Is a "Air Seperator" really needed???

[Summit]

need to order a bigger/better (GDP392) pump like last week but need to know how important having the air seperator is. I am EXTREMLY hesitant about going with the 200gph FASS kit after my current pump but they seem to be the only ones with it. do we need this or not?? if so why.

 

[BLACKJACK]

Im not gonna try to sound like some expert but I think I gained mileage from that alone. Some people say no but withb the FASS 150 on there know the overhead reads 2. 5 mph higher at the same everything, speed, distance, everything than it did before it. I know the overhead aint exact but this is from one reading to the next. So "do you need it?" i dont know but I think "I" do if that is what created my gain.

 

[Mark Craig]

Summit,



Removing the air out of the fuel is a bigger deal the higher the fuel pressure goes, the CR trucks are much higher than the VP trucks so I would go with air seperation for sure.



Mark @ DPPI

 

[BRayls]

the way mine drains the rail. I think all the air I could get out before hand would help.

 

[drury]

I've brought this issue up a couple of times on this forum, and no one has given me a coherent explanation of the theory of why we need a fuel/air separator. The only thing air in the fuel does is make your CP3 work a little harder to compress it. IF you have a lot of air in the fuel and IF the FASS takes out the air and IF your performance is limited by your CP3 then a FASS might help by a small percentage. Once the fuel is put under high pressure in the rail, any entrained air has about . 02% of the volume that it had in the fuel tank, and all of the fuel that is commanded to go through the injectors will go through the injectors, FASS or no FASS. Once the fuel is through the injectors, the whole point is to mix it with air. I have heard of absolutely no convincing theoretical reason why a truck that was not CP3 limited should gain fuel mileage by use of a FASS. The overhead is notoriously unreliable. I went with the Glacier, and I have absolutely no relationship -- business or otherwise -- with Richard. If I was going to go with a FASS, I'd choose an Airdog instead based on the posts I've read on this forum.

 

[daytripper63]

I've brought this issue up a couple of times on this forum, and no one has given me a coherent explanation of the theory of why we need a fuel/air separator. The only thing air in the fuel does is make your CP3 work a little harder to compress it. IF you have a lot of air in the fuel and IF the FASS takes out the air and IF your performance is limited by your CP3 then a FASS might help by a small percentage. Once the fuel is put under high pressure in the rail, any entrained air has about . 02% of the volume that it had in the fuel tank, and all of the fuel that is commanded to go through the injectors will go through the injectors, FASS or no FASS. Once the fuel is through the injectors, the whole point is to mix it with air. I have heard of absolutely no convincing theoretical reason why a truck that was not CP3 limited should gain fuel mileage by use of a FASS. The overhead is notoriously unreliable. I went with the Glacier, and I have absolutely no relationship -- business or otherwise -- with Richard. If I was going to go with a FASS, I'd choose an Airdog instead based on the posts I've read on this forum.

O. K. I read this a while back, I think this is what you are looking for about the damage air can cause

http://www.bigrigowner.com/articles/0506hpd.html

 

[cerberusiam]

I've brought this issue up a couple of times on this forum, and no one has given me a coherent explanation of the theory of why we need a fuel/air separator.

Do you actually read the threads after you post this question just disappear until the next time it comes up? I know at least 3 threads you posted on addressed it and you never questioned the answer. If you don't like the answer post it. That what discussion forums are for.



One more time for the record, in addition to everything Mallinson covered and what he touched on, is what happens when the air is injected with the fuel.



Take a soda pop bottle and shake it up, pop the top and try to pour liquid out of it. What you get is a lot more than liquid into a glass and everywhere else. Now imaginee that bottle is the rail, the cap is the injector, and the CP3 is you shaling the bottle. Both shaking and the CP3 impart energy to the liquid and it has no place to go due to the pressure. Drop the pressure and that energy is released. Yes the air compresses but when the pressure drops it expands right back to equilibrium with the environment. There is a significant drop in pressure from 20k psi in the rail to about 500 psi at injection time. The stream from the injector looks like the stream coming out of the bottle, a little liquid and a whole lot of foam.



Imagine what effect that has on a combustion event that is predicated on a constant burn of existing fuel. Under thermal imaging you would see temps spiking and dropping all across the stream where they should be pretty constant in the injection stream. Across the burn time you get dips and spikes in pressure and a some what less than adequate burn because you have injected air that increases the charge density and robs power. Power is down so throttle is advanced to make up for the loss. Economy drops. The ECU is reading boost and metering fuel for available air. It thinks it is correct on its duration because it doesn't know about the entrained air so you constantly have an imbalance that is adjusted by your foot or CC advancing the throttle.



Will the air removal be noticeable on an over fueled HP chasing truck? Not likely but one that is fueled for economy and driven as such it will make an impact along with the lessened wear on components.

 

[AMassaro]

My next question would be, "If this air in fuel thing is really a problem, how can someone without a FASS get rid of the air?"... I think I could fab something up and make it work with my current fuel pump, if I thought it were necessary. Which I'm still on the fence. Do high end diesel vehicles (Mercedes) or any other diesel engine builders (CAT, Cummins, etc. ) utilize a system to reduce the air in their fuel lines? My guess is with all of their engineers, and the thousands of hours spent designing these engines, they would have added something this simple to reduce vibrations, make engines smoother and more effiecient???

 

[bmoeller]

AM, I'm sure they are aware of it, but, it also costs more money. Not everyone will want to spend the extra money for it. But, really, another $5-600 doesn't mean a whole lot when you are spending $75k+ on a new big truck.



Air in the system is compressible, the fuel itself is not. You can usually tell when you have air in a hydraulic system, asuming there is enough to make a noticeable difference.



The more air in a system, the more it can retard the timing of the injection of the fuel. If you ever what the display stands that the FASS/AirDog dealer have setup in a truck show, you can see how much air is really in the fuel. More than one might think.

 

[drury]

O. K. I read this a while back, I think this is what you are looking for about the damage air can cause

http://www.bigrigowner.com/articles/0506hpd.html

Thanks for posting that. It's the first time I've seen it. It does have some interesting real world examples, and it's also written by Bruce Mallinson, who is the CEO of Diesel Injection of Pittsburgh, which claims to be a "Master Distributor for the Fuel Air Separation System". I'll keep my skepticism for a bit longer.

Do you actually read the threads after you post this question just disappear until the next time it comes up?

Yes, I do read the responses. I just haven't been impressed with them, and I don't feel like getting into an extended argument over it.

The stream from the injector looks like the stream coming out of the bottle, a little liquid and a whole lot of foam.



Imagine what effect that has on a combustion event that is predicated on a constant burn of existing fuel. Under thermal imaging you would see temps spiking and dropping all across the stream where they should be pretty constant in the injection stream. Across the burn time you get dips and spikes in pressure and a some what less than adequate burn because you have injected air that increases the charge density and robs power. Power is down so throttle is advanced to make up for the loss.

This is what I find completely unconvincing. Because the rail fuel pressure is so high, the air has essentially no volume in the fuel when it is on the rail side. When the injector opens for its programmed duration, a certain volume of fuel air/mixture will pass through it. The volume of fuel that goes through it will be will be about the same regardless of whether there is air in it or not, because the volume of the air will be so small. Once the fuel enters the cylinder, the air will expand and foam up the fuel just like your shaken Coke bottle analogy. The whole point of an efficient injection event is to mix the fuel with air so you can get a good burn. Increased atomization of the fuel improves fuel economy. That's the principal of the mileage gains that are alleged with a pressure box such as the EZ. I fail to see how foaming the fuel with additional air is going to give you anything other than improved atomization of the fuel and mixing with air. How is increasing the amount of air in the cylinder going to rob power? The whole principal of cold air induction, bigger turbos, nitrous, porting the head, etc. is to get more air into the cylinder. Have you seen actual pictures taken with an IR camera of the burning fuel stream that demonstrates your point, or is this just conjecture?



If you guys want to put FASS's on your vehicles and believe in them, that's fine with me. I just thought that Summit ought to hear an opposing viewpoint to all the "FASS is great" posts.

 

[BRayls]

Thanks for posting that. It's the first time I've seen it. It does have some interesting real world examples, and it's also written by Bruce Mallinson, who is the CEO of Diesel Injection of Pittsburgh, which claims to be a "Master Distributor for the Fuel Air Separation System". I'll keep my skepticism for a bit longer.





Yes, I do read the responses. I just haven't been impressed with them, and I don't feel like getting into an extended argument over it.







This is what I find completely unconvincing. Because the rail fuel pressure is so high, the air has essentially no volume in the fuel when it is on the rail side. When the injector opens for its programmed duration, a certain volume of fuel air/mixture will pass through it. The volume of fuel that goes through it will be will be about the same regardless of whether there is air in it or not, because the volume of the air will be so small. Once the fuel enters the cylinder, the air will expand and foam up the fuel just like your shaken Coke bottle analogy. The whole point of an efficient injection event is to mix the fuel with air so you can get a good burn. Increased atomization of the fuel improves fuel economy. That's the principal of the mileage gains that are alleged with a pressure box such as the EZ. I fail to see how foaming the fuel with additional air is going to give you anything other than improved atomization of the fuel and mixing with air. How is increasing the amount of air in the cylinder going to rob power? The whole principal of cold air induction, bigger turbos, nitrous, porting the head, etc. is to get more air into the cylinder. Have you seen actual pictures taken with an IR camera of the burning fuel stream that demonstrates your point, or is this just conjecture?



If you guys want to put FASS's on your vehicles and believe in them, that's fine with me. I just thought that Summit ought to hear an opposing viewpoint to all the "FASS is great" posts.

I think the point your missing is the injection event is calibrated to have x fuel for x amount air. you inject air in the fuel and you now have a spot that is lean on fuel. because the air was in its place.

 

[telliott]

i dont mean to steal the thread, but this seems to be saying that an air seperator can be benificial on a high pressure rail, but what about in a VP system where it is a lower pressure? will an air seperator be benificial?

 

[p-Bar]

I think the point your missing is the injection event is calibrated to have x fuel for x amount air. you inject air in the fuel and you now have a spot that is lean on fuel. because the air was in its place.





I'm wondering if that is taken into consideration , to run more lean and engine temp hotter to pass smog??

 

[BRayls]

I think the point your missing is the injection event is calibrated to have x fuel for x amount air. you inject air in the fuel and you now have a spot that is lean on fuel. because the air was in its place.





I'm wondering if that is taken into consideration , to run more lean and engine temp hotter to pass smog??

lean in a diesel is not hotter , thats in a gasser.

 

[drury]

I actually did a lot of research on the FASS & Airdog before going with my Glacier. I just spent some time hunting around for one of the threads I remembered reading and found this:



https://www.turbodieselregister.com/forums/showthread.php?t=89707



If you read all the way through it, you will find two separate sets of 3rd party dyno numbers on a 2nd gen. One claims 0 HP for the FASS, and one claims 10HP. You will also find a lot of interesting commentary by the inventor of the fuel/air separation system, Charles Ekstam. If you aren't familiar with the story, Charles is the father, and his company sells the Airdog. Brad Ekstam is the son, and his company sells the FASS. Back in 2004, Charles sued Brad for patent infringement, but I never heard how it came out.



Also, as near as I could make out from Charles comments, there are two supposed benefits of the FASS that I would like to comment on:



1) Reduced cavitation. Cavitation seems to be the presence of a vacuum on the trailing edge of the pump impeller/piston produced when the pump is unable to draw in sufficient fuel. The FASS claims to eliminate the vapor caused by cavitation, but it seems to me that this effect is due more to installing a bigger lift pump that can supply more fuel to the VP44 or CP3 than due to any fuel/air separation function. As far as cavitation induced in the lift pump itself goes, if I read Charle's claims right, he seems to believe that the Airdog's design filters out any vapor produced by cavitation in the lift pump, and that the FASS design doesn't.



2) Retarded injection timing. In the thread above, Charles said this was because any air/fuel vapor in the injection pump cylinder was compressible, so that as the injection event started, there was a slight delay while the air/vapor was compressed before the fuel/air mixture entered the cylinder. I really don't think this applies on a common rail engine because the fuel/air vapor is already compressed in the rail, and if anything the decompression as it goes from 10,000 psi to 500 psi will force the fuel/air mixture out in a manner similar to the way CO2 forces Coke out of a shaken up can once it is opened.



In summary, I think putting a Glacier, FASS, or Airdog on your truck is a great idea, because they all seem to be good at their primary job of getting fuel to the injection pump. Most of the owners of all 3 systems seem to be pretty happy campers and many seem to be quite happy to defend their chosen product religiously. Factors I would look at are performance, reliability, filtration, and noise. The benefits of the fuel/air separation function itself are highly debateable for the 2nd gen and 3rd gen trucks.



p-bar,

I think you missed my point. If you have 10% entrained air in the fuel tank at 14. 7psi (sea level pressure), and compress it to 10,000 psi in the fuel rail, then since the air compresses and the fuel doesn't, by volume you only have . 015% air in the fuel. So 99. 985% of the fuel that is supposed to be injected into the cylinder is. If you are concerned about that last . 015%, then by all means get a FASS. Diesel engines are designed to run lean. Extra air in the cylinder isn't going to do anything other than help the fuel burn better.