chinese flame detectors+ boilers
Do not have schematic, but it use the ultraviolet sensitive photo detect (at least for spark detect). You can find example in many app note for silicon detector amplifier. Try Motorola very old data book or Hammamatsu or EGG or search for silicon detector.
Silicon is not particular sensitive to UV so it is with filter used. Filter is part of coating on sensor.
Can use the transimpedance amp (I > V) as a topology to start. Then follow with the comparator.
Good luck.