Actual Fuel Quantity

[SmokeShow]

How can I figure out the actual fuel quantity injected per "shot"??? talking about volume.

i.e. 24,000psi * 2500ms = _____ amount of fuel injected.


Seems like there is a PID for this or one that can calulate it is or can be written.

 

[McRat]

There is a mm3-DMA pid, but it's not correct.

I had a formula that would be close, but you never know the real amount without bench testing using an injector.

If you look at the factory main injection pulse table, it isn't "perfect", they did corrections to it to alter amounts just like we do.

 

[vortecfcar]

How can I figure out the actual fuel quantity injected per "shot"??? talking about volume.

i.e. 24,000psi * 2500ms = _~165 mm3_ amount of fuel injected.


Seems like there is a PID for this or one that can calulate it is or can be written.

Not perfect...

Nick

 

[zfuller123]

calculating injected quantity per stroke

Pat:

I too would like to know this. I'm trying to do alot of figuring on the new motor i have, and i like to see my tuning ideas backed up with a little math, just so i have a true idea of whats happening.

Basically, i would like to know the same thing. how much fuel per shot. Given that there are lots of variables (exact fuel rail pressure, etc.) - there are still some knowns.

For example, i know that i have 30 over injectors - i had each tip broken down and flowed, so i know that the injectors can flow 26 liters +/- about .125 of a litre.

Also, i know that i put the LBZ regulator on my single CP3, and ported the fuel rail fittings. While it doesn't increase PSI of the rail really, it does increase the volume. this changes things of course when you factor in 8 injectors all open for x amount of time - as the capacity of the rail diminishes from long injector pulses, PSI of course will drop.

But what i really want to know - for a baseline - is the formula for figuring out, if possible, how much fuel is injected just as in the example given. 24000 psi @ 2500 msec pulse width = ??? mm3? If there is some base calculation to this, i am going to try and figure out given the size of the injector (allowed flow) how much fuel is being squoze out. I'm going to take it one step further when i get reasonable comfortable with calculating this # and throw in timing and other engine / tuning paramaters so that i can 'see' where in the stroke the injector opens, and given the pulse width, where in the stroke the injector closes (all of course dependent on other variables).

To me, if i can figure out the math, i can build a handy little windows application to mimmick the functioning of the motor for tuning purposes. It'd be handy for me... as i'm a believer of getting the fuel in the bowl - and i even know the sizes of my fuel bowls... the spray pattern is the one piece of informaiton i dont have (calculating the size of the patter and a given distance from the injector tip)...

Anyways - i have some ideas - more to be aids to tuning these things - but i need some math to help back me up. i know i'll have to study my ass off to figure it all out, but i think it could be a pretty handy app for the hardcore tuners, and for wanna be's like myself. It could at least help a tuner make sure they were tuning as efficiently as possible once i get it to that point. the math is the hard part, the windows app is the easy part.

Let me know what you have. Any and all parameters you might have for such a formula would be greatly appreciated..! Or that ANYONE has access to..

Thanks!

-->Zach

 

[SmokeShow]

let me dig, but the spray angle of the injectors is posted on here somewhere.... 116 or 117* rings a bell but I can't swear to it. I'll go look for it and post it up for you.

Unfortunately the math for this isn't going to be easy because it's not exactly linear... two of the components of the equation (pressure and elapsed time open) are ever changing and not always in direct relation to one another. so, you can't just say that the volume increases X-amount for every unit more of time open or PSI. Bunches of combinations to figure out. Definately gonna need a spreadsheet to do it.


We can figure it out if we can find the stock injector hole opening (all the holes combined) size. Then apply some hydraulic equations to figure out how much volume theoretically will be squeezed out by X-pressure for Y-amount of open time.


Then, to get it to a knats ass, on the theoretical level, we'd have to take into account the effective hole size going from closed to open back to closed. It'll go from no hole to full hole back to no hole. In between the closed and open the hole size will be somewhere between 0 and the fully-open size. That adds a bit more difficulty to the math side but still figurable nonetheless.


THEN, with all the equations figured out, we can plug them into a spreadsheet that can calculate for all the varying times and pressures seen. And ultimately, the equation can be used in a custom calculated PID referencing timing and pulsewidth to get a better number.

I was hoping someone already had the spreadsheet.

 

[SmokeShow]

LLY injector size: 7 x .0059", or .00019 sq in,
(per Pat)

If my memory serves me right, the LB7s have the largest injectors... still looking for their size and the spray angles.

 

[SmokeShow]

looks like they are 158*

some good reading... Injector Discussion

 

[zfuller123]

ya i got stuck on that thread for a couple hours last night. lots of good reading and theory and yada yada.

I was thinking even more about the injector thing - thinking i 2 of the critical numbers i'd need... then thinking about it more, i thought how could? Hours on the net looking through hydraulic and fluid formulas...

I know my injectors are rated to flow 26 liters... but then, i started asking - there's a big variable there.. 26 liters at WHAT PSI of fluid? Thats the question i went in hunt of today. However, looking at the hydraulic formulas - seems that the # you found for the injector size is more the value we need to calculate. However, there were enough formulas to compute velocity, etc etc etc that i don't know where the hell to start.

i think this information really could be useful for all of us. And having a handy little app that we could even run on our smart phones if we wanted to might make it all the more useful down the road for quick tuning or whatever. I'd like to know what we can put together and i'm about ready to put the question to a college instructor.... just have to find the right one.

If you come across anything in the mean time - let me know. i'd love to get rolling on this. i think it'd be way useful to see some of it on a screen all put together... I know the app will take me a while to build but i'm ok with that if i know i've got good formulas. Lots to take into account though as you said...

Thanks for the info!

 

[duramaximizer]

Pressure and flow is all dependant upon viscosity and that is dependent upon temperature. Therefore you need to start with the temperature of the fuel, and figure viscosity. You will come up with a number So then you can start figuring flow by the size of the hole and the pressure. It shouldn't be that hard.

http://www.lasalle.edu/~gentry/C302/Lab 1C. Viscosity biodiesel.pdf

Then using that, you can get derivatives to put into a pressure formula. Then get a flow chart using pressure and temperature. Then once you get a flow chart, then you can figure fuel injection timing based on flow and the length of time it will take the computer to tell the injector to fire and the best possible time to fire your desired ammount of pulse width based on intake air temperature, boost pressure, and mass air flow.

The end goal is hp and torque with the most area under the curve. This is the most cylinder pressure at (whatever degree produces the most mechanical advantage) for the longest period of time excluding bottom dead center and top dead center where no hp is made.

I was told that you will always have maximum torque at 90* to the crank shaft which will be 1/2 of the stroke. But that is not where you want to inject fuel because you want to inject fuel into your peak cylinder pressure which is up closer to 30* After TDC?

On edit that last bit didn't come out right because peak pressure is at top dead center and that doesn't do any good to inject fuel there. There is an ideal number but IDK what that is. I forgot.

 

[zfuller123]

ug

looks like its time to bust out the lab coat and trusty old HP nerd calculator. As with all my simple ideas, this one will surely be 100 times more complex than i bargained for. i was intending to keep it simple in my head - but that wouldnt really yield anything terribly useful for a result.

After reading that paper i think there are additional factors to be considered that werent part of their equations. Ill have to do some digging to find out the thermal properties of our fuel as i would imagine it has the same type of properties as all gasses in that when comprssed, and viscosity increases, so does heat. hence our fuel coolers and all the other garbage.

Too much to think about on a sunday, but i can see a few more factors coming into play - and instead of just theory i'm thinking that some actual testing might need to be done, or found. for example, what can a stock cp3 flow from an lly? from an lbz? i would think to have valid numbers we'd need to know that. also, we'd need to know the inside diameter of the rail (for the formulas referenced in that link you gave). might need to also factor in the smaller, and more limited in diameter, rail fitting - which people often drill out (or buy PPE's ported rail fitting, for example). In fact, the calculation may have to be performed a number of times to actually arrive at the correct number of 'how much fuel will be injected' because of all the restrictions in the system before actually flowing out the injector tip... yuck. this is sounding like more work than fun now

thanks for your info. anything else you think to add please let me know. i'm not sure how i'll gather all the data i need unless i can find people that have already gathered at least some of it...:angel:

 

[duramaximizer]

If I think of something, I'll let you know. But right now, I am in over my head at the thought of reading my own post.