Six Stroke 'Blackburn Cycle'
The main version of the 'Blackburn Cycle' uses 4 stroke 'air only' cycles between usual fuel/air 4 stroke cycles, when less than half load is needed for cruising and idling. This 8 stroke cycle increases fuel efficiency in several ways.
The same increase in combustion efficiency can also be achieved using a Six Stroke 'Blackburn Cycle'. The strokes are as follows:-
1 Variable fuel/air induction depending on the engine power required, 2 Compression, 3 Power, 4 Exhaust, 5 Maximized 'air only' induction, 6 'Air only' exhaust. This leaves an 'air only' residue in the cylinder to be mixed with the next fuel/air induction.
The 6 Stroke 'Blackburn Cycle' is not easily changed to 4 stroke for high power. It remains in 6 stroke mode for all speeds and loads. This means that a 50% increase in engine capacity is needed if the combustion and compression ratio are the same as 4 stroke.
However, it is possible to increase the compression ratio due to the cool charge at the start of the cycle. The extra capacity then needed is about 25%. The large increase in thermal efficiency easily outweighs any increased friction.
Separate 'air only' and combustion exhaust systems and valves can be used to suit usual catalytic converters.
An advantage for the 6 Stroke 'Blackburn Cycle' is that can be used on well balanced 2, 4 , 6 and 8 cylinder engines which are impossible for the 8/4 stroke 'Blackburn Cycle' engines which need an odd number of cylinders. .