19-07-2014, 04:43 PM
SIX STROKE ENGINE
Introduction
Malcolm beare built an innovative hybrid design of the I C engine , by combining a two stroke with a four stroke engine.
The Beare Head is a new type of four stroke engine head design known as the “Beare Head”
The Beare Head uses a piston and ports very much like a two stroke engine to replace the over head valve system that is found in four stroke engines today. The four stroke block, pistons and crankshaft remain unaltered. This combination of two stroke and four stroke technology has given the engine its name – the “six stroke engine
Thermodynamic Advantages
The intake begins at 0 degrees on the X-axis. The effect of the additional volume changes that the upper piston has on the volume of the engine is all positive from a thermodynamic point of view. If the engine were a normal 4 stroke the cylinder capacity would be 340cc. Of note - maximum volume at the end of the intake stroke occurs at 173 degrees instead of 180 degrees- the change in volume is 308cc which is less than a 4 stroke (340cc)- yet the total volume at the end of the intake stroke is 415cc as opposed to 375cc for a conventional stroke.
Thermodynamic advantages
Hence the 6 stroke system is better from a thermodynamic point of view because more energy is extracted from the expansion process.
During the critical combustion period the rate of change in volume in the 6 stroke is less than a 4 stroke. Minimum volume is not reached until after T.D.C., at 361 deg. This is because of the phasing of the upper piston. It is retarded in reaching its T.D.C. until 20 deg. after T. D.C. (380). This is much better from a thermodynamic view in that combustion occurs at a more constant volume; hence ignition timing is not as critical as in a 4 stroke. There is room in the combustion chamber for up to 4 spark plugs and two direct injectors if needed.
Conclusion
In a six stroke engine the energy absorption is less because of slower acceleration of reciprocating parts The piston speed of the upper piston is about a quarter of the main piston; therefore its service life should be at least twice that of the main piston.
In the Beare design, per single cylinder, the number of parts is 15 compared to a four stroke of approx 40 to 50 parts. Also, to reduce manufacturing costs the head and block can be machined in one piece.