Question 61 3AE01 - Third Assistant Engineer

The Correct Answer is C Fuel injection systems are fundamentally designed to fulfill three primary, intertwined functions necessary for efficient internal combustion: **1. Meter fuel:** Precisely control the amount of fuel delivered to match the engine load and speed (the air-fuel ratio). **2. Atomize fuel:** Break the liquid fuel into a fine mist for rapid and thorough mixing with air. **3. Inject fuel at the proper time:** Ensure the fuel is introduced into the cylinder or manifold at the precise moment in the engine cycle (timing) necessary for optimal combustion, performance, and emissions control. This timing is critical, especially in direct injection systems. --- ### Why Option C ("inject fuel at the proper time") is correct: Timing is a core operational requirement of any modern fuel injection system (whether port injection or direct injection). The Electronic Control Unit (ECU) dictates exactly when the injector opens and closes relative to the piston position and valve timing. Accurate timing is essential for: * **Performance:** Injecting too early or too late compromises power output. * **Efficiency:** Optimal timing ensures the most complete combustion of the metered fuel. * **Emissions:** Timing is heavily adjusted to meet strict emissions standards. Therefore, metering, atomizing, and timing (injecting at the proper time) represent the three foundational functions of a fuel injection system. --- ### Why the other options are incorrect: **A) create turbulence in the combustion chamber:** While turbulence (or "swirl" and "tumble") is highly desirable and actively promoted within the cylinder to ensure good air-fuel mixing, it is primarily achieved through the design of the **intake port and the piston head**, not the primary function of the injector itself. The injector’s role is delivery, not generating bulk airflow patterns. **B) aid in completing cylinder scavenging:** Scavenging (pushing out exhaust gases) is a function of the **exhaust and intake valve timing overlap** and the pressure differentials within the system, especially in two-stroke engines. The fuel injection system plays no direct role in completing this gas exchange process. **D) minimize fuel penetration into the cylinder:** This statement is misleading. While excessive penetration (where the liquid fuel impinges on cylinder walls or piston crowns) is generally detrimental in spark-ignited engines, the overall goal is not simply to "minimize penetration." The design goal is to achieve **optimal penetration and spray pattern** to ensure the fuel evaporates before it hits surfaces while covering the necessary area for efficient combustion. This is part of the atomization and metering function, not a third distinct primary function separate from metering and atomizing.