MDE 1 Power Stroke

Answer: C) To convert the energy from combustion into mechanical work
Explanation: The power stroke is the phase in the engine cycle where the combustion of fuel generates high pressure, forcing the piston downward. This movement converts the energy from the combustion into mechanical work, which drives the engine and propels the vessel.

Answer: D) It starts high and decreases as the piston moves downward
Explanation: The temperature inside the cylinder is highest at the beginning of the power stroke due to the combustion of the fuel. As the piston moves downward and the gases expand, the temperature decreases slightly, but it remains much higher than the initial intake temperature.

Answer: D) Both valves are closed
Explanation: During the power stroke, both the intake and exhaust valves are closed. This ensures that the force from the combustion is fully applied to the piston, driving it downward without any loss of pressure or energy through the valves.

Answer: A) Chemical energy from the fuel
Explanation: The chemical energy stored in the fuel is converted into heat energy through combustion. This heat energy increases the pressure in the cylinder, which is then converted into mechanical work as it forces the piston downward during the power stroke.

Answer: C) Immediately after the compression stroke
Explanation: The power stroke occurs right after the compression stroke, where the air-fuel mixture has been fully compressed. At this point, the fuel ignites, causing the power stroke that drives the piston downward.

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.

Answer: C) Spontaneous ignition of the fuel due to high pressure and temperature
Explanation: In a diesel engine, the fuel spontaneously ignites due to the high pressure and temperature created during the compression stroke. This ignition causes the rapid expansion of gases, initiating the power stroke and pushing the piston downward.