Hi Martin,
Glad to hear that you are continuing to progress well with your Masters
research. As is the nature of the game, hiccups always seem to show up from
time to time. Indeed, ignition of rocket motors has plagued me on occasion.
Steve and Rick provided some excellent comments and suggestions. I'll add
mine, which will overlap to some extent.
1. core burner motors, from my experience, can be tricky to ignite
effectively and achieve rapid startup. The geometry has no "sharp corners"
in which to initiate burning, as is the case with BATES.
2. to achieve quick startup you'll need a slower burning igniter, not a
fast "pow" type pyrotechnic igniter. A pyrogen type is best. The following
design is what I use now for my KNSB and KNDX motors and it results in
instant thrusting:
http://www.nakka-rocketry.net/igniter.html#MDP-pyrogen
3. Primer, as Steve mentioned, should be a simple KN/charcoal/IPA
composition, very thin layer. Don't use metal flakes, they won't help and
will in fact hinder ignition.
4. The biggest factor, however, may be your surfactant. Scott Jolley has
reported that surfactant can make grain ignition difficult. I guess it
depends of the type. I use sodium laureth sulphate (same as you use, I
believe). However, you are using a lot, 6 drops per 100 grams. I have used
0.1% which works out to about 2 drops per 100 grams, without causing
ignition problems.
Richard
On Mon, Oct 22, 2018 at 11:47 AM M.C. Olde <mr.m.c.olde@xxxxxxxxx> wrote:
Dear people,
For my master thesis I am characterizing both course and fine KNSB
(KNO3-Sorbitol) propellants at various conditions (pressure/ grain initial
temperature) as it is a readily available solid propellant that has not
been characterized overtly much. In addition it would allow me to almost
freely publish my test data/ propellant characteristics and other results
which cannot be said of many commercial solid propellants or when
collaborating with companies.
However during my experiments I have run into considerable issues with the
fine (100 mu average KNO3) propellant, I cant get it to ignite while the
course (350 mu average KNO3) propellant burns alright. I've tried most of
the textbook solutions but currently I am completely out of ideas. I have
the feeling that my current igniter charge burns too fast for the KNSB to
properly start combusting. I'm looking for answers to for instance the
following questions:
- What would be potential physical mechanisms that make the fine KNSB
more difficult to initiate than course KNSB?
- What igniter redesigns could I implement to give it a better chance
of ignition? (Other compositions/ different geometries/ slower burning
suggestions?) - bonus points for reuse of current hardware and non
space-grade energetic materials such as BKNO3.
I have condensed my thoughts and a summary of the problem in a small Root
Cause Analysis. I sincerely thank any suggestions in the right direction.
kind regards/ vriendelijke groeten,
Martin Christiaan Olde
*MSc student, DARE member*
*Delft University of Technology*
