# What is the fuel/air ratio of the CFM56-5A1 engine (in the A320 model)?

I could find the fan-bypass ratio, which was 6:1 (on some models 5:1) but I was unable to find the fuel to air ratio used in this engine. For reference, it is a high-bypass turbofan engine.

• I don't think I've ever seen it quoted directly, but if you get calculate it from the mass flow rate, fuel flow rate and bypass ratio. May 4 '20 at 6:31

The ratio can be different for different phases of flight. It is easy to calculate for the Takeoff (TO) case because the required numbers are easily available:

• TO Thrust: $$25 \, 000 \, \text{lbs}$$ [1]
• TO TSFC (thrust specific fuel consumption): $$0.3316 \, \text{lbs/h}$$ per $$1 \, \text{lbs}$$ of thrust [2]
• Airflow: $$852 \, \text{lbs/h}$$ [1]
• bypass ratio: $$6.0 : 1.0$$ [1]

The takeoff fuel flow $$\text{FF}$$ is then given by

$$\text{FF} = 25 \, 000 \times 0.3316 \, \text{lbs/h} \approx 8290 \, \text{lbs/h} \approx 2.30 \, \text{lbs/s} \approx 1.04 \, \text{kg/s}$$

and the airflow $$\text{AF}$$ through the core is given by

$$\text{AF} = \frac{1}{6 + 1} \times 852 \, \text{lbs/s} \approx 122 \, \text{lbs/s} \approx 55.2 \, \text{kg/s}$$

This results in a fuel/air ratio of

$$\frac{\text{FF}}{\text{AF}} \approx \frac{1}{52.9} \approx 0.0189$$

Sources:

• "Fuel/air ratio" would normally refer to a stoichiometric value, often comparing internal combustion devices, but the core of a turbofan engine is not an internal combustion device. Air/fuel mixture is just one of many purposes for core intake. Much less than half of this core airflow is mixed with fuel & then combusted; most airflow is used for cooling, with some used to separate the flame from the inside surface of the combustors, some directed outside of the combustors, some used to cool the interior of turbine blades, and some used to manipulate pressure gradients for sealing purposes. May 5 '20 at 2:50