Electronic Fuel Mixture Controller
Jam Racer
Posts: 3
Hi all, I race nitro powered radio controlled boats, and getting the air/fuel mixture correct is critical to getting the maximum performance out of the engines. I would like to build a fuel mixture controller that reads exhaust gas temperature, and drives a servo to move a needle valve that controls the fuel flow to the engine. The ideal exhaust gas temperature for these engines is between 650 and 750 degrees, depending on application. What is the best way to go about this?
Thanks,
Jam Racer
Thanks,
Jam Racer
1600 x 1200 - 363K
Comments
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- Stephen
Reading the exhaust tempature and adjusting the mixture until you read the peak tempature and then richening the mixture slightly so the engine won't overheat and fry·is a great way to tune and engine for peak power. This is how we tuned the Racing engines on a dyno for Tractor pulling.
You could probably do this with less than 10 lines of code with a·BASIC stamp. I like this idea... What a great learning project and possibly a racing secrete.
Anyways heres a sensor that should get you going. The sensors are towards the bottom of the page
·http://www.eagletreesystems.com/Car/car.html
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Team K.I.S.S
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Post Edited (slamer) : 11/19/2007 4:36:16 PM GMT
I am just getting to the servo controlling part of the book, so I will understand how to generate the pulse wave modulation, then I have to do the light measurement experiment to understand that, then figure out how to measure temperature from that lesson, and then figure out how to tie them together. I'ts probably easy to do if you know the right buttons to push, but I'm as newbie as it gets here.
Thanks again,
Mike
This is the un-moddified program from the book. This is a good program to modify
' What's a Microcontroller - ControlServoWithPot.bs2
' Read potentiometer in RC-time circuit using RCTIME command.
' Scale time by 0.724 and offset by 500 for the servo.
' {$STAMP BS2}
' {$PBASIC 2.5}
DEBUG "Program Running!"
time VAR Word
DO
HIGH 7
PAUSE 10
RCTIME 7, 1, time
time = time */ 185 ' Scale by 0.724 (X 256 for */).
time = time + 500 ' Offset by 500.
PULSOUT 14, time ' Send pulse to servo.
LOOP
·The one thing that is unknown at this point is what is the resistence range of the thermocouple sensor and where you set your baseline fuel needle valve·position·(servo position) Then you can lean or richen the mixture from there.
Heres a simple program I wrote that will read your servos position with the basic stamp.
'Radio control with the Basic Stamp 2
·'This program READs· 75 Mhz radio reciever servo output channels.
· 'by scanning the Pulse Width Modulation OUTPUT frequency of each channel.
'Test Receiver channel outputs with the Pulsin command by reading servo signal line
'Receiver outputs connected to pin zero on the Board of Education'
'Receiver ground is connected to the VSS ground on the Board of education
'Receiver 4.8 VDC is not connected
' {$STAMP BS2}
' {$PBASIC 2.5}
'Variables
·channel0 VAR Word
Receiver:
··PULSIN 0,1,channel0 'Measure· positive pulse pin 0
·· DEBUG "Channel0= ", DEC ? channel0,CR
··· PAUSE 500
GOTO· Receiver
'Use (1) FOR logic HIGH OR (0) FOR logic LOW
' aproxamately a pulsewidth reading of 750 it stick centered on transmitter
' test for tranmitter stick movement from center position then jump to subroutines to move servos
Basically you can plug the basic stamp into your receiver and read the position of the channel that talks to your fuel valve control servo. This will give you the baseline reading from what you normally send with your radio. Once you have this value·youll want to write it down somwheres handy. This would be your normal starting and engine warm up servo position.
Since you have been controlling the needle valve manually with a radio you have probaly noticed that as you lean the engine for max power it will run faster until it gets too lean and then if falls over at that point. Yep thats too much and it's very bad for the engine. But if you could make a note of that position you could limit the PWM signal to never go that far. You always want to run sightly rich·so not to cook the engine.
Now that you know these limits you can take some ohm readings fro the sensor that you will have installed in the engines exhaust pipe then you can set up the RC time circuit and your darn near there.
I wish I had the Data on that sensor, But I don't. I did do a bit of reading on RC Nitro engines today and just about everyone only takes a tempature reading on the cylinder head About 275-300 deg F. is considered pretty hot and there always the old school spit on the cylinder head test.
But taking the reading on the head is not a very accurate way to see whats really going on since the cylinder head heats and cools at differnt rates depending on ambient air tempature, humidity, available·airflow and other stuff.
I think your totally on the right track by reading the exhaust tempature directly. You will be looking at tempatures of around 1300-1500 deg F. This is were the Real action is happening. Keep me informed on your progress. This is a cool/HOT project·...[noparse];)[/noparse]
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Team K.I.S.S
Build Safe, Build Mean, Build Strong!
Post Edited (slamer) : 11/20/2007 6:16:08 AM GMT
I found it thanks to the Helicopter guys since they have a similar problem. This system reads the cylinder head tempature. I'd still prefer reading the actual exhaust tempature. The project using a stamp·still sounds like fun to me.·But this is an exsisting product and it has been tested in RC egg beaters.
Check this out...
http://www.teambob00.com/#07.Sep.06_-_Needles
http://www.rcmodels.org/csm/carbsmart.htm
http://www.rcmodels.org/csm/carbsmart.pdf
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Team K.I.S.S
Build Safe, Build Mean, Build Strong!
Post Edited (slamer) : 11/20/2007 6:45:13 PM GMT
Thanks for the code, I will get some time over the next couple weeks to get it all done and working. Race season starts in February, so I really have to get moving, and I still have a complete boat to build.
I think you would find this an interesting read, a buddy of mine wrote it several years ago, and was really the inspiration for me to try to use science to figure things out on these little monsters. He was just beginning to do some serious dyno and EGT work when he unfortunatley passed away. His data showed EGT's in the range of 700 to the mid 800's was the sweet spot. I can tell you from experience that I have ruined a fair amount of parts getting too lean.
http://findarticles.com/p/articles/mi_qa3918/is_199912/ai_n8865292/pg_1
Thanks again for your help, I will let you know how it goes.
Mike
Ah thats not too bad you got a couple of months. I love time pressure..
·I compete in or build for·lots of wacky event's myself, from Robotic Combat to Fire Art and of course Power Tool Drag Racing. I've used various small gas engines for many of my robotic and ride on toys and have fought with those pesky mixture screws a billion times. Especially with two stroke engines.
It's truely amazing how crazy two little needle valves can make you. It's even harder·when you don't have a way to load the engine so it won't exsplode·while you·make the high speed adjustments. This is what got me interested in your Automatic Mixture Control idea.
Basically I see it a possible way to preserve what sanity and hearing·I may still have left. I usually tune by ear in a parking lot. I'm quit familiar with the Trial and Terror meathod..[noparse];)[/noparse]
I have this Inertia launched (Ride On) Power Tool Dragster that could possibly benifit from this idea.
The engine noise has been measured at 113 db at 10 feet, So leaning over it and·tuning it at 10,000 rpm's·is a bit painfull for the·NUT with the screwdriver. This looks like a Good·job for the basic stamp2 and a servo.
http://www.teamkiss.com/ptdr2006/mattdawg.html
If you need any help let me know. Rock On.. buddy
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Team K.I.S.S
Build Safe, Build Mean, Build Strong!