Ok, if the title didnt bore you already, lets follow on from here as requested whilst Rob's car warms up.........
https://passionford.com/forum/viewtopic.php?t=65299

Induction Stroke Time Base...
The basis is as follows: To get fuel into an engine, most of you know that we simply open and close an injector, releasing as much or little fuel as the cylinder needs at that particular time to keep the stoichiometry at the desired level.. What most of you probably wont have considered is the limitations placed upon us with regards how and when we are able to do this.....

Lets take 3000RPM for example.
At 3000rpm with a cam of 260 degrees duration, we have approximately 38milliseconds available to us when the intake valve is actually OPEN... Now this time, in injection terms.. is a fookin eternity and allows us to spray loads of fuel into the eagerly awaiting cylinder so we can have lots of boost and lots of torque...

Now lets look at 6000rpm...
The same engine now only has 19ms of intake valve open time available to us because the engine is spinning twice as fast!! So we can now only add half as much fuel as we could at 3000rpm...

Do we need to even consider 9000rpm? 8ms? What the fook are we going to do with that tiny time frame?

What we will do is choose an injector that can supply the fuel required for the horsepower expected, and deliver it in the "Induction Stroke Time Base" available to us. IE: If we expect peak power to be 600bhp at around 9000rpm then we choose an injector that can flow the fuel for 600BHP (Or 150bhp actually if a 4cyl and 4 injectors ) in approx 9ms and still not be flat out (No more than 85% load on the injector if possible)

Now the above is VERY simplified.. but im sure it helps you to grasp the reason why sometimes we will increase fuel pressure and also sometimes we have to use a far bigger injector than the man in the street can understand.... Basically as peak power moves higher and higher up the rev range, we need an exponentially bigger injector to deal with it.....

I hope the above has been usefull to you and helps you sleep. Please think of me whilst im out mapping tonight while you all drink beer.

 

stu,

try working out the timings for a 5-port A series engine!!!

its about 5 ms at 6k rpm!!

alex

 

no

 

You LOVE it!!!!!!!!!

 

start the injection cycle earlier Stu, before the valve starts opening?

 

I am thinking of u whilst i am drinking beer and getting happily drunk LOL

 

oohh Nicole, that's just mean...

 

Stu, at 6000rpm you have 7.2ms of open inlet valve with a 260deg cam NOT 19ms.

Also I disagree about your comment about needing exponentially bigger injector as rpm rises.

Injector size is totally dependant on number of cylinders and bhp alone, rpm does not play any significant part.

This is because to obtain the same power as rpm rises the torque decreases with the same relationship. Since the torque is falling (i.e. the bmep and hence air consumption) so does the need for fuel in maintaining the correct AFR.

In Laymans terms the cylinder specific air consumption for 600bhp @ 9000rpm is much lower than an engine making 600bhp@6000rpm, though they will both require the SAME size injector!!

 

another intresting post!

stu/karl have you ever though about writing a book, as you seem to be able to get your point across alot easyer then alot of people books that i have read!

 

how do you work out how much time you've got? Do you take into account the time the valve takes to open and the time where its only part open?

 

i worked it out as 18.05555555555555

 

It really is'nt a topic thats easy to discuss because its far more complicated than the figures imply. The actual time span available is not linked to the inlet valve open time, and neither is the engine air consumption linked specifically to the inlet valve open time.

However one fact that remains categorically is that we have 720degrees ABSOLUTE in every cycle of a 4 stroke engine to actually flow fuel from the injector.

As such the critical parameters are time available for 720degrees crank rotation at the point of peak bhp. From this we can determine what size injector we would use based on 100% duty cyle and then scale from this to use an injector size capable of less than 85%.

 

Gareth what figures are you using to get 18ms.

 

half engine speed to get cam rpm, ratio of cam duration to total degrees,

and i am a little drunk so ignore anything i say i think

 

Karl,
presumably in practice, injection cycle starts a variable time before inlet opens, but always finishes before inlet closes?

ie, you're not actually trying to inject only into an open inlet valve?

 

Gareth,

I'm affraid you've got a little muddled up.

Let me give you the figures to try for yourself.

At 6000 rpm it takes 10ms for one rotation of the crankshaft to occur. For a cam of 260 duration the inlet valve open time per cycle is 10ms X 260/360. It really is that simple. (Rememeber the total cycle time is 20ms at 6000rpm but the inlet valve open time is ONLY 7.2ms)

You're forgetting that 4 stroke engines are 720 degree per cycle and that cam duration is quoted as crankshaft rotation per cycle.


rich,

It depends what we are trying to achieve. In an ideal world we would only inject fuel that is fully atomised into a fast flowing air stream. (i.e. inlet valve open)

In practice we actually end up using ALL the time available per cycle (720 degrees) and continue to inject even after the inlet valve is shut so that when it opens again we've had the maximum time possible to flow as much fuel through the injector as possible.

I.E we are more concerned with flowing the MAXIMUM amount of fuel than at the theoretically correct time.

Please bare in mind the above info is only with regard to injector flow on high power turbo engines at WOT and is not an issue that we would normally consider for an N/A engine that have a much lower specific bhp figure, or a turbo engine at light throttle.

Its perhaps also worth me mentioning here that this issue is actually quite acute to the fact we only have 4 cylinders on the YB. This means the specific bhp per cylinder ends up extremely high and why we end up using virtually ALL of the 720 degree time span!!

For example my engine running 1000cc injectors actually has to run them open for 650 degrees when running 650bhp.

 

Karl,

i did 260/720 and thats how i got my numbers

 

interesting post Karl, thank you.
I've only really considered the injection duration with respect to N/A applications...

That must make for a large quantity of fuel hanging around in the port while the valve is shut..

 

Rich,

The problem with discussing this topic is the fact that it varies with air consumption.

I'm only really considering getting the maximum bhp from an injector at WOT on a turbo engine as it's not normal practice to run a seqential injection engine at 720 deg inj duration.

Regards port puddling, No believe it or not its no issue at all!!

Fuel puddling behind the valve does not have any real detriment at all!!!

As a good example consider bosch K jet which sprays fuel continuously yet the emissions are FAR superior to any carburettor setup despite the fact the carburetor setup is in essence an inlet valve open time only fed system as opposed to the k jet full cycle duration.

 

yeah, I can appreciate what you say about puddling - it was an initial reaction that I didn't think about too deeply.. the idea of a 1000cc injector going at 85% against a closed valve conjured up interesting images!!

 

LOL for sure it sounds a lot BUT if you work out the maths its less than 0.5cc of fuel behind the pair of valves.

 

What's this? Informative posting? On an internet forum?

Everybody here needs a Dan Dare badge and a choc ice. I'm drunk. But top reading all the same, very simplified for those of us with small brain.

 

Injection phasing is a key element to getting the required fuel into the cylinder atomised correctly ands i hoped we would drift naturally onto that but it seems Karl cant sleep and has saved me the trouble now anyway...


Roflol.. like i said earlier it was a quick few lines whilst a car warms up for mapping, i wasnt wasting time putting any hard calculated figures in at almost 11pm, i wanted it to be very simple for people to understand the theory, nothing more, nothing less... I considered describing it accurately as time between intake valve closing and then opening again but decided that 95% of peeps would simply think i worded it wong anyway, so i left it oversimplistic with exagerated numbers....

Whats this anyway? Tuner wars? Have i a cap in my ass yet?

I will however tell you where my original numbers came from in my head, they are in fact the correct total injector ontime available figures for our antiquated Cosworth speed density management systems. Im sure it will occur to you where the ontime figures effectively "double up" once you think about it, but it wasnt remotely relevant to this topic at all...

I wasnt saying 600bhp at 9000rpm required a bigger injector than 600bhp at 6000rpm i was saying that we are running higher power now at higher revs and requiring larger injectors...

As for RPM having "No Significant part in injector choice" im afraid i disagree Karl. A simple example of why i disagree is this: At 8000 RPM the intake valve is opening and closing at 66 times a sec. And is only open for an average of 6ms. At this cyclic rate the transient time to complete the delivery of fuel, from injector to cylinder, is critical and as a result, we rely heavily on pre valve event phasing to deliver the fuel to the valve before it opens at all. the one thing that will never ever change no matter how hard we rev the engine is the fact that an average peak and hold injector operating on a saturated (or otherwise) circuit driver typically has a reaction time of 2 milliseconds while a peak and hold injector typically responds in a much better 1.5 ms dont forget it has to close again too so please double this figure.... It also has whats known as a dead time of 0.6ms on average. Couple these facts to the obvious injector duration issue with high speed switching and the technical need to start limiting inj duty to 70% instead of the 85% that was safe at lower engine speeds and i stand by my reasoning that for higher horsepower and higher RPM we should be using a bigger injector for safety.

Anyway.. its 03:30am and ive no time or inclination to start any technical chat this morning as i need to go home to sleep, but i thought id best quickly redress this post since it seems to be dig at Stu week and ive no "defensive" time available during a busy Saturday.. lol

 

What is "WOT" ?

 

Wide Open Throttle..

 

Working Operating Temperature ?

 

richm, right
FAST AS FORD, wrong

and this morning i am in a better frame of mind and can see where i was going wrong

 

Hey FFS this was not a dig at you Stu.

"At 3000rpm with a cam of 260 degrees duration, we have approximately 38milliseconds available to us when the intake valve is actually OPEN..."

I read the above sentance by you, and simply said I disagree. I'm sorry if you feel I'm having a dig but I was simply saying that I disagree. (It's open for 14.4ms at 3000rpm)

However I know you were actually quoting available open injector time, but this is'nt the same open inlet valve!

You also said that injector size must increase exponentially as rpm rises and again I disagreed with this. Of course injector size goes up as bhp goes up, and the fixed switching time of the injector time does add a constant factor that must be calculated into the time available BUT it is'nt what I'd call an exponential factor. (For example it amounts to around 4% loss of injection time between 6000rpm and 8000rpm)

Rpm is not a significant factor in determining injector size. If for example you max out a grey at 500bhp at 6000rpm at 35psi, if you lower the boost to lets say 28psi it will still max out at around 500bhp (just under at say around 490) but this time at 7000rpm. It's a very simple example but shows that bhp is the significant factor in injector size NOT rpm.

Anyway I've had enough of this, seems like I've come back off my hols to some people in a bad mood!

 

awww dont feel that karl!

any my question...

how does injector latency (is that the right word for injector reaction time) come into this?

alex

 

Stu, if Speed/Density is considered out dated now, what would a modern day advanced ECU be using? Or were you just refering to the system as a whole?

 

Karl,
Im sorry if i missunderstood you, it was 3.30am and i was still at work and very tired. I simply thought it was a dig due to you correcting what i had done as a simple to understand example foir joe bloggs instead of perhaps saying "Just to clarify for those requiring more detail" or some other such method of posting.... anyway.. sorry again for being a mardy fooker...

Alex,
Thats the dead time i mentioned. 0.6ms average.

Katie,
There are very very few management systems in the world that rely on manifold absolute pressure now. It really is older than T-rex himself.

Mass Air Flow is where its at. With this system the ecu has a near as damn it perfect indication of torque output too and can limit or raise torque as it sees fit...

 

Katie......OMG Beauty AND brains!!! Thats a good question you've asked..

NOW, tell me: It is Phil asking that question on your log in?

If i'ts not Phil asking, then

 

do any of the modern day high power cars run batch injection rather than sequential?

 

Yes they do Matt, its still a great way to do things, with batch (Or Gang as some folk may know it) being preferable over Constant (Bosch K for EG: the "K" Means KONSTANT") although all the "De Facto" stuff is fully sequential with both fuel AND spark... IE it can retard JUST one cylinder when det occurs or fuel just that one extra etc etc..

As far as horsepower goes though, that doesnt really make a toss of difference

 

one thing i wondered...

will moving from batch to sequential injection literally HALF you fuel consumption...

i assume it doesnt... and if not why not

 

I can state the obvious Doug, fair play I was on a dumb one yesterday, but I was terrified of my picture being taken and/or being stung by a binful of wasps =)

 

Blatantly Phil (accidently ) posting as Katie, shes bloody clever in a school type way, but dont belive in a car type way!

Stu- You say MAF is far better? Most/All decent aftermarket managment and hightly modded road/race cars use MAP tho

Ive binned my AFMs, dont understand em, dont like em, lol, MAP sensor for me, lol.

 

the reason mass air flow is so great is, its measuring how much air is going into the engine, so it knows how much fuel to add to get the right air to fuel ratio,, simple

 

Exactly Gareth, and it also knows the DENSITY of the air too.. and we all know how important that is....

No Jim it wont:
Batch fire generally adds fuel in 2 pulses. One with valve closed and one with it open, just 50% each time.

 

well that goes without saying