PWC, Two-Stroke vs. Four-Stroke Engines
Two-stroke and 4-stroke engines derive their power in similar ways but they differ widely in their operational efficiency and emission levels. Both engine types burn a mixture of gasoline and air in an airtight cylinder. This combustion results in a buildup of gas pressure that pushes a piston down through the cylinder to create potential energy. In outboard motorboats, the potential energy is then transferred via connecting rods from the cylinder to the driveshaft where it powers a propeller and pushes the watercraft (Kuzminski and Jackvicz 1972). In PWC, the energy is transferred from the cylinder to an impeller that drives a pump and creates a pressured water jet that propels the vessel.
Two-stroke and 4-stroke engines utilize different lubrication methods that affect their overall emissions levels. Four-strokes have a separate lubricating system that minimizes the release of unburned oil into the water but 2-strokes require oil to be added directly into the fuel. The use of this mixture releases more oil, hydrocarbons and particulate matter than pure gasoline and results in a smoky blue exhaust (ENSR 1998).
