Fuel Leak Error Model

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Description

The Fuel Leak Error Model simulates fuel leakage at any point in the fuel network. It can be attached to fuel pumps, valves, interconnects, or fuel sources to model progressive seal degradation and the resulting propellant loss. The model tracks cumulative fuel flow through the parent component and computes a degradation level that increases the leak fraction over time. Leaked fuel is removed from downstream components, creating an observable flow rate discrepancy that operators can use to locate the leak.

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Example Use Cases

• Seal Wear Simulation: Model gradual seal degradation in fuel system components over mission lifetime.
• Fault Detection Testing: Generate realistic leak signatures to test fault detection and isolation algorithms.
• Contingency Analysis: Evaluate mission impact of fuel leaks and validate mitigation procedures such as reducing pump speed.

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Module Implementation

Degradation Tracking

The model tracks the total mass of fuel that has passed through the parent component. Each simulation step, the cumulative fuel passed is updated based on the effective flow rate $\dot{m}$ of the parent component:

$$M_{\text{cumulative}}=M_{\text{cumulative}}+\dot{m}\cdot \Delta t$$

where $\Delta t$ is the simulation time step.

The degradation level $D$ increases proportionally with cumulative fuel flow, scaled by a configurable degradation rate $k_d$:

$$D=\min (M_{\text{cumulative}}\cdot k_d,1)$$

The degradation level ranges from 0 (new component) to 1 (fully degraded).

Leak Fraction Calculation

The fraction of flow lost to leakage is determined by the degradation level and a leak coefficient $k_L$:

$$f_{\text{leak}}=\min (D\cdot k_L,f_{\text{max}})$$

where $f_{\text{max}}$ is the maximum allowable leak fraction, preventing total flow loss even at full degradation.

Leak Rate

The instantaneous leak rate is computed by the Fuel System during network flow solving. When the parent component’s flow rate exceeds the leak onset threshold ${\dot{m}}_{\text{onset}}$, the leak rate is:

$${\dot{m}}_{\text{leak}}=\dot{m}\cdot f_{\text{leak}}$$

When the flow rate is below the onset threshold, leakage is zero regardless of degradation level. This models the behavior of seals that retain sufficient contact pressure at low flow rates.

Forced Failure

The model supports immediate failure through a force failure flag. When enabled, the degradation level is set to 1.0 regardless of cumulative fuel passed, simulating sudden seal rupture or testing worst-case scenarios.

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Assumptions/Limitations

• The leak rate scales linearly with flow rate; pressure-dependent leak behavior is not modeled.
• Leaked fuel is removed from the network but does not contribute mass or momentum to the spacecraft dynamics.
• The degradation process is irreversible; seals cannot self-heal or be repaired during simulation.
• Temperature effects on seal degradation are not considered.
• The model assumes a single leak point per component; multiple simultaneous leaks require multiple model instances.