The Evolution Of 6 Stroke Engines
6 Stroke Engine:
The 6-stroke engine is a next step to the current 4-stroke engine used in automobiles. The only difference is the 4-stroke engine with four strokes (i.e. Intake, Compression, Power and Exhaust), while the 6-stroke engine provides an extra power and exhaust strokes in addition with normal 4-stroke engines. The heat of combustion which is leftover after the exhaust stroke (fourth stroke) is used to produce an additional expansion stroke. Air or the distilled water can be used as the fuel for the fifth stroke.
Working Principle of 6-Stroke Engines:
The principle of 6-stroke engines is to capture the waste heat from the exhaust stroke of Otto cycle or Diesel cycle and utilizing that waste heat to generate an additional power stroke and exhaust stroke. Air or the distilled water is used as the working fluid for the additional power stroke.
Design of 6 stroke engines:
The design of the 6-stroke engine is quite similar to the conventional 4-stroke IC engine. The piston moves up and down in the combustion chamber from the BDC (Bottom Dead Centre) to the TDC (Top Dead Centre). Apart from the existing intake and exhaust valves, there are additional air suction valve and air exhaust valve for the fifth and the sixth strokes respectively.
How the 6-Stroke Engine Works:
First Stroke (Intake stroke):
Consider a 6 stroke engine with normal Otto cycle, the intake valve opens and air-fuel mixture is sucked into the combustion chamber due to the piston movement from top dead centre (TDC) to bottom dead centre (BDC). The movement of piston from TDC to BDC creates suction pressure in the engine cylinder, that sucks the air+fuel mixture inside combustion chamber.
Second Stroke (Compression stroke):
In the compression stroke, all 4 valves will remain closed. The air+fuel mixture remains inside the combustion chamber. Now the piston starts moving from BDC to TDC and compressed the air+fuel mixture inside the combustion chamber results in the compression stroke.
Third Stroke (Power stroke):
Just before the piston reaches the TDC in the combustion chamber, a spark plug ignites the compressed air+fuel mixture (In case of CI engine the fuel is injected into the combustion chamber). This generates a lot of heat and the piston is forced to move down from TDC to BDC again. The expansion of these burnt gases releases tremendous amount of energy that is used to drive the vehicle via transmission. All 4 valves remain closed during this operation of the power stroke.
Fourth Stroke (Exhaust stroke):
In the fourth stroke, the exhaust valve gets opened and the movement of piston from BDC to TDC pushes the exhaust gases out through the exhaust valve. This process is quite similiar to the normal four strokes in a conventional 4 stroke engine. And after this process there is some amount of leftover heat remains in the combustion chamber. That leftover heat is used in the fifth stroke of 6-stroke engine.
Fifth Stroke (Air Suction):
The fresh air from the atmosphere is sucked into the combustion chamber through the air suction valve or the distilled water is injected. The high temperature inside the combustion chamber heats the fresh air and this tends the expansion of the air (the distilled water is converted into the pressurised steam), which forces the piston to move down from TDC to BDC to provide an additional power stroke. The air for fifth stroke can also be pre-heated before being sent into the combustion chamber, that will result in better expansion.
Sixth Stroke (Air Exhaust):
The air exhaust valve opens and as the piston moves up from BDC to TDC, the expanded air ( steam) is sent out through the air-exhaust valve. This provides better gas scavenging. In case of injecting distilled water, cooling is also achieved.
1) Higher fuel economy up to 40%
2) No cooling system required as heat is carried away during fifth and sixth stroke
3) Significant reduction in emissions especially NOx, that means lesser pollution and better scavenging
4) Two power strokes per six strokes and hence better thermal efficiency
5) Multiple types of fuel can be used, including LPG
Disadvantages of 6-Stroke Engines:
4) Engine will require best mapped ECU to control power and torque for better performance.
5) Sudden addition of water at high temperature in the cylinder may result in change of mettalurgical properties of components and may weaken the machine. So we have to choose the best suited material for that purpose, and it will also add the cost to the total cost for engine.
6) 6-stroke engines require additional cams, injectors (the combustor for pre-hearing if specified) etc., that increases complexity. That also makes it very difficult for a regular mechanic to repair it in case something, as he doesn't know, how to operate and fix that issue.
Important:
Working Principle of 6-Stroke Engines:
The principle of 6-stroke engines is to capture the waste heat from the exhaust stroke of Otto cycle or Diesel cycle and utilizing that waste heat to generate an additional power stroke and exhaust stroke. Air or the distilled water is used as the working fluid for the additional power stroke.
Design of 6 stroke engines:
The design of the 6-stroke engine is quite similar to the conventional 4-stroke IC engine. The piston moves up and down in the combustion chamber from the BDC (Bottom Dead Centre) to the TDC (Top Dead Centre). Apart from the existing intake and exhaust valves, there are additional air suction valve and air exhaust valve for the fifth and the sixth strokes respectively.
How the 6-Stroke Engine Works:
First Stroke (Intake stroke):
Consider a 6 stroke engine with normal Otto cycle, the intake valve opens and air-fuel mixture is sucked into the combustion chamber due to the piston movement from top dead centre (TDC) to bottom dead centre (BDC). The movement of piston from TDC to BDC creates suction pressure in the engine cylinder, that sucks the air+fuel mixture inside combustion chamber.
Second Stroke (Compression stroke):
In the compression stroke, all 4 valves will remain closed. The air+fuel mixture remains inside the combustion chamber. Now the piston starts moving from BDC to TDC and compressed the air+fuel mixture inside the combustion chamber results in the compression stroke.
Third Stroke (Power stroke):
Just before the piston reaches the TDC in the combustion chamber, a spark plug ignites the compressed air+fuel mixture (In case of CI engine the fuel is injected into the combustion chamber). This generates a lot of heat and the piston is forced to move down from TDC to BDC again. The expansion of these burnt gases releases tremendous amount of energy that is used to drive the vehicle via transmission. All 4 valves remain closed during this operation of the power stroke.
Fourth Stroke (Exhaust stroke):
In the fourth stroke, the exhaust valve gets opened and the movement of piston from BDC to TDC pushes the exhaust gases out through the exhaust valve. This process is quite similiar to the normal four strokes in a conventional 4 stroke engine. And after this process there is some amount of leftover heat remains in the combustion chamber. That leftover heat is used in the fifth stroke of 6-stroke engine.
The fresh air from the atmosphere is sucked into the combustion chamber through the air suction valve or the distilled water is injected. The high temperature inside the combustion chamber heats the fresh air and this tends the expansion of the air (the distilled water is converted into the pressurised steam), which forces the piston to move down from TDC to BDC to provide an additional power stroke. The air for fifth stroke can also be pre-heated before being sent into the combustion chamber, that will result in better expansion.
Sixth Stroke (Air Exhaust):
The air exhaust valve opens and as the piston moves up from BDC to TDC, the expanded air ( steam) is sent out through the air-exhaust valve. This provides better gas scavenging. In case of injecting distilled water, cooling is also achieved.
Advantages of 6 Stroke Engines:
1) Higher fuel economy up to 40%
2) No cooling system required as heat is carried away during fifth and sixth stroke
3) Significant reduction in emissions especially NOx, that means lesser pollution and better scavenging
4) Two power strokes per six strokes and hence better thermal efficiency
5) Multiple types of fuel can be used, including LPG
Disadvantages of 6-Stroke Engines:
1) More water may cause engine to stall, because we can not use the water as fuel and when engine will out of secondary fluid (water), heat will be wasted without use.
2) The fifth stroke is not that energetic enough to propel a vehicle. There is need of bigger flywheel to fix it. It will be common issue in this engines to feel non continuous motion accompanying jerks while driving as the diference between first two consecutive power stroke is two strokes (360 degree) and four strokes (720 degree) for next two power strokes. First power stroke is very powerful as the combustion of the air+fuel takes place (Due to high calorific value of the petroleum fuels) and 2nd power stroke is comparatively very weak. It will result in complete imbalance in power delivery with very high vibrations. Vehicle will not travel smoothly even by maintaining constant throttle.
3) There will be need of extra water tank in vehicle which will further occupy more space and increase the weight of vehicle.
4) Engine will require best mapped ECU to control power and torque for better performance.
5) Sudden addition of water at high temperature in the cylinder may result in change of mettalurgical properties of components and may weaken the machine. So we have to choose the best suited material for that purpose, and it will also add the cost to the total cost for engine.
6) 6-stroke engines require additional cams, injectors (the combustor for pre-hearing if specified) etc., that increases complexity. That also makes it very difficult for a regular mechanic to repair it in case something, as he doesn't know, how to operate and fix that issue.
Important:
As a coolant we can use the water. There’s a new technology introduced by Bosch to inject water into the combustion chamber after exhaust stroke (fourth stroke), to reduce the temperature in the combustion chamber which results in increased efficiency.
Applications:
Applications:
Here are some of the applications of 6-stroke engine, the application right now is very low but can be incredibly high after 2025. The reason is because of it's complex structure with four valve openings, advanced cam profile etc., six stroke engine is in still research level.
And on the basis of most recent news, BMW is trying to adopt this six stroke engine and it's called M4+2 engine. The idea of M4+2 engine is first developed at the Silesian University of Technology, Poland, under the leadership of Dr. Adam Ciesiolkiewicz.
And on the basis of most recent news, BMW is trying to adopt this six stroke engine and it's called M4+2 engine. The idea of M4+2 engine is first developed at the Silesian University of Technology, Poland, under the leadership of Dr. Adam Ciesiolkiewicz.
Malcolm John Beare also developing 6-stroke engine technology and on other hand the Bruce Crower's engine is also under development. Let's wait for arrival of better engines.
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