gmctd wrote:
Any official body in the Diesel industry states that all Diesel fuel is always no less than 10% aerated - you can see this in a clear container - now, accepting that (or not, atcmb)
Perhaps there is some clarification required for the benefit of those unfamiliar with physics. When many use the term "aeration", they are referring to two separate phenomena. True Aeration is the presence of physical bubbles in the liquid under discussion. These bubbles may be quite small but they are still bubbles. A liquid can never have 10% of it's volume consist of bubbles without correctly being called a foam. The other phenomenon which is often incorrectly included in the term "aeration" is Gas Saturation. Gas saturation is also air in the fuel, but it is not in bubble form. It is the concept of the individual molecules of gas slipping in between the liquid's larger molecules. Diesel fuel can never have 10% aeration and still be a non compressible liquid , but it can have up to 100% saturation.
All of this is fascinating and entertaining but is also mostly irrelevant in a pressurized fuel supply system. It becomes relevant in Draw type systems where there is a pressure drop such as that found at the restrictive fuel filter which can either cause gas to come out of solution, or can mechanically "strip" the air bubbles out of the fluid. In the OE CRD fuel system there can be a pressure drop of as much as -138 kPa. This causes the fuel to shed it's excess gas into the fuel manager head or other high point in the system as a large bubble.
In the case of a Holley Blue LP, the pressure rise can be as much as 103 kPa, which will raise the Partial Pressure Equilibrium point or "saturation point" by a factor of 1. This is assuming that the diesel was already at 100% saturation, which would be highly unlikely. If the saturation point is doubled, there is no possible way for ANY gas to come out of saturation and form bubbles at the temperatures which we are encountering. All visible aeration is also compressed to half of it's original size which causes it to be driven into saturation almost instantaneously, where it can cause no problems.
gmctd wrote:
and if you think about it, the engine consumes about 3gph at 60mph at 20mpg - if the lift pump pumps 45gph at rated pressure, returning the excess to the tank, that would mean the full 20 gallons in the tank would be recirculated twice per hour.....if the tank volume were constantly replenished - which it is not: fuel level is constantly dropping while the engine is running, and is constantly warming when the engine is running and is constantly sloshing while the vehicle is moving - sloshed Diesel fuel is aerated Diesel fuel
Again, this is irreverent to what we are talking about.
http://en.wikipedia.org/wiki/Aeration The sloshing is indeed causing more aeration, but the aeration cannot ever pass 100% saturation no mater how much it is sloshed. What can happen is that with enough agitation foam can be formed on the surface of the fuel.The sloshing is entirely determined by the movement of the vehicle. I have yet to encounter a rough enough road to cause my fuel to foam uncontrollably. The amount of fuel being returned to the tank cannot in any way affect the amount of sloshing which occurs from driving down the road. As long as the return is below the level of the fuel, such as in the CRD, no increased aeration can occur.
gmctd wrote:
- warm Diesel fuel is more easily aerated - while we see the results of aerated fuel in the oem system, we don't see much of the effects of aerated fuel due to the miniscule volume consumed per per minute at low rpm , and while we cannot do anything to prevent aeration, there is no benefit to be had by increasing any process contributing to aeration
Yes. According to henry's Gas Law, As the temperature of a liquid increases, the solubility of a given gas decreases. This causes any excess gas saturation to leave the fluid usually at the liquid/atmosphere interface. but it can appear as visible bubbles on the sides of a container if it happens quickly enough. Any bubbles big enough to be visible in the liquid itself, will quickly rise to the surface where they pop and return to the atmosphere.
http://en.wikipedia.org/wiki/Henry%27s_Law If the fuel circulation is increased at the Fuel/air interface, saturation equilibrium is more quickly achieved and thus, aeration is decreased, which is a good reason for more fuel flow within the fuel tank. I have never seen fuel heated quickly enough to cause persistent foam on the surface of the fuel, even when brought to a boil.
gmctd wrote:
- the engineers put a lot of thought into designing the in-tank pump for the Cummins trucks (after they were forced to do so by the incredible volume of VP44 failures!!), and the output of that pump is spec'ed to service a larger displacement engine (by twice) with higher output (by twice) than our little baby Diesel - thusandso, so far it has only improved operation over the as-supplied configuration - thus, my usual recommendation for the factory pump, or a pump with similar low volume low pressure specs - merely throwing a Carter or Holley pump at Diesel fuel is not a good solution
As with nearly all automotive engineering, the designers came up with a product which would perform adequately for functional operation. Adding a higher capacity pump would have added more expense to the bottom line . That does not mean that a higher fuel flow would have been detrimental the the CP3. It just means that the Cummins lift pump is adequate for the normal life expectancy of the CP3 IP. Any added cooling of the CP3 can only increase it's life span. Adding a more robust alternator would increase it's life but would also involve more expense in production. It's all a balancing act.
gmctd wrote:
The Carter\equiv pumps do not return excess fuel to the tank - the excess is continually recirculated back around to the inlet side (think about constantly recirculating a small portion of 3gallons per hour flowrate at 45gph pumped rate), not bad for gasoline, not good for Diesel fuel due to aeration - the CP3 lift pump does similar, but is orificed to bleed entrained air to the tank-return outlet, then excess fuel - air is less dense, will pass where fuel cannot B4 fuel pressure overcomes spring-loading to flow thru - this accomplishes air-free fuel recirculation to the inlet to help maintain the ~80psi housing pressure, fed to the injection pump section - fyi, the Cummins CP3 runs ~180psi housing pressure
As you point out, the CP3 has a built in feature that causes any entrained air to be routed back to the tank. Adding a Holley, Carter, etc.. cannot make it suck more bubbles into the IP. besides which, the circulation within the lift pump can have no effect on aeration, seeing as how aeration can only occur where there is an air/fuel interface.
http://en.wikipedia.org/wiki/Aeration The inside of the Carter/ Holley has no such air supply from which to add more aeration. Even it the Holley/Carter could add more aeration, it would be bled back to the return line by the CP3 inlet.
At any rate all of this is academic to me because I don't like the increased noise of the Holley. When my inline Airtex fails, I will install the Cummins option (thanks for all the work on that by the way) because I like it's quality, the fact that it provides pressure all the way from the tank, and is even quieter than what I currently have.
If someone wanted to install a Holley and can put up with the noise, more power to them. It should only improve the life of the IP. The non flow through design is something to consider as well.
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The plumbing is less then ideal for a vacuum system that CRD's use 
4/11)..Bus gone to Scarp 8/23/11 
15 psi i thought was too high 
