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Post by racket on May 3, 2020 20:27:51 GMT -5
Hi Scott
We might need to get back to basics .
Firstly , can you remove the entire exhaust system and attempt a spoolup ??
If you need some exhaust pipe to clear the gases away from the bike , maybe just an elbow pointing vertically .
My reasoning is the bangs may be creating shock waves ...............creating a "tuned" exhaust :-(
Secondly , could you attempt a spoolup using a BBQ propane bottle instead of kero .
Thirdly, you need a manual P2 gauge ...............we need to remove as many electronics as possible at this stage .
Fourthly, the air start needs to be more variable , rather than on/off .
What we need to try is a very basic spoolup , ...............oil pressure , ignition , some spoolup air to get things rotating at a few hundred RPM , add some propane , get ignition, then slowly increase the propane until your exhaust temps start to get >500C , the rpm will be increasing from the heated gases but add some more scuba air along with propane to coax the engine into life .
My gut feeling is that things are currently happening too quickly , ............lotsa RPM , lotsa air , lotsa fuel , then a big bang which will probably "reverse" airflows from the comp , the system is then non combusting for a short period , .................then the process repeats itself , its like a surge scenario.
Some of the RC aircraft turbine engines refused to start if they had long "ejector" tubes in the fuselage to carry the engines exhaust rearwards ...................hence my concerns about your exhaust system potentially causing prpoblems .
Yep , trials and tribulations ...........all part of the "enjoyment??" ;-)
Cheers
John
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jetric
Veteran Member
Joined: December 2014
Posts: 149 
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Post by jetric on May 3, 2020 20:57:53 GMT -5
Hi Scott, One thing I have noticed in one of your posts you say (correct me if I'm wrong) that you only open your combustion chamber drain after you have ran the engine, the combustion chamber drain needs to be open all the way through the start cycle on your engine due to your under-slung combustion chamber, If fuel builds up in your combustion chamber you know the consequences! as Andy found out once when he had a runaway due to him not having a combustion chamber drain, this caused the turbo to rev so high that it snapped the turbine wheel off from its shaft due to the shaft dynamics at such a high rpm, The turbine wheel rattled around in the exhaust scroll outlet enlarging the outlet hole big enough for the turbine wheel to eject itself out the hole at unimaginable speed never to be found again! He had a very lucky escape. As with your current problem I have had two instances when this type of flame out has occurred, The first one was with the twin turbo DIY engine that was made by Nick Haddock that Andy fitted into the jet powered Mini called the Turbonator that was owned by Andy's mate Dan. Andy asked me to come and have a look at the engine as he was having the same starting issues as you are 'it would light off then blow out as it approached idle speed' I concluded that the issue with this engine was too much air flow in the primary zone of the flame tube causing the flame front to be blown further down the flame tube out of the primary zone and ultimately extinguishing it as the airflow increased during start-up, this also caused a lean mixture in the primary zone, Luckily it was an easy fix as Nick Haddock had used bent slots to feed the compressor air to the top face of the flame tube in the primary zone, so I reduced the open area of the slots slightly in order to richen up the mixture in the primary zone and hey presto it started perfectly on its next test run. The second instance of this type of start-up flame out was on the engine that I made for my brother's jet kart (that you saw when you popped down) The original design of this engine had a tangential compressor air feed onto the combustion chamber, this tangential feed caused high amounts of swirl in the combustion chamber and flame tube and caused a low pressure area to be formed in the center of the flame tube, which caused the flame to burn as a narrow streak straight down the middle that was highly unstable, all due to the tangential feed (I did a atmospheric test to see this), this caused the engine to light off fine but as the engine speed reached idle it would instantly blow out. I moved the compressor feed to be central on the combustion chamber and never had the starting problem again, the flame was perfectly formed and anchored right in the primary zone the full width of the flame tube (I did a atmospheric test to see this) as you know this engine and kart went on to set the land speed record at 104 mph until Tom Bagnall beat it, not bad for saying how small the turbo is on my brothers kart. The video of the stable flame has been shown on a previous post recently (its the one with the large outlet on the flame tube) as both videos are on Andy's YouTube page as he did the filming whilst I did the test. Have you changed anything on the combustion chamber or flame tube since the engine last ran properly? Even something as simple as changing the spray angle on the fuel nozzle can cause this problem! Hope this helps, these are just my experiences with this type of start-up flame out problem, I'm sure other people will have better ideas how to solve this problem for you. Richard S. Thanks for the info John, I awoke with plenty of ideas and a list of code updates and things to try. - I verified without any scuba air and constant spark that EMC was still causing problems. In particular it was knocking out the MAX6675's (Thermocouple measurement PCBs), either making TOT read high (Arduino thinks engine is started then), or TOil Read high (arduino increases PWM on oil pump to compensate for reduced oil viscosity when hot). - I tried to make a metal shield to cover ignition box but the spark then went straight to the shield and caused arduino reset - I sealed all the gaps and the lid on the box with silicone, which looked to reduce EMC and I no longer had issues with a constant spark - I modified the code so that during startup at throttle >5% there is constant fuelling, at throttle >20% there is also spark I was lucky that my boss at work let me take the high pressure compressor home, so I can now recharge the scuba bottle in my garage. I tried several fireup attempts and got close again, but still when its almost at sustain it just starts banging (exploding/relight) to the upset of several locals! I think I may have then started barking up the wrong tree, and thought maybe this was due to the engine leaning out when P2 increased. I tried 2.5bar and 3.5bar fuel pressures. However I still remember with the engine running before it idled at P2 1 bar with 2bar fuel and nothing has changed. Andy had the good idea of filming the digital dash to see what might be happening. Sure enough it caught the arduino resetting on the last attempt, although it appears to reset after the bangs when there is still fuel on. However I tried this attempt with constant spark (to give it every chance of lighting) so maybe after 20 seconds or so it did cause enough EMC to give an issue. In short, I am still a bit confused about the engine going out and then relighting. The videos from yesterday (the last one) show it almost being fine at 2bar fuel. I plan to try and fully quash the EMC issues by fitting stainless braid to HT lead (when it arrives). I will also try a resistor type spark plug cap. Finally I may see if the kero lights without the spark plug gap, as this will reduce the voltage and EMC. Another thing I can do is alter the arduino code so that it goes directly into "starting" mode when it switches on, therefore after any resets it will fuel the engine again - but this is a bodge really. My last resort is to try an aircraft ignitor plug and bang box, being that they are 2kv I would think they should have less EMC, but this may not be the case with them having a copper spark plug lead and at least 1Joule of energy per spark! If anyone has experienced the engine lighting and then going out repeatedly, please chime in! I had it with the "jet sledge" on propane when running lean with too small a drilling but thats all I can reference. Videos of today: Trials and tribulations, I will keep at it! It seems so close! Cheers Scott |
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Post by slittlewing on May 4, 2020 14:27:00 GMT -5
Dear All, Today has been an amazing day. I finally got the bike to run properly with the ECU!!  I am absolutely over the moon, even more so than when i first got it to run years ago.The story is as follows.. Rich, in terms of your concern about how the fuel drain was - I have a port on the combustion chamber lid to a 6mm push in PTFE tube (high temp fitting also). The line goes to an analog pressure gauge and has a Tee to open air for drain, but the drain was about 6" higher than the top cap (combustion chamber underslung). Thus with no pressure, fuel could pool in the chamber but with P2 pressure it should be ejected hence I was draining it after each run. I heeded yours, Johns and Andys advice and moved the Tee to the lowest point this morning to allow drain at all conditions. I considered Rich's comments about lean primary zone, but i had the engine running nice before so I didn't feel this was an issue. Also John your advice about a simpler propane start or back to basics approach was the backup plan. But first I wanted to try some things and leave the engine (and ECU code) as it has been. The resistor spark plug caps arrived in the post and I fitted one. the spark was still strong and ignited the kero easily. Andys idea was to get the engine sparking and fuel running for a while to see what happened so I put a plug outside the combustion chamber (grounded to engine). After a minute or so I could see the arduino reset from EMC. I tried with a stainless braid on the HT lead, but the spark went to it and it shutdown the ECU immediately. I then tried putting a ferrite on the HT lead and all was good with over a minute of sparking and fuel simultaneous. I then tried to start the engine with 2 bar fuel pressure. It "banged" again after spoolup: I thought maybe the engine was leaning out with increasing P2, causing the flame to blow out and re-ignite. I tried again with 2.5 bar: This seemed worse. I thought maybe the engine might actually be too rich, causing ignition in the afterburner tube. The pressure shockwave then could be blowing out the flame in the combustor. I reduced fuel pressure to 1.25 bar, and it was quite alot better (banged again, but got boost showing): I reduced the demand further, to 1 bar, again saw some improvement: I could hear electrical noise on the camera, and with more evidence of EMC something occured to me that Andy had said about turbos causing static. I couldn't figure it out because the turbo is grounded to the battery negative. However I realised that I have fitted an aluminium bellmouth, which is spaced off the combustor with a 3d printed adaptor. Thus it is not grounded. I grounded this to the chassis negative with a croc clip lead and tried again with slightly reduced fuel pressure.... Finally, the engine started!!! Once started, it ran perfectly. Silky smooth, no bangs, 2 bar max P2 at 10bar fuel pressure and a nice low idle. Everything worked well, even the shutdown. The only thing that is amiss was the thermocouple readings (TOT and TOil) whereby the MAX6675 pcbs seem to have got EMC issues. I am absolutely over the moon to get it going, and would really like to thank this forum and especially thank Andy, John and Rich whos input and knowledge (through years of hard work) has been absolutely instrumental in getting to this point. I have ordered more ferrites, which I will fit to the Afterburner ignition 12v & HT, the fuel pumps and oil pump 12v and the arduino 12v supply to try and finally get rid of these EMC issues once and for all (fingers crossed). Thanks again to everyone, Scott |
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Deleted
Joined: January 1970
Posts: 0
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Post by Deleted on May 4, 2020 14:41:35 GMT -5
Scott.....Am so pleased you got this wonderful build working, am happy to of been some help to you, looking forward to its first track outing  All The Best Andy |
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Post by racket on May 4, 2020 19:36:33 GMT -5
Hi Scott
Thats fantastic , congratulations .............perseverance always pays off ...........excellent detective work :-)
LOL.............now you know why I try and keep things as "agricultural" as possible, I've seen so many guys have problems when using electronics on their engines , but I think you'll get it sorted now that the engine works , much easier chasing down issues on a known working engine.
Congrats again , well done , time now to get mobile .
Cheers
John
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Post by slittlewing on May 5, 2020 16:25:20 GMT -5
Thankyou John and Andy, I am looking forward to the inevitable test ride!!
I found about about some minor grief within the neighbourhood, on an app that I hadn’t heard of before. Not that unexpected I guess, but I profusely apologised for the noise (it was the explosions that people were concerned about) and now I seem to have gained a good amount of positive encouragement which is nice and unforseen. I flyered 130 houses in 1/4 mile radius this morning explaining and offering people to come and look and have had some nice emails.
So after giving it a rest for a day, I hope to light the AB tomorrow providing the engine starts again.
I fitted 6 more ferrites today to reduce EMC further and siliconed the AB ignitor box the same as the main one.
I need to decide on fuel demand, Andy thinks richer is safer- I am trying to avoid the pulsed banging. Last time with manual control I slowly opened a needle valve and it smoked a little until it lit. This time I have to do some more trial and error to find a suitable ratio of P2 to AB fuel pressure, which is how I have programmed the ECU to run I order to get successful afterburn at all throttle positions (I remember rich advising me that max afterburn fuelling and thrust is proportional to airflow).
One question, I couldn’t achieve more than 2 bar P2 with 10 bar fuel yesterday. Considering the hx50 should be able to do 3.5PR (3.5 bar), for max thrust should I swap the nozzle for a larger GPH? I know this will make startup more difficult but it could give me more power, obviously all of this dependant on TOTs being sensible which I hope to verify at current P2 level.
I totally agree it was beneficial getting the engine running previously with manual controls, but I am pleased to have gone down the electronics route as it offers a huge amount of automation and flexibility in how the engine is run with minimal user input (throttle and an AB button). On a little bike with no space for controls I think this is necessary! The EMC issues have been unexpected and a real learning curve though!
Thanks again,
Scott
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Post by racket on May 5, 2020 17:41:36 GMT -5
Hi Scott
Yep, you'll probably be needing a larger GPH nozzle to not only get you up to your 3.5:1 PR - 2.5Bar P2 but also your design temperatures which currently should be rather modest due to the "oversized" jet nozzle size , though without a TOT gauge and the uncertainties of the turb stage flow matching to the comp, your TOTs could already be getting near design .
You were very "couragous" going full electrics with a new build , its generally advisable to keep things simple/manual until its working/sorted and then add the sophistication of electronics , but its perfectly understandable of you to go "electric" with your bike build , bikes are horrible things to put a turbine engine into , never enough space for all the bits and pieces .............heh heh , wait until you try fitting a freepower stage as well, the poor old Suzuki GS750 frame I used for my bike was crammed full by the end of development with bits hanging off everywhere .
Your build is a real credit to you, looking forward to seeing more of your work in the future , but be prepared for a learning curve that has no end :-)
Cheers
John
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Post by slittlewing on May 5, 2020 18:54:14 GMT -5
Excellent - thanks for confirming John, of course you are completely right I need to get my TOT working before doing anything else! With the extra ferrites added I am hopeful this could potentially be fixed but will find out tomorrow. One other option I have is to automatically power cycle the thermocouple reader pcbs every X seconds to reset them but I would rather not bodge it!
I guess a 17.50GPH nozzle should be about spot on (currently at 13.5) but I will wait until I have sussed the AB side of things before messing with it!
The packaging has indeed been a “challenge”, albeit a fun one - I seem to have got lucky in that the 125cc bike frame is literally just big enough for everything, albeit that I have crammed the battery, ECU and some other bits into the (extended) swingarm! I can’t imagine how difficult it must have been putting the freepower in a factory sized 750 frame! What was it like to ride? Terrifying or an absolute hoot?! I have been needing to go for a wee before starting the engine each time due to some nerves hahha.
Thankyou for your kind encouragement and support, as you can see on page1 of the thread I was pretty clueless before the help of this forum, totally invaluable! These bloody jets are addictive 😂
Cheers
Scott
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Post by racket on May 5, 2020 20:36:57 GMT -5
Hi Scott Theres something worrying me about your fueling rate , a 13.5 GPH nozzle , assuming thats US GPH and is rated at 100 psi pressure drop across the nozzle , you will be flowing ~14.8 GPH with a 120 psi drop ( 150 supply minus 30 P2) . 14.8 US gallons of kero will weigh ~99 lbs . Your 2.5" inducer - 4.9 sq ins will flow ~ 60 lbs/min of air , so ~60 lbs/hour of fuel required if running "safe" temperatures from an overall 60:1 A/F ratio , Your current fuel flow , if I've made the correct assumptions, is >50% greater than required , could your fuel pressure readout be playing up , or your fuel nozzle not flowing correctly ?? Can you run a static insitu fuel flow test , run the fuelpump at your measured 10 bar and see what flows out of your combustor drain in 1 minute, I do this with my engines as a quick, pressure vs flow, check to make sure none of my 18 injectors are blocked. The Garrett TV84 turbo bike with ~115 RWHP was very easy to ride , no clutch and no gears to worry about , the idling was set just below takeoff torque , so a tad of throttle got the bike moving , for a homemade contraption weighing in at 280 kgs , and with my 90 kgs flapping in the breeze , it was still able to cover a quarter mile in ~12 seconds with a terminal speed of ~120 mph www.youtube.com/watch?v=P-5PgWqgIJo no sound on digital cameras in those days, and only 12 seconds of filming .............how times have changed :-) It was a bit terrifying having a red hot turbo pumping out >40 lbs of boost just inches below a tank of fuel between ones knees Cheers John |
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spartablades
Member
hi i m new here ..i m start to build that project ..a have a turbo with intake inducer diameter 7,4
Joined: February 2020
Posts: 33
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Post by spartablades on May 6, 2020 5:47:28 GMT -5
I cunt understand how cun increase/decrease the rpm
Here I m stack
In my mind thinking to use arduino to
With 12 v relay and programs to open/ close a back from car in m/s
Sorry if my English isn't well
Please i want help here
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feez
New Member
Joined: April 2020
Posts: 2
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Post by feez on May 6, 2020 10:16:45 GMT -5
Fantastic to see that the engine is running with the electronics!
I'm quite surprised at the fact that it's maintained combustion at such a low fuel pressure, the oil burner nozzles don't atomise very well below ~5 bar but it's good to know that it can work.
The flameouts were undeniably unstable combustion in the primary zone. What I experienced on a very small turbine that I built about 13 years ago is if even a small amount of fuel pooled somewhere in the combustor it would cause the turbo to accelerate rapidly on startup and supply too much air and the combustion in the primary zone would go out. Without the main fuel burning the pooled fuel would also go out. Your 13.5 nozzle can flow a fair bit of fuel in the few seconds before it lights up properly.
I think the little bit of air you gave it in the successful start made all the difference. The fuel stayed burning from the point you introduced fuel and did not go out and reignite later, the airflow through the combustor made sure that fuel did not get a chance to pool anywhere or stick to the flame tube walls.
I used a glow plug about an inch from the nozzle which made ignition reliable even with air already flowing.
Keep up the good work!
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Post by slittlewing on May 6, 2020 10:35:12 GMT -5
Hi Scott Theres something worrying me about your fueling rate , a 13.5 GPH nozzle , assuming thats US GPH and is rated at 100 psi pressure drop across the nozzle , you will be flowing ~14.8 GPH with a 120 psi drop ( 150 supply minus 30 P2) . 14.8 US gallons of kero will weigh ~99 lbs . Your 2.5" inducer - 4.9 sq ins will flow ~ 60 lbs/min of air , so ~60 lbs/hour of fuel required if running "safe" temperatures from an overall 60:1 A/F ratio , Your current fuel flow , if I've made the correct assumptions, is >50% greater than required , could your fuel pressure readout be playing up , or your fuel nozzle not flowing correctly ?? Can you run a static insitu fuel flow test , run the fuelpump at your measured 10 bar and see what flows out of your combustor drain in 1 minute, I do this with my engines as a quick, pressure vs flow, check to make sure none of my 18 injectors are blocked. -It was a bit terrifying having a red hot turbo pumping out >40 lbs of boost just inches below a tank of fuel between ones knees Cheers John it sounds wonderful to ride! I’m sure you were twitchy when you first got on it though haha. Good idea John. I did it this morning and it flowed almost exactly 13GPH at max pump pressure albeit at 140psi rather than 100, I don’t think it’s blocked 👍 I will try a new 17.50 and get another 13.50 maybe as a spare? I replaced TOT Tc after it had died. It worked for the first fireup today which went nice and smooth. Repeated the process of a bit of air first and then fuel and away it went TOT readings were good before it died. andy informs me it needs to be in a stainless tube so I will buy one accordingly. I have had one attempt at afterburn and didn’t have enough fuel to light. I will try again shortly with a decent amount more fuel pressure demand programmed in. |
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Post by slittlewing on May 6, 2020 10:36:34 GMT -5
I cunt understand how cun increase/decrease the rpm Here I m stack In my mind thinking to use arduino to With 12 v relay and programs to open/ close a back from car in m/s Sorry if my English isn't well Please i want help here No relays needed, the pump speed (and therefore fuel pressure) is controlled with PWM (pulse width modulation). If you google it in Spanish it should make sense. arduino can do PWM easily, then you need some MOSFET and diodes to step the voltage and current up. |
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Post by slittlewing on May 6, 2020 10:40:08 GMT -5
Fantastic to see that the engine is running with the electronics! I'm quite surprised at the fact that it's maintained combustion at such a low fuel pressure, the oil burner nozzles don't atomise very well below ~5 bar but it's good to know that it can work. The flameouts were undeniably unstable combustion in the primary zone. What I experienced on a very small turbine that I built about 13 years ago is if even a small amount of fuel pooled somewhere in the combustor it would cause the turbo to accelerate rapidly on startup and supply too much air and the combustion in the primary zone would go out. Without the main fuel burning the pooled fuel would also go out. Your 13.5 nozzle can flow a fair bit of fuel in the few seconds before it lights up properly. I think the little bit of air you gave it in the successful start made all the difference. The fuel stayed burning from the point you introduced fuel and did not go out and reignite later, the airflow through the combustor made sure that fuel did not get a chance to pool anywhere or stick to the flame tube walls. I used a glow plug about an inch from the nozzle which made ignition reliable even with air already flowing. Keep up the good work! Thanks for the informative response feez, it sounds entirely plausible and fuel could have been pooling a bit at the time! Also Good to know a glowplug worked for you!! I am using a monarch PLP nozzle which their datasheet says has good atomisation at low pressure compared to some others. It’s a semi solid cone spray so the outer edges have less spray which probably is helping not soak the spark plug further down 👍 |
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Post by slittlewing on May 6, 2020 16:45:12 GMT -5
Well today has been another great day for the Jetbike, i got the afterburner running.
Firstly I fixed the TOT by fitting a spare TC. It lasted about 30 seconds 😂 but that was enough to verify sensible TOT at 2 bar P2 without AB. Andy has since advised me I need to run it in a stainless shroud tube so I will source one going forward.
Tot video:
The engine now starts very nicely with a bit of air before fuel. Andy advises me I need a stainless tube over the Tc which I know you can buy so I will procure one.
I tried to light AB with a ratio of 1:1 ab to P2 pressure but it wasn’t enough fuel to light.
I upped to 2.5 ratio and the AB lit albeit only at idle. Once alight you can throttle the engine with ab and it’s stable and nice!! Not sure I got to 100% throttle but I got close. I will probably drill my restrictor out 0.1mm for a bit more flow at high boost.
Video here:
I have a double skinned heatshield over th hottest part of the AB and the gold foil over the outer skin set on fire during the run which was half expected - no big deal.
However a brass compression fitting on AB fuel feed expanded more than the stainless tube and leaked causing another small fire in the drain tray under the engine. I shut it down immediately and extinguished it with co2, no damage done or injury thankfully. Stainless fittings only from here on out (that was the only brass fitting on the whole bike) and a valuable lesson!!
So a great last test, now to fit brakes and seat and a larger 17.5GPH injector, fix the leak.
i also conducted a small thermal survey on the seat mounting points and under the fuel tank using a pico logger thermocouple reader I borrowed from work (great bit of kit). All the Tc readings were below 130deg so I may get away with the stock seat. However it’s probably a good idea to take a mould off it incase I need to make a carbon version in which I could get 50mm ceramic insulation under it!
Many thanks!
Scott
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