'Blackburn Cycle' or Ideal Explosion Engine is more fuel efficient than 4 Stroke, the cool charge allows a 15:1 compression ratio

'Blackburn Cycle' engines have 'air only' cycles between usual 4 stroke combustion cycles.

There are several version of the 'Blackburn Cycle'. The earlier 8 Stroke version includes two 4 stroke cycles. These adjacent 4 stroke cycles are usual 4 stroke cycles for high power, but they are different for low power.

This version of the 'Blackburn Cycle' has alternate 'air only' 4 stroke cycles in each cylinder, between usual fuel/air 4 stroke cycles for cruising and idling.

This 'air only' flushes all exhaust gas through the engine so that the next combustion contains an ideal explosive charge of cool fuel/air with no exhaust gas. It changes to usual 4 stroke for higher powers.

Exhaust gas has burnt once it will not burn again but, if present with fuel and air, will increase the temperature at the start of the cycle and reduce the temperature and pressure increase during combustion. An ideal fuel/air mixture of 1:14, free from any exhaust gas, gives more power from less fuel.

The later 6 Stroke 'Blackburn Cycle' has 2 stroke 'air only' cycles between usual fuel/air 4 stroke cycles. This version is not easily changed to 4 stroke for higher power and so needs an increase in capacity, with more friction, compared with 4 stroke.

The Mazda Skyactiv petrol engine uses a 14:1 compression as a result of a cooler charge at the start of the cycle, than the usual 4 stroke. All 'Blackburn Cycle' engines have an even cooler charge which allows a compression ratio about 15:1.

The 6 Stroke 'Blackburn Cycle' does not change to 4 stroke and so can use 15:1 compression for all speeds and loads. Alternate opening exhaust valves and ports allow usual catalytic converters.

The nature of combustion and the laws of Physics mean that the 'Blackburn Cycle' is 30%-50% more fuel efficient overall and should replace the 4 stroke Otto Cycle.