MDE 1 End of Unit Quiz

Answer: C) It generates the force needed to produce mechanical work
Explanation: The power stroke is crucial because it is the only stroke that generates the force needed to produce mechanical work. This work is what ultimately powers the engine and allows it to drive the vessel.

Answer: B) Downward away from the cylinder head
Explanation: During the power stroke, the combustion of the fuel-air mixture generates high pressure, pushing the piston downward. This downward movement is crucial as it translates the force from the combustion into rotational energy that powers the engine.

• Correct Answer: A) Diesel engines intake pure air, while gasoline engines intake an air-fuel mixture
• Explanation: In diesel engines, the intake stroke draws in only air, which is then compressed and heated before fuel is injected. In contrast, gasoline engines mix air with fuel before it enters the cylinder during the intake stroke. This difference is a key characteristic that distinguishes the operation of diesel and gasoline engines.

Answer: C) It increases
Explanation: As the air is compressed during the compression stroke, its temperature increases significantly. This rise in temperature is crucial because it allows the fuel to ignite spontaneously when injected into the compressed air.

Answer: C) It increases
Explanation: As the air is compressed during the compression stroke, its temperature increases significantly. This rise in temperature is crucial because it allows the fuel to ignite spontaneously when injected into the compressed air.

• Correct Answer: C) Pure air
• Explanation: In a diesel engine, only pure air is drawn into the cylinder during the intake stroke. The fuel is injected directly into the compressed air at a later stage, during the power stroke. This is different from gasoline engines, where a mixture of air and fuel is drawn in during the intake stroke.

Answer: C) It decreases as the piston moves upward
Explanation: As the piston moves upward during the exhaust stroke, the volume of the cylinder decreases, forcing the exhaust gases out through the open exhaust valve. This movement causes a reduction in pressure inside the cylinder as the gases are expelled.

Answer: C) Worn piston rings or cylinder liner
Explanation: Worn piston rings or a damaged cylinder liner can lead to a loss of compression, as they allow air to escape from the cylinder during the compression stroke. This reduces the pressure and temperature of the compressed air, leading to inefficient combustion and lower engine performance.

Answer: C) Worn piston rings or cylinder liner
Explanation: Worn piston rings or a damaged cylinder liner can lead to a loss of compression, as they allow air to escape from the cylinder during the compression stroke. This reduces the pressure and temperature of the compressed air, leading to inefficient combustion and lower engine performance.

Answer: A) Both intake and exhaust valves
Explanation: Both the intake and exhaust valves remain closed during the compression stroke to ensure that the air inside the cylinder is fully compressed. This helps in achieving the high pressure and temperature needed for efficient combustion.

Answer: D) It maintains efficiency by ensuring complete removal of exhaust gases
Explanation: The exhaust stroke is crucial for maintaining engine efficiency because it clears the cylinder of exhaust gases. If exhaust gases are not fully expelled, they can dilute the fresh air intake, reducing the efficiency of combustion in the next cycle. Properly expelling the gases ensures that the engine operates efficiently.