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,[1] 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.


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

Gas flow and thermodynamic features


Claimed and measured performance

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[14] for its performance are unlikely to be borne out by real tests[citation needed]. Many of the claims are contradictory.[15]

  1. Seal friction from the seal between the air compressor chamber and the crankcase, against the connecting rod, will reduce the efficiency.[16]
  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.[17][18]
  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.[19]
  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.[20] 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.[21]
  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.[22]
  6. Use of excess air will reduce the torque available for a given engine size.[23]
  7. Forcing the exhaust out rapidly through small ports will incur a further efficiency loss.[24]
  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.[25]
  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.[26]
  10. Increased dwell time at TDC will allow more heat to be transferred to the cylinder walls, reducing the efficiency.[27]
  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.[28]
  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.


Russell Bourke obtained British and Canadian patents for the engine in 1939: GB514842[29] and CA381959.[30]

He also obtained U.S. patent 2,172,670 in 1939.[31]


  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". 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". Retrieved 2011-12-06.
  10. ^ [bare URL image file]
  11. ^ "Unbenannt-1" (PDF). Archived from the original (PDF) on 2011-10-02. Retrieved 2011-12-06.
  12. ^ "aircraft engine development". 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". 2009-03-18. Archived from the original on 2012-01-27. Retrieved 2011-12-06.
  28. ^ Hot bulb engine
  29. ^ "Espacenet - Bibliographic data". Retrieved 2013-01-21.
  30. ^ "Espacenet - Bibliographic data". Retrieved 2013-01-21.
  31. ^ "Bourke".