Which scavenging method in two-stroke engines has the disadvantage of poor scavenging at full throttle and has the necessity of water cooling? 

Explanation:

Cross Scavenging in Two-Stroke Engines

• Cross scavenging is a method used in two-stroke engines to remove the burnt exhaust gases from the cylinder and replace them with a fresh air-fuel mixture.
• In this method, the incoming air-fuel mixture enters the cylinder from one side and pushes the exhaust gases out from the opposite side, typically through ports located near the top of the cylinder.
• In a cross-scavenged two-stroke engine, the fresh charge enters the cylinder from the intake port, which is located on one side of the cylinder wall.
• As the piston moves downwards during the power stroke, it uncovers the exhaust port on the opposite side, allowing the burnt gases to escape.
• The incoming fresh charge then pushes the remaining exhaust gases out through the exhaust port, completing the scavenging process.

Advantages:

• Simplicity in design and construction, making it easier to manufacture.
• Suitable for small and medium-sized engines where space constraints are important.

Disadvantages:

• Poor scavenging efficiency at full throttle, leading to incomplete removal of exhaust gases and reduced engine performance.
• Necessity of water cooling to manage the heat generated due to the inefficient scavenging process.
• Potential for fresh charge to escape through the exhaust port before complete scavenging, resulting in fuel wastage and higher emissions.

Applications: Cross scavenging is commonly used in smaller two-stroke engines, such as those found in motorcycles, small boats, and handheld power tools, where simplicity and cost are critical factors.