Turbojet Idling Thrust Control via Adaptive Fuel Flow Adjustment
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Solution Overview
Problem
Current methods for controlling idling thrust in turbojets are inadequate in addressing the stringent requirements of modern aircraft, leading to risks of underspeed and acceleration-blocking due to measurement inaccuracies and phenomena like fuel flow rate overestimation or air leaks, which can result in unstable operation.
Innovation Solution
A method and device for controlling idling thrust in turbojets that adaptively adjust the thrust levels based on real-time measurement inaccuracies, specifically considering fuel flow rate underestimates to prevent underspeed, while maintaining protection against surging, by transitioning from a low thrust value to a higher value when underspeed is detected, ensuring stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high limit value for fuel flow rate is used to protect against surging, then protection against compressor surging is improved, but the turbojet may experience underspeed or acceleration-blocking due to measurement inaccuracies
Solution Approach 1:
The control system continuously monitors actual engine speed and compares it with the expected speed corresponding to the commanded fuel flow rate. When a discrepancy indicating underspeed is detected, the system provides feedback to adjust the fuel flow rate upward, compensating for measurement inaccuracies and preventing acceleration-blocking
Solution Approach 2:
The system dynamically adjusts the fuel flow rate based on real-time engine performance. Instead of using a static high limit value, the control method modifies the fuel flow rate command according to the detected engine speed deviation, enabling adaptive protection against both surging and underspeed conditions
2Reliability
If fuel flow rate measurement inaccuracies are considered, then protection against underspeed is improved, but thrust control precision deteriorates due to conservative margin increases
Solution Approach 1:
The system applies a conservative margin only when necessary - specifically when underspeed is detected. Under normal operating conditions, the full precision of the fuel flow rate measurement is utilized for accurate thrust control. The excessive fuel flow rate command is applied partially, only to the extent needed to compensate for detected measurement inaccuracies
3Productivity
If idling thrust is reduced to meet manufacturer requirements, then compliance with stringent idling thrust limits is improved, but the risk of underspeed and unstable operation increases
Solution Approach 1:
The control system performs preliminary detection of underspeed conditions by comparing actual engine speed with expected speed before unstable operation occurs. When the engine is operating at reduced idling thrust, the system proactively identifies when measurement inaccuracies are causing the engine to operate below the safe speed threshold, and preemptively increases fuel flow rate to maintain stable operation
Data Source
AI summary
A method for controlling thrust from a turbojet that is fuel flow rate regulated by a high limit value for providing protection against surging of a compressor of the turbojet is provided. The method includes: obtaining a first thrust value corresponding to a first operating point of the compressor on the high limit value, the high limit value taking account of an underestimate of the fuel flow rate; controlling the turbojet to reach the first thrust value; monitoring the turbojet to detect underspeed of the compressor; and where applicable: obtaining a second thrust value corresponding to a second operating point that guarantees a predetermined margin relative to the high limit value so as to obtain protection against underspeed of the turbojet; and controlling the turbojet to reach the second value.