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2π r

2pir fireing all effects NiChrome ignition system for 2π r— a fire art installation consisting of 16 flame effects triggered by motion sensors on a central podium.

Criteria: Ignition without ambient flame, able to reliably ignite rapid pulses of fuel

Box tube steel arms with a joint able to be adjusted to compensate for wind and variations in ignition range, and a nickle-chromium alloy ignition coil, with perforated steel enclosures. The ignition coil heats to red hot to ignite propane gas without a continuous flame.

More in-depth description of problems and solutions:
The prior ignition system (two torch heads for redundancy) would be extinguished by oxygen deprivation, so ignition needed to be able to withstand choke conditions. The new ignition system creates a region of unstable propane above autoignition temperature; this can ignite in a wider range than a spreading flame can, adds to the aesthetic of 2π r, and increases the percussive nature of the effects.

Optimal ignition zone changes strongly by altitude, tank pressure, and wind, and weakly by day-to-day weather conditions and the private whims of our system; the system had to be adjustable both on a large scale on setup, and on a small scale during a run. The arms for the effects were created out of box tube for strength, heat resistance, and thermal mass, and the wires insulated with ceramic fiber intended for kiln use. I fabricated hinges to allow the arms to move in an arc through the column of fuel, as well as shaft collars to move the entire assembly vertically along the nozzle.

The NiChrome ignition system was an experiment, and has been used in other fire art pieces after my implementation, including False Profit Labs' Hydrogen Economy. The system is documented in the Instructable NiChrome "Hot Wire" Ignition for Propane Flame Effects.

Copyright 2010, Sam Reese Gawthrop