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Old 3rd March 2011, 01:12   #61
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Default Re: FIP Flop

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Originally Posted by Sutripta View Post
Hi,
You mean throttling the input? Will that not lead to flash boiling of the fuel, and maybe even cavitation?

BTW, what is the nature of the pump?
Hi,
Throttling the input, YES. The following video should explain you if it results in cavitation or not. it is CP1H which is similar to CP1(first generation with PCV control) and modified by adding a metering unit to it.


the metering unit is solenoid valve and quite similar to the shutoff/release valve that we have in distributor pumps which is located on the suction side of the plunger element. in this case also it should result in cavitation when the fuel is shutoff at suction side. the engine dies as the plunger cannot pull and hence cannot deliver the fuel and it can neither create any cavity.
similarly the metering unit controls the flow at the suction side for the CR pump.
you can have a closer look at the metering unit in this video.
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Old 3rd March 2011, 15:44   #62
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Default Re: FIP Flop

^^^
Hi,
Thanks for the clips.

However, I for one, can't make out anything about the topic under discussion. All I see is an animation of a radial piston pump. Can't even make out that the input (check) valve is controlled.

In a hot environment, a sudden reduction of pressure is going to cause the volatiles to boil off. (Does anyone have the vapour pressure chart for commercial HSD). Is it undesirable or harmful on its own? Unlikely, until it causes some sort of vapour lock.

Cavitation, I don't think even the CFD people can answer. However, that would be harmful. And I think inlet side metering increases the chances of that.

When we use a similar scheme to stop the engine, well then everything stops. If nothing is working, nothing gets damaged.

Regards
Sutripta
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Old 3rd March 2011, 18:14   #63
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Default Re: FIP Flop

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Originally Posted by Sutripta View Post
^^^
If nothing is working, nothing gets damaged.
ROFL: Correct and you are stranded in the middle of nowwhere...

IMO, the animations were pretty clear showing how cavitation is solved by CR pumps.

Maybe the experts can explain that in detail..
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Old 3rd March 2011, 20:16   #64
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Default Re: FIP Flop

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ROFL: Correct and you are stranded in the middle of nowwhere...
Why stranded? You stoppem, you startem.

Quote:
IMO, the animations were pretty clear showing how cavitation is solved by CR pumps.
I don't get it. Could you please point out what to watch for, when (seconds mark), and give some explanatory notes.

Regards
Sutripta
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Old 3rd March 2011, 20:34   #65
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Default Re: FIP Flop

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Originally Posted by Sutripta View Post
I don't get it. Could you please point out what to watch for, when (seconds mark), and give some explanatory notes.
Yes, that would be great, please share your understanding of the video.

@Star, do you have any links to videos with explanations?

Spike
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Old 3rd March 2011, 21:28   #66
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Default Re: FIP Flop

Quote:
Originally Posted by Sutripta View Post
Could you please point out what to watch for, when (seconds mark), and give some explanatory notes.
Quote:
Originally Posted by SPIKE ARRESTOR View Post
Yes, that would be great, please share your understanding of the video.

@Star, do you have any links to videos with explanations?

Spike
Watch from 0.24 to 1.09 to see a drop travelling inside the pump.

Honestly I think Vijay Reddy [star_aqua] is the man to give correct explanation!

My doubts are at 1.28 and 1.58 !!!!

Last edited by headers : 3rd March 2011 at 21:32.
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Old 3rd March 2011, 23:14   #67
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Default Re: FIP Flop

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Originally Posted by headers View Post
Watch from 0.24 to 1.09 to see a drop travelling inside the pump.

Honestly I think Vijay Reddy [star_aqua] is the man to give correct explanation!

My doubts are at 1.28 and 1.58 !!!!
Hi,
My understanding: the drop traces the flow path. Done by an animation tech, with no regard for timing/ phasing. But even if one does not nitpick on those, I still don't get it. I mean avoiding conditions conducive for cavitation.

1:58 or 1:48?

Vijay will post when we are trying to get some sleep. It's like playing postal chess!

@ Vijay: The new pump seems to have 2 pistons at 90 deg. The cam has 2 lobes. So it will behave like a radial piston pump with 4 pistons. Won't that lead to extreme pulsations?

Regards
Sutripta
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Old 3rd March 2011, 23:38   #68
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Default Re: FIP Flop

Quote:
Originally Posted by Sutripta View Post
^^^

When we use a similar scheme to stop the engine, well then everything stops. If nothing is working, nothing gets damaged.
Hi,
You did not consider the drop of engine rpm from 800 to 0. the pump will make at least few rotations before reaching 0rpm. anyways that is negligible.

Quote:
Originally Posted by SPIKE ARRESTOR View Post

@Star, do you have any links to videos with explanations?
No spike :( i did not find anymore videos that is available with explanations, but i try my best to explain what i know.

Quote:
Originally Posted by headers View Post
Watch from 0.24 to 1.09 to see a drop travelling inside the pump.
My doubts are at 1.28 and 1.58 !!!!
the video is divided into 3 parts, before that the color coding is
GREEN: lubrication circuit
YELLOW: low pressure circuit
RED: high pressure circuit

at every part of the video, please observe the white bright light which will trace all the above mentioned circuits one at a time.

0:25 to 1:09, the first part shows the fuel flow from inlet on low pressure side->metering unit->plunger pump -> exit from high pressure side.

1:09 to 1:28 and 1:30 to 1:55, Second part shows the relief valve for excess fuel and the lubrication circuit.

2:22 to 2:40, Third part shows the functioning of the metering unit.



EDIT:
Quote:
Originally Posted by Sutripta View Post
@ Vijay: The new pump seems to have 2 pistons at 90 deg. The cam has 2 lobes. So it will behave like a radial piston pump with 4 pistons. Won't that lead to extreme pulsations?
This CP4 seems to be based on CP2 which comes with two inline pistons. These pumps are used for heavy duty engines. 6 cylinders and above. But the pulsations are taken care in the cam profile. i don't think it is 2 lobes, it may be 2 in CP4. but it is 3 lobes in CP2. That is one of the reason we have 3 radial pistons at 120 deg apart from each in CP1 and CP3. but this 3 radial piston pump is mainly used for passenger cars and light duty commercial vehicles. it is 3 times pumping per rotation and in CP4 and CP2 it will be 2x2 and 3x2 pumping per rotation respectively. at least 3 times pumping per rotation will reduce the pulsation. The cam profiles are made in such way that the pulsation is reduced to max possible.

Last edited by star_aqua : 4th March 2011 at 00:12.
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Old 4th March 2011, 00:34   #69
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Default Re: FIP Flop

^^^^
Hi,
Cams are commonly either tangential or mushroom (constant velocity or acc). However, that is not the point. For radial or swashplate piston pumps, one needs an odd number of pistons to reduce pulsations. 3, 5, 7 etc. Check the number of pistons in an AC compressor.

Am sure pulsation is not a problem in this design. Solved how?

Regards
Sutripta
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Old 4th March 2011, 00:55   #70
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Default Re: FIP Flop

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Originally Posted by Sutripta View Post
^^^^
.

Am sure pulsation is not a problem in this design. Solved how?
There is overlapping delivery strokes between the two adjacent plungers. is it not possible?
in the first video from 0:08 to 0:17, please observe the movement of the eccenter.
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Old 4th March 2011, 06:16   #71
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Default Re: FIP Flop

^^
Hi,
The first is a 3 plunger design, an accepted norm.

But you are right.

Quote:
Originally Posted by star_aqua View Post
i don't think it is 2 lobes, it may be 2 in CP4. but it is 3 lobes in CP2.
In the second design, a trilobe cam is perfect.

Now back to why input side metering, and then to the nature of Diesel combustion!

Regards
Sutripta
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Old 4th March 2011, 09:21   #72
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Default Re: FIP Flop

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Originally Posted by Sutripta View Post
^^
Now back to why input side metering, and then to the nature of Diesel combustion!
Sir, I am getting confused with your question -

If metering is not on the input side, where will it be?

My understanding is that the electric pulse from the engine ECM triggers the pump to meter a certain quantity of fuel based on a host of other parameters from various sensors.

If metering is not done on input side, where will it be from?
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Old 4th March 2011, 12:20   #73
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Default Re: FIP Flop

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Sir, I am getting confused with your question -

If metering is not on the input side, where will it be?
Vikram, his question is valid and anybody would still think why there is no chance for the cavitation.
@sutripta: why do you assume the plunger return springs are very rigid?
and why do you think the high pressure pump is also designed to suck the fuel? it is designed only to pump. the high pressure pump is always coupled with presupply pump. it could be geared or electric or both. but without presupply the high pressure pump will not work and will it run dry when there is no supply? NO it will not. the inlet valve of high pressure pump plunger will not open without the presupply pressure. the plunger return spring will only aid in filling the cavity quickly and the fuel is always pushed in by the presupply pressure.
the basic reason why the metering done on intake side is to reduce the load on the engine and also to reduce the heating of the complete fuel line.
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Old 4th March 2011, 14:08   #74
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Default Re: FIP Flop

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Originally Posted by star_aqua View Post
...but without presupply the high pressure pump will not work and will it run dry when there is no supply? NO it will not. the inlet valve of high pressure pump plunger will not open without the presupply pressure. the plunger return spring will only aid in filling the cavity quickly and the fuel is always pushed in by the presupply pressure.
So you mean to say the high pressure pump plunger will NOT open without the presupply pressure - Interesting

BTW, how many stages are there in the CR pumps and what is the difference between Audi / Skoda TDI versus the Common Rail adopted by the others?
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Old 4th March 2011, 15:34   #75
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Default Re: FIP Flop

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Originally Posted by star_aqua View Post
@sutripta: why do you assume the plunger return springs are very rigid?
......
the plunger return spring will only aid in filling the cavity quickly and the fuel is always pushed in by the presupply pressure.
That means that the plunger will float off the cam. The fact that a meticulously designed, precision engineered product would have that as a standard operating mode hadn't crossed my mind.

Quote:
Originally Posted by headers View Post
Sir, I am getting confused with your question -

If metering is not on the input side, where will it be?

My understanding is that the electric pulse from the engine ECM triggers the pump to meter a certain quantity of fuel based on a host of other parameters from various sensors.

If metering is not done on input side, where will it be from?
Considering you are no newbie, I'm confused by your confusion. So I hope I'm addressing the right question. As you know, in a CRDI, metering is not done by the pump, but by the injectors. Here we were discussing the means employed in controlling rail pressure.

Regards
Sutripta
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