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Enzo777

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I am trying to find peak pressure of a diesel engine injection pump.. It doesn't have to be exact but +/- 1000psi would be fine. The basic principle is the same as an engine. Piston goes up and covers a fill hole, once it is covered the only way it can flow fuel is through the injector, so injection starts the instant that fill hole is covered. The injector itself will not open until 4500psi and there is a delivery valve (check valve) at the top of the piston to prevent the pressure from bleeding back and having to build pressure throughout the injection line which would delay timing and cause bad things to happen. I attached a pic of this for better understanding.

Also there is a cam with a roller tappet that rides the cam profile. On the actual pump I used a dial indicator and measured the lift of the plunger at every single degree of cam rotation. From this I found that from one degree to the next the biggest difference was 0.017 inches, so this would be the peak piston velocity per degree.

To get a flow calculation, I just assumed it to have a constant "pumping" lift rate of 0.017" per degree the entire time. I realize this is not true by design but being all I want to know is the peak pressure at this velocity, I decided to use it get a flow measurement. So I took 0.017*360 to get a full pump rotation since it is gallons per minute I'm after and the pump uses revolutions a minute. This gets me to 6.12 of total virtual stroke at the continuous 0.017" lift per degree velocity.

Use that as the height for the volume of a cylinder formula and I end up with 1.259 cubic inches. The piston is 13mm so I did all the conversions there.. Multiply that by 2000 for 2000RPM and you get 2518.2 CI per Minute. Multiply by 0.004329 to get GPM and you're at 10.9GPM

Then it goes through a little 2ft injection line 0.120" diameter, then through the injector and out the tip. The pintle in the injector will not open until 4500psi is reached. There are 5 holes in the injector each 0.035" in diameter and that comes out to a combined cross sectional area of 0.00481 sq. in.

Apparently this needs to be in sq. ft. for a formula I found so that converts to 0.0000334067 sq. ft. I then converted the GPM from earlier into Cubic Feet a second and got 0.024289. Then I divided that by the hole area and got the final velocity of 727 fps.

Density of diesel is 1.64 slugs. Using pressure formula of 0.5 * density * velocity and converting to PSI I get 3010psi.

The injector doesn't pop until 4500psi though so I assume since it is a positive displacement pump it would be shoving 3010psi out in addition to the 4500, for a total peak pump pressure of 7510psi.

This seems very low to me and if I use a smaller injector which is what was on the engine stock, I'm seeing almost 200,000psi. So I think my math is wrong somewhere.

I attached a spreadsheet that I've been doing this math with.

Anyone that can help is much appreciated.

Also there is a cam with a roller tappet that rides the cam profile. On the actual pump I used a dial indicator and measured the lift of the plunger at every single degree of cam rotation. From this I found that from one degree to the next the biggest difference was 0.017 inches, so this would be the peak piston velocity per degree.

To get a flow calculation, I just assumed it to have a constant "pumping" lift rate of 0.017" per degree the entire time. I realize this is not true by design but being all I want to know is the peak pressure at this velocity, I decided to use it get a flow measurement. So I took 0.017*360 to get a full pump rotation since it is gallons per minute I'm after and the pump uses revolutions a minute. This gets me to 6.12 of total virtual stroke at the continuous 0.017" lift per degree velocity.

Use that as the height for the volume of a cylinder formula and I end up with 1.259 cubic inches. The piston is 13mm so I did all the conversions there.. Multiply that by 2000 for 2000RPM and you get 2518.2 CI per Minute. Multiply by 0.004329 to get GPM and you're at 10.9GPM

Then it goes through a little 2ft injection line 0.120" diameter, then through the injector and out the tip. The pintle in the injector will not open until 4500psi is reached. There are 5 holes in the injector each 0.035" in diameter and that comes out to a combined cross sectional area of 0.00481 sq. in.

Apparently this needs to be in sq. ft. for a formula I found so that converts to 0.0000334067 sq. ft. I then converted the GPM from earlier into Cubic Feet a second and got 0.024289. Then I divided that by the hole area and got the final velocity of 727 fps.

Density of diesel is 1.64 slugs. Using pressure formula of 0.5 * density * velocity and converting to PSI I get 3010psi.

The injector doesn't pop until 4500psi though so I assume since it is a positive displacement pump it would be shoving 3010psi out in addition to the 4500, for a total peak pump pressure of 7510psi.

This seems very low to me and if I use a smaller injector which is what was on the engine stock, I'm seeing almost 200,000psi. So I think my math is wrong somewhere.

I attached a spreadsheet that I've been doing this math with.

Anyone that can help is much appreciated.