Flame Detector System

Flame detectors are required for applications with fuel nozzle steam injection and water injection for 42 ppm NOx (or lower). In these applications, the possibility of loss of flame during severe drop load conditions requires flame detection means. Flame detectors are recommended for all other installations to protect the engine against explosive relights due to momentary interruption of the fuel supply.

Recommended controls response to flame detector indication is given in Controls Table 1. The additional 300 msec time delay should be applied after the simultaneous loss of flame to produce an engine shutdown signal. This prevents shutdown due to momentary flicker or line noise. Kits for flame detection systems are available which include sensors, brackets and viewing sight glasses. The remainder of the system is supplied by the Purchaser.

The flame detector kit consists of two ultraviolet type detection tube assemblies, each with an integral current limiting resistor, polarity protection diode, and pigtail lead, two sapphire viewing window assemblies, and all necessary bracketry and fasteners required for mounting on two of the standard borescope port holes in the top portion of the compressor rear frame. The flame detectors are positioned radially from the combustion section of the gas generator and in line with the axis of symmetry of the sapphire viewing windows, and detect flame in the combustor by sensing ultraviolet radiation and indicating its presence or absence.

Installation and customer interface details are described on Drawing No. 537L358 and electrical schematic L24329.

Physical and functional characteristics of the flame detectors are as follows:

z Excitation voltage: 355 + 15 volts dc

z Power: five watts maximum instantaneous peak

z Wave Length:  Responds to ultraviolet radiation over the special range of 190 to 260 nanometers (1900 to 2600 Angstrom units)

z Sensitivity:  Flame detection occurs at a minimum radiation intensity of one candlepower at a distance of two feet.

z Flange Detection: Presence of flame results in the conduction of pulses of current

z Response Time:  Responds to occurrence of flame within one second, and to loss of flame within 200 milliseconds.

The necessary power supply, electrical cables, and amplifier and logic circuitry are to be provided by the Purchaser.

For proper utilization of the redundancy afforded by two flame detectors, the Purchaser’s logic circuitry must be designed such that both detectors sense loss of flame before logic or control action initiates a shut down.

It is recommended that the user employ a signal conditioning system which incorporates provisions for a

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visual indication on the control panel, capable of indicating either momentary or permanent loss of flame from either flame sensor channel.

Figure 1 is a schematic block diagram of a typical amplifier with logic circuit, suitable for use with the flame detector kit, as manufactured by the Avionics Division of Minneapolis Honeywell, or equivalent.

Figure 1. Recommended Flame Detector System Block Diagram

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