife compounded to prevent his engine from ever coming successfully to market. The main claimed virtues of the design are that it has only two ], is lightweight, has two power pulses per revolution, and does not need oil mixed into the fuel.
It is thought that the design features that increase its efficiency create emission problems. The higher combustion temperatures combined with the increased cycle time around top-dead-center lead to increased ] emissions. There have not been any verified nitrous oxide tests on running engines to verify this emmision problem.

The Bourke engine is basically a ], with one horizontally opposed ] assembly using two pistons that move in the same direction at the same time, so that their operations are 180 degrees ]. The pistons are connected to a ] mechanism in place of the more usual ] mechanism, thus the piston acceleration is perfectly ]. This causes the pistons to spend more time at ] than conventional engines. The incoming charge is compressed in a chamber under the pistons, as in a conventional crankcase-charged two-stroke engine. The connecting-rod seal prevents the fuel from contaminating the bottom-end lubricating oil.

==Operation==
The operating cycle is very similar to that of a current production spark ignition ] with crankcase compression, with two modifications:
# The fuel is injected directly into the air as it moves through the transfer port.
# The engine is designed to run without using spark ignition once it is warmed up. This is known as auto-ignition or dieseling, and the air/fuel mixture starts to burn due to the ], and/or the presence of ] in the combustion chamber.


==Design features== ==Design features==
* Scotch yoke instead of connecting rods to translate motion to rotary motion
** Fewer moving parts
** Smoother operation
** Longer percentage of cycle spent at top-dead-center and bottom-dead-center for more complete combustion and exhaust scavenging
* Two power strokes for every rotation from the opposed pistons instead of one every other rotation (]) resulting in nearly twice the power at a given engine speed
* High compression and temperatures to cause an instantaneous and ] reaction as opposed to a drawn out combustion
* Lean fuel/air mixture combined with the adiabatic reaction resulting in zero unburnt hydrocarbons in the exhaust
* Sealed underside of the piston to isolate the fuel/air mixture from the crankcase
** Eliminate the need to mix oil with the fuel as with standard 2-cycle engines
** Prevents the ] blow by from polluting the crankcase oil extending the life of the oil


The following design features have been identified:

===Mechanical features===

* ], and linearly sliding connecting rods.
* Fewer ]s (only 2 moving assemblies per opposed cylinder pair) and the opposed cylinders are combinable to make 2, 4, 6, 8, 10, 12 or any even number of cylinders.
* The ] is connected to the Scotch yoke through a ] (a type of hydrodynamic tilting-pad ]).
* Mechanical ].
* ]s rather than ]s.
* Easy maintenance (]) with simple tools.
* The Scotch yoke does not create lateral forces on the piston, reducing friction and piston wear.
* ]s are used to seal joints rather than ]s.
* The Scotch yoke makes the pistons ] very slightly longer at ], so the fuel burns more completely in a smaller volume.

===Gas flow and thermodynamic features===

* Low exhaust temperature (below that of boiling water) so metal exhaust components are not required; plastic ones can be used if strength is not required from exhaust system.
* 15:1 to 24:1 ] for high efficiency and it can be easily changed as required for different fuels and operation requirements.
* Fuel is vaporised when it is injected into the transfer ports, and the turbulence in the intake manifolds and the piston shape above the rings stratifies the fuel–air mixture into the combustion chamber.
* Lean burn for increased efficiency and reduced emissions.

===Lubrication===

* This design uses oil seals to prevent the pollution from the combustion chamber (created by piston ring blow-by in four-strokes and just combustion in two-strokes) from polluting the ] oil, extending the life of the oil as it is used slowly for keeping the rings full of oil. Oil was shown to be used slowly, but checking the quantity and cleanness of it was still recommended by Russell Bourke, its creator.
* The ] in the base is protected from combustion chamber pollution by an oil seal over the connecting rod.
* The ]s are supplied with oil from a small supply hole in the cylinder wall at bottom dead center.

==Claimed and measured performance==
*'''Efficiency''' - 0.25&nbsp;(lb/h)/hp is claimed - about the same as the best diesel engine,<ref> {{webarchive |url=https://web.archive.org/web/20100716202400/http://people.bath.ac.uk/ccsshb/12cyl/index.html.o |date=July 16, 2010 }}</ref> or roughly twice as efficient as the best two strokes.<ref></ref> This is equivalent to a thermodynamic efficiency of 55.4%, which is an exceedingly high figure for a small ]. In a test witnessed by a third party, the '''actual''' fuel consumption was 1.1&nbsp;hp/(lb/hr),<ref>{{cite web|author=Paul Niquette |url=http://www.niquette.com/books/sophmag/bourke.htm |title=The Bourke Engine |publisher=Niquette.com |access-date=2011-12-06}}</ref> or 0.9&nbsp;(lb/hr)/hp, equivalent to a thermodynamic efficiency of about 12.5%, which is typical of a 1920s steam engine.<ref>GS Baker "Ship Form, Resistance, and Screw Propulsion" p215</ref> A test of a 30 cubic inch Vaux engine, built by a close associate of Bourke, gave a fuel consumption of 1.48 lb/(bhp hr), or 0.7 (lb/hr)/hp at maximum power.<ref>Sport Aviation March 1980 p 60 fig 18</ref>
* '''Power to weight''' - The Silver Eagle was claimed to produce 25&nbsp;hp from 45&nbsp;lb, or a ] of 0.55&nbsp;hp/lb. The larger 140 cubic inch engine was good for 120&nbsp;hp from 125&nbsp;lb, or approximately 1&nbsp;hp/lb. The Model H was claimed to produce 60&nbsp;hp with a weight of 95&nbsp;lb, hence giving a power to weight ratio of 0.63&nbsp;hp/lb. The 30 cu in twin was reported to produce 114&nbsp;hp at 15000rpm while weighing only 38&nbsp;lb, an incredible 3&nbsp;hp/lb <ref>Sport Aviation March 1980 p 54</ref> However a 30 cu in replica from Vaux Engines produced just 8.8&nbsp;hp at 4000 rpm, even after substantial reworking.<ref>Sport Aviation March 1980 p 54</ref> Other sources claim 0.9<ref>{{cite web|url=http://bourke-engine.com/general_info.htm |title=Bourke Engine Com |publisher=Bourke-engine.com |access-date=2011-12-06}}</ref> to 2.5&nbsp;hp/lb, although no independently witnessed test to support these high figures has been documented. The upper range of this is roughly twice as good as the best four-stroke production engine shown here,<ref>http://www.sportscardesigner.com/hp_per_lb.jpg HP per Lb. table (portscardesigner.com)</ref> or 0.1&nbsp;hp/lb better than a ] G58 two-stroke.<ref>{{cite web |url=http://www.graupner.de/fileadmin/downloadcenter/anleitungen/20060502130007_Anleitung_1903_05_08_09.pdf |title=Unbenannt-1 |access-date=2011-12-06 |url-status=dead |archive-url=https://web.archive.org/web/20111002212953/http://www.graupner.de/fileadmin/downloadcenter/anleitungen/20060502130007_Anleitung_1903_05_08_09.pdf |archive-date=2011-10-02 }}</ref> The lower claim is unremarkable, easily exceeded by production four-stroke engines, never mind two strokes.<ref>{{cite web|url=http://www.pilotfriend.com/aero_engines/aero_eng_dvmt.htm |title=aircraft engine development |publisher=Pilotfriend.com |access-date=2011-12-06}}</ref>
*'''Emissions''' - Achieved virtually no ]s (80 ppm) or ] (less than 10 ppm) in published test results,<ref> {{webarchive |url=https://web.archive.org/web/20070928121407/http://bourkeengine.net/confirmedtestresults.htm |date=September 28, 2007 }}</ref> however no power output was given for these results, and ] was not measured.
*'''Low Emissions''' - The engine is claimed to be able to operate on hydrogen or any hydro-carbon fuel without any modifications, producing only water vapor and ] as emissions.


==Engineering critique of the Bourke engine==
== Simplified explanation: ==
{{criticism section|date=May 2014}}


The Bourke Engine has some interesting features, but the extravagant claims<ref>]</ref> for its performance are unlikely to be borne out by real tests. Many of the claims are contradictory.<ref>JB Heywood "Internal Combustion Engine Fundamentals"
{{ISBN|0-07-100499-8}} pp240-245|Trade-off between efficiency, emissions and power</ref>


# Seal friction from the seal between the air compressor chamber and the crankcase, against the ], will reduce the efficiency.<ref>{{cite web
The Bourke engine should be considered an "explosion" engine because of the extremely fast burn time of the fuel air mixture.
|url=http://www.scipub.org/fulltext/ajas/ajas23626-632.pdf
|title=Friction Forces in O-ring Sealing
|access-date=2007-12-16
|url-status=dead
|archive-url=https://web.archive.org/web/20100629171644/http://www.scipub.org/fulltext/ajas/ajas23626-632.pdf
|archive-date=2010-06-29
}}
|Friction of seals</ref>
# Efficiency will be reduced due to pumping losses, as the air charge is compressed and expanded twice but energy is only extracted for power in one of the expansions per piston stroke.<ref>JB Heywood "Internal Combustion Engine Fundamentals" {{ISBN|0-07-100499-8}} p723|Pumping losses</ref><ref>C Feyette Taylor "The Internal Combustion Engine" 4th edition, p194 para 2-3, p205 fig 124b, p258|Pumping losses in two strokes</ref>
# Engine weight is likely to be high because it will have to be very strongly built to cope with the high peak pressures seen as a result of the rapid high temperature combustion.<ref>C Feyette Taylor "The Internal Combustion Engine" 4th edition, p119|stresses due to detonation</ref>
# Each piston pair is highly imbalanced as the two pistons move in the same direction at the same time, unlike in a ].<ref>] Balance of single-cylinder engines</ref> This will limit the speed range and hence the power of the engine, and increase its weight due to the strong construction necessary to react the high forces in the components.<ref>JB Heywood "Internal Combustion Engine Fundamentals"
{{ISBN|0-07-100499-8}} p20|Importance of primary balance</ref>
# High speed two-stroke engines tend to be inefficient compared with four-strokes because some of the intake charge escapes unburnt with the exhaust.<ref>JB Heywood "Internal Combustion Engine Fundamentals" ISBN
0-07-100499-8 pp240-245, p881|Scavenging ratio and low efficiency</ref>
# Use of excess air will reduce the torque available for a given engine size.<ref>JB Heywood "Internal Combustion Engine Fundamentals"
{{ISBN|0-07-100499-8}} pp240-245|Scavenging ratio effect on torque output</ref>
# Forcing the exhaust out rapidly through small ports will incur a further efficiency loss.<ref>C Feyette Taylor "The Internal Combustion Engine" 4th edition p194 para5|Pumping losses in two strokes</ref>
# Operating an internal combustion engine in detonation reduces efficiency due to heat lost from the combustion gases being scrubbed against the combustion chamber walls by the shock waves.<ref>JB Heywood "Internal Combustion Engine Fundamentals" {{ISBN|0-07-100499-8}}
p452-3|Increased thermal losses due to detonation</ref>
# Emissions - although some tests have shown low emissions in some circumstances, these were not necessarily at full power. As the scavenge ratio (i.e. engine torque) is increased more HC and CO will be emitted.<ref>JB Heywood "Internal Combustion Engine Fundamentals" ISBN
0-07-100499-8 pp240-245, p881|Scavenging ratio and high emissions</ref>
# Increased dwell time at TDC will allow more heat to be transferred to the cylinder walls, reducing the efficiency.<ref>{{cite web|url=http://sciencelinks.jp/j-east/article/200609/000020060906A0236528.php |title=Science Links Japan &#124; Effect of Piston Speed around Top Dead Center on Thermal Efficiency |publisher=Sciencelinks.jp |date=2009-03-18 |access-date=2011-12-06 |url-status=dead |archive-url=https://web.archive.org/web/20120127050010/http://sciencelinks.jp/j-east/article/200609/000020060906A0236528.php |archive-date=2012-01-27 }}</ref>
# When running in auto-ignition mode the timing of the start of the burn is controlled by the operating state of the engine, rather than directly as in a spark ignition or diesel engine. As such it may be possible to optimize it for one operating condition, but not for the wide range of torques and speeds that an engine typically sees. The result will be reduced efficiency and higher emissions.<ref>]</ref>
# If the efficiency is high, then combustion temperatures must be high, as required by the ], and the air fuel mixture must be lean. High combustion temperatures and lean mixtures cause ] to be formed.


==Patents==
The rising piston compresses the mixture heating it, because of the cool piston head and cylinder walls the mixture is not heated enough to start a burn. The piston "latches" at top dead center because of the action of the scotch yoke. Spark plug fires causing an explosive burn. All of fuel is burned completely because of explosive burn time. Sharp rise in pressure causes scotch yoke to "unlatch" piston. Piston moves down cylinder, expanding gasses following piston cause cooling of piston and cylinder walls. Since all of fuel was burned during "latching" of piston no fuel is being burned at this time, no heat is being added, all expansion results in cooling. When piston reaches the bottom of the cylynder it again "latches" until "unlatched" by the explosion in the opposite cylynder. This gives time for scavaging of explosive gases.
Russell Bourke obtained British and Canadian ]s for the engine in 1939: GB514842<ref>{{cite web|url=http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=0&ND=3&adjacent=true&locale=en_EP&FT=D&date=19391120&CC=GB&NR=514842A&KC=A |title=Espacenet - Bibliographic data |publisher=Worldwide.espacenet.com |access-date=2013-01-21}}</ref> and CA381959.<ref>{{cite web|url=http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=1&ND=3&adjacent=true&locale=en_EP&FT=D&date=19390613&CC=CA&NR=381959A&KC=A |title=Espacenet - Bibliographic data |publisher=Worldwide.espacenet.com |access-date=2013-01-21}}</ref>


He also obtained {{US Patent|2172670}} in 1939.<ref>{{Cite web | url=https://patents.google.com/patent/US2172670 |title = Bourke}}</ref>
The mixture must be lean enough so that compression heating of the mixture does not cause it to ignite prior to the "latching". If this occurs engine will not run, or will run rough. Mixture of the fuel must be in the "explosive" range for the engine to run correctly. Any fuel that is used that is mixed into its "explosive" range will work on this engine. Because of this it is a muti-fuel engine.


== References ==
The maximum pressure on the piston occurs right after the release of the piston from top dead center. It is not spread over the whole length of the piston travel as in a conventional engine. For this reason this is an extremely high torque engine.


{{reflist|30em}}
The complete burn of the fuel while the piston is "latched" gives this engine its high efficiency and low emmissions.


==External links==
The cooling caused by the expanding gases, behind the piston head and the non burning of fuel while piston is traveling, causes the low temperature exaust gases. This also prevents dieseling during the next compression cycle, because of the cooling of the piston head.
{{commons category|Bourke engine}}
*


{{Piston engine configurations}}
== External links ==
*
*
*
*
*


{{DEFAULTSORT:Bourke Engine}}
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Latest revision as of 11:50, 19 July 2024

Type of internal combustion engine
Four-cylinder Bourke engine
Figure 2 from Patent US 2172670 A
Figure 1 from Patent US 2172670 A
Animation of a four-cylinder bourke engine

The Bourke engine was an attempt by Russell Bourke, in the 1920s, to improve the two-stroke internal combustion engine. Despite finishing his design and building several working engines, the onset of World War II, lack of test results, and the poor health of his wife compounded to prevent his engine from ever coming successfully to market. The main claimed virtues of the design are that it has only two moving parts, is lightweight, has two power pulses per revolution, and does not need oil mixed into the fuel.

The Bourke engine is basically a two-stroke design, with one horizontally opposed piston assembly using two pistons that move in the same direction at the same time, so that their operations are 180 degrees out of phase. The pistons are connected to a Scotch yoke mechanism in place of the more usual crankshaft mechanism, thus the piston acceleration is perfectly sinusoidal. This causes the pistons to spend more time at top dead center than conventional engines. The incoming charge is compressed in a chamber under the pistons, as in a conventional crankcase-charged two-stroke engine. The connecting-rod seal prevents the fuel from contaminating the bottom-end lubricating oil.

Operation

The operating cycle is very similar to that of a current production spark ignition two-stroke with crankcase compression, with two modifications:

  1. The fuel is injected directly into the air as it moves through the transfer port.
  2. The engine is designed to run without using spark ignition once it is warmed up. This is known as auto-ignition or dieseling, and the air/fuel mixture starts to burn due to the high temperature of the compressed gas, and/or the presence of hot metal in the combustion chamber.

Design features

The following design features have been identified:

Mechanical features

  • Scotch yoke, and linearly sliding connecting rods.
  • Fewer moving parts (only 2 moving assemblies per opposed cylinder pair) and the opposed cylinders are combinable to make 2, 4, 6, 8, 10, 12 or any even number of cylinders.
  • The piston is connected to the Scotch yoke through a slipper bearing (a type of hydrodynamic tilting-pad fluid bearing).
  • Mechanical fuel injection.
  • Ports rather than valves.
  • Easy maintenance (top overhauling) with simple tools.
  • The Scotch yoke does not create lateral forces on the piston, reducing friction and piston wear.
  • O-rings are used to seal joints rather than gaskets.
  • The Scotch yoke makes the pistons dwell very slightly longer at top dead center, so the fuel burns more completely in a smaller volume.

Gas flow and thermodynamic features

  • Low exhaust temperature (below that of boiling water) so metal exhaust components are not required; plastic ones can be used if strength is not required from exhaust system.
  • 15:1 to 24:1 compression ratio for high efficiency and it can be easily changed as required for different fuels and operation requirements.
  • Fuel is vaporised when it is injected into the transfer ports, and the turbulence in the intake manifolds and the piston shape above the rings stratifies the fuel–air mixture into the combustion chamber.
  • Lean burn for increased efficiency and reduced emissions.

Lubrication

  • This design uses oil seals to prevent the pollution from the combustion chamber (created by piston ring blow-by in four-strokes and just combustion in two-strokes) from polluting the crankcase oil, extending the life of the oil as it is used slowly for keeping the rings full of oil. Oil was shown to be used slowly, but checking the quantity and cleanness of it was still recommended by Russell Bourke, its creator.
  • The lubricating oil in the base is protected from combustion chamber pollution by an oil seal over the connecting rod.
  • The piston rings are supplied with oil from a small supply hole in the cylinder wall at bottom dead center.

Claimed and measured performance

  • Efficiency - 0.25 (lb/h)/hp is claimed - about the same as the best diesel engine, or roughly twice as efficient as the best two strokes. This is equivalent to a thermodynamic efficiency of 55.4%, which is an exceedingly high figure for a small internal combustion engine. In a test witnessed by a third party, the actual fuel consumption was 1.1 hp/(lb/hr), or 0.9 (lb/hr)/hp, equivalent to a thermodynamic efficiency of about 12.5%, which is typical of a 1920s steam engine. A test of a 30 cubic inch Vaux engine, built by a close associate of Bourke, gave a fuel consumption of 1.48 lb/(bhp hr), or 0.7 (lb/hr)/hp at maximum power.
  • Power to weight - The Silver Eagle was claimed to produce 25 hp from 45 lb, or a power-to-weight ratio of 0.55 hp/lb. The larger 140 cubic inch engine was good for 120 hp from 125 lb, or approximately 1 hp/lb. The Model H was claimed to produce 60 hp with a weight of 95 lb, hence giving a power to weight ratio of 0.63 hp/lb. The 30 cu in twin was reported to produce 114 hp at 15000rpm while weighing only 38 lb, an incredible 3 hp/lb However a 30 cu in replica from Vaux Engines produced just 8.8 hp at 4000 rpm, even after substantial reworking. Other sources claim 0.9 to 2.5 hp/lb, although no independently witnessed test to support these high figures has been documented. The upper range of this is roughly twice as good as the best four-stroke production engine shown here, or 0.1 hp/lb better than a Graupner G58 two-stroke. The lower claim is unremarkable, easily exceeded by production four-stroke engines, never mind two strokes.
  • Emissions - Achieved virtually no hydrocarbons (80 ppm) or carbon monoxide (less than 10 ppm) in published test results, however no power output was given for these results, and NOx was not measured.
  • Low Emissions - The engine is claimed to be able to operate on hydrogen or any hydro-carbon fuel without any modifications, producing only water vapor and carbon dioxide as emissions.

Engineering critique of the Bourke engine

This article's "criticism" or "controversy" section may compromise the article's neutrality. Please help rewrite or integrate negative information to other sections through discussion on the talk page. (May 2014)

The Bourke Engine has some interesting features, but the extravagant claims for its performance are unlikely to be borne out by real tests. Many of the claims are contradictory.

  1. Seal friction from the seal between the air compressor chamber and the crankcase, against the connecting rod, will reduce the efficiency.
  2. Efficiency will be reduced due to pumping losses, as the air charge is compressed and expanded twice but energy is only extracted for power in one of the expansions per piston stroke.
  3. Engine weight is likely to be high because it will have to be very strongly built to cope with the high peak pressures seen as a result of the rapid high temperature combustion.
  4. Each piston pair is highly imbalanced as the two pistons move in the same direction at the same time, unlike in a boxer engine. This will limit the speed range and hence the power of the engine, and increase its weight due to the strong construction necessary to react the high forces in the components.
  5. High speed two-stroke engines tend to be inefficient compared with four-strokes because some of the intake charge escapes unburnt with the exhaust.
  6. Use of excess air will reduce the torque available for a given engine size.
  7. Forcing the exhaust out rapidly through small ports will incur a further efficiency loss.
  8. Operating an internal combustion engine in detonation reduces efficiency due to heat lost from the combustion gases being scrubbed against the combustion chamber walls by the shock waves.
  9. Emissions - although some tests have shown low emissions in some circumstances, these were not necessarily at full power. As the scavenge ratio (i.e. engine torque) is increased more HC and CO will be emitted.
  10. Increased dwell time at TDC will allow more heat to be transferred to the cylinder walls, reducing the efficiency.
  11. When running in auto-ignition mode the timing of the start of the burn is controlled by the operating state of the engine, rather than directly as in a spark ignition or diesel engine. As such it may be possible to optimize it for one operating condition, but not for the wide range of torques and speeds that an engine typically sees. The result will be reduced efficiency and higher emissions.
  12. If the efficiency is high, then combustion temperatures must be high, as required by the Carnot cycle, and the air fuel mixture must be lean. High combustion temperatures and lean mixtures cause nitrogen dioxide to be formed.

Patents

Russell Bourke obtained British and Canadian patents for the engine in 1939: GB514842 and CA381959.

He also obtained U.S. patent 2,172,670 in 1939.

References

  1. "War Department". Archived from the original on 2007-12-30. Retrieved 2008-01-13.
  2. The Most Powerful Diesel Engine in the World Archived July 16, 2010, at the Wayback Machine
  3. best two strokes
  4. Paul Niquette. "The Bourke Engine". Niquette.com. Retrieved 2011-12-06.
  5. GS Baker "Ship Form, Resistance, and Screw Propulsion" p215
  6. Sport Aviation March 1980 p 60 fig 18
  7. Sport Aviation March 1980 p 54
  8. Sport Aviation March 1980 p 54
  9. "Bourke Engine Com". Bourke-engine.com. Retrieved 2011-12-06.
  10. http://www.sportscardesigner.com/hp_per_lb.jpg HP per Lb. table (portscardesigner.com)
  11. "Unbenannt-1" (PDF). Archived from the original (PDF) on 2011-10-02. Retrieved 2011-12-06.
  12. "aircraft engine development". Pilotfriend.com. Retrieved 2011-12-06.
  13. The Bourke Engine Project L.L.C. - Confirmed Test Results Archived September 28, 2007, at the Wayback Machine
  14. Bourke Engine#Claimed and measured performance
  15. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245|Trade-off between efficiency, emissions and power
  16. "Friction Forces in O-ring Sealing" (PDF). Archived from the original (PDF) on 2010-06-29. Retrieved 2007-12-16. |Friction of seals
  17. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 p723|Pumping losses
  18. C Feyette Taylor "The Internal Combustion Engine" 4th edition, p194 para 2-3, p205 fig 124b, p258|Pumping losses in two strokes
  19. C Feyette Taylor "The Internal Combustion Engine" 4th edition, p119|stresses due to detonation
  20. Engine balance#Single-cylinder engines Balance of single-cylinder engines
  21. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 p20|Importance of primary balance
  22. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245, p881|Scavenging ratio and low efficiency
  23. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245|Scavenging ratio effect on torque output
  24. C Feyette Taylor "The Internal Combustion Engine" 4th edition p194 para5|Pumping losses in two strokes
  25. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 p452-3|Increased thermal losses due to detonation
  26. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245, p881|Scavenging ratio and high emissions
  27. "Science Links Japan | Effect of Piston Speed around Top Dead Center on Thermal Efficiency". Sciencelinks.jp. 2009-03-18. Archived from the original on 2012-01-27. Retrieved 2011-12-06.
  28. Hot bulb engine
  29. "Espacenet - Bibliographic data". Worldwide.espacenet.com. Retrieved 2013-01-21.
  30. "Espacenet - Bibliographic data". Worldwide.espacenet.com. Retrieved 2013-01-21.
  31. "Bourke".

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