Everything combustible ignites easily in a pure oxygen atmosphere and Jet A
evaporates surprisingly fast compared to standard kerosene or RP-1.
Ethanol also has a volumetric O/F of unity and easily adjusted by biasing
the mass O/F and/or water concentration, also the least toxic of the common
alcohols,
there are denaturing formulas that are lower toxicity than others just shop
around. You can get a federal permit to make your own ethanol too w/o the
$28/gallon excise tax. Also has a somewhat pleasant sweetish odor
especially compared to the doctor's office smell of rubbing isopropyl
alcohol, but that is subjective. And there's tons of data on LOx/Ethanol
systems being by far the most used alcohol in history as rocket fuel
including the V-2 and Redstone ballistic rockets, the X-1 LR-11 manned
rocket planes etc. See pic of a single chamber LR-11 captive test of one
metric ton thrust, LOx/75% ethanol.
Again it all depends on your requirements and cooling method. Performance
wise you can't beat hydrocarbon fuels compared to the alcohols.
K
On Tue, Oct 13, 2020 at 11:41 PM Wyatt Rehder <wyatt.rehder@xxxxxxxxx>
wrote:
I've long maintained that Isopropyl Alcohol is the ideal propellant for
the amateur liquid rocketeer.
- Has a close to 1:1 volumetric O:F ratio with LOX which simplifies your
feed system some (can use similar tank design for both)
- Is easy to obtain at 99% without additives for a low cost (~$500 for 55
gal last I checked) and no regulation issues
- Has a high vapor pressure and does not leave a film. So spills take care
of themselves, doesn't leave residues in your chamber after you purge it
- You can perform your LOX service cleaning with it
- Has a short bio-persistance, as it readily biodegrades in soil and
water. So regular spills at your test stand, or a splattered rocket isn't
going to contaminate the ground soil unlike how kerosene can. Granted this
isn't a huge issue at amateur scales.
- Wyatt
On Tue, Oct 13, 2020 at 10:01 PM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
Alcohol is easier to source and to work with, yes. Generally easier to
get to ignite reliably and combust stably/efficiently than kerosene, also
considerably easier to purge completely from small engine passages between
firings too. If you do go with alcohol, you might consider isopropyl
rather than ethanol - it also can be watered down for extra cooling at
need, it's generally cheaper, and there are no concerns over what they may
have "denatured" it with since it's not drinkable in the first place.
One factor to keep in mind in deciding, by the way, is how close to the
limits of your team's available time, talent, and resources will your
project push? (Keep in mind the first rule of projects: EVERYTHING takes
longer and costs more than planned.) One way to improve the odds your team
won't hit a wall short of useful results is to simplify wherever possible
at the start.
If you do prefer to work with kerosene for the better post-graduation
industry applicability, one possible lower-cost easier-availability
substitute for RP-1 is a refined-kerosene industrial solvent called Exxsol
D40. It does not have RP-1's density, thus is somewhat lower performance,
but it is non-coking, fully evaporable with no residue, is reliably
consistent chemically, and you can buy it by the drum for a few bucks a
gallon. And it's more or less as difficult to get to ignite, combust, and
purge cleanly as any other kerosene, so you will get plenty of relevant
experience.
FWIW XCOR used LOX/isopropyl for the EZ-Rocket (before my time there) and
LOX/Exxsol D40 kerosene for the X-Racer. Never saw a trace of coking with
it in many, many firings of the copper-chamber regen-cooled X-Racer engine,
and I was the guy who photo-documented the state of the engine components
every time Mike Laughlin disassembled it to inspect condition and service
the seals.
good luck!
Henry
On 10/13/2020 9:42 PM, Yucca Works wrote:
Hello all, my team is considering RP-1 and ethanol right now (to be
paired with LOX) for our main propellant and I was wondering if anyone has
any input on which fuel to use given some constraints and thoughts to
follow. For one, we don't have an infinite budget at our disposal so
Ethanol becomes immediately appealing because it is easy to source, this is
on top of the fact that Ethanol is not ITAR protected and can be mixed with
water for "inherent" cooling. What made RP-1 appealing was the fact that it
is used in the industry so gaining experience with it seems extremely
appealing and, I think, would make our work more "useful/notable" but
sourcing RP-1 is difficult and it is expensive. A slightly tangential
consideration is using lower grade kerosene which I have seen other college
students do but I am concerned with using low-grade kerosene in regen
cooling channels and it obviously has poor performance.
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