Misplaced Pages

This is an old revision of this page, as edited by Bourke Engine TV (talk | contribs) at 17:43, 22 May 2014 (→Comparing apples to oranges). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

The Bourke Engine was an attempt to improve the two-stroke engine by Russell Bourke in the 1920s. 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 light weight, powerful, 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 instead of connecting rods to translate linear motion to rotary motion
• 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
• Smoother operation due to elimination of crank and slider mechanism
• 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, vibration and piston wear.
• O-rings are used to seal joints rather than gaskets.
• The use of the Scotch Yoke reduces vibration from the motions of the connecting rod—for example, the peak acceleration in a Scotch yoke is 25% less than the acceleration in a conventional crank and slider 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 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 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.

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 to hold and use to lubricate. Oil was shown to be used slowly by the dropfull as needed, 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/h), or 0.9 (lb/h)/hp, equivalent to a thermodynamic efficiency of about 12.5%, which is typical of a 1920s steam engine.

• Power to weight 0.9 to 2.5 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, 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.

All two strokes use this arrangement. Any losses here are countered by not having to overcome valve spring compression work loads.

1. 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.

A stock Bourke 30 C.I.D. weighs in at 38 pounds. Previous author discounts the linear rod motion which eliminates piston side loading and allows for lighter parts due to less stress. All forces are to a dead center and are compressive forces.

1. 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.
2. High speed two-stroke engines tend to be inefficient compared with four-strokes because some of the intake charge escapes unburnt with the exhaust.

Bourke uses a turbulating fin on the pistons. This feature causes the incoming charge to pass the only slightly open exhaust ports at a 90 deg. angle, minimizing loss. Unburned HC measured at 80 ppm on Hamilton Standard gas analyzer, without catalytic converter.

1. Use of excess air will reduce the torque available for a given engine size.

True for an engine that burns the fuel at 12.7/1 fuel air ratio. Bourkes produce power a much leaner ratios due to longer time at TDC (fixed volume), and higher compression ratios, to trigger a flame speed of over 5,000 ft/sec. Conventional articulated rods and pistons will sustain damage if operated under detonation.

1. Forcing the exhaust out rapidly through small ports will incur a further efficiency loss.

Ports are sized to deal with ptoducts of complete combustion and not still flaming gasses which take up greater volume as in conventionals.

1. 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.

As Bourke uses a longer piston dwell at TDC and a much faster reaction, combustion chamber is a minimum size, reducing losses. Conventional engines have cylinder walls bathed in flame for the whole power stroke resulting in greater losses.

1. 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.

Of course more CO2 will be emitted because more fuel is being used. Bourke EGT does rise slightly with additional fuel, but nowhere near conventional engine EGT. 220 deg. F EGT stays fairly consistent due to thermodynamic expansion on the downstroke.

1. Increased dwell time at TDC will allow more heat to be transferred to the cylinder walls, reducing the efficiency.

Again, with Bourke, the detonation reaction goes to completion while at minimum surface area in the combustion chamber. This means less heat radiated out of the engine.

1. 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.

Once in detonation mode, Bourke will maintain 100% HCCI ( homogenous charge compression ignition), as long as it runs above certain minimums.

1. 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.

Temperature increase stops as soon as the charge detonates. This is the explosive combination of the hydrogen and oxygen at 1800 deg. F. Author also discounts thermodynamic cooling during the power stroke. Since oxides of nitrogen are formed at higher temperatures, there is conjecture that the Bourke Cycle produces any NOX at all.

Conventional engines are LICE (limited internal combustion engines), while Bourke is a DICE (detonation internal combustion engine). Confusing the two is understandable, since many researchers simply do not understand the differences. Bourke offers a way to greatly improve the operational envelope of what we have now.

Patents

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

References

1. http://bourke-enginefiles.i8.com/146.htm
2. The Most Powerful Diesel Engine in the World
3. Paul Niquette. "The Bourke Engine". Niquette.com. Retrieved 2011-12-06.
4. GS Baker "Ship Form, Resistance, and Screw Propulsion" p215
5. "Bourke Engine Com". Bourke-engine.com. Retrieved 2011-12-06.
6. http://www.sportscardesigner.com/hp_per_lb.jpg
7. "Unbenannt-1" (PDF). Retrieved 2011-12-06.
8. "aircraft engine development". Pilotfriend.com. Retrieved 2011-12-06.
9. Bourke Engine#Claimed and measured performance
10. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245|Trade-off between efficiency, emissions and power
11. http://www.scipub.org/fulltext/ajas/ajas23626-632.pdf Seal friction on a real Bourke engine, including rod seals and main seals, is 4 lb/inches and is not a great addition to work load. |Friction of seals
12. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 p723|Pumping losses
13. C Feyette Taylor "The Internal Combustion Engine" 4th edition, p194 para 2-3, p205 fig 124b, p258|Pumping losses in two strokes
14. C Feyette Taylor "The Internal Combustion Engine" 4th edition, p119|stresses due to detonation
15. Engine balance#Single-cylinder engines Balance of single-cylinder engines
16. JB Heywood "Internal Combustion Engine Fundamentals" The previous author discounts Bourke's dynamic balance scheme. The roller cam assembly does use counterweights to offset the weight of the slipper bearing. The rod assembly is balanced by equal and opposite kinetic pulses, the cycle being in millisecond. All forces cancel each other. ISBN 0-07-100499-8 p20|Importance of primary balance
17. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245, p881|Scavenging ratio and low efficiency
18. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245|Scavenging ratio effect on torque output
19. C Feyette Taylor "The Internal Combustion Engine" 4th edition p194 para5|Pumping losses in two strokes
20. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 p452-3|Increased thermal losses due to detonation
21. JB Heywood "Internal Combustion Engine Fundamentals" ISBN 0-07-100499-8 pp240-245, p881|Scavenging ratio and high emissions
22. "Science Links Japan | Effect of Piston Speed around Top Dead Center on Thermal Efficiency". Sciencelinks.jp. 2009-03-18. Retrieved 2011-12-06.
23. Hot bulb engine
24. "Espacenet - Bibliographic data". Worldwide.espacenet.com. Retrieved 2013-01-21.
25. "Espacenet - Bibliographic data". Worldwide.espacenet.com. Retrieved 2013-01-21.

External links

• Running engine and Cad modeling

• Proposed engines
• Piston engines
• Engine technology
• Two-stroke engine technology