Question 29 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is D ### Why Option D is Correct Turbocharging is a form of forced induction that uses the kinetic energy of the exhaust gases to spin a turbine, which in turn drives a compressor. This process directly affects both the exhaust and intake systems: **1. Exhaust Gas Pressure is Increased:** For the turbocharger's turbine to extract energy from the exhaust, there must be a pressure differential. The turbocharger physically restricts the flow of exhaust gases coming out of the engine cylinders (it acts as a blockage). This necessary resistance results in a higher back pressure in the exhaust manifold compared to a free-flowing, naturally aspirated system. This elevated pressure is often referred to as Exhaust Gas Back Pressure (or P3). **2. Intake Air Temperature is Increased:** The compressor wheel rapidly pressurizes the incoming ambient air. According to the Ideal Gas Law and the principles of thermodynamics, compressing a gas increases its temperature. This phenomenon is known as the heat of compression. Therefore, the air exiting the turbocharger compressor and entering the intake manifold (before any intercooling) is significantly hotter than the ambient air used by a naturally aspirated engine. Thus, turbocharging simultaneously results in **increased exhaust back pressure** and **increased intake air temperature**. *** ### Why Other Options Are Incorrect **A) The exhaust gas pressure on the engine exhaust manifold is increased, and the intake air temperature to the cylinders is decreased.** While the exhaust pressure is correctly stated as increased, the intake air temperature is incorrect. Compression inherently heats the air; it does not decrease the temperature. (Note: An intercooler is often added *after* the turbocharger to decrease this temperature, but the *act* of turbocharging itself causes the increase.) **B) The exhaust gas pressure on the engine exhaust manifold is decreased, and the intake air temperature to the cylinders is increased.** The exhaust gas pressure is incorrect. The presence of the turbine creates resistance and increases back pressure, it does not decrease it. The intake air temperature is correctly stated as increased. **C) The exhaust gas pressure on the engine exhaust manifold is decreased, and the intake air temperature to the cylinders is decreased.** Both statements are incorrect. Turbocharging increases exhaust back pressure due to the turbine restriction and increases intake air temperature due to the heat of compression.