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{{Short description|Type of internal combustion engine}}
{{prose|date=December 2011}}
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The '''Bourke Engine''' was designed by Russell Bourke in the 1920s, as an improved ] engine, based around detonation combustion instead of using the more progressive burn normally found in ] engines. Despite finishing his design and building several working engines, the onset of ], lack of test results,<ref>http://bourke-enginefiles.i8.com/146.htm</ref> the poor health of his wife and investors moth-balling further developments in 1958<ref>Bourke Engine Documentary, Published 1968, p75 para 2</ref> 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 light weight, powerful, has two power pulses per revolution, and does not need oil mixed into the fuel. 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.


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.
The ] also employs high temperature shock wave fuel detonation instead of lower temperature progressive burn.

==Overview==
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 ]s are connected to a ] mechanism in place of the more usual crankshaft mechanism, thus the piston motion is perfectly ]. This causes the pistons to spend a longer time near ] than in a conventional engines so as to allow more complete combustion of the fuel to occur at constant volume (as opposed to slower, progressive burning whilst undergoing expansion, as is the case with a standard gasoline engine).<ref>Bourke Engine Documentary, published 1968, p71 para4</ref> 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== ==Operation==
The operating cycle is very similar to that of a typical production spark ignition ] with crankcase compression, with two modifications: 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 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. # 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.

===Mono-stroke Cycle ===
Bourke's work was within living memory of the design of the ] engine: his documentation therefore uses the term "Mono-stroke", which is equivalent to the modern ]. One crank revolution therefore has the following stages<ref>Bourke Engine Documentary, Published 1968, p38, "Bourke Cycle Chemistry Defined"</ref><ref>Bourke Engine Documentary, Published 1968, p33, "Bourke Cycle"</ref> :
# The crank bearing rolls across the yoke for a significant period (at the top of the sine wave), holding the piston for a prolonged period at or close to TDC, such that the gases burn very quickly at very high pressure and temperature until completely consumed and there is no longer a flame. Maximum pressure is developed. During this time at TDC, the piston has aligned with the intake ports in the crankcase and, due to the vacuum which was created, a fuel-air mixture is sucked quickly into the area underneath the piston.
# As the crank turns, the yoke begins to move the piston: the intake port is no longer aligned and the fuel-air mixture on the other side of the piston is compressed. At the same time, on the other side of the piston, the gases (which were fully combusted due to high-explosive detonation) expand, pushing the piston and thus turning the crank.
# When the piston reaches the other end of the chamber, the window in the piston lines up with the transfer ports, and at the same time the exhaust ports line up with the exhaust, and the compressed fuel escapes under pressure into the cylinder head, forcing the exhaust gases out the open exhaust ports. On its way through intake port, the air-fuel mixture passes a fin which causes it to become turbulent, thus fully mixing the air and fuel and causing cyclonic vortices.
# At the same time, the opposing cylinder is beginning its power impulse cycle: expansion is occurring in the opposing cylinder, and compression in the original.
# The original piston is now compressing the air-fuel mixture as it is no longer lined up with the transfer ports or the exhaust ports.
# As the original piston compresses the air-fuel mixture, there is a vacuum created on the other side.
# At around 90 degrees into crank travel before TDC, ignition occurs (of a low-grade fuel, taking considerable time to burn due to being a Carbon-Oxygen reaction) and compression continues
# The air intake port lines up, either allowing in an air-fuel mix or air to mix with the injected fuel, beneath the piston.
# On the other side (in the chamber), as compression continues the temperature increases, and fuel burns more rapidly (1800F). As TDC is reached, the fuel is completely burned, and the pressure causes the piston to move.


==Design features== ==Design features==
]


The following design features have been identified: The following design features have been identified:
# The high expansion ratio means that the temperature of the exhaust gases is considerably lower.
# Use of lower-grade fuels and ignition pre-TDC results in an initial slow burn that becomes a highly explosive combustion (detonation) at ].
# An arrangement of 4 cylinders on two crankshafts (two on each crank) with each pair firing in opposite directions results in a completely mechanically-balanced engine.
# The scotch yoke results in a pure sine wave, end-result being that compression at TDC is very slightly longer than on a normal crank slider mechanism, as can be seen from graphs comparing ] with the standard design.
# There are no valves, only ports, reducing complexity and maintenance.
# Piston blow-by does not go into the crankcase, because the chamber under the piston is also ring-sealed and is used to store (lower-pressure) incoming charges. Piston blow-by therefore gets recirculated and mixed with incoming charges.<ref>Bourke Engine Documentary, Published 1968, p72 para 9</ref>
# Exhaust ports are ''deliberately'' similar sized as the inlet ports; the intake air-fuel charge ''deliberately'' smaller than the piston chamber's size at BDC; a small amount of completely burned exhaust (comprising water vapour and carbon dioxide) is ''deliberately'' left in the piston chamber; these factors combine so that there is a residual amount of water mixed with the air-fuel mixture to catalyse the detonation at ].<ref>Bourke Engine Documentary, Published 1968, p59, "Velocity of Reactions and Catalysts"</ref>

]


===Mechanical features=== ===Mechanical features===

* ] instead of ]s to translate ] to ]: ] for standard ] mechanisms show reduced dwell time at ].
* ], 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
* 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.
* Smoother operation due to elimination of ] mechanism: ] motion is ].
* The ] is connected to the Scotch yoke through a triple-sleeved bearing. * The ] is connected to the Scotch yoke through a ] (a type of hydrodynamic tilting-pad ]).
* Mechanical ], using vacuum in the chamber under the piston to suck air-fuel mixtures in. * Mechanical ].
* ]s rather than ]s. * ]s rather than ]s.
* There are effectively three separate main chambers: main piston chamber, underside of the piston, and crank-case chamber (shared between cylinder pairs).
* Use of transfer channels that line up with the ports, to arrange for the air-fuel mixture to enter the piston chamber under pressure.
* Easy maintenance (]) with simple tools. * Easy maintenance (]) with simple tools.
* The Scotch yoke does not create lateral forces on the piston, reducing friction, vibration and piston wear. * 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. * ]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.
* The use of the Scotch Yoke reduces vibration from the motions of the ]—for example, the peak acceleration in a Scotch yoke is less than the ] ] arrangement. The piston movement and therefore vibration is sinusoidal so the engine could theoretically be perfectly counterbalanced, unlike a conventional engine which has harmonics in the piston movement courtesy of the lateral movement of the crankpin.
* The Scotch Yoke makes the pistons ] very slightly longer at ], so the fuel burns more completely, much faster, at higher temperatures, at constant volume. In combination with increased air intake, this results in completely different chemical reaction: a hydrogen-oxygen combustion (which has a flame speed of 10&nbsp;ft/sec <ref>http://www.nrel.gov/docs/fy09osti/45408.pdf</ref>as opposed to 25 to 75&nbsp;ft/sec for the carbon-oxygen combustion that is normally seen in ] Engines).


===Gas flow and thermodynamic features=== ===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 * 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.
* Combustion is initiated at 90 degrees in advance of ], taking advantage of the low flame speed of lower-temperature carbon-oxygen progressive burn times (25 to 75&nbsp;ft per second) to allow the crank and scotch yoke to pressurise the burning gases and bring them up to detonation temperatures (1800 F).
* 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.
* Extremely fast hydrogen detonation burn time (5000&nbsp;ft per second) of the lean mixture so the engine can be considered to be a hydrogen ] (i.e., explosion not deflagration) engine. If the mixture is not lean enough, detonation will not occur and the Bourke Engine will not operate correctly or efficiently.
* Lean burn for increased efficiency and reduced emissions.
* 15:1 to 24:1 ] for high efficiency and it can be easily changed as required by 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: the high oxygen content results in no Carbon Monoxide emissions.


===Lubrication=== ===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 to hold and use to lubricate. Oil was shown to be used slowly by the dropful as needed, but checking the quantity and cleanness of it was still recommended by Russell Bourke, its creator. * 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 ] 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. * The ]s are supplied with oil from a small supply hole in the cylinder wall at bottom dead center.


==Claimed and measured performance== ==Claimed and measured performance==
*'''Efficiency''' 0.25&nbsp;(lb/h)/hp is claimed - about the same as the best diesel engine,<ref></ref> or roughly twice as efficient as the . This is equivalent to a thermodynamic efficiency of 55.4%, which is an exceedingly high figure for a small ]. In a test (carried out after Bourke's death, by enthusiasts insufficiently familiar with Bourke Engine Chemistry) witnessed by a third party, the '''actual''' fuel consumption was 1.1&nbsp;hp/(lb/h),<ref>{{cite web|author=Paul Niquette |url=http://www.niquette.com/books/sophmag/bourke.htm |title=The Bourke Engine |publisher=Niquette.com |date= |accessdate=2011-12-06}}</ref> or 0.9&nbsp;(lb/h)/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> (Note: Bourke points out in the Documentary that if such poor efficiency is achieved, the engine setup has been mis-configured) *'''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.
* '''Power to weight''' 0.9<ref>{{cite web|url=http://bourke-engine.com/general_info.htm |title=Bourke Engine Com |publisher=Bourke-engine.com |date= |accessdate=2011-12-06}}</ref> to 2.5&nbsp;hp/lb is claimed, although no independently witnessed test to support this 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</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 |format=PDF |date= |accessdate=2011-12-06}}</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 |date= |accessdate=2011-12-06}}</ref>
*'''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.

*'''Emissions''' Achieved virtually no ]s (80 ppm) or ] (less than 10 ppm) in published test , 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== ==Engineering critique of the Bourke engine==
{{criticism section|date=May 2014}}


The Bourke Engine has some interesting features, but many of the claims are contradictory to those familiar with ] Engines, making it difficult for people familiar only with ] Engines to accept the efficiency, emissions and power claims.<ref>JB Heywood "Internal Combustion Engine Fundamentals" 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>
ISBN 0-07-100499-8 pp240-245|Trade-off between efficiency, emissions and power</ref> When reading the critiques below it has to be pointed out that Bourke himself observed many people attempting not to duplicate his work, failing to first fully understand the chemistry behind the design decisions made, but to tamper detrimentally with the design, usually by applying lessons learned from ] Engine development which is based around a completely different chemical combustion process.<ref>Bourke Engine Documentary, Published 1968, p75 para 10</ref>


* Seal friction from the seal between the air compressor chamber and the crankcase, against the ], will reduce the efficiency.<ref>http://www.scipub.org/fulltext/ajas/ajas23626-632.pdf # Seal friction from the seal between the air compressor chamber and the crankcase, against the ], will reduce the efficiency.<ref>{{cite web
|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> |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> # 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> # 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> It is claimed that this would 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> # 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
** Note: in 1953, Bourke demonstrated a 30 cubic inch Engine running at 15,000 RPM to Boeing Engineers (5 years later in 1958, Boeing announced the invention and use in its Jet Engines of the same triple-sleeved bearing invented by Bourke),<ref>Bourke Engine Documentary, Published 1968, p51-52</ref> Bourke also occasionally tested the engine up to 20,000&nbsp;rpm (a limit imposed by the spark plugs!)<ref>Bourke Engine Documentary, Published 1968, p73 para2</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> 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"
** Note: Bourke points out that ] engines are based around lower temperature (Carbon-Oxygen) progressive burn of fuel, which occurs during the expansion phase (pressure drop and temperature drop): thus of course the intake charge will escape unburnt from the exhaust of an ] engine. The Bourke Engine is based around much higher temperatures (above 1800F), much higher pressures and much higher air-fuel mixture ratios, resulting in "detonation". In a correctly-operating Bourke Engine, there ''is'' no unburnt fuel escaping with the exhaust.<ref>Bourke Engine Documentary, Published 1968, p34-36</ref>
{{ISBN|0-07-100499-8}} pp240-245|Scavenging ratio effect on torque output</ref>
* When the charge is transferred from the compressor chamber to the combustion chamber it will cool down, reducing the efficiency of the engine.<ref>]</ref>
* Use of excess air will reduce the torque available for a given engine size.<ref>JB Heywood "Internal Combustion Engine Fundamentals" # 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}}
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 (significant) 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> 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. It is claimed that 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 # 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> 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 |accessdate=2011-12-06}}</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> # 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 is lean. High combustion temperatures and lean mixtures in engines cause ] to be formed. # 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==
==Design Controversy==
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>
Bourke spent 14 years of study - 1918 to 1932 <ref>Bourke Engine Documentary, Published 1968, p72 para4</ref> - prior to creating the first prototype.<ref>Bourke Engine Documentary, Published 1968, p73 para5</ref> In 1933 he showed a set of blueprints to the Professor of Engineering at Berkeley University, California, and, on pointing out that a working engine was in the back of his truck, received a curt response, "There is no use wasting your time and mine, Mr Bourke - this engine cannot possibly run. Good day.".<ref>Bourke Engine Documentary, Published 1968, p73 para8</ref>


He also obtained {{US Patent|2172670}} in 1939.<ref>{{Cite web | url=https://patents.google.com/patent/US2172670 |title = Bourke}}</ref>
==Replication of Bourke Engines==
Bourke trusted some investors with the future of his engines: in April 1958 they took control of the Corporation, moved the workshop and commercially-developed engines being assembled to a secret location and terminated all development.<ref>Bourke Engine Documentary, Published 1968, p75, para2</ref> Decades later, these mothballed engines found their way into the hands of Roger Richards.<ref>http://rogerrichard.com/4436.html</ref> Between 1958 and 1968, many people contacted Russ Bourke, attempting to replicate the engine: almost all of them failed, by virtue of attempting to make modifications to the design before fully understanding it.<ref>Bourke Engine Documentary, Published 1968, p75 para9</ref> From having access to a number of original engines that were still operational after 40 years, Roger Richards is one of the very few people to have not only succeeded in replicating the Bourke Engine but also in having made some incremental improvements of the earlier designs, based on improvements learned by Bourke in his later work.<ref>http://rogerrichard.com/14207.html</ref>


== References ==
From bitter experience, Richards patiently explains why it is so critical that, prior to replication of a Bourke Engine,<ref>http://rogerrichard.com/4436.html, para6</ref> it is so absolutely essential to understand that the chemistry involved is very different,<ref>Bourke Engine Documentary, Published 1968, p57-59</ref> and also that every part of the engine's design is critically inter-related.<ref>Bourke Engine Documentary, Published 1968, p71-72, p75-76</ref>


{{reflist|30em}}
There is however evidence of other people making successful replication and incremental improvements on the Bourke Engine design. Daniel M. Reitz is the registered holder of an expired patent, granted in 1975,<ref>http://www.freepatentsonline.com/4013048.html</ref> that allows the piston rod some lateral play, to overcome issues associated with the scotch yoke when the engine is run under design conditions different from those envisaged by Bourke himself.<ref>Bourke Engine Documentary, Published 1968, p51, "Important Factors in Engine Design" and p51 para 7</ref>

==References==
{{Reflist|30em}}
Note: The Bourke Engine Documentary, referenced above, was not published with an ISBN number.

Patents (expired) include:
* http://www.freepatentsonline.com/2172670.html
* http://www.freepatentsonline.com/2172677.html
* http://www.freepatentsonline.com/2172676.html


==External links== ==External links==
{{commons category|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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