Modern Concept Six Stroke Engine

To make an engine more efficient and to reduce emissions a new concept called six stroke engine is taken into consideration but practically this type of engine not used because it has some drawbacks which i explain later. The six-stroke engine is a type of internal combustion engine based on the four-stroke engine, but with additional complexity intended to make it more efficient and reduce emissions. There are two types of approaches with this type of engine-

• In this approach, the pistons in this type of six-stroke engine go up and down three times for each injection of fuel. The pistons in this type of six-stroke engine go up and down six times for each injection of fuel. There are two power strokes in this type of engine: one with fuel, the other with steam or air as shown in fig-

Fig-Six Stroke Engine(Steam/Water Based)

• In this approach, a second small piston is used called second opposed piston. It uses a second opposed piston in each cylinder that moves at half the rate of the main piston, thus giving six piston movements per cycle. Functionally, the second piston replaces the valve mechanism of a conventional engine but also increases the compression ratio. Fig illustrate this type of engine-

  

  Fig-Six Stroke Engine(Opp Piston Type)

Notable Six Stroke Engines Are-

1. Velozeta Six-stroke engine
2. German Charge pump
3. Crower six stroke engine
4. Griffin six stroke engine
5. Velozeta six-stroke engine
6. Bajulaz six stroke engine

Students from the college of engineering, Trivandrum, India, also proposed the mechanism of six stroke engine in which, the first four strokes are the same as a four stroke internal combustion engine. After the exhaust stroke i.e last stroke of four stroke engine, instead of air/fuel mixture (as in case of petrol engines), fresh air is sucked into the cylinder from the air filter, and is removed during the sixth stroke. The engine shows 40% reduction in fuel consumption and dramatic reduction in pollution. Its specific power is not less than that of a four-stroke petrol engine. 

Advantages of six stroke engine-

1. Reduction in fuel consumption by at least 40%.
2. Dramatic reduction in pollution.
3. Better efficiency.
4. The maximum torque developed in case of six stroke engines is much more higher than four stroke engines.
5. Reduction in radiator in case of first approach.

Disadvantages of six stroke engine-

1. Six stroke engines would require additional tank/cylinder for storing compressed air or water or steam at high pressure this would increse the weight. 
2. You need an air compressor for compressed air.
3. More complex engine dueto additional cams, injectors .
4. When you out of secondary source, you will be having 2 extra strokes which are wasted. This would reduce performance and efficiency of the engine.
5. Exposure to air or water or steam may cause corrosion to engine parts.

Because of this disadvantages six stroke engines are not commonly used, however technologies has been made in future to overcome this type of problems.