Surge Tank + Fuel Pump, When Do You Need Them And Why?

[rednose]

Surely there are surge tanks on the market with the return line going to the main tank making that point moot?

No point in that because when your at WOT and fuel rushes to the back of the tank where the intank cant pick it up all the fuel being returned is useless,

where as when the returned fuel from the rail goes back into the surge it can be used again by the main pump, sure it may be hotter but id rather hotter fuel then no fuel.

[JETURBO]

God dam george timing hahaha but I think we can say they have same or greater results if they have not thrown the data out by now to support there claims

[ratter]

do either of you believe there is a benefit in cooler fuel, forget about which type of system it comes from

[JETURBO]

Yes I do, have seen numbers to support this so by no means being pig headed

But how much cooler is the Q

If fuel in 1 systems starts at 25 A and raises to 60 after 1hr

Fuel in system 2 starts at 25 A and raises to 58 after 1hr

I feel is negligible and I think u would also

It does not take a genius to say that the fuel in system 2 needs to be cooler by a substantial amount I would say anything less than 10 degrees is piss poor if this is the foundation of the claim

Anything greater than 10 degrees I say has merit without a doubt ...... Lets see this happen its an extremely basic test for system 2's supplier to complete even with the same test method as george

[KPM Motorsport]

No point in that because when your at WOT and fuel rushes to the back of the tank where the intank cant pick it up all the fuel being returned is useless,

where as when the returned fuel from the rail goes back into the surge it can be used again by the main pump, sure it may be hotter but id rather hotter fuel then no fuel.

A simple way to look at it is the intank set up is a surge tank, Just housed in the main tank.

[rednose]

do either of you believe there is a benefit in cooler fuel, forget about which type of system it comes from

Of course, more power can be made with cooler fuel

Yes I do, have seen numbers to support this so by no means being pig headed

But how much cooler is the Q

If fuel in 1 systems starts at 25 A and raises to 60 after 1hr

Fuel in system 2 starts at 25 A and raises to 58 after 1hr

I feel is negligible and I think u would also

It does not take a genius to say that the fuel in system 2 needs to be cooler by a substantial amount I would say anything less than 10 degrees is piss poor if this is the foundation of the claim

Anything greater than 10 degrees I say has merit without a doubt ...... Lets see this happen its an extremely basic test for system 2's supplier to complete even with the same test method as george

Exactly, I also beleive the difference would be minor

A simple way to look at it is the intank set up is a surge tank, Just housed in the main tank.

Where does the returned fuel from the rail go Dave?

Edited 30/10/14 12:32 AM by rednose

[ratter]

How fuel temp can affect your tune accuracy, a copy and paste not written by me

"In last month’s TechnoRant, I discussed the difference between injector volume flow, and mass flow, and described how mass flow is dependent on fuel density. I also hinted at the fact that fuel density is dependent on temperature. This month, I will detail that dependence, describe how it affects your tune, and give you a tool to compensate for it.

Let’s start with what really matters, which is how it affects your tune. Have you noticed that even a well-tuned engine runs leaner when the fuel is hot?

There’s a reason for that…

The reason is that the density of the fuel changes with temperature, which changes the injector mass flow rate. Predictably, your air fuel ratio changes because your fuel injector is now effectively smaller. (Remember, air fuel ratio is mass based.)

This change in density can be predicted with a parameter called the “Coefficient of Thermal Expansion” (CTE) which is a description of how much the fuel expands with temperature.

It sounds complicated, but like many things related to performance, most of us already have an intuitive feel for it. For instance, we all know that our pistons expand when they get hot, which is why we specify a cold clearance. And we all know that the fluid in the radiator expands when it gets hot, which is why we need an overflow tank. It should come as no surprise then that our fuel also expands when it gets hot, and in fact it expands at a greater rate than either water or aluminum.

So let’s consider how this expansion changes the fuel density.

Let’s start by filling a cylinder to the very top with ethanol. Ignoring evaporation, if we heat the ethanol, it will expand and overflow just like the fluid in our radiator. The cylinder contains the same volume of ethanol, but because a portion has spilled out, the mass of ethanol in the cylinder has changed.

Referring to last month’s TechnoRant, we know that density is defined as mass divided by volume. As we divide our unchanged cylinder volume into a lesser mass, we get a lesser density, which we already know will reduce our injector mass flow rate.

The situation is the same on a running engine. The fuel injector delivers a specific volume of fuel to the cylinder, but as the temperature of that fuel changes, so does the mass, and so does our mass based air fuel ratio.

The hotter the fuel gets, the smaller the fuel mass delivered to the cylinder, and the leaner the air fuel ratio becomes.

Let’s move beyond generalizations, and be more specific.

Gasoline, ethanol, methanol, toluene, etc all have a similar CTE value of approximately .001 per degree Celsius. This means that for every change in temperature of 1 degree C, our volume will change by a factor of .001, which you math geeks will recognize as 1/10 of one percent per degree Celsius.

Let’s apply this to a sample 1000 cc/min injector, and calculate the mass flow rate at a few different temperatures.

We start by looking up the density of ethanol, and we find that the density of .789 is stated at a temperature of 20 degrees C.

Multiplying our 1000cc/min by ethanol’s specific gravity of .789, we get a mass flow rate of 789 grams per minute at a fuel temperature of 20 degrees C. Now let’s consider what happens after a half hour of driving in stop and go traffic when the fuel temperature climbs to 70C, using the following formula:

(((Reference Temp – New Temp) * CTE) + 1) * Reference Density = New Density

Using the values from our example:

(((20 – 70) * .0011) + 1) * 0.789 = 0.746

As a result of the density changing from 0.789, to 0.746, our injector mass flow rate has now gone from 789 g/min (13.2 g/sec, or 104.4 lbs/hr) to 746 g/min (12.4 g/sec, or 98.7 lbs/hr)

Putting that to numbers that we can more easily relate to, our air fuel ratio of 11.5 to 1 has just become 12.2 to 1 and would need a trim of approximately 6% to bring it back in line. Not the end of the world as long as our tune is conservative, but potentially ugly if we are cutting it close.

And I think most would agree that a 6% trim is unnecessary if we can compensate for it in the tune right?

While half of you are nodding your heads in agreement, and planning to perform the calculations to account for this density change, the rest of you are shaking your heads violently, thinking “There is NFW I am going to struggle with a bunch of math just to fix a 6% trim!”

[JETURBO]

Brilliant write up !!

We/I also made the equivalent choice when selecting the lambda target on a tune dependant on the time of year/ ambient temp of the day

That was a good reference almost simular to georges data so we can see what happens

But

The differance of as I said 60 degrees and a luke warm difference to say 50 or 53 degrees would be in the vacinity of 0.5 AFR so trimming of sub 0.5% and that's something any tuner would live with

Correct ?

So as it stands if u tune to suit the temp and make an allowance u can keep trims under control

But were talking about making power or at least maintaining power

The real question is how many hp's go out the door from 25 to 60 degrees as per georges data say its 0.5 and that's a massive loss so doubtful but say u gain 35 degrees in temp then loose 17.5hp .......

The intank system of KPM would still have temp gain no doubt

Say its better by heaps ( 20 degrees ) so it goes from 25 to 45 degrees the loss is still 10hp

7.5hp better than the old "fuel boiler"

7.5hp into rwkw 5.25rwkw

Now george makes 475rwkw ~ he goes to 482.5 with the KPM unit .........

These are in favour if the kpm unit and still nothing to go banannas about imho !!!

Edited 30/10/14 01:10 AM by Butt Plug

[rednose]

I'll wait till Dan gets the intank and tests it.

He may even put a ZT in the car and rum similar tests to mine.

[ratter]

every tuner is different, I'm sure you are aware of this with what you have seen, pity Ford Australia did not include a rail temp sensor on our cars to keep things more consistent. But injector flow is only one aspect of fuel getting hotter, but agree it will be hard to record unless you had an engine dyno and complete control of coolant and air temps to keep things consistent in order to do the testing