Hi
This might help , it was from when I was having the same queries ...............
I'm currently up to the stage of constructing the fuel injection system for the karts A/B , .................. due to the design of the A/B my thermocouples for TOT measurement are displaced to the outlet of the diffuser , and to prevent fuel spray from contacting the thermocouples I needed to determine the axial distance between the spray ring and thermocouples to minimise "wasted" A/B length .
The engine will require ~4 litres/min of fuel to the A/B ,................... with 20 spray orifii , thats ~200 cc/hole/min .
A test rig was manufactured using a short "blind ended" length of the same 3/8" OD stainless tubing as the fuel ring is constructed from and a single 0.7mm hole was drilled in its side , the tubing was then pressed into a fitting that was screwed onto a garden tap .
When water pressure was applied to the test rig it squirted horizontally ~10 feet at the required 200ml/min flow through the 0.7mm oriface , this was much further than expected :-(( ........................but upon application of the leafblower to simulate the gases exiting the turb exducer , the jet of water was reduced to ~2 - 3 inches before it disintergrated into a spray going "backwards .
This was still a considerable axial distance so I opened up the hole to 1.0mm diameter , this increases flow area by about 2 times , so a decision to reduce the number of holes in the A/B sprayer to 16 was made , this would now require a flow of ~250ml/hole/minute , ....................this produced a horizontal jet of ~6 feet when the test rig was fitted to the garden tap .
The leafblower reduced the axial squirt to between 1 and 2 inches ................getting more like it :-)
There was one unfortunate side effect of having a squirt of fuel going axially towards the imaginary turb wheel exducer's gas flow and that was that some of the "fuel/water" was blown straight back onto the spray ring where it flowed around to the downstream side of the tubing and was blown off in large droplets , not the best thing for fast combustion :-(
I then tried "offsetting" the fuel to gas flow ,.......... this dramatically affected the outcome by not only shortening the fuel squirt length ( to<1 inch ) compared to a "head on " approach but also blew the fuel spray to the side of the tubing in a well broken up spray without any large droplets .
It only required an "offset" of ~15 degrees between fuel squirt and gas flow for this to occur , this should easily be accomplished by drilling the 16 X 1.0mm dia holes in a staggered pattern slightly to each side of the centreline of the spray ring , the centreline of my spray ring is ~90 mm diameter , the A/B crossectional area "outside" the sprayring should be roughly equal to that inside the ring, allowing for a cooling airflow along the inside of the A/B wall , I want more fuel in the "centre" than near the "outside" to keep wall temps down .........................
As for the fuel pump flow vs voltage , Smithy did some very accurate flow tests on an 044 clone at voltages between 12 and 18V , and at 40 psi and 18V it flowed 430 lbs/HR of fuel .
With your 98 mm inducer you'll flow ~2.3 lbs/s of air , 138 lbs/min , assuming 30% of that is "burnt" in the flametube , that leaves ~97 lbs/min to be burnt in the A/B , 97/min = 5820 lbs/hr , divide by 15 = 388 lbs/hr of fuel for the A/B .
You just need to adjust the A/B fuel ring hole area so as to require that ~40 psi and a flow of ~6.5 lbs/min - 3.8 lpm
Hope this helps
Cheers
John
