The fuel-air ratio, or equivalence ratio (φ), for a High Bypass Ratio turbojet engine is a measure of how the actual fuel-air mixture ratio in the engine compares to the stoichiometric fuel-air mixture ratio. The stoichiometric ratio represents the ideal proportion of fuel and air required for complete combustion. The formula for calculating φ is the same as for other types of engines:
Where:
- φ is the equivalence ratio.
- m_dot_fuel is the mass flow rate of fuel in kg/s.
- m_dot_air is the mass flow rate of air in kg/s.
- (m_dot_fuel / m_dot_air)_stoichiometric is the stoichiometric fuel-air mass ratio, which depends on the specific fuel being used.
The stoichiometric ratio will depend on the specific fuel being used in the engine. For hydrocarbon-based fuels like Jet-A or Jet-A1, a typical stoichiometric ratio is approximately 14.7:1, meaning 14.7 kg of air is required for every 1 kg of fuel to achieve complete combustion.
This calculation will give you the equivalence ratio (φ) for the given operating conditions of the High Bypass Ratio turbojet engine. The value of φ will help determine whether the fuel-air mixture is rich or lean compared to stoichiometric conditions, which is important for engine performance and emissions control. The engine control system can adjust the fuel flow rate to maintain the desired φ value for optimal operation.