Engine Fuel and Fuel Metering Systems practice questions

Answer: A) Difficult restarting while the engine is still warm

After a hot shutdown, heat soak can vaporize fuel in the injection lines (vapor lock). Liquid fuel then cannot reach the nozzles, which makes warm restarts difficult.

• ACorrect. Heat soak after shutdown can vaporize fuel in the injection lines. The vapor keeps liquid fuel from reaching the nozzles, so a restart before the engine cools is difficult.
• BIncorrect. Hydraulic lock comes from liquid oil or fuel collecting in the lower cylinders of radial or inverted engines. It is not caused by fuel vapor.
• CIncorrect. Lead fouling comes from extended low-power operation with leaded fuel and an overly rich mixture. It is not caused by vapor in the injector lines.
• DIncorrect. Detonation comes from excessive cylinder temperatures and pressures under high power, lean mixtures, or low-grade fuel. Fuel vapor left after shutdown does not cause it.

Answer: B) Blue

• AIncorrect. Jet fuel is clear or straw-colored.
• BCorrect. 100 is green and 80 is red.
• CIncorrect. That's grade 100.
• DIncorrect. That's grade 80.

Answer: A) Sliding vane

• ACorrect. Vane-type engine-driven pumps are common.
• BIncorrect. Ejectors move fuel in tanks.
• CIncorrect. This is not common.
• DIncorrect. These are engine-driven.

Answer: A) Venturi airflow is too low to draw fuel from the main discharge nozzle, so engine-side suction pulls fuel from that opening instead

At a nearly closed throttle, venturi suction is too weak to work the main discharge nozzle. The idle system uses the low pressure next to the throttle valve to discharge fuel through the idling jet.

• ACorrect. With the throttle valve nearly closed, venturi velocity is too low to lift fuel from the main discharge nozzle. Low pressure on the engine side of the throttle valve pulls fuel from the idling jet near the valve edge. An idle air bleed and an idle mixture adjustment are part of this system.
• BIncorrect. The float and needle valve hold the fuel level. The float chamber is vented to air-inlet pressure, not to manifold suction, and that venting does not supply idle fuel.
• CIncorrect. The economizer (power enrichment) system adds fuel at high power settings, not at idle, and it is not what supplies fuel when the throttle is nearly closed.
• DIncorrect. The accelerating pump only gives a momentary squirt of fuel when the throttle is opened quickly. It does not supply fuel continuously at idle.

Answer: A) Sprays fuel for starting

• ACorrect. It delivers fuel directly to the cylinders or intake for a cold start.
• BIncorrect. This is pre-oiling.
• CIncorrect. This is unrelated.
• DIncorrect. That is carb heat.

Answer: C) In the intake ports

• AIncorrect. Fuel is not injected there.
• BIncorrect. That is a carburetor.
• CCorrect. Nozzles spray fuel continuously into each cylinder's intake port.
• DIncorrect. This is not a fuel location.

Answer: D) Prevent ice crystals from dissolved water

• AIncorrect. That's dye.
• BIncorrect. It doesn't raise energy content.
• CIncorrect. Turbine fuel doesn't use octane ratings.
• DCorrect. It also inhibits microbial growth.

Answer: A) Localized hot streaks that can burn combustion liners and turbine nozzle vanes

Partially clogged turbine fuel nozzles produce a distorted spray pattern. This causes uneven combustion and hot streaks that can damage combustion liners and turbine components.

• ACorrect. A partly blocked nozzle gives a distorted, uneven spray pattern. Combustion becomes uneven and forms hot streaks that overheat and crack hot-section parts downstream.
• BIncorrect. Clogging distorts the spray pattern and makes the temperature distribution uneven. It does not cool the engine evenly, and the resulting hot spots can damage the hot section.
• CIncorrect. Clogged nozzles restrict flow at the affected nozzles. They do not cause high pressure at every nozzle, and nozzle condition is not the classic cause of compressor surge.
• DIncorrect. Nozzle coking affects how fuel is atomized in the combustor. It does not route carbon into the lubrication system or raise oil consumption.

Answer: A) The venturi

• ACorrect. Air speeds up in the venturi, lowering pressure at the discharge nozzle.
• BIncorrect. It controls fuel level in the bowl.
• CIncorrect. This limits throttle travel.
• DIncorrect. This filters fuel.

Answer: B) During starting and continuously at every engine power setting

In a duplex nozzle, the primary orifice carries all the fuel during starting and at low flow, and keeps flowing at all times. The flow divider adds secondary flow when fuel flow or pressure gets higher.

• AIncorrect. The flow divider opening above a set pressure describes the secondary flow. Below that pressure the flow divider sends all fuel to the primary passages.
• BCorrect. The small primary orifice atomizes fuel well even at low pressure, so it carries all the fuel during starting. It keeps flowing when the flow divider opens the secondary passage at higher fuel flow.
• CIncorrect. The secondary flow is added to the primary flow and does not replace it. The primary flow continues at higher power.
• DIncorrect. This reverses the two roles. The secondary orifice adds flow at high power, while the primary orifice handles low-flow conditions such as starting.