One thing I will mention is that for a regen engine using kerosene-type
fuels (kerosene, Jet A, RP-1), you get a benefit from the carbon
deposits in the combustion chamber. There are some plots in NASA SP-125
as it acts as an insulator and reduces the heat transfer to the walls.
Obviously people have made LOX/alcohol work but just thought I'd point
it out as it could potentially help your cooling problem converge,
especially at smaller thrust levels. It does make it harder to clean
up afterwards as you have to use an abrasive (scotchbrite) to clean it
off. Other than the potential for coking in the cooling passages on
long runs, Jet A, RP-1, and kerosene should be equivalent. I've never
seen any coking in the cooling passages for runs < 30 seconds. However,
if I was doing a new engine, I would try to make LOX/alcohol work before
I went with kerosene, just from the cleanup factor. I will say one
thing though, you know when you've cleaned all the kerosene out as it
has a strong smell so maybe it's less likely that you'll leave some fuel
in a place where it shouldn't be.
-Bob
On 10/14/20 3:03 AM, roxanna Mason wrote:
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 <mailto: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 <mailto: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.