Introduction to Fuel Injection Systems test

Identify the system shown

• Single point throttle body unit

• Mechanical injection under hood bay

• Carburettor device from early engines

• Electronic multipoint injection system

Answer explanation

The system shown is an Electronic multipoint injection system, which uses multiple injectors to deliver fuel directly into the intake manifold, optimizing fuel-air mixture and improving engine efficiency compared to older systems.

Given the shift shown from carburettors to fuel injection, which outcome is most directly improved by this change?

• Higher raw fuel consumption rates

• Lower exhaust emissions overall

• Removal of spark ignition needs

• Elimination of air intake components

Answer explanation

The shift from carburettors to fuel injection improves fuel atomization and combustion efficiency, leading to lower exhaust emissions overall, making this the most direct benefit of the change.

Match the pictured system to the most accurate functional description.

• Single point injects at throttle body

• Electronic multipoint injects at each cylinder

• Mechanical injection uses pumps and metering

• Carburettor mixes fuel using airflow vacuum

Answer explanation

The system described is a single point injection, where fuel is injected at the throttle body, allowing for a simpler design compared to multipoint or mechanical systems. This matches the correct choice.

Which action most directly increases airflow into the engine during acceleration?

• Opening the throttle flap wider

• Reducing fuel rail pressure slightly

• Closing the intake manifold runner

• Delaying injector pulse duration

Answer explanation

Opening the throttle flap wider allows more air to flow into the engine, directly increasing airflow during acceleration. This action enhances engine performance by improving combustion efficiency.

How does the ECU influence the fuel delivery system to maintain the correct air–fuel mixture?

• By venting vapour directly to cylinders

• By electronically controlling injector timing

• By mechanically moving the throttle plate

• By pressurizing air through the intake

Answer explanation

The ECU influences the fuel delivery system by electronically controlling injector timing, ensuring the correct amount of fuel is injected to maintain the optimal air-fuel mixture for efficient combustion.

An engine is tuned to the stoichiometric air‑fuel ratio. Which lambda value and mixture description best match this condition?

• λ = 1.10

• λ = 0.80

• λ = 1.0

• λ = 0.90

Answer explanation

The stoichiometric air-fuel ratio corresponds to a lambda (λ) value of 1.0, indicating a perfect mixture of air and fuel. Values above or below 1.0 indicate a rich or lean mixture, respectively.

A driver wants the lowest specific fuel consumption on a highway cruise. Which mixture choice achieves this goal?

• λ 1.05–1.10

• λ 0.85–0.95

• λ 1.00

• λ 0.75–0.80

Answer explanation

The mixture choice λ 1.05–1.10 provides a slightly richer fuel mixture, optimizing combustion efficiency and reducing specific fuel consumption during highway cruising, making it the best option for fuel economy.

An emission engineer must keep the catalytic converter effective. What mixture strategy is commonly applied?

• Cycle between rich and lean

• Hold steady ultra‑lean

• Keep constantly rich

• Disable closed‑loop control

Answer explanation

To maintain catalytic converter efficiency, cycling between rich and lean mixtures allows for optimal oxygen storage and reduction of harmful emissions, making this strategy the most effective.

Calculate: For complete combustion of 1 kg of petrol, how many kilograms of air are ideally required?

• 14.7 kg of air

• 12.5 kg of air

• 10.0 kg of air

• 16.0 kg of air

Answer explanation

For complete combustion of petrol, approximately 14.7 kg of air is required per kg of petrol. This is based on the stoichiometric ratio of fuel to air, making 14.7 kg the correct choice.

Identify which statement best explains why λ = 1.0 is not optimal for best power in practice.

• Rich mixtures decrease exhaust temperature

• Rich mixtures increase flame speed

• Lean mixtures increase torque

• Stoichiometric reduces intake air

Answer explanation

Rich mixtures increase flame speed, which enhances combustion efficiency and power output. Therefore, λ = 1.0 is not optimal, as richer mixtures can provide better performance by improving flame propagation.