Which statement about environmental control and performance is true?

Which statement about environmental control and performance is true?

• A. Humidity can affect combustion and emissions.
• B. Humidity has no effect on engine performance.
• C. Inlet temperature and humidity do not affect mass flow.
• D. Inlet temperature only affects emissions.

Answer: (A)

Humidity in the intake air can change how the fuel–air mixture burns and what pollutants are formed. When water vapor is present, it dilutes the air and lowers its density, so for a given volume of air entering the compressor the actual mass flow can be reduced. The water vapor also requires energy to vaporize and to heat, which cools the flame and lowers the adiabatic flame temperature. That cooler flame temperature slows thermal NOx formation and can alter flame speed, ignition, and combustion completeness, which in turn affects emissions and overall performance. Because inlet temperature and humidity influence air density and mass flow, they do affect how much air mass reaches the combustor and how the engine performs, so statements claiming they don’t affect mass flow or that inlet temperature only affects emissions aren’t accurate.

Humidity in the intake air can change how the fuel–air mixture burns and what pollutants are formed. When water vapor is present, it dilutes the air and lowers its density, so for a given volume of air entering the compressor the actual mass flow can be reduced. The water vapor also requires energy to vaporize and to heat, which cools the flame and lowers the adiabatic flame temperature. That cooler flame temperature slows thermal NOx formation and can alter flame speed, ignition, and combustion completeness, which in turn affects emissions and overall performance. Because inlet temperature and humidity influence air density and mass flow, they do affect how much air mass reaches the combustor and how the engine performs, so statements claiming they don’t affect mass flow or that inlet temperature only affects emissions aren’t accurate.