Newbie question - batch vs sequential

[ckucia]

I understand the difference between batch and sequential injection conceptually.

I've been researching Megasquirt and have a question to refine (or maybe confirm) my understanding...

Assuming a port-injected, four cycle engine;

If a batch system is firing the injectors 3x when the intake valve is closed on an individual cylinder for every 1x when the valve is open, does this mean that a sequential system is going to send 4x the fuel in one injector firing event as opposed to batch?

In other words, is the batch system, in a sense, averaging the total fuel requirement for one combustion cycle across four injector firings, where a sequential would send all the fuel in one injector firing?

Or, is the sequential just able to better "tune" the same four (or whatever number) of injector firings per combustion cycle to the individual cylinder?

[78Spit1500Fed]

I understand the difference between batch and sequential injection conceptually.

I've been researching Megasquirt and have a question to refine (or maybe confirm) my understanding...

Assuming a port-injected, four cycle engine;

If a batch system is firing the injectors 3x when the intake valve is closed on an individual cylinder for every 1x when the valve is open, does this mean that a sequential system is going to send 4x the fuel in one injector firing event as opposed to batch?

There's one very important concept you're missing here. In a batch system, the injections aren't timed to anything at all. You say the injectors fire 3x when the intake valve is closed and 1x when it's open, but that's not the case. The simple fact of the matter is that with 1 squirt per cylce set, the injector will fire 1/4 of the fuel required 4 times. They may or may not occurr when the valve is open/closed/opening/closing... see?

A sequential system does indeed need to get that much fuel in all in one squirt. At some point, that's not possible and the engine begins to behave like a batch-fire one. At idle and cruise at low RPM's is really the only opportunity for the sequential system to do it's magic.

In other words, is the batch system, in a sense, averaging the total fuel requirement for one combustion cycle across four injector firings, where a sequential would send all the fuel in one injector firing?

Exactly.

Or, is the sequential just able to better "tune" the same four (or whatever number) of injector firings per combustion cycle to the individual cylinder?

Under light load and at idle, the first scenario is true... all the fuel gets one big injection while the valve is open, or just before. Above those loads/RPMs it's a different story.

-Brian

[ckucia]

Thanks Brian,

I think I understand now.


Learning about MS really forces you to take you understanding of engines and FI to a higher level than when you're just keeping OEM systems running.


Is there any possibility of the fuel puddling or coming out of suspension between the injector and the valve when the engine is cold and idling? I'm sure it would be minor, but I'm just curious. I assume once the engine is warm, any fuel would be vaporized by the heat of the intake runners and head.

[erikbuzz]

Yes, this can and often does occur. This is the reason that using a high RPM intake on a low RPM motor is not a good idea. If the mixture isn't moving quickly through the intake manifold and runners(carb, TBI, or TPI) the fuel will come out of its atomized state and settle on the walls of the intake system. How does this effect your engine's performance? It really depends on the engine and the extent of the problem. All engines will experience it to an extent, but it effects are only noticiable when parts and intake are way too large for the engine's intended use. This can potentially cause low RPM bog, poor mileage, decreased drivability... the list goes on.

Will there be a noticible difference in power between batch and sequential injection? no. The effects of fuel pooling are not very drasticly effected by when the injector fires.

[ckucia]

That makes sense.

I am considering fabbing up my own manifold for a fairly low-rpm engine (torque peak at 2500, max RPM around 5000). Are there any guidelines for building an appropriate manifold?

My initial guess would be that long runners would help to keep the air moving and it appears that many port-injected factory manifolds (GM TPI, LS1, Mustang 5.0) had long runners off a central "log".

Of course, my guesses are often wrong...