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Revision as of 16:07, 10 June 2006
The Bourke engine was designed by Russell Bourke in the late 1930s, who endeavored to improve upon the Otto Cycle engine. Despite finishing his redesign and building several working engines; bad luck (WWII 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 Scotch yoke 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.
Unfortunately 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 nitrogen oxide emissions. This more than anything else has stopped the Bourke engine from gaining widespread acceptance today.
- Design Points:
- 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 scavanging.
- One power stroke per rotation (2-cycle) opposed to one every other rotation (4-cycle) resulting in nearly twice the power at a given engine speed.
- High compression and temperatures to cause an instantaneous and adiabatic reaction as opposed to a drawn out combustion.
- Lean fuel/air misture 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 piston ring blow by from polluting the crankcase oil extending the life of the oil.
- Scotch yoke instead of connecting rods to translate motion to rotary motion.