We have heard about two and four stroke engines. Two stroke engines got its name from the fact that the required strokes are completed in one revolution. In short there is one power stroke in one revolution. In the case of four stroke engines the four strokes are completed in two revolutions, or there is a power stroke in two revolutions. Then how about a six stroke engine. The name of the engine has nothing to do with the number of revolutions or anything of that sort. This engine got its name due to its construction. A six stroke engine derived its name from the fact that it is a mixture of two and four stroke engine. This engine is a radical hybridization of two and four stroke engines. This engine combines the top portion of two stroke engine and the bottom rather the middle section of a four stroke engine. These types of engines have many advantages compared to OHC four stroke engines. They are as follows 1) Increased torque and power output
2) Better fuel economy
3) Cleaner burning with reduced emission
4) Longer service intervals
5) Reduced tooling costs
Six stoke engines were developed in the year 1998 by Malcolm Beare. This technology is under going tremendous research works for improving the six stroke or Beare technology as it is popularly known. This type of engine is not commonly available because of two main reasons 1. This technology is patented by Ducati
2. Research works are going on for improvement of this technology Construction and Working
The six stroke engine basically works just like a four stroke engine. The major difference is in the construction. The major drawbacks of conventional engines were poppet valves, its basic problems being and - inertia, inhibiting flow especially the exhaust valve hot-spot in the combustion chamber. So a six stroke engine was simplified with the objective of improving efficiency and increasing performance compared to a conventional engine by overcoming the drawbacks of poppet valves, by means of a rotary valve application to four-stroke engine. Of course, a two-stroke doesn't suffer such problems as it had no poppet valves. So these drawbacks were resolved by he basic taking the components of a rotary disc induction two-stroke engine, and grafting them on to a four-stroke to produce the best of both worlds. Below the cylinder head gasket, everything is conventional, so one advantage is that the Beare concept can be transplanted on to existing engines without any need for redesigning or retooling the bottom end. But the cylinder head and its poppet valves get thrown away. To replace the camshaft and valves, Beare has retained the cam drive belt and fitted an ultra short-stroke upper crankshaft complete with piston, which the belt drives at half engine speed just as it previously drove the cam. This piston drives up and down in a sleeve, past inlet exhaust ports set into the cylinder wall, very much like on a two-stroke: these are all exposed during both inlet and exhaust strokes. This being it's only function, the rotary valve is lightly loaded, reducing lubrication and sealing problems. During the compression and expansion strokes, the upper piston seals off both ports, leaving the pressure contained between the two pistons, with the lower one a conventional flat-top three-ring design, while the conical upper one (so shaped to aid gas flow during both inlet and exhaust cycles by guiding it towards the ports) has two rings - one compression, one oil. In the combustion phase, twin spark plugs provide ignition via the stock Ducati CDI and a pair of Harley coils - one per cylinder - and not only does the engine run on pure petrol (no need to add oil, because all required surfaces are positively lubricated, in spite of the application of two-stroke technology), it's also happy on low octane unleaded fuel. Obviously there are no valve seats to suffer from lack of lead, and Malcolm says the compression ratio can be increased significantly from the...