Engine Knock

[RyanbabZ71]

Ok i am really getting into finding a true answer to many gm owners engine knock problems.  Today in my thermo 2 class we got into the gas power cycles.  Only the second class of the semester and i am really intregued.  I would like to quote something from our book Thermodynamics an engineering approach.  Written by Cengek and Boles (last names) 4th edition 2002.  Page 460

 

"The premature ignition of the fuel cell called autoignition produces an audible noise, which is called engine knock.  Autoignition in spark-ignition engines cannot be tolerated because it hurts performance and can cause engine damage. The requirement that autoignition not be allowed places an upper limit on the compression ratios that can be used in spark-ignition internal combustion engines."

 

Ok i have to question is what we are hearing actually engine knock?  Because i have yet to hear anyone speak of any performance problems.  I just really got into thinking about this and i am learning day by day.  I dont have the engine knock everyday.  Mine likes to come and go. Sometimes i dont hear it for a few wks.  I think my next course of action is to talk to my professor and see if i can get any answers from him (PHD in engineering and is very involved in thermo and fluid dynamics). I may even try and get him to listen to my truck and hopefully get him to hear it.  The supposed engine knock doesnt really bother me (i can live with it since its not horrible) i just would like to study it a bit.

 

Please any constructive criticism would be helpful.  Also anything you would like me to ask my professor?

[siume99]

Congratulations on finding Thermo interesting.  My prof was from Poland.  His accent didn't help me understand thermo much.  I also wasn't interested in trucks and engines then.    I know, hang and quarter me.    But, I do now.  I just don't have the time to go and read through my books and homework. ???  Someday

 

The newer trucks have electronic sensors on each cylinder to monitor conditions.  I'm at work and don't have my owners manual or my truck service manuals so I can't check right now what they montior.  ??? A way to counter the "knocking" is to retard the timing.  Impossible to do while driving since the Vortechs work with overhead cams.  Another way to retard timing is to increase the octane of your gas.  High Performance Chevy had a nice article on selecting the right gas for your engine this month.  Try using a higher octane "more expensive" gas.  I'm still new to auto mechanics, but it sounds like something else if it doesn't do it all the time.  IMO

[RyanbabZ71]

What was brought up on another board was that what i posted in my 1st post here only happens under load and when the engine is warm.  Dont know if this is true or not.  I emailed my professor and maybe he can shed some light on the issue.  

 

TO me rightnow i think people are confusing the actual term engine knock with something else just because it sounds like a knock

[siume99]

Very true.  You now have me going through some books here at work "Internal Combustion Engine Fundamentals" John Heywood copyright 1988 (don't tell the engines that I'm applying knowledge written about them 14yrs ago)    

[RyanbabZ71]

That discussion in class about engine knock really got my wheels turning.  I stayed up till like 2 last night reading and trying to figure things out.  

 

I feel like i am on a mission

[siume99]

Sorry for the long delay.  My friend at work needed to tell me a story about last night.  It involved a police car and his '86 mustang.  And he wonders why I don't ride in his car!!! :sneek:

 

Its funny how you get the urge to stay up until you find "the answer."  Fortunately, you did it on Thursday nite so you can recover after class and still have the likelyhood of going out tonight.  

[RyanbabZ71]

no class on fridays.  So i can stay up late on thursday night

[siume99]

You lucky.    How do you respond so quickly to posts?  Do you keep hitting refresh?

[RyanbabZ71]

i guess i have a fast computer?  Cable really flies

[01z71]

Ryan -- I'm glad that you have a way to find thermo interesting.  Good luck with the mission.  I haven't heard the knock yet -- knock on wood.  

[siume99]

i guess i have a fast computer?  Cable really flies

Honestly though Ryan, how do you respond so quickly?  Is there a setting on the forum that automatically notifies you, I mean besides the email response in Topic tracker?

[RyanbabZ71]

heres the reply from my professor

 

Ryan,

Combustion in an actual engine is a complex process. It involves processes of evaporation, mixing, turbulence and chemical reaction. It depends also on the compression ratio, air-fuel mixture, amount of charge, charge temperature, octane and cetane numbers of fuel, shape of cylinder and piston, location of ignition source, location of exhaust valve and ignition timing among other variables.

 

It appears at startup the knocking you briefly hear is due to the rich mixture at startup. The richer mixture (which closer to the correct mixture ratio) needed for the warmup increases the flame speed and ignitability which may result in the short period of knock at startup. I will talk more about this in our next class since it has been of interest to you and some of your classmates. Let us enjoy the long weekend for now! See you next Tuesday.

 

How do i reply so fast: well i just click the link under my username where it says light duty (1500,2500) and that refreshes the page

[NewbieZ71]

I have read this thread.  Thoroughly.  There was a small doubt in my mind prior to reading it but now I am absolutely convinced -  my talents, such as they are, really DO belong in the LST Forum.  If I ever do hear a ping or knock I am going to ignore it with the full confidence that if an answer to the problem exists you guys will find it.  I have no doubt!!

[Kansas Kid]

A way to counter the "knocking" is to retard the timing.  Impossible to do while driving since the Vortechs work with overhead cams.

???   I'm pretty sure that the Vortec motors are overhead valve, not overhead cam.....

[chevy4x4trucks]

A way to counter the "knocking" is to retard the timing.  Impossible to do while driving since the Vortechs work with overhead cams.

???   I'm pretty sure that the Vortec motors are overhead valve, not overhead cam.....

Must you always embaress everyone.  Just smile and nod like I do.  Unless it's JP, then you can embaress him