anyone experience this effect of injecting on intake stroke ?

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Belgian1979
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anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Tue Apr 17, 2018 5:09 pm

For several reasons I changed my injection timing such that it would inject right into the engine at the time the intake valve opened. What I noticed was a substantial increase in exhaust noise. Anyone experience this ? Is there a reason for this ?

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Amilcar » Tue Apr 17, 2018 5:33 pm

Is that more noise at the exhaust all you could notice?
At which operation range was this?
You burned a lot more fuel inside OR, the burn time leaned more towards the open exhaust valve.
The output in power will give a better answer on what happened I think...

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Orr89rocz » Tue Apr 17, 2018 6:09 pm

Could possibly be sending fuel out the exhaust valve during the overlap period

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Re: anyone experience this effect of injecting on intake stroke ?

Post by digger » Tue Apr 17, 2018 6:24 pm

How do you know you injected it only while valvevwas open?

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Brian P » Tue Apr 17, 2018 6:26 pm

Injection during the intake stroke (and being completed before the intake valve closes) is less likely to send raw fuel out the exhaust during overlap than the traditional arrangement of injecting against a closed intake valve for at least some of the injection period. If you inject against a closed intake valve, the part of the charge initially drawn into the cylinder (during overlap) is extremely rich and may still have liquid fuel in it. If you inject during the intake stroke, it's still going to have some fuel because of fuel accumulated on the cylinder walls evaporating, but at least it doesn't have nearly the full charge of fuel sitting there waiting to get drawn in.

Maybe the lean charge drawn across during overlap is causing afterburn in the exhaust pipe (acts like air injection) and maybe that's where the noise is coming from ... just a hypothesis, nothing more.

I'd be more interested in the effect on torque and BSFC figures than in a slight change in sound level.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by ptuomov » Tue Apr 17, 2018 6:33 pm

You want to start injection after the exhaust valve closes, right? So the injection period length is EVC-IVC, at least at low to medium rpms?
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Re: anyone experience this effect of injecting on intake stroke ?

Post by RednGold86Z » Tue Apr 17, 2018 9:10 pm

On our small OEM engines that I did a few years ago, low RPM and low load injection on the open valve had much worse engine out emissions and rougher running. Idle was much rougher.

I believe the logic is the hot valve aids evaporation, and the residual cylinder pressure right at IVO blasts fuel up the intake a bit, aiding vaporization - vs. open valve injection where tons of fuel hit's the oily wall and never gets swept into the weak airstream (liquid doesn't turn as easily, and it smacks right into the wall). I've read some things about Honda GDI over here, where they are having issues with the oil level going drastically up (several quarts) over a few weeks period, due to fuel hitting the wall from early IN CYLINDER injection (vs. late in cylinder injection that has too high smoke from droplets not mixing enough).

They also do studies to figure out the best part of the valve to aim for, and I think the consensus was short turn side, to help avoid cylinder wall impacts for cold starting.

For WOT, high enough RPM, I've scoped other OEM ecu's and found they switch to later OPEN valve injection too, in order to get max VE or piston cooling, or some combination. But, the trick is to finish about 8ms before the valve closes (flight time of the fuel).
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Re: anyone experience this effect of injecting on intake stroke ?

Post by MadBill » Wed Apr 18, 2018 12:44 am

A big factor here must be injector capacity. Even the most radical of intake cams won't keep the valve open for much more than ~ 40% of the cycle, whereas conventional injector sizing typically targets a max duty cycle of as much as 85%. Under those conditions the fuel cannot all be injected through an open valve. :-k
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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:16 am

I haven't run it yet as some of the mods on my intake aren't complete, but like I said the exhaust was a lot louder. Not just a bit but quite noticable. I do agree on the statements above that one would want to aim for a closed valve but this was to eliminate other effects that made me try injecting it on an open intake valve.
I only once have tried it while driving (injecting into an open intake valve) but that was when I didn't perform the current mods. Back then I remember that the exhaust while driving became quite a bit louder too. Not sure how much more power it gave as it wasn't on a road where I could push it at the time.
I also remember that I had the impression it was running rougher with that timing.
Last edited by Belgian1979 on Wed Apr 18, 2018 2:21 am, edited 1 time in total.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:17 am

MadBill wrote:
Wed Apr 18, 2018 12:44 am
A big factor here must be injector capacity. Even the most radical of intake cams won't keep the valve open for much more than ~ 40% of the cycle, whereas conventional injector sizing typically targets a max duty cycle of as much as 85%. Under those conditions the fuel cannot all be injected through an open valve. :-k
This was at idle not at higher rpms. Opening time is ca. 3 ms which is roughly 15% of the injector capacity.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:20 am

RednGold86Z wrote:
Tue Apr 17, 2018 9:10 pm
On our small OEM engines that I did a few years ago, low RPM and low load injection on the open valve had much worse engine out emissions and rougher running. Idle was much rougher.

I believe the logic is the hot valve aids evaporation, and the residual cylinder pressure right at IVO blasts fuel up the intake a bit, aiding vaporization - vs. open valve injection where tons of fuel hit's the oily wall and never gets swept into the weak airstream (liquid doesn't turn as easily, and it smacks right into the wall). I've read some things about Honda GDI over here, where they are having issues with the oil level going drastically up (several quarts) over a few weeks period, due to fuel hitting the wall from early IN CYLINDER injection (vs. late in cylinder injection that has too high smoke from droplets not mixing enough).

They also do studies to figure out the best part of the valve to aim for, and I think the consensus was short turn side, to help avoid cylinder wall impacts for cold starting.

For WOT, high enough RPM, I've scoped other OEM ecu's and found they switch to later OPEN valve injection too, in order to get max VE or piston cooling, or some combination. But, the trick is to finish about 8ms before the valve closes (flight time of the fuel).
I remember this Jeremy but I thought the intent was to have an 8 ms time lag between starting injection and intake valve opening. But I could be wrong here. I normally start injection at 408° before TDC on the power stroke which gives smooth running. This goes up with rpm obviously but at higher rpms it seems to create issues as well, so it might need to be kept constant througout the rpm range.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:22 am

Amilcar wrote:
Tue Apr 17, 2018 5:33 pm
Is that more noise at the exhaust all you could notice?
At which operation range was this?
You burned a lot more fuel inside OR, the burn time leaned more towards the open exhaust valve.
The output in power will give a better answer on what happened I think...
idle only so far but when blipping the throttle it stays the same.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:38 am

Orr89rocz wrote:
Tue Apr 17, 2018 6:09 pm
Could possibly be sending fuel out the exhaust valve during the overlap period
Hm, that possibility also exists when you inject during the time the valve is closed I would think. It's not like there's a stream of fuel going straight through the intake into the exhaust.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by Belgian1979 » Wed Apr 18, 2018 2:41 am

ptuomov wrote:
Tue Apr 17, 2018 6:33 pm
You want to start injection after the exhaust valve closes, right? So the injection period length is EVC-IVC, at least at low to medium rpms?
I'm not fully convinced that injection on the valve when it closes would be a solution. I mean, it would have roughly 540° that it stays in the runner where it can be drawn into another runner or it can condens back on the runner walls imo. I would inject somewhat prior to the opening of the intake valve such that, knowing that at lower pulsewidths the fuel will have time to vaporize and then be sucked into the cylinder. At higher rpms the timing becomes less relevant as the more one goes above the earlier mentioned 8 ms you will be injecting fuel half of the time available for injecting fuel so roughly 360° of your crank rotation fuel will be injected (more or less) So the chance that you will be injecting into an open intake valve increases a lot.

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Re: anyone experience this effect of injecting on intake stroke ?

Post by joe 90 » Wed Apr 18, 2018 3:06 am

55 deg ABDC is when "some" OEMs start injection.
That's when the intake valves are closed.
Injecting onto the back of a closed intake valve helps with vaporisation which improves combustion and reduces emissions.
It keeps the valve cooler and the fuel hotter.


Why would you want to do it any other way?

That's a better question?

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