Question 37 AEL01 - Assistant Engineer - Limited

The Correct Answer is B. ### Why Option B ("displacement") is Correct: In a naturally aspirated engine (both diesel and gasoline), the engine's **displacement** is the total volume swept by the pistons in all cylinders. This displacement dictates the **maximum theoretical volume of air** the engine can draw in per complete cycle (four-stroke or two-stroke). Since the engine relies solely on atmospheric pressure and the vacuum created by the descending pistons to pull air in (naturally aspirated), the volume of air intake is fundamentally constrained and defined by the physical volume change capacity of the cylinders, which is the displacement. ### Why the Other Options are Incorrect: * **A) compression ratio:** The compression ratio (the ratio of cylinder volume at BDC to volume at TDC) is a fixed design parameter that primarily determines the maximum pressure and temperature achieved *after* compression, not the volume of air taken *during* the intake stroke. * **C) fuel pressure:** Fuel pressure in a diesel engine (managed by the injection pump or common rail system) determines the rate and quality of fuel atomization and injection timing. It does not dictate the volume of air drawn into the cylinder, which is a function of mechanical design (displacement). * **D) cylinder clearance volume:** The clearance volume (or combustion chamber volume) is the volume remaining above the piston at Top Dead Center (TDC). It is a component used to calculate the compression ratio but, by itself, does not define the large volume of air drawn in during the intake stroke, which is defined by the full sweep (displacement).