problem with injection timing

[James]

Ok thanks! That gives me a good time to start with– and that's with it set to end of pulse.

I presume on a rolling road you could adjust the timing at set RPMs and loads and see the difference in power?

Could be costly

[hassmaschine]

I think differences in power are likely to be small - you might see an increase in combustion efficiency and a resultant increase in power. But I think mostly, you would use less fuel for the same amount of power, as less of it would simply go out the exhaust as liquid, unburned fuel. So perhaps you'd get a fuel economy boost.

If you look at the theory behind direct injection, they are trying to get all of the fuel to vaporize - of course it's in the chamber, but the vaporized fuel is what increases combustion efficiency and increases MPG. They have an advantage of vaporizing fuel inside the cylinder on the hot cylinder walls, I bet an intake valve isn't as hot, but I think the idea is sound..

[racingmini_mtl]

... the transit time (which can be calculated if you know the distance from the injector to the valve, and the port velocity at that load/RPM) ...

Transit time will also be dependent on fuel velocity out of the injector and injector orientation. Paul S did mention that he needed a significant timing difference when using pencil stream injectors compared to fogging injectors.

Jean

[davcol]

i have tried injecting at idle on a closed valve and gradually decreases it as RPM increases but testes shows that the air ratio became much leaner and the duty cycle much larger , that just doesn't work for me , all the fuel at higher rpm probably not getting into the engine , my duty cycle was at 80% and when i turn it around my duty cycle went to 56% all at full load , so i am convince that advancing the injection timing as rpm increases is the way to go, but the next question is how much advancing is ideal for better efficiency , intake valve open at 7 degrees BTDC and close 57 degrees ,it is toyota 3stge engine , seen that it is a turbocharged engine where the intake manifold is pressurized with air is the velocity still as high as the aspirated engines.

[hassmaschine]

I'm getting somewhere --

I found a formula for calculating port velocities based off mean piston speeds. I'm sure my calculation for velocity vs pressure is wrong, but I'm assuming it goes down with lower pressure, and up with higher pressure (100kpa as baseline). In the end I have a velocity map, using that with my port length (injector to valve) I can come up with a "transit time" for each load site (not accounting for injector spraying - that's another animal!).

adjusting my timing table until the times match up gives me a "transit" corrected map.

Taking it a step further - there's a wiki article that explains some basic principles of the evaporative rate of a liquid. Basically, as RPMs increase, the evaporative time decreases. as the load increases, the evaporative time increases. Here I'm just guessing as a baseline, so I took my calculated "min" transit time using 100kpa as a baseline, and adjusted it for load/RPM based on the two principles above. I then added it to my "transit" corrected map - resulting in a transit + evaporative corrected map.

Now these are all basically huge edjucated guesses, but at least I have a starting point. I'm not confident it will even matter in the end - I went for a short drive with the "transit" corrected map (a LOT more timing than I was using before) and barely noticed any difference. But when I go to the dyno, I'll have 4 different maps with different assumptions to test, at least..

[PaulS]

Sounds like you are getting a good handle on this.

My only comment would be that the speed of the fuel exiting the injector will not be at air speed. However, it should be fixed. You need to allow for the fuel either decelerating or accelerating to match the air speed. You should then be able to factor in the different nozzle arrangements.

[Peter Florance]

Sounds like you are getting a good handle on this.

My only comment would be that the speed of the fuel exiting the injector will not be at air speed. However, it should be fixed. You need to allow for the fuel either decelerating or accelerating to match the air speed. You should then be able to factor in the different nozzle arrangements.

Agreed.
I was going to try to find it empirically but not sure if I can.

[Ligerzero]

fuel particle speeds will be changing since fuel pressure changes with vac/boost in most cases.

[dontz125]

The absolute pressure changes, but the relative pressure across the injector should not - assuming you have a referencing pressure regulator, which is a REALLY good idea on a boosted vehicle! The fuel is effectively an incompressible fluid (at the pressures under discussion), and so the particle velocity should remain relatively constant through the orifice.

[Peter Florance]

The absolute pressure changes, but the relative pressure across the injector should not - assuming you have a referencing pressure regulator, which is a REALLY good idea on a boosted vehicle! The fuel is effectively an incompressible fluid (at the pressures under discussion), and so the particle velocity should remain relatively constant through the orifice.

And as long as the intake valve is closed, it should be pretty constant methinks.

[Ligerzero]

The absolute pressure changes, but the relative pressure across the injector should not - assuming you have a referencing pressure regulator, which is a REALLY good idea on a boosted vehicle! The fuel is effectively an incompressible fluid (at the pressures under discussion), and so the particle velocity should remain relatively constant through the orifice.

Makes sense. Never really thought about it that way

[Wergilius]

The absolute pressure changes, but the relative pressure across the injector should not - assuming you have a referencing pressure regulator, which is a REALLY good idea on a boosted vehicle! The fuel is effectively an incompressible fluid (at the pressures under discussion), and so the particle velocity should remain relatively constant through the orifice.

That I could understand, but if you like me running a turbo with rather low boost pressure (1.0 -1.1bar) and have rather big injectors on a race only engine (fuel economy or other restrictions do not apply) how should injector timing be compensated for boost pressure? If running a referencing pressure regulator no compensation for boost would be needed?

I was running batch last year but rebuilt to full sequential for this season and is going to the dyno in late mars but some good thoughts would be helpfull

[dontz125]

The relative pressure needs to stay the same, but the pulse width will increase as the MAP goes up = more air in the intakes. It's actually pretty straightforward, and your MAP, AFR table and WBO2 will take care of a lot of it.

If the absolute pressure is fixed (non-referencing regulator), then the relative pressure will go down across the injector as boost builds, and you now need to compensate by increasing your VE. Since the flow through an orifice is not directly proportional to pressure drop (it's an inverse square), this can be very tricky, and probably expensive.

[hassmaschine]

The absolute pressure changes, but the relative pressure across the injector should not - assuming you have a referencing pressure regulator, which is a REALLY good idea on a boosted vehicle! The fuel is effectively an incompressible fluid (at the pressures under discussion), and so the particle velocity should remain relatively constant through the orifice.

That I could understand, but if you like me running a turbo with rather low boost pressure (1.0 -1.1bar) and have rather big injectors on a race only engine (fuel economy or other restrictions do not apply) how should injector timing be compensated for boost pressure? If running a referencing pressure regulator no compensation for boost would be needed?

I was running batch last year but rebuilt to full sequential for this season and is going to the dyno in late mars but some good thoughts would be helpfull

forget about the injectors for a second - you would still need to compensate for boost because of the effect pressure has on things like evaporation rates and velocity. as to how, I have no clue..

[Wergilius]

ok, thank you, as for VE that I understand and have done that at the dyno last spring, I have access to dyno-time for rather low hour cost

Then I'll do some trial and testing at dyno regarding injector timing.

[hassmaschine]

I meant to, but I ran out of time on the dyno

[Peter Florance]

I meant to, but I ran out of time on the dyno

We'll do some playing on dyno with the TR8 AFA injector timing. I'm not sure we'll have time to do a lot though
I'm pretty sure I know where to start and as long as PW are not too long, I think the injection angle setting will be pretty forgiving

[Wergilius]

I agree on that, my main goal with individual injector control is to trim pw time and get more equal EGT and AFR on each cylinder, timing is a bonus and could not be so critical since it running pretty well with bank injection

[hassmaschine]

there may be small gains if you manage to increase burn efficiency, but I bet they are 1-2% or less..

[racingmini_mtl]

Dieselgeek reported that the engine he tuned for the dyno competition gained 8HP out of about 600HP from injection timing.

Jean