Plenum fuel injection for reduced IATs?

[NewbVetteGuy]

What is the reason that in port & direct fuel injection apps, that we don't see fuel injection into the plenum for reduced IATs?


In all the various carb vs. EFI threads, one of the distinct advantages of a carb is reduced IATs from the evaporation of fuel through the intake tract -wouldn't having a 9th injector in the plenum do the same thing?

Water / Meth injection is used to get more timing and a bit more oxygen into the cylinder through evaporative cooling -how does simple gasoline compare at temp reduction / knock resistance enhancement vs. just water vs. water+meth?

In racing apps I see the dual injector strategy to get some cooling effect but a single BIGASS injector in the plenum would provide more cooling as it's in the air stream longer, wouldn't it? (Distribution issues aside) -A single big injector is certainly cheaper than 8 extra injectors placed high up in a runner...


Just adding a 9th injector would be DEAD SIMPLE and CHEAP compared to a water / meth setup, too; if you are running out of injector, adding a 9th injector in the plenum could potentially run your regular injectors at a lower duty cycle, too...



I've done as much Google searching trying to figure this out as I can and I haven't come up with anything...

Thanks,
Adam

[2seater]

The Buick GN guys did a 7th injector back when there wasn't the wide selection of higher performance injectors available but mostly for additional capacity. You might try one of the GN forums.

[digger]

you do see people using port injectors in the bellmouth for this reason, its not that common though and it needs to be phased correctly with airflow not continuous that you effectively get with high duty cyles. if you are running port fuel injector near the head and one in the plenum the benefit is reduced compared to injecting all the fuel in bellmouth

[mk e]

Shower injectors (injector in the bell mouth) are pretty common these days...I think all the sport bike have them?

the issue as I understand it is that its very hard to get good low power performance with high mounted injectors which leads to systems with 2 injectors and attempts to phase or switch over which leads to mid power issues...o most just mount the injectors low knowing they are probably giving up a little peak hp.

[midnightbluS10]

The Buick GN guys did a 7th injector back when there wasn't the wide selection of higher performance injectors available but mostly for additional capacity. You might try one of the GN forums.

The Syclone & Typhoon guys had an ATR 7th injector setup, also. It was installed into the TPI/LT1 throttle body that was used on those trucks, where the cover plate goes on top. It never did work right. Guys had better luck just using 6 bigger injectors rather than trying to bandaid it with the 7th injector.

[David Redszus]

In all the various carb vs. EFI threads, one of the distinct advantages of a carb is reduced IATs from the evaporation of fuel through the intake tract -wouldn't having a 9th injector in the plenum do the same thing?

A high position injector, much like a carb, will allow additional time to evaporate the fuel and provide
charge cooling benefits.

On of the distinct dis-advantages is that fuel vapor will displace inlet air, and change sonic velocity.
Evaporative fuel cooling will also cool the inlet manifold losing its effectiveness.
The issue then becomes one of trade-offs between charge density vs charge air mass.

Fuels with higher boiling points sometimes require greater inlet length (and time) to evaporate.
Multiple injectors are often preferred over larger injectors in order to provide a finer droplet size,

[Nwguy]

I don't remember when exactly, but at Indianapolis an additional injector was used just downstream of the turbo to cool the intake charge. I believe it was only used for qualifying. I seem to recall that it was outlawed shortly thereafter.

[Warp Speed]

In all the various carb vs. EFI threads, one of the distinct advantages of a carb is reduced IATs from the evaporation of fuel through the intake tract -wouldn't having a 9th injector in the plenum do the same thing?

A high position injector, much like a carb, will allow additional time to evaporate the fuel and provide
charge cooling benefits.

On of the distinct dis-advantages is that fuel vapor will displace inlet air, and change sonic velocity.
Evaporative fuel cooling will also cool the inlet manifold losing its effectiveness.
The issue then becomes one of trade-offs between charge density vs charge air mass.

Fuels with higher boiling points sometimes require greater inlet length (and time) to evaporate.
Multiple injectors are often preferred over larger injectors in order to provide a finer droplet size,

How does cooling the inlet manifold lessen its effectiveness?!?

[David Redszus]

In all the various carb vs. EFI threads, one of the distinct advantages of a carb is reduced IATs from the evaporation of fuel through the intake tract -wouldn't having a 9th injector in the plenum do the same thing?

A high position injector, much like a carb, will allow additional time to evaporate the fuel and provide
charge cooling benefits.

On of the distinct dis-advantages is that fuel vapor will displace inlet air, and change sonic velocity.
Evaporative fuel cooling will also cool the inlet manifold losing its effectiveness.
The issue then becomes one of trade-offs between charge density vs charge air mass.

Fuels with higher boiling points sometimes require greater inlet length (and time) to evaporate.
Multiple injectors are often preferred over larger injectors in order to provide a finer droplet size,

How does cooling the inlet manifold lessen its effectiveness?!?

The evaporative cooling cools the manifold instead of cooling the inlet air.
One reason to use plastic inlet tubes instead of aluminum. Or, to coat the insides of aluminum tubes.

[digger]

Shower injectors (injector in the bell mouth) are pretty common these days...I think all the sport bike have them?

the issue as I understand it is that its very hard to get good low power performance with high mounted injectors which leads to systems with 2 injectors and attempts to phase or switch over which leads to mid power issues...o most just mount the injectors low knowing they are probably giving up a little peak hp.

i think the S1000RR has 2 sets one above bellmouth and another post itb

[modok]

Most Fi manifolds aren't made to flow fuel. Not enough velocity.
if you have a carb manifold converted to port FI, then SURE, good idea.

[Warp Speed]

A high position injector, much like a carb, will allow additional time to evaporate the fuel and provide
charge cooling benefits.

On of the distinct dis-advantages is that fuel vapor will displace inlet air, and change sonic velocity.
Evaporative fuel cooling will also cool the inlet manifold losing its effectiveness.
The issue then becomes one of trade-offs between charge density vs charge air mass.

Fuels with higher boiling points sometimes require greater inlet length (and time) to evaporate.
Multiple injectors are often preferred over larger injectors in order to provide a finer droplet size,

How does cooling the inlet manifold lessen its effectiveness?!?

The evaporative cooling cools the manifold instead of cooling the inlet air.
One reason to use plastic inlet tubes instead of aluminum. Or, to coat the insides of aluminum tubes.

It actually cools the inlet air, and thus cools the manifold and intake tract. The trick is to make the intake tract easy to cool. Be it by material, as you mentioned, or design.

[ptuomov]

Why wouldn't the spray cool mostly air instead of the manifold runner, if the spray pattern is a narrow cone and there's a clear line of sight to the intake valve? The reason why I am questioning this is that cooling or heating the intake manifold makes very little difference to the air temperature entering the head when the engine is running at WOT. This is a question, not a statement.

Hotter intake manifold however seems to vaporize fuel on the wall better and the acceleration x-tau adjustment changes "seem" to be "necessary" based on "feel" -- no scientific evidence or measurements on that though. If a hot intake manifold vaporizes fuel better and doesn't make much of a difference to air temperature, it's not out of question in my mind that a hot intake manifold might in some cases make more power than a cold one. Comments?

[SchmidtMotorWorks]

Why wouldn't the spray cool mostly air instead of the manifold runner, if the spray pattern is a narrow cone and there's a clear line of sight to the intake valve? The reason why I am questioning this is that cooling or heating the intake manifold makes very little difference to the air temperature entering the head when the engine is running at WOT. This is a question, not a statement.

Hotter intake manifold however seems to vaporize fuel on the wall better and the acceleration x-tau adjustment changes "seem" to be "necessary" based on "feel" -- no scientific evidence or measurements on that though. If a hot intake manifold vaporizes fuel better and doesn't make much of a difference to air temperature, it's not out of question in my mind that a hot intake manifold might in some cases make more power than a cold one. Comments?

There may be something to this line of thinking.
When I have prototyped intake manifolds by 3D printing and then later cast the same geometry in aluminum I found that sometimes the aluminum manifold was down on power 25hp on a 500hp engine.
These were EFI manifolds with front facing inlets and injectors at the conventional location for Coyote Ford engines.
Measuring air temp at the throttle body, just before the front injector and just before the rear injector showed that the air temps became near equal within 2 seconds of WOT on an aluminum manifold. This was important because the air temp was always assumed to be the reason for the performance difference.
The biggest gains I found with aluminum manifolds was polishing the inside to 320 grit paper. By this I mean properly proceeding through coarse grits and not leaving any scratches from previous grits. In other words a shiny surface with deep scratches in it does not work.

[David Redszus]

Why wouldn't the spray cool mostly air instead of the manifold runner, if the spray pattern is a narrow cone and there's a clear line of sight to the intake valve? The reason why I am questioning this is that cooling or heating the intake manifold makes very little difference to the air temperature entering the head when the engine is running at WOT. This is a question, not a statement.

Fuel spray that strikes the manifold wall stays on the wall until removed by rivlets or evaporation. If by evaporation, the manifold wall is cooled well before the air stream. Measurement of inlet air temperature once fuel has been introduced is very difficult, if not impossible by ordinary means.

The main problem with cooling the wall is that the full potential benefits of evaporative cooling are not realized.

A pencil beam fuel spray down the center, with minimum wall contact is ideal. Unfortunately, there is a nasty bend found in the inlet port.

One significant benefit of direct injection is the elimination of air displacement by fuel vapors thereby increasing air mass flow.