Injection pressure idea

[OLDBULL8]

I didn't say the DB2 was not capable of higher pressure. Yes a stock DB2 is capable of 5000 PSI. It's what the injector spring pressure is set at when it "POPS".

 

[FordGuy100]

What I'm asking is if when the injector pops, is if the DB2 is still pressurizing the fuel so that as the injector pops open, fuel pressure is still increasing throughout the whole system (neither declining, or staying even, but increasing in psi).

 

[OLDBULL8]

Look at it this way. You have a valve (injector) full of fuel and a hard line to it full of fuel, the IP capable of ~5000 PSI, the piston's in the IP have built up that pressure, now it's ready to release that pressure when the IP rotor reaches it's rotation point to the port that feeds that particular injector, in a micro second that IP pressure increases the line/injector pressure to whatever the injector spring is set at, then POP, the valve (pintle) closes, the IP also feeds low pressure fuel to the injectors thru interconnecting lines back to the filter and fuel tank to keep the fuel system full. An engine running at 2000 RPM, that cycle of (injection) happens about four times a second. That's the best I can explain it.

 

[hesutton]

I just wonder where he gets all that extra pressure from on an IDI IP. Me thinks he's confused between an IDI injector and a PSD injector.

I agree. That's not what happens. Have you ever tested an injector? Look at the pressure gauge. The pressure in the line and injector will build and nothing should come from in the injector (if it isn't a leaker). But, once the opening pressure is reached, it opens and sprays fuel until spring pressure is greater than the hydraulic pressure in the line and closes. Happens very quickly, but there is no way in the world "injection pressure" jumps to 10K or whatever. As soon as that injector opens pressure immediately starts falling in the injection line and the injector itself. It doesn't increase. Otherwise, the injector would never close and you'd fill your cylinders with fuel.


On Edit: We know Justin gave you that info. It's OK. No one is going to freak out.
Heath

 

[Matrix37495]

Lots of good info here. I saw on Stanadynes site that the DB2 is capable of "Peak Injection Pressures" of 11,400 psi. What do they mean by peak injection pressure, if its not the pop pressure?

 

[Matrix37495]

More requested postings....

please just post this as I typed it in here. I don't think I put anything inappropriate.

Then you have different schools of thought about how performance is effected by atomization in an IDI. The DPS school of thought is that atomization doesn't matter. Torque is increased by pooling the fuel on the precup walls which slows the burn and makes it last longer. The sacrifice there is that you can get an incomplete burn and more smoke.

I will start off with giving respects to Mel and the moose products. I don't think the moose school of thought is wrong, just different from my needs.

I will start off with a little lesson on how pre-chambered indirect-injection works.

In our engine the pre-cup occupies 40%+/- of the total cylinder volume. During the compression stroke, air from the main cylinder enters the precombustion chamber. At this moment, fuel is injected into the precombustion chamber and combustion begins. Pressure increases and the fuel droplets are forced through the small holes into the main cylinder, resulting in a very good mix of the fuel and air. The bulk of the combustion actually takes place in the main cylinder. This type of combustion chamber has multi-fuel capability because the temperature of the prechamber vaporizes the fuel before the main combustion event occurs.

Now that we all know exactly how IDI is supposed to work we can analyze the DPS school of thought. The DPS school of thought acknowledges that pattern is not as important as consistency and quantity. Less fuel is burnt in the pre-cup, and more sent into the main chamber where it can be put to use to make power. Another point that I will touch on later, but pertains here as well, is that DPS injection pumps increase injection pressure. My DB4 pump in specific is set for 14,000psi +/- which in itself is enough to cause auto-ignition as it enters the chamber.

As for pop pressure being negligible in the range we have to work with. Completely agree. The reason the DPS's are set @ 2100 vs 1800 is that is just that much quicker they will close after they are opened.

I agree. That's not what happens. Have you ever tested an injector? Look at the pressure gauge. The pressure in the line and injector will build and nothing should come from in the injector (if it isn't a leaker). But, once the opening pressure is reached, it opens and sprays fuel until spring pressure is greater than the hydraulic pressure in the line and closes. Happens very quickly, but there is no way in the world "injection pressure" jumps to 10K or whatever. As soon as that injector opens pressure immediately starts falling in the injection line and the injector itself. It doesn't increase. Otherwise, the injector would never close and you'd fill your cylinders with fuel.


On Edit: We know Justin gave you that info. It's OK. No one is going to freak out.
Heath

I will give you guys a quick lesson on how the DB2 works.

The DB2 has a single pumping element that feeds all injectors. The high pressure pumping action is carried out in a single barrel, which houses two opposing plungers operated by two rollers. These plungers are pushed together by a cam ring with internal lobes acting on the rollers and it is this action that pressurizes the fuel.
The number of lobes on the cam ring corresponds to the number of cylinders in the engine, so each thrust of the plungers by a pair of cam lobes results in a pulse of fuel to one particular cylinder injector.

The metering valve is actuated by the throttle lever at all engine speeds above idle and by the governor linkage, when the engine is at idle or maximum speed.
The metering valve flows a measured fuel quantity into the center of the hydraulic head where the distributor rotor is turning and from there the fuel goes to the center of the rotor, which has two inlets at one end and an outlet at the other end.
As the rotor spins, the inlets line up with ports in the hydraulic head and fuel is forced out into the pumping chamber.
The pumping chamber consists of two sets of rollers, shoes, and plungers, which rotate inside a cam ring. The cam ring has lobes for each injector on the inside.
The force of the fuel entering the pumping chamber, along with the centrifugal force generated by the spinning rotor, moves the plungers apart. The plungers move outward a by an amount directly proportional to the volume of fuel passed by the metering valve.
As the rotor turns, the cam ring lobes, squeeze the rollers together, which in turn push in the rollers. As the plungers are pushed together, they pressurize fuel until Injection pressure is reached.
The fuel at injection pressure is forced back along the center passage of the rotor and into the discharge port and released when the discharge port lines up with a injector line outlet in the hydraulic head.
As the single discharge port rotates with the rotor it lines up with each of the hydraulic head injector line outlets in a sequence matching the engine’s firing order.
Each injector outlet is connected to an injector nozzle by a high-pressure line. The injector pump varies the rate and quantity of fuel delivered to the nozzles as demanded by the throttle and/or governor.

The DB4 is basically the same, except instead of having 2 plungers and 1 barrel you have 4 of each.

Now, the injector does not dictate injection pressure. The only thing the injector dictates is the pop off pressure.

Ken grinds custom cam rings, advance mechanism, mods the metering blocks and so on to make the pump perform exactly as he wants. Ken's cam's are designed for higher injection pressure, and have much higher ramp rates to reach peak injection pressure faster, ect.

Remember, Ken has a flow bench, so all of these numbers are confirmed, not on paper.

As stated before, my current DB4 is built for 14,000psi +/-. Although the DB4 I'm using is setup for higher pressures than the stocker, the Turbo-cal DB2's are jumped up as well. I would be lying if I told you I remember exactly what Ken said the stock pumps were, so I'm not even going to take a stab at it.

Hope this helps guys,

Justin

 

[flareside_thun]

Peak injection pressure is the pressure that the pump is capable of producing.

 

[hesutton]

No offence/disrespect to Justin, but that pump stuff is from THIS ARTICLE. Read it if you are interested. Read several times myself. I not going to argue this as it really makes no difference to me one way or another but the injectors aren't seeing 10K of pressure. And, we are talking about pop pressure in this tread so again it's really just getting off on a tangent here.

Heath