Propellants

Disclaimer: The information provided herein is intended solely for educational purposes. This document is not intended to serve as a guide for construction or implementation.

So, basically for anything to burn, you would need fuel, an oxidizer and an ignition source. A combination of a fuel and oxidizer is termed as a propellant. Now, these propellants come in different forms. The most commonly used are solid and liquid propellants. Liquid propellants carry the advantage of building engines with controllable throttle, Active Thrust Vector control but at the cost of a complex construction and expensive engine hardware. Also the propellant must be cryo-cooled so that they have the highest density at the lowest volume. Coming to solid propellants, they usually consist of a mixture powdered fuel and oxidizer along with some additives such as a binder to hold the propellant together. Speaking of ignitors is a broad topic in itself, its discussed in a separate section. The discussion here is limited to fuels and oxidizers.

Match Powder Propellant (seriously, just ignore this) (deprecated)

• In the beginning, we needed something that burns, very fast. We hypothesized that matchsticks would fulfil our requirement as the match head consisted of Potassium Chlorate (the oxidizer) and Sulphur (the fuel). But it also had another component, powdered glass that rendered the preparation of the mix, extremely dangerous. 
  The process involved extracting match heads from matchsticks and manually powdering it slowly. As foolish as this may sound, which it actually was, it did teach us a couple of things:
  The mixture combusted rapidly not giving enough time for the exhaust gases to escape and produce thrust.
  The mixture after combusting produced a solid sticky residue which at all times would block the nozzle orifice.

Black Powder Propellant (deprecated)

• It is an explosive mixture of Sulphur, Charcoal and Potassium Nitrate. It is a mixture that burns rapidly without producing any coalescing residue, rather producing hot solids and gases, generating thrust. Though it was quite expensive to procure in prebuilt forms, we had sourced it from commercially available fireworks. This too, however had a few drawbacks.
  The process of extracting the black powder through this method was cumbersome and the quantities extracted were too low for practical testing.
  The thrust produced was not sufficient enough for a liftoff, even on the lightest of our vehicles.

black powder extracted from fireworks

Potassium Nitrate Sugar Propellant

• One of the most tried and tested rocket propellant in the field of amateur rocketry is the Potassium Nitrate (oxidizer), Sugar (fuel) propellant. Maintaining a O/F ratio of 65/35 by mass, is known to give the best overall performance as per Nakka. 
  The Sucrose that we used was the very fine powdered form, commonly referred to as icing (or confectioners) sugar, rather than the common granular (table) sugar. Granular sugar is also useable, it simply needs to be ground to a fine powder first. Potassium nitrate, also known as saltpetre, is a commonly used chemical. We have purchased potassium nitrate in 2 kg. lots at an online chemical supply store. Potassium nitrate is also sold as 14-0-45 fertilizer at farm supply stores, typically 98-99% pure. This is by far the most economical form, and the performance is generally no different than purer grades.

KNO3 Sugar Mixture

• Though the recommended procedure was to heat the mixture, blending It finely and casting it, we were able to achieve pretty good results by mixing the fine powders and compacting it.