Thanks Robert and Rick for your feedback -
I didn't think I had noticed anyone on this list mention that approach before
and I thought it might be something interesting to test out. I would have liked
to read a bit more about this but sadly the authors did not include a reference
to this particular design test.
I suppose in order to compare the difference between, I would need two
injectors (1) with a constant 1.8:1 mixture ratio and the other with the
variable ratio described below.
Kind Regards,Graham
On Saturday, November 26, 2016, 9:38:36 PM EST, Robert Watzlavick
<rocket@xxxxxxxxxxxxxx> wrote: It seems like a good idea so I would definitely
try it. A problem you may run into is that your hole sizes may end up being
too small for an inner and outer circle. Your engine is larger than mine but
with my 250 lbf LOX/kerosene engine, I had 10 unlike doublet pairs with fuel
holes of 0.045 inches and oxidizer holes of 0.055 inches. You can go smaller
of course but I think 0.025 is the minimum recommended. Definitely use a
filter if you go with small orifices. So, you might want to pick a minimum
hole size, then see what types of patterns are possible.
-Bob
On 11/26/2016 12:21 PM, Graham Sortino (Redacted sender gnsortino for DMARC)
wrote:
Hi Rick-
Apologies, I may have made a mistake. Let me use the actual mass flow numbers
for my design and I'll try to illustrate: Total Ox Flow = 0.5709 kg/sec
Total Fuel Flow = 0.3172 kg/sec Target Mixture Ratio ~= 1.8:1 O/F
Now, what I was proposing is having an inner core of injection orifices where
the mixture ratio is slightly higher. This would be approximately 2.1:1 O/F.
Inner Core Ox Flow = 70% of 0.5709 or 0.3996 kg/sec Inner Core Fuel Flow = 60%
of 0.3172 or 0.1903 kg/sec Inner Core Mixture Ratio = 0.3996 / 0.1903 ~= 2.1
O/F
Then there would be an outer core closer to the chamber walls that is fuel
rich in order to reduce the adiabatic combustion gas temp near the wall as well
as gas side heat transfer. This would be approximately 1.35 O/F Outer Ox Flow =
30% of 0.5709 or 0.1713 kg/sec Outer Fuel Flow = 40% of 0.3172 kg/sec or 0.1269
kg/sec Outer Mixture Ratio = 0.1713 / 0.1269 ~= 1.35 O/F
If I add up the Fuel and Oxidizer flows I *believe* the total O/F ratio is
the same but the lower mixture ratio toward the walls could (might)
theoretically help more with cooling without the subsequent reduction in
performance caused by more traditional film cooling. (Recalculated) Total Ox
Flow = 0.3996 + 0.1713 = 0.5709 kg/sec (Recalculated) Total Fuel Flow = 0.19032
+ 0.1269 = 0.3172 kg/sec (Recalculated) Mixture Ratio = 0.5709 / 0.3172 ~=
1.8:1 0/F
Kind Regards, Graham
On Saturday, November 26, 2016, 12:07:08 PM EST, Rick Dickinson
<rtd@xxxxxxxxxxxx> wrote: Graham,
Your numbers don't seem to add up to 100% for either the inner or outer
injectors, so I'm a little bit confused by what you're asking, and how you got
from those percentages to your mixture ratios. Can you clarify a bit, please?
Thanks,
Rick "confused" Dickinson
On November 26, 2016 8:47:00 AM PST, Graham Sortino
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Hi -
I was reading through the heat transfer / cooling sections in Huzel and
Huang and I wanted to ask two questions, which I’m struggling a bit
with:
In regards to #2, I’m working on a LOX/Kerosene 500 lbf engine running
at a 1.8:1 mixture ratio and I’m very tempted to try this but I wanted
to see if anyone has experience or advice with this? I'm not sure that
I recall anyone on Arocket who mentioned using this injector patter but
it seems like it could be quite beneficial. Essentially, what I was
thinking of doing is as follows:
Inner Injector Rings:
60% Kerosene Flow / 70% LOX = 2.1:1 mixture ratio
Either unlike triplet or like doublet configuration
Outer Injector Ring:
40% Kerosene Flow / 30% LOX = 1.35:1 mixture Ratio
Unlike doublet configuration
Kind Regards,Graham
