"Fat Boy" 12/118 thrust engine

[racket]

Hi Guys

Conducted another test run this morning with some "improvements" .

The new battery setup works well , no dramas with decaying oil/fuel pressures on application of the starter .

The first attempt failed , just not quite enough fuel pressure set prior to spoolup ,I need 50 psi but only had 45 , but second attempt went off OK , it was a cool 12 degrees C at the time so oil a bit thick .

I found that the fuel pressure required for both 1 Bar and 1.5 Bar P2 were appreciably lower , so perhaps the 50/50 petrol/kero mix has helped get combustion going with less fuel passing through the engine unburnt.

I was able to get more than 5 minutes run time on the 10 litre tank of fuel , so some improvement there.

I've refitted the new "BIG" jet pipe which gave me starting problems when last tried , but with the improved battery situation I might just get her fired up .

Cheers
John

[Johansson]

Good news John! Did the exhaust temps at 1 and 1.5bar change with the petrol mix?

[racket]

Hi Anders

Not much change in temps from last time with straight kero , so I can only assume that some of the previous runs kero was simply unburnt , there was ~4 psi difference in the injector pressure drop at 1 Bar and nearly 6 psi at 1.5 Bar , this equates to fuel flow rates of ~1260 ml/min vs 1500 ml/min at 1 Bar and 1800 ml/min vs 2200 ml/min at 1.5 Bar, or an ~19% drop at 1 Bar and 22% at 1.5 Bar ..............mmmmmmmmmmm, I might try a bit higher percentage of petrol .......JP3 is 65-70% petrol and 30-35% kero .......LOL, I might end up on straight petrol :-)

More testing required to verify .

One thing I did notice this time was my comp efficiencies , they dropped a few points compared to last time, maybe my T2 gauges aren't reading right , it was only 12C today but 16C last run , so would have expected better effic this morning .

I've still got a big temp difference between my TOT thermos , at 1.5 Bar one sensor is at an acceptable 681 C whilst the other at a "warm" 809 C , the 809 C sensor will be measuring the temp of any fuel burnt that dribbled to the bottom of the flametube .

Now that the starting batteries have been sorted I might do a short run first to warm the engine and oil , refuel , then do some "numbers" , today I found that by the time I'd measured at 0.5 Bar , 1 Bar and 1.5 Bar , the fuel pump was already starting to suck air as I was getting a bit of vibration , and by the time I'd worked that out there wasn't time to try for higher P2s , with a warm engine I'll go straight to 1.5 Bar and test upwards .

Slow steps , but progress I feel :-)

Cheers
John

[Johansson]

Being able to mix in a percentage of petrol in the kero to improve combustion speed is something worth remembering.

A friend once tried to run his RC jet on pump diesel and it wouldn't even start because of the veg oil crap mixed into it, most of the combustion was taking place downstream the turbine wheel...

Did you still hit that same spot when the temps skyrocket?

[racket]

Hi Anders

Yep temperatures are starting to get kinda high at 1.5 Bar , but not as high as before , I'm hopeful the bigger jetpipe will help , also if I can get the temps on both sides of the jetpipe to be the same it'd help ...............I might need to add a half metre of "mixing pipe" downstream and do some temp measurements in it to determine if the average temp is closer to the low or high temp I'm currently experiencing from the individual sensors, its the average that the wheel sees , so if I can get it down by 50-100 degrees C it'll help . .

Then theres flametube mods to think about , maybe add 18 little "air hats" to the front wall where the evap tubes discharge , the hats will spread air radially from the evap tube across the front wall so as mix earlier with the fuel and "add" some length/time to the combustion process.

Cheers
John

[stoffe64]

Congratulations to your positive run of the engine (i guess it was a positive one?)Cheers /stephan

[Chuks]

Congratulations Sir! Positive this time.

[Deleted]

Hi John

Glad its running again, new battery doing the job :-)

Nothing worse than before.... :-) like you say, get to bottom of the temp's, a bit more petrol perhaps,

Chat Soon
Andy

[racket]

Hi Guys

Yep , it was nice for a change to have something positive to report even though I wasn't able to get up to higher PRs , but my long suffering offsider felt it was singing sweeter than normal and for longer before running out of fuel, so I'm looking forward to the next test run .........time to mix up a new brew :-)

When I went to recharge the batteries I found the "starter pack" were still indicating some healthy charge despite two spoolups , it didn't take long to recharge them , during the spoolups the starter was only activated for ~15 seconds before deactivation at >30,000 rpm , I need at least 30,000 to prevent a hung start , the starter will be OK to probably 40,000+

I'll do a bit more "debriefing" today whilst things are still fresh in the memory, then get back into finishing off some bits for the gearbox.

Cheers
John

[racket]

New brew mixed and ready for the next test run , 2 Parts Petrol to 1 Part Kero , hopefully a tad more combustion improvement to come :-)

[racket]

Hi Guys

Another week , another test run , this time with the new "brew" and the "BIG" jetpipe , but as with last time I tried this jetpipe , I couldn't get to self sustain :-(

After the first attempt I thought I'd give it a second try as things were nice and warmed up , so I engaged the starter to purge any stale gases from the engine before attempting the spoolup , but on retracting the starter it didn't stop spinning , theres a micro switch which should have deactivated it as soon as the starter is moved a couple of millimetres .................bugger I thought , this is unusual :-(

With the starter screaming its head off I madly started pulling wires off the starter toggle switch and its relay , still nothing , ............the starter was getting hotter and hotter in my hand , eventually I had to try and stand it on its end whilst I found tools to disconnect the battery terminal , only with the battery disconnected did the squealing stop ..............the starter's no load speed is ~20,000 rpm , and with my bespoke 4.4:1 stepup gearbox the output shaft was spinning pretty quick, I think it was its bearings that were squealing. , I was half expecting something to explode ..............heh heh , almost scared me as much as starting the engine .

It appears that the starter solenoid welded itself together , its only a 12V unit so am looking for a heavy duty 24 V one to replace it with , and have sourced a battery isolation switch ............LOL, I don't want to repeat that experience again , the hot starter left me with a bloody great big blister on my hand :-(

On a brighter note , the new fuel brew burnt with a nice blue blowtorch from the jetpipe and the batteries gave no problems , so more mods to make before the next testrun .

Cheers
John

[Johansson]

Bugger!

[CH3NO2]

Right on John.

Setbacks during scientific experimentation are normal and expected. It comes with the territory. Knowledge gained from a setback is progress.

And Blue flame from a jet pipe indicates good mixing efficiency progress.

[stoffe64]

Bugger bugger, but Good that it stayed in One piece,better luck next time!

[racket]

Hi Guys

Yep , more knowledge gained , theres always some positives :-)

Today I'll start pulling the solenoid apart to see whats gone on inside , recharge batteries and think about some solutions for the getting up to self sustain , the scuba tank is looking likely.

Cheers
John