The difference between 4-stroke and 6-stroke marine engines

4-stroke and 6-stroke marine engines differ in their design, operation, and efficiency.

Number of Strokes:
4-stroke engine: Operates on the conventional 4-stroke cycle - intake, compression, power, and exhaust.
6-stroke engine: Utilizes an additional two strokes - water injection and air expansion - on top of the traditional 4 strokes.

Working Principle:
4-stroke engine: Intake stroke draws in air-fuel mixture, compression stroke compresses the mixture, power stroke ignites the mixture to generate power, and exhaust stroke expels the burned gases.
6-stroke engine: In addition to the 4 strokes, it incorporates a water injection stroke where water is injected into the cylinder to cool it down, followed by an air expansion stroke where the heated water evaporates, expanding into steam to drive an additional power stroke.

Efficiency:
4-stroke engine: Traditional 4-stroke engines have a certain level of efficiency but may not utilize heat recovery mechanisms effectively.
6-stroke engine: The additional strokes in a 6-stroke engine aim to improve efficiency by utilizing waste heat to produce additional power through the water injection and air expansion strokes. This theoretically leads to better fuel efficiency and reduced emissions.

Advantages and Disadvantages:

4-stroke engine:
Advantages: Simplicity in design, widely used and understood, relatively lower cost.
Disadvantages: Limited efficiency, higher emissions compared to more advanced designs.

6-stroke engine:
Advantages: Potential for increased efficiency, reduced emissions, and better utilization of waste heat.
Disadvantages: Complex design, potentially higher manufacturing and maintenance costs, may require specialized knowledge for operation and maintenance.

Applications:

4-stroke engine: Commonly used in marine vessels, vehicles, and various industrial applications.
6-stroke engine: Still in experimental stages for marine applications, with limited commercial availability. Research is ongoing to improve its design and feasibility.
In summary, while both 4-stroke and 6-stroke engines serve similar purposes, the 6-stroke engine offers potential advantages in terms of efficiency and emissions reduction, albeit with added complexity and developmental challenges.