Question 3 QMED03 - Oiler

The Correct Answer is C ### Explanation of Correct Option (C) **Aftercooling of a turbocharged diesel engine will result in higher torque and higher brake horsepower.** 1. **The Function of Aftercooling:** Aftercoolers (or intercoolers) reduce the temperature of the compressed air coming from the turbocharger before it enters the intake manifold and the cylinders. 2. **Increased Air Density:** According to the ideal gas law, cooling the air increases its density (more air molecules occupy the same volume). 3. **Improved Combustion:** Denser, cooler air entering the cylinder allows the engine control unit (ECU) to inject a greater mass of fuel while maintaining the optimal air-fuel ratio (AFR). This process is known as increasing volumetric efficiency. 4. **Higher Power Output:** Burning a greater mass of fuel efficiently in each combustion cycle results in higher mean effective pressure (MEP) within the cylinder. Since power (BHP) and torque are directly proportional to MEP, the engine produces **higher torque** and, consequently, **higher brake horsepower** (BHP) at any given RPM. ### Explanation of Incorrect Options **A) higher torque but lower brake horsepower:** This is incorrect because torque and brake horsepower (power) are fundamentally linked by engine speed (BHP = Torque × RPM × Constant). If the torque increases at a specific RPM, the power output must also increase. Aftercooling increases both simultaneously. **B) lower torque but higher brake horsepower:** This is contradictory and incorrect. An increase in BHP without a corresponding increase in torque would only be possible if the engine speed (RPM) significantly increased while the torque decreased, but aftercooling is a fixed mechanical feature that affects the combustion process directly, increasing the force (torque) produced by the engine. **D) lower torque and lower brake horsepower:** This is the opposite of the intended effect of aftercooling. Lowering the power and torque would result from decreasing air density (e.g., heating the air) or reducing the amount of fuel injected, which are negative outcomes that engine designers try to avoid. Aftercooling is a performance enhancement.