Formula & Calculator
Fuel Flow Rate
Rate of fuel consumption for a jet engine, computed from thrust-specific fuel consumption and thrust setting.
Interpretation
Fuel flow rate: ṁ_f = TSFC·T, where TSFC is thrust specific fuel consumption, T is thrust. It is the mass flow of fuel consumed per second. Example: TSFC=0.00005 s⁻¹, T=5000 N → ṁ_f = 0.25 kg/s.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| mdot_f | Fuel flow rate | kg/s |
| TSFC | Thrust-specific fuel consumption | kg/(N*s) |
| T | Thrust | N |
What it means
Fuel flow rate is the rate at which fuel is consumed by the engine. It is directly proportional to thrust and TSFC. This parameter is used to calculate fuel consumption for a given flight phase and to estimate total fuel required for a mission. It also appears in the Breguet range equation. Understanding fuel flow is essential for fuel planning, cost analysis, and environmental impact assessment.
Worked example
Fuel Flow Rate – Two Examples
Real‑World| Parameter | Value |
|---|---|
| TSFC | 1.8×10⁻⁵ |
| T | 20,000 N |
| Parameter | Value |
|---|---|
| TSFC | 2.0×10⁻⁵ |
| T | 25,000 |
Common mistakes
- Fuel flow rate: ṁ_f = TSFC · T.
- TSFC: Thrust specific fuel consumption (kg/(N·s) or 1/s).
- T: Thrust (N).
- Units: kg/s.
- TSFC varies with throttle setting, altitude, and Mach.
Applications
Fuel flow rate, ṁ_f = TSFC·T, relates the engine fuel consumption to thrust. It is used to compute fuel burn for missions, to size fuel systems, and to select engines. Engineers use this to estimate flight costs and to plan refuelling stops. By understanding fuel flow rate, aerospace engineers can design efficient propulsion systems and operate aircraft economically. The TSFC (thrust specific fuel consumption) is a key performance parameter for gas turbine engines.
- Engine fuel consumption prediction for flight planning
- Fuel system sizing (pumps, lines, tanks)
- Cost analysis for airline operations
- Environmental impact assessment (CO₂ emissions)
- Engine performance monitoring and diagnostics
Frequently Asked Questions
It computes the rate of fuel consumption for a jet engine, given the thrust‑specific fuel consumption and thrust setting.
ṁf = fuel mass flow rate (kg/s)
TSFC = thrust‑specific fuel consumption (kg/(s·N))
T = thrust (N)
It determines the fuel consumption and the range. It is a key engine performance parameter.
- Civil turbofans: 0.000015–0.000020 kg/(s·N) (≈ 0.5–0.7 lb/(lbf·hr))
- Military turbojets: 0.000025–0.000035 kg/(s·N)
- Using TSFC values quoted in per‑hour units (common in industry) without converting to per‑second SI units before multiplying.
- Confusing thrust‑specific fuel consumption with power‑specific fuel consumption.
- Using a constant TSFC over the entire flight envelope.
TSFC = 0.00002 kg/(s·N), T = 40,000 N. ṁf = 0.00002 × 40000 = 0.8 kg/s.
TSFC generally decreases with altitude (due to lower temperature) and increases with Mach number (due to higher inlet temperature).
Range is inversely proportional to TSFC; lower TSFC gives longer range.
Divide by 3600. For example, 0.6 lb/(lbf·hr) = 0.6/3600 ≈ 0.000167 lb/(lbf·s), then convert to kg/N·s using conversion factors.
Specific range = V / (TSFC × T). A lower fuel flow for a given thrust increases range.