Originally Posted by HOHN

I believe you are referring to a PINTLE, correct?

Injector flow is ultimately determined by only two factors: the hole area and the injection pressure. The use of additional, smaller holes seems to be only of marginal significance in power production and atomization.

Cummins calls this spec "cupflow"-- literally how much fuel will flow through the nozzle tip under standardized test conditions. Units are in Lb/hr.

But POWER production for a given cupflow has a good amount of variance. There are simply MANY factors at work that determine the benefits of a certain nozzle design relative to flow.

Injectors are designed to work with a certain piston crown, in general. This is because the crown affects how the flame propagates through the cylinder, and thus how cylinder pressure and temp will rise relative to time and crank position.

If I advance the timing of the injection event, the ideal spray angle changes, and I have to inject the fuel farther down into the cylinder to preserve the relationship between piston bowl position at SOI (start of injection).

Flow VELOCITY matters a lot too. Consider Don's famous Mach 6s injectors. They flow a pretty good amount (which I don't know). They make tons of power. Yet they don't have 9 or 11 or 15 holes. They have 6 or 7, which is the same or less than a 7-hole RV injector.

Doesn't atomization suffer if you don't have more holes? Moreover, should better atomization make more power?

Yes and no. Atomization is important, but so is velocity. This is because a good portion of the "atomization" happens when the burning stream of fuel hits the piston crown and splashes all over the place.

This is why Don's early injector experiments with the 11 hole nozzle made great power and had good response until boost hit 40psi or so, then all of a sudden they would smoke like nuts and power would fall of radically. There was simply not enough velocity of the fuel spray.

Another huge variable is the shape of the injection pressure curve-- i.e., how the injector goes from pop pressure to closing pressure and all the points in between for a given volume of fuel.

This can actually have an affect on the RPM at which injection efficiency is optimized. At higher RPM, you have less time to inject the charge and you need a more aggressive rate of discharge (compressed timeframe). This is one of the reasons that larger injectors will seem to help an engine pull past the factory 24V 2700rpm defuel point, even without software manipulation like a Drag Comp would do. It's not that only reason, but it's ONE of the reasons.

The penalties to be paid with bad injector design can be pretty steep. Aside from engine failure if a Nozzle fails, you have the possibility of washing the oil off the cylinder walls and increase wear at the top ring reversal (already a high wear point because of the absence of a hydrodynamic oil wedge for the ring to ride on).

Nozzle tip temperatures have to be managed not only because of the effect on thermal fatigue (and thus, nozzle failure), but also because of possible coking when carbon fouls the spray holes.

There's a joke at Cummins that we wish we could make injectors out of carbon fouling, because it seems to withstand the erosion of fuel injection pressures over 2200 bar!


So, when a person take a simplistic "dimension X hole count=hp" view of injectors, it may seem to make sense.

But a serious analysis of the injection process reveals that there's a heck of a lot more to it than that. That's why, in some cases like with Don't injectors, it's just a lot easier to accept the manufacturers advertised HP rating, assuming it's valid.

With a quality injector maker, the HP rating is pretty valid. With a company whose research is a little less stringent, things can get pretty dicey.

Justin

Originally Posted by braxton357

Your comment on carbon fouling brings up a question of mine...How would cummins suggest one cleans a used injector?