Porsche 928 Electrics

Electrical information & supplies for late model 928s

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Engine Fire Detection System

Project In specification & early development

To go along with my halon extinguisher install and engine compartment halon distribution system I feel there is a need for an automatic fire detection & warning system.

Such a system should detect temperature rise from a fire but should also pre-emptively detect and provide early warnings for smoke/smoldering & fuel leakage prior to an actual fire occurring.

Why is this needed? Early warnings can provide time to act before any expensive damage is done and even after a fire breaks out it may not be obvious to the driver. Any smoke from combustion will normally be swept under & behind the vehicle at speed and may not be immediately seen.

Automatic deployment is not a goal of this system. Automating the extinguisher deployment risks expensive false alarms and also deploying halon into the engine compartment at high speed simply results in virtually all the halon joining the smoke trailing behind you - in the case of a real fire - rendering you virtually helpless when you do stop.

However an automatic system can provide various warnings to the driver and can disable the cooling fans from running after the car is shutdown (avoiding feeding the fire & losing the desired Halon blanketing on deployment).

The anticipated technologies are:

  • High temperate (315C) thermal switching elements & collectors (low mass reverse heat-sinks)
    - Location: multiple per side at top of engine compartment
  • Predictive Rate of Rise temperature detectors
    - Location: one per side at top of engine compartment
  • Ionization Smoke Detector
    - Location in airflow path under car - single sensor near bell housing
  • Photo-electric Smoke detector
    - Location in airflow path under car - single sensor near bell housing
  • Gasoline & other volatiles detector
    - Location in airflow path under car - single sensor near bell housing

Expected configuration of the warnings is to combine the sensor outputs and provide a weighted result. The most common false alarms should be from the smoke detectors (e.g. while traveling through smoke, fog or dust) and the gasoline detector (uncombusted gasoline in traffic & gas stations).

So the following is proposed - higher levels = more severe risk

  • Level 1 - Smoke warning
  • Level 2 - Gasoline Warning
  • Level 3 - Heat Detection Warning (either)
  • Level 4 - any 2 Warnings combined (except dual smoke)
  • Level 5 - Any 3 Warnings combined

Indication is via audible and visual alerts keyed to the levels above:

  • Level 1 - Beep & Dashboard Indicator - Green fire Symbol
  • Level 2 - Beep & Dashboard Indicator - Yellow Fire Symbol
  • Level 3 - Continuous Tone & Dashboard Indicator - Orange Fire Symbol
  • Level 4 - Continuous Tone & Dashboard Indicator - Red Fire Symbol
  • Level 5 - Beep Beep Beep... & Dashboard Indicator - Flashing Red Fire Symbol

Tones should be cancelable with the pod cancel stalk - Indicators should not cancel

Implementation can use a blank window in the dashboard and a specially mounted tri-color LED mounted into a neo-wedge bulb holder (no other connections made).

The fire detection system should be enabled with the ignition switch accessory position but stay on during engine cranking for continuous protection.


Copyright (c): Alan Moore 2006, 2007, 2008, 2009       Page Updated: 04/03/2009