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Knock sensors

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dean.psiropoulos(at)veriz
Guest

Posted: Fri Oct 12, 2007 6:53 pm Post subject: Knock sensors

I'm not aware of anyone who's tried this on a big bore aircraft engine and

I've been wondering why also.  My 1981 Turbocharged Trans Am had a rather

simple knock sensing system.  There was a piezo-electric sensor screwed into

the engine block.  The signal from the sensor was amplified and converted to

digital to be analyzed by the microprocessor in the crude engine controllers

of the time.  If the engine started knocking the microcontroller would

detect the spike in the voltage of the piezo sensor and send a signal to the

distributor to retard the spark.  This wouldn't be real easy to do with

magneto ignition but folks like e-mag/p-mag and Lightspeed should be able to

incorporate the amplifier and A/D convertor into their boxes and sell them

along with a commercially available piezo sensor.  One would have to find a

suitable place on the crankcase to solidly mount the sensor but there is no

reason it shouldn't work.  Even if the sensor output could be sent to a

display that helped the pilot identify detonation would be better than no

detection at all.  Then more of us could run mogas with better piece of mind

and stop using it if we get a bad batch.



Dean Psiropoulos

RV-6A IO-360



____________________ Original Message _______________________________



From: Fiveonepw(at)aol.com

Subject: Knock sensors?



We've had knock sensors on cars for many years that retard timing in the 

event of detonation to keep engines running at peak fuel efficiency.  I'm

kinda guessing that it is difficult in an air-cooled engine or because of

the large cylinder displacement.  



Anyone aware of any attempts to do this on Lycs or Conts?



Mark Phillips

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AzevedoFlyer(at)aol.com
Guest

Posted: Sat Oct 13, 2007 5:51 pm Post subject: Knock sensors

Dean and All,

 No question that an electronic means of knock detection is the preferred  route, given its sensitivity and ease of integration to the electronic ECU. For  altogether different reasons, I developed (...and have a Form 337 granted by  FAA) what I call an Engine Health Monitor Indicator (EHMI) and have it in my  instrument panel.

 Among several other factors, detonation beyond light (light as defined as a  ping or two here and there or continuous, barely audible in a test cell) will  cause ring flutter. Flutter will change blowby emission. The EHMI monitors  (passively) the blowby emitted. On a modified meter, there are bands colored  Green / Yellow and Red. During take off you have the worst condition in which  detonation could become a problem. That sets your upper limit of your Green  band. If, at any time, you see a trend towards this upper value, for sure  something is steadily deteriorating and you should do something about it  regardless of the source. You know it is affecting your PCU (power cylinder  unit), so its bad news.

 The great thing about monitoring BBY is that it is the first variable to  indicate something going wrong. For example, our engines are prone to ring and  valve sticking. If a ring is intermittently stuck in its groove, not even JPI  exhaust temperature indicators will catch it, as exhaust temps will remain the  same. But the BBY will be affected...and EHMI will catch it! I've been flying  with this indicator in my plane for the last two years.

 I can tell when oil reaches the upper parts of the cylinder after a cold,  long inactivity.

 I can tell when  oil has reached an ideal operating temperature.

 I can use it as a leaning indication instrument.

 I can tell if a plug has shorted or I left mags on Left or Right and not in  BOTH.

 I can distinguish between Left and Right mags firing.

 I can...(still learning...)

 The guys at the local FAA FISDO were sufficiently impressed to say "...you  have turned $4-$5K instruments out there obsolete! Yours should be a required  instrument in every new piston engined plane". Felt complimented!

 Anyway, this is not a commercial/propaganda email. Purpose is to say that  if we satisfy ourselves with less than perfection, something can be  done on the cheap to improve engine health monitiring.

 Sorry for the lengthy mail. Just got carried away I guess.

 Miguel

 PA22/20-150

 N8714D



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glcasey

Joined: 01 Jul 2007
Posts: 23

Posted: Sun Oct 14, 2007 5:37 am Post subject: Knock sensors

Very interesting.  Does it measure pressure or flow?  At my day job  

we build both for large engines, typically multi-thousand hp mining  

truck engines.  The flow is still measured by pressure - pressure  

drop in a venturi.  I agree, one nice thing about measuring crankcase  

pressure is that it is totally non-invasive and doesn't affect the  

base engine operation at all.  Having such a thing would have stopped  

me from taking off when a ring broke on my IO-360.  Turns out I was  

stopped by someone driving up and blocking my way, telling me I was  

blowing smoke (come to think of it, I've had people tell me that a  

number of times...

Gary Casey



 	  Quote: 	
		  

 Time: 06:51:36 PM PST US

 From: AzevedoFlyer(at)aol.com

 Subject: Re: Knock sensors



 Dean and All,

 No question that an electronic means of knock detection is the  

 preferred

 route, given its sensitivity and ease of integration to the  

 electronic ECU. For



 altogether different reasons, I developed (...and have a Form 337  

 granted by

 FAA) what I call an Engine Health Monitor Indicator (EHMI) and have  

 it in my

 instrument panel.

  The EHMI monitors

 (passively) the blowby emitted. On a modified meter, there are  

 bands colored

 Green / Yellow and Red. During take off you have the worst  

 condition in which



(snip)
	


 	  Quote: 	
		   Miguel

 PA22/20-150

 N8714D

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_________________
Gary Casey

AzevedoFlyer(at)aol.com
Guest

Posted: Sun Oct 14, 2007 4:42 pm Post subject: Knock sensors

Gary,

 It translates pressure measured through a modified Pitot Tube into  flow.

 Thanks,

 Miguel



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glcasey

Joined: 01 Jul 2007
Posts: 23

Posted: Mon Oct 15, 2007 5:43 am Post subject: Knock sensors

Miguel,

Thought about taking it commercial?  Sounds possible.

Gary

On Oct 14, 2007, at 11:56 PM, Engines-List Digest Server wrote:



 	  Quote: 	
		  



 Time: 05:42:14 PM PST US

 From: AzevedoFlyer(at)aol.com

 Subject: Re: Re: Knock sensors



 Gary,

 It translates pressure measured through a modified Pitot Tube into   

 flow.

 Thanks,

 Miguel

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_________________
Gary Casey

AzevedoFlyer(at)aol.com
Guest

Posted: Mon Oct 15, 2007 5:05 pm Post subject: Knock sensors

Yes Gary.

 However, right now I do not have the time!

 Maybe a few years from now when I retire?

 FAA people that supervised development is most enthusiastic and want me to  proceed to an STC and get it into the marked. From their point of view, safety  is greatly enhanced and that is enough incentive for them...

 Cheers,

 Miguel



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