MDE 5 End of Unit Quiz

Answer: C) By modifying the position of the scroll or cam mechanism
Explanation: In scroll type fuel injection pumps, the delivered quantity of fuel is varied by modifying the position of the scroll or cam mechanism. This adjustment changes the volume of fuel that is pumped and delivered to the injector, allowing for control over the fuel quantity injected into the engine.

Answer: B) To inject fuel into the combustion chamber at high pressure
Explanation: The primary function of a diesel engine fuel nozzle is to inject fuel into the combustion chamber at high pressure, ensuring proper atomization and mixing with air for efficient combustion.

Answer: C) To prevent backflow of fuel from the high-pressure side to the low-pressure side
Explanation: The delivery valve in scroll type fuel injection pumps prevents the backflow of fuel from the high-pressure side to the low-pressure side. This ensures that the fuel remains under pressure within the injection system, maintaining the correct amount of fuel delivered to the injector.

Answer: A) Scroll mechanism, camshaft, delivery valve, and pump housing
Explanation: The main components of a scroll type fuel pump include the scroll mechanism (which moves the fuel), the camshaft (which drives the scroll mechanism), the delivery valve (which controls fuel delivery), and the pump housing (which encloses the pump components). These parts work together to ensure efficient fuel delivery and operation.

Answer: A) Clogged nozzle orifices
Explanation: Clogged nozzle orifices can affect the performance of the fuel nozzle by disrupting the spray pattern and reducing the efficiency of fuel injection, which can lead to poor engine performance and increased emissions.

Answer: C) Leaking nozzle seals
Explanation: Leaking nozzle seals can allow fuel to continuously leak into the combustion chamber, leading to excess fuel consumption and potential engine damage.

Answer: C) By changing the position of the plunger within the pump cylinder
Explanation: In Bosch or Jerk type fuel injection pumps, the delivered quantity of fuel oil is controlled by varying the position of the plunger within the pump cylinder. This adjustment changes the volume of fuel drawn into the pump and subsequently delivered to the injector, thereby controlling the amount of fuel injected into the engine.

Answer: A) Incorrect spray pattern
Explanation: An incorrect spray pattern from the injector can lead to poor fuel-air mixing, causing erratic engine operation and knocking.

Answer: B) Leaking nozzle tip
Explanation: A leaking nozzle tip can cause uneven fuel delivery, leading to a rough engine idle and excessive exhaust smoke due to incomplete combustion.

Answer: A) Increased engine knocking and reduced power output
Explanation: Retarded fuel injection, where the fuel is injected later in the engine cycle, can lead to increased engine knocking and reduced power output. This is because the combustion process starts later, potentially causing incomplete combustion and higher pressure in the cylinder, which can result in knocking and decreased performance.

Answer: B) It increases the spray pattern's spread and improves atomization
Explanation: High fuel pressure improves the atomization of the fuel by forcing it through the nozzle more forcefully, which increases the spray pattern’s spread and enhances mixing with air for better combustion.

Answer: A) Clogged nozzle orifices
B) Leaking nozzle seals
D) Corrosion or erosion of the nozzle tip
Explanation: Diesel engine fuel nozzles may encounter defects such as clogged nozzle orifices, leaking nozzle seals, and corrosion or erosion of the nozzle tip. These issues can impair the nozzle's performance by affecting fuel atomization, causing leakage, or altering the spray pattern, which can lead to inefficient combustion and reduced engine performance.