Chaotic_FC

i will be building a direct injection fuel system for my engine.
the fuel injectors will have a machined piece to house them side by side in one of the coolant passages near the top of the rotor housing.
I have a couple of questions to ask those who are knowledgeable.

one, how wide are injectors at there widest point? I don't have any around me right now, and need to know if i can fit 3 in a row, or if there is only room for 2. (the rotor housing is 3 inches wide, and i need there to be some metal support left, mabey an 1/8th of an inch)

two, if i only have one firing that is off center, as apposed to directly in the middle of the rotor housing. Will this be bad, or would it be ok to have the fuel entering off center only during low RPM, not into the center of the rotor housing directly.

i need to know these things relatively soon because i am about to start work with my machinist and need to make my parts' blueprints.

thank you in advance

jfolley

iTrader: (1)

What kind of injectors will you be using? I'm pretty sure that regular injectors can't handle the intense environment inside the combustion chamber. Look at some diesel forums... they have been using direct injection technology since the beginning of time.

Sounds like a cool idea, good luck with the build!

-John

Chaotic_FC

thank you

they wont be in the combustion chamber, just on the top of the rotor housing. so they wont experience very high compression.

i will be using some 1600cc injectors, mabey 800ccs for primarys

philiptompkins

iTrader: (4)

the idea is good, the implementation is fail.

classicauto

iTrader: (3)

They will be experiencing compression for sure, and it'll likely be higher then the fuel pressure.

I second the notion to read up on diesel injectors, or try to dig up info on what Mazda's using in the direct injected 16X engine.

rotarygod

iTrader: (1)

There are a couple of things to worry about with DI and it only gets worse the closer you move the injectors towards the spark plugs. The first thing is with injector open and close times. You absolutely must now have them open and close at certain times. It can't be like in the intake manifold where you can keep them open as long as you want without worry. This is all a carb does. Of course FI makes control better but you still need to deal with this.

The second thing to deal with is the fact that since you need to control how long the injectors are open for and when, you have limited time to be spraying fuel into the engine. You can no longer think in conventional terms of duty cycle as you don't have as much time to work with. Since you need to inject fuel over less time, you need more pressure. A larger injector is one way but pressure is necessary to do it properly. The farther around the chamber you get, the more and more pressure you have from compression. You need to raise the fuel pressure just to stay ahead of this but you definitely need to do it for proper control.

You also need to factor in how large the injector hole(s) will be in the chamber. They need to be as small as possible as pressures on each side of the apex seal in opposing chambers is very different. You don't want the hole large enough that some gas can go around the apex seal to bleed off a little bit of pressure. This is why the spark plug hole sizes are like they are. The trailing plug location is in a very unequal pressure location when the apex seal is crossing that location but the pressure is about equal when the apex seal crosses the leading spark plug hole which is why it can be larger.

I'm not sure what engine management you are using but if all you are going to do is just locate the injectors there and do nothing else, it's not going to work very well. I'm not saying it won't work. Just not well.

You need an ecu advanced enough that you can tell it at what crak rotation degrees you want the injectors to fire. Then you need to figure out at what point is a good point to get them to start firing. You need to figure out what the latest you can close them is and then figure out what this would be in terms of duty cycle so you don't go over it. Finally you'll want to raise your fuel pressure to help. You don't need to go stratospheric but 200 psi or so should be a good starting point. Then you'll have to look into a fuel system to match.

If you can do all of this I say go for it and report back. However don't just expect a simple relocation of the injectors to work well. I think you'll be quite surprised.

Chaotic_FC

i believe i will be using haltech e11v2
I am aware of having to make an small hole for the injector, probably abut an 1/8th of an inch will be about right. it will also be relatively close to the intake, so there shouldn't be THAT much pressure increase. It will only house the primary injectors, for this engine will be running high boost on the street, so i want good fuel efficiency at lower load and power levels. At higher boost there will be a traditional set of injectors in the manifold, also to help with the cooling effects that the fuel will have.
do you really think that it will be necessary to use fuel pressure as high as 200 psi? why not just keep it at around 80 psi, and since they are primary's, they wont experience very much boost at all, and therefore should be ok at that psi level... well, at least thats my theory.

I will defiantly be doing this, but as far as my knowledge in this field, i dont know much more than what i have shown.. so any information out there that could help, please let me know.

Chaotic_FC

This is what i was thinking as far as injector placement

fritts

iTrader: (5)

DI from the papers I have read normally only controls injector pulsewidth a low load. Anywhere beyond that the pressure is used to control the amount of fuel injector. You probably would gain the same atomization effects by just injecting at higher pressures in the stock locations.

On the pressures required I think you need to figure out just how high the pressures are before thinking you can get away with 80 psi. Also depending on how much opening your give the injector and the rotors relationship to the end of injection you may be seeing much higher pressures. You could also see combustion gases running through the injector if placement is not correct.

Chaotic_FC

i was thinking possibly using this regulator
http://www.aeromotiveinc.com/prod_im...50-1-large.jpg


it says it goes up to 100PSI, mabey in combination with their eliminator pump i could get where i want to be.

rotarygod

iTrader: (1)

You don't HAVE to go up to 200 psi. I just threw that number out there. Higher is better overall though. Common rail diesel engines which are direct injected run upwards of 20,000+ psi which is insane but even the direct injected gasoline MZR Mazda engine runs over 2000 psi.

If you could get by running 100 psi in conventional injector locations you'd be good. More pressure when it comes to fuel is a good thing provided everything else is taken into account. I run 50 psi currently on my engine and it's nothing more than a streetported 6 port. The catch that no one can comprehend though is that I purposely only run 2 injectors where I used to run 4. That's another discussion though.

rotarygod

iTrader: (1)

These are the rotor housings out of the '95 Racing Beat Bonneville land speed record 3rd gen. Check out the injector location. The first time I saw these housings I completely missed it but last year I made sure to take some pictures. I'm not sure what their fuel pressure was but it was probably pretty close to standard levels.

Chaotic_FC

check that out
thats basically what i am looking to do
the only real reason for it is because i want to get decent mileage, and peripheral ports have too much overlap to get good mileage with a regular port injection.. well, at least at low rpms.

digitalsolo

iTrader: (2)

Just caught this thread....

DI is ~2000 PSI, and not at all possible with the methods you're discussing, period. Do some reading.

Are you guys sure that Bonneville motor isn't just injecting the fuel into the chamber "off compression" so that when it spins to the next face, the air charge is already fuel filled, and THEN is compressed and fires?

Direct injection requires fuel pressures that exceed the combustion chamber pressure during combustion, or it won't be capable of injecting anything. Relative pressure and all.

This is the same reason you use a boost referenced fuel pressure regulator on a turbo car. 58 psi of fuel pressure into an intake at 15 psi of boost = a net of 43 psi of fuel pressure, so you have to raise the rail pressure equally to the manifold pressure...

Chaotic_FC

well, my primary injectors are gunna have roughly double manifold pressure on them, and my secondaries will have a tad over ambient pressure on them. at the very most i would be running 40 lbs of boost.
i am thinking of having 8 1600cc injectors total.
4 where the boniville car has them, and 4 where i drew them in red.
if i run 100psi of pressure, my primaries should be getting the equivilent flow of a 800cc injector at maximum boost, and my secondaries should be flowin around 2500ccs.

this is what i'll be doing with my fuel setup. My machining is about to start, so i hope i got things right.

Zero R

iTrader: (1)

Beat me to it, I have pics of housings like that somewhere.

philiptompkins

iTrader: (4)

sorry man, I really don't think you understand.
You need to do more reading on how direct injection works... For a direct injection setup compensating for boost pressure is like pissing on a forst fire. There has been some very good info posted in this thread, you should read it.

Chaotic_FC

it will not be the kind of direct injection that goes directly into the combustion chamber. It will be right above the intake port, in a part of the rotor housing that does not experience very much compression. there is absolutely no need for the kind of fuel pressure that a normal direct injection setup has, simply because it would not be a regular direct injection setup. The boniville race car has the same setup as i am planning, and from the looks of it, it has regular injectors, at what is probably a slightly higher fuel pressure.

I can see why you'd think i am confused, but i believe that you don't understand my direct application.

turbodsm17

turbodsm17

cpubugs

http://www.sae.org/technical/papers/930677 some one buy it and then discreetly repost it.