The best fuel IMO is a hydrocarbon wax. It's basically solid kerosene. With an appropriate opacifier, it can be vaporized efficiently, and should behave similar to a premixed liquid motor without the startup headaches of a liquid. And wax is cheap and easy to form. Sugars can also be used as fuels that are similar to alcohols, and sugar is also cheap.
I agree. Here's a post I made
somewhere online back in 2010 (I saved it in a txt file which is why I still have it) with links which
might still work. I've got a bunch of stuff on this in a subdirectory, including a few tested wax/additive formulations:
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I've read in the various reports I've linked to below that the Stanford group is using what is commonly referred to as "hurricane wax" as the main component of their SP-1A fuel. So, I went looking for the characteristics of that wax and found IGI-1260, a common hurricane candle wax:
https://www.igiwax.com/downloads/tis/1260.pdf
Since I've read that shrinking of the wax grain during grain casting can be problematic, I noticed the high-temp (just as high-temp as hurricane wax), low-shrinkage petroleum/synthetic wax mix, IGI-4761, and wondered if this might provide at least a partial answer to the grain shrink problem:
https://www.igiwax.com/downloads/tis/4761.pdf
https://www.igiwax.com/downloads/tis/4761B.pdf
IGI-4761 has physical characteristics that are nearly identical to IGI-1260, but it shrinks much less during cooling. Although IGI doesn't mention the low-shrink property of IGI-4761 in the PDF above, this candle wax site does:
https://www.lonestarcandlesupply.com/wax.html#IGI-4761
They claim that IGI-4761 is a "Low Shrink Votive Candle Blend" that, consequently, "requires only one pour."
This group seems to be successful at pour casting hurricane wax grains:
https://psas.pdx.edu/FuelGrain
But they do mention experiments with spin casting like that done by the Stanford people:
https://psas.pdx.edu/ParaffinSpinCasting?action=AttachFile&do=get&target=forthspincasting.pdf
Those spin-cast grains don't look too successful to me and actually look inferior to the grain photo shown on their page covering the simpler pour casting method.
I'd like to request the posting here of recommendations/experiences relating to paraffin grain casting techniques. I'd also like to see grain opacifier recommendations/experiences with respect to ease of use, uniformity, resistance to stratification, etc.
Finally, I'd like to see a topic or forum section for the posting of links to free technical data and reports on the web relating to hybid rockets. I'll give it a start with the following links that I've found over the last few days. As a note to those on dial-up connections, most of these files are in the multi-megabyte file size range:
A nice Aviation week article on Stanford's paraffin hybrids:
https://www.stanford.edu/~cantwell/AviationWeek_Feb20_03.pdf
Stanford paraffin fuel paper and patent:
AIAA 2003-6475 "Scale-Up Tests of High Regression Rate Liquefying Hybrid Rocket Fuels":
https://www.stanford.edu/~cantwell/AA283_Course_Material/AA283_Course_Notes/Reno_paper2003.pdf
United States Patent 6880326 - "High regression rate hybrid rocket propellants and method of selecting":
https://www.freepatentsonline.com/6880326.html
Stanford hybrid presentation:
AA283 - Aircraft and Rocket Propulsion - Chapter 11 - Hybrid Rockets
https://www.stanford.edu/~cantwell/AA283_Course_Material/Ch_11_Hybrid_RocketSlides.pdf
US Air Force Academy Paper - "Testing of Paraffin-Based Hybrid Rocket Fuel Using Hydrogen Peroxide Oxidizer":
https://www.usafa.af.mil/df/dfas/Pa... Using Hydrogen Peroxide Oxidizer - Brown.doc
NASA report - "System Modeling and Diagnostics for Liquefying-Fuel Hybrid Rockets":
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040030497_2003072415.pdf
Other interesting papers/patents:
"Optical Studies of Combustion Chamber Flame in a Hybrid Rocket Motor":
https://hybrid.ualr.edu/papers/optical_combustion_chamber_study.pdf
"Laboratory Scale Testing of Nitrous Oxide Hydrocarbon Hybrid Rocket Propellants for Small Launch Vehicle Applications":
https://www.zigaero.com/blog/docs/AbstractReno2006.pdf
AIAA 92-3301 "Results of Labscale Hybrid Rocket Motor Investigation":
https://users.rowan.edu/~marchese/rockets05/paper2.pdf
"The Performance of a Hybrid Rocket With Swirling GOx Injection":
https://www.itam.nsc.ru/users/libr/eLib/confer/ICMAR/2002/part_1/leets.pdf
United States Patent 5101623 - (Hybrid) "Rocket motor containing improved oxidizer injector":
https://www.freepatentsonline.com/5101623.html
"Design, Optimization, and Launch of a 3 Diameter N2O/Aluminized Paraffin Rocket":
https://pdf.aiaa.org/GetFileGoogle.cfm?gID=34110&gTable=Paper
AIAA 97-2802 - "Development Work on a Small Experimental Hybrid Rocket":
https://www.aeroconsystems.com/ts_pics/Grosse_AIAA-97-2802.PDF
"Introduction to Hybrid Design":
https://www.aspirespace.org.uk/aspireold/TechSeries/Introduction to hybrid design.pdf
"The Physics of Nitrous Oxide":
https://www.aspirespace.org.uk/aspireold/TechSeries/The physics of N2O.pdf
And, although it's not a hybrid, here's an interesting, 157 page technical report to DARPA on a non-cryogenic liquid fueled rocket engine:
GASL TR No. 387 - "The Nitrous Oxide - Propane Rocket Engine"
https://handle.dtic.mil/100.2/ADA393448
On general rocketry technologies, the entire online collection of Penn State's Propulsion Engineering Research Center Symposium papers can be found here:
https://www.psu.edu/dept/PERC/