Sequential(?) Fuel Injection

[DEWFPO]

I know what Port Fuel Injection is, I know what Central Fuel Injection is, but what the heck is Sequential Fuel Injection?

Thanks, DEWFPO

 

[Ferb]

The basic types of injection systems are TBI (throttle body), TPI/MPI (tuned port), SPI (sequential), and direct injection.

TBI uses an injector in the throttle body to act like a carb. Easy enough.

TPI uses a fuel runner, but fires all the injectors at the same time. This provides ~15% better power over TBI, but allows the fuel to sit on some valves for too long causing a possible carbonization.

SPI uses the same injector runner system as TPI, but uses individually firing injectors. When the proper time to fire the injector comes, that LONE injector fires. Better economy, better emissions.

That help any?

ferb!

 

[DEWFPO]

Thanks Ferb,

It's very clear now. But I have to wonder why a manufacturer would fire all 4,6 or 8 injectors when only one is needed at a time. I understand the 15% power improvement over CFI, but what about fuel economy and emissions? Seems very wasteful and inefficient (but simpler). Any thoughts?

DEWFPO

 

[Ferb]

When a TPI system fires, it really only has one or two injectors. These injectors fire into the injector-rail itself, which injects the fuel at the intake valve runner.

So in a V-8, the whole system fires once for every two revolutions. It doesn't waste too much fuel, but the fuel atomization isn't perfect. The fuel can be coming out of the injector when the valve opens (low atomization) or have been sitting for almost two engine revolutions (too much buildup).

But it's much cheaper to have one or two injectors and a metal rail, than 4, 6, or 8 injectors and fuel lines.

The emissions didn't go down drastically with the SPI over TPI, but it did make a dent.

ferb!

 

[ralan]

quote:

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Originally posted by Ferb:
When a TPI system fires, it really only has one or two injectors. These injectors fire into the injector-rail itself, which injects the fuel at the intake valve runner.

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The fuel rail supplies fuel to the injectors, not the other way around!! On Bosch systems, there is one injector for each cylinder. The injectors squirt fuel into the intake port, usually on top of the valve. I think they all squirt at once because of a limitation of the older microprocessors used back when the first MPI systems came out, in the late 60's.

 

[cryptokid]

it depends upon which bosch injection system you are refering to. cis (continous injection system) they all squirt at once. k-jet and d-jet i believe fire in banks of 2, a hybrid so to speak. l-jet i am not sure of. motronic fires individile injectirs, and of course the bosch diesel fuel injection fires individually into the head or prechambers.

 

[DJ]

Some of the older GM systems fires one bank at a time as in one side of the engine, I think the TPI was one of those so 4 injectors at once, computers have come a long way since.

 

[Gary Allan]

The Mopar MPI batch fires 3 cylinders at once for the 4.0 L6. The cam sensor in the distributor triggers it.

Batch firing is just easier to program. You need less switching circuits and less firmware.

quote:

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or have been sitting for almost two engine revolutions (too much buildup).

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Some allege that the "puddling" that you assert causes build up ...actually is used as a valve cleaning characteristic. That is, after warm up, the cool fuel hits the back of the hot valve and keeps it free of deposits. I'm not arguing with you ..just relaying the alleged advantage of "puddling".

 

[ralan]

quote:

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Originally posted by cryptokid:
it depends upon which bosch injection system you are refering to. cis (continous injection system) they all squirt at once. k-jet and d-jet i believe fire in banks of 2, a hybrid so to speak. l-jet i am not sure of. motronic fires individile injectirs, and of course the bosch diesel fuel injection fires individually into the head or prechambers.

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I think K-jet is CIS and squirts all the time. L and LH squirt once every two rpm's, unless its on a v-8, then it alternates cylinder banks once per RPM. Some other engines, i.e. v-6 and straight six may also use this scheme. The D-jet on my buddy's 914 alternates banks via an extra set of points beneath the ignition point plate in the distributor. (Old!!)

Sequential injection doesn't have an RPM restriction like TBI.

 

[Ferb]

quote:

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Originally posted by Gary Allan:
Some allege that the "puddling" that you assert causes build up ...actually is used as a valve cleaning characteristic.

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Oh no. I definately agree that at a "proper" firing time, the fuel can provide a necessary cleansing element. It also allows for more complete atomization of the fuel. Thats the biggest benefit to SFI-- complete control over how much the fuel is atomized.

ferb!