Plenum fuel injection for reduced IATs?

[dwilliams]

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

Because you can get too much of a good thing, particularly on a humid day. It can get cold enough to ice up the intake tract. Then you'll have a very slow race car.

Icing is why most OEM intake carburetor and TBI manifolds have exhaust heat crossovers, "hot spots", or water jackets. Heck, I put a 2" spacer on a small block Chevy once, and it built up a thick layer of frost on the outside after idling for a while, even with the fan blowing hot radiator air over it.

If your engine management system doesn't have some means to detect and deal with icing, you'll eventually run into the proper weather conditions to promote icing. You'd need a humidity sensor to do it right; otherwise, you could watch IAT and diddle EGR.

[ptuomov]

There was a time when Porsche (I think) intentionally heated the fuel before injecting it, which sometimes resulted in spectacular explosions if there was a leak that led to immediate vaporization as the pressure went down. From memory, the system was banned. Then there were the F1 fuel injection systems that also run the fuel really hot and under some thousand(s?) bar or something, after which the rules were changed to maximum fuel pressure of 500 bar. I don't know if the extremely high injection pressures were also used to supercharge the engine near IVC, but that might be one motivation, too. The F1 system always sprayed into the trumpet that was extremely straight and you could see the valves from the trumpet.

[ptuomov]

So what does the math say? If the entire latent heat if evaporization cools the intake charge and thus increases density and if the vaporized gasoline displaced some oxygen, is the net effect more oxygen or less oxygen in a given volume?

[Truckedup]

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

Because you can get too much of a good thing, particularly on a humid day. It can get cold enough to ice up the intake tract. Then you'll have a very slow race car.

Icing is why most OEM intake carburetor and TBI manifolds have exhaust heat crossovers, "hot spots", or water jackets. Heck, I put a 2" spacer on a small block Chevy once, and it built up a thick layer of frost on the outside after idling for a while, even with the fan blowing hot radiator air over it.

If your engine management system doesn't have some means to detect and deal with icing, you'll eventually run into the proper weather conditions to promote icing. You'd need a humidity sensor to do it right; otherwise, you could watch IAT and diddle EGR.

From what I have seen, the icing happened at or near the carburetor venturi .On some it could block airflow and stall the engine..Pilots know about...The heated intakes also helped vaporize fuel at part throttle..

[MadBill]

So what does the math say? If the entire latent heat if evaporization cools the intake charge and thus increases density and if the vaporized gasoline displaced some oxygen, is the net effect more oxygen or less oxygen in a given volume?

Some years ago, David Redszus made reference to equations he had that would parse the opposing effects of charge displacement vs. evaporative cooling for various fuels and percentages of vaporization.

[Racer71]

The 410 sprint car engines use 8 injectors in the ram tubes to help with cooling then have 8 nozzles in the heads pointed at the back of the intake valves

[ClassAct]

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.

Then in your experience, at least with EFI a burr finish would be less than ideal. Or I'm not reading your post correctly.

[jmarkaudio]

So what does the math say? If the entire latent heat if evaporization cools the intake charge and thus increases density and if the vaporized gasoline displaced some oxygen, is the net effect more oxygen or less oxygen in a given volume?

Some years ago, David Redszus made reference to equations he had that would parse the opposing effects of charge displacement vs. evaporative cooling for various fuels and percentages of vaporization.

Can we see those? I'm inclined to believe at least for a high end NA drag engine even with gasoline that has low overall vaporization curves such as C25 you will see gains from early vaporization. The better you vaporize the fuel the better distribution will be, the leaner you can make the fuel curve, the less fuel there is to displace air. Considering AFR is a measure of the ratio of mass you would have to determine the actual mass of the small amount of fuel for each cylinder and figure how much volume it actually displaces, considering as well the density change from charge cooling due to the state change. Add to the fact that classes like Pro Stock work heavily to cool the engines, I'm told at or even below 70˚ before each run. Early vaporization becomes even more important when there is less engine heat available to aid early vaporization.

[jmarkaudio]

Understand too that very few have the capability to engineer fuel to work with a specific application that runs at a fixed temp.

[Rick!]

From what I have seen, the icing happened at or near the carburetor venturi .On some it could block airflow and stall the engine..Pilots know about...The heated intakes also helped vaporize fuel at part throttle..

My experience is similar to this. Along with high humidity such as snowing with temps at or near freezing, the expansion after the venturi created the condition to create condensate that froze on throttle blades and makes for unintentional cruise control and rich part throttle.

[ptuomov]

So what does the math say? If the entire latent heat if evaporization cools the intake charge and thus increases density and if the vaporized gasoline displaced some oxygen, is the net effect more oxygen or less oxygen in a given volume?

Some years ago, David Redszus made reference to equations he had that would parse the opposing effects of charge displacement vs. evaporative cooling for various fuels and percentages of vaporization.

Can we get a repost of that!

In any case, that's just one part of the proverbial equation. Better vaporization of the fuel can also increase combustion efficiency a fair bit, I believe.

[Warp Speed]

So what does the math say? If the entire latent heat if evaporization cools the intake charge and thus increases density and if the vaporized gasoline displaced some oxygen, is the net effect more oxygen or less oxygen in a given volume?

I dont know the math, or what it says, but we constantly measure intake manifold temprature. And I have never seen, under any circumstances, a hotter intake make more power. Actually, we go to great lengths ro keep the intake tract as cool as possible.
Same with fuel temp.....
Math says a hotter running engine should make more power, due to less heat loss in the system, and keeping more heat for work. But have yet to experience this either!?!

[RCJ]

We were making back to back pulls on the dyno last night, as fast as possible.As the temp increased hp when down.Any ideals on surface finish ,coatings ,plumbing air from outside the vehicle,etc.. to cool the intake and heads.

[ptuomov]

I think it's pretty clear that once the air and fuel has been mixed into a single homogeneous mixture, lower its temperature the greater the power that it makes. It's probably also the case that colder the air that goes into the manifold, the higher the power. What I'm not sure about is whether one makes more power having the fuel vaporize in the cylinder or in the intake runner. I am also not sure whether hot intake manifold surfaces make more power or less power, do they heat up the charge more and reduce power or help with vaporization and increase power or both?

[MadBill]

Referencing air-fuel to manifold heat transfer but in the opposite direction, I once compared inlet air temps just downstream of the throttle body in a TPI Camaro on a road course. Bypassing the TB coolant heating circuit produced a barely measurable 3°F. drop at 4-5,000 RPM WOT.