Turbine Engine Low-Speed Start via Periodic Fuel Pulses
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Solution Overview
Problem
Starting a turbine engine from a very low engine speed is challenging due to rapid temperature increases, which can lead to over-temperature damage, especially under conditions of limited rotational assistance or low airflow.
Innovation Solution
A method involving alternating fuel flow cycles of acceleration and deceleration in the engine's combustor to gradually increase engine speed while preventing overheating, by introducing fuel, igniting it, then ceasing before maximum temperature limits are reached, and repeating this process to accumulate speed augmentations until normal starting conditions are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If fuel is introduced into the combustor at a normal continuous rate to achieve proper fuel atomization, then fuel combustion efficiency is improved, but engine temperature increases rapidly causing over-temperature damage
Solution Approach 1:
The patent applies periodic action by introducing fuel in alternating pulses rather than continuously. The fuel flow is cycled between on and off states, creating periodic combustion events that provide sufficient energy for acceleration while allowing temperature to drop between pulses, thus preventing over-temperature damage while maintaining combustion efficiency.
Solution Approach 2:
The patent applies dynamics by making the fuel flow rate variable rather than constant. The fuel introduction rate is dynamically adjusted based on engine speed conditions - higher rates during acceleration phases and lower or zero rates during deceleration phases - allowing the system to adapt to changing thermal and mechanical conditions.
2Adaptability or versatility
If the engine is started from very low speed with limited rotational assistance, then adaptability to poor starting conditions is improved, but the risk of over-temperature damage increases
Solution Approach 1:
The periodic fuel introduction pattern allows the engine to build speed through repeated acceleration cycles while the off-periods allow temperature to dissipate, enabling starts from very low speeds without the continuous thermal buildup that would cause damage under normal continuous fuel introduction.
Solution Approach 2:
The control system monitors engine speed and adjusts fuel introduction accordingly. When engine speed falls below a threshold during a fuel-off period, the system automatically reintroduces fuel to provide another acceleration cycle, creating a feedback-controlled process that adapts to the engine's real-time state.
3Productivity
If the engine speed is increased rapidly to achieve normal operating speed quickly, then productivity is improved, but the engine components are exposed to excessive thermal stress
Solution Approach 1:
The periodic fuel pulses create a series of controlled acceleration events that collectively achieve the target speed over time. Each pulse provides a controlled amount of energy, and the cumulative effect of multiple cycles reaches the desired operating speed without creating excessive thermal stress that would occur with a single continuous high-rate fuel introduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables successful engine start from low speeds without overheating, allowing for a slow and controlled acceleration to normal operating conditions, avoiding the need for additional fuel nozzles and ensuring engine safety.
Implementation Method 1
introducing fuel into a combustor of the engine at an original low value of an engine speed and igniting the fuel
Implementation Method 2
the reduced air flow that results from the low rotational speed of the fan and compressors, causes most of the energy produced during combustion to increase temperatures within the engine's turbine section rather than converting the energy to rotational acceleration of the turbine rotor
Data Source
AI summary
A method of starting a turbine engine at a first engine speed value which is lower than a second engine speed value designed for a normal engine starting operation, comprises varying a fuel flow into a combustor of the engine to start the engine in repeatedly alternating speed acceleration and deceleration cycles in order to create an engine speed augmentation in each of the speed acceleration and deceleration cycles, thereby achieving the second engine speed value while preventing the engine from being overheated, and then beginning the normal engine starting operation.