Ignition of a motor


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Ignition of motor

Ignition is much empirical, but some calculations can be made to increase understanding of the ignition. The info here is mostly based on Ammoniumperchlorate propellant mixed with PVC or other similar plastisol fuel.

Characteristics of motorignition:

bulletIgnition is very fast, and normal time from zero to full chamberpressure and thrust is typical 0.01-0.04 seconds.
bulletThe igniter itself is a dangerous device that must be handeled with properly care.
bulletDifferent mixes of the propellant and motors give different needs of the igniter.
bullet"Hangfire" sometimes happens. It is not fully understood why it happens, but hangfire is a unplanned delayed ignition. At a hangfire the igniter blow but is unable to fully ignite the motor, and for a couple of seconds the motor burn very very little and give no actual thrust. And after a few seconds (Up to 20 sec) it suddenly ignite with full power and act as normal.
bulletSome propellantmixtures require that a burstingdiaphragm is inserted in the nozzle. This device burst when the pressure in the chamber has reached the minumum pressure needed for stable burning. Mostly used in low-percentage oxidizers mixtures (typical 60-65% AP).
bulletThe club developed a method to measure the actual characteristics of the diaphragm.

Copyright (c) Raketgruppen IRA/UT 2004.
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Last updated: november 09, 2005.


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