Question 37 QMED01 - Junior Engineer

The Correct Answer is C ### Explanation for Option C (Higher Torque and Higher Brake Horsepower) Aftercooling (or intercooling) is the process of cooling the compressed air coming out of the turbocharger compressor before it enters the engine's intake manifold. This process significantly benefits engine performance: 1. **Increased Air Density:** Cooling the air increases its density (as per the Ideal Gas Law: $PV = nRT$). Denser air means a greater mass of air can be packed into the same cylinder volume during the intake stroke. 2. **Increased Oxygen Mass:** Since more air mass is entering the cylinders, a proportionally larger mass of oxygen is available for combustion. 3. **Ability to Inject More Fuel:** With more oxygen available, the engine control unit (ECU) can safely inject and burn a larger quantity of fuel while maintaining the correct air-fuel ratio. 4. **Higher Combustion Pressure and Efficiency:** Burning more fuel efficiently generates a greater force on the piston during the power stroke. 5. **Resulting Performance Gain:** Since **Torque** is directly related to the mean effective pressure (MEP) within the cylinders, higher combustion pressure results in **higher torque**. Since **Brake Horsepower (BHP)** is a function of torque and rotational speed (RPM), higher torque at the same operating speed results in **higher brake horsepower**. Therefore, aftercooling leads to both higher torque and higher brake horsepower. ### Explanation for Incorrect Options **A) higher torque but lower brake horsepower:** This is contradictory. BHP is calculated using the formula $\text{BHP} \propto \text{Torque} \times \text{RPM}$. If torque increases and RPM is maintained or also increases (which is typical for a performance-enhancing modification), BHP must also increase. Torque and BHP do not typically move in opposite directions in this context. **B) lower torque but higher brake horsepower:** This is also contradictory for the reasons stated above. Lower torque would necessitate a massive, unrealistic increase in RPM to achieve higher BHP, which is not the primary function or outcome of aftercooling. Aftercooling primarily boosts cylinder pressure (torque). **D) lower torque and lower brake horsepower:** Aftercooling is a performance-enhancing modification designed to increase the mass of oxygen available for combustion. Since the fundamental purpose of this system is to improve volumetric efficiency and allow more fuel to be burned, resulting in higher power output, this option is the exact opposite of the observed effect.