Technical How can a valve cover heat up fuel lines?

Jeffman

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I’m really interested in this topic (I’m a ChemE). While fuel density isn’t expected to change much with temperature, keep in mind that fuel viscosity and surface tension will vary a lot more with temperature, which will affect fuel spray behavior coming out of the injectors. I found the following data in a tech article on this topic, linked below.

IMG_6285.jpeg


The article discusses, among other things, how fuel spray evaporation mode and the droplet breakup mechanism varies with fuel temperature for both gasoline and ethanol. The ChemEs on this forum should have a lot of fun reading the article, especially seeing how the temperature-dependent Droplet Weber number (Fig. 10) predicts droplet destabilization as a function of temperature.

IMG_6286.jpeg


It all kind of makes sense - cold fuel sprays differently than hot fuel. So if cold fuel helps to prevent knock, then thermally insulating the fuel rail from the heat of the engine should help to prevent knock.
 
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martymil

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I'm going to admit all this stuff is a little bit over my head.

Nothing wrong with running cooler fuel which will also help with cylinder cooling especially when using high concentrations of e85 and
if it works it works. We are starting to hit 100f temps so now will be a great time to start testing here again.
 
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martymil

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I measured injector temps way higher than that scale when the fuel was hovering around 400k or 125c in the rail alone on a 100f day.

There is no way to measure the temp at the tip but assume that the fuel entering the cylinder would be 450 to 500k coming from the injector.

Cooler fuel would help keep the injector cooler and give a better spray pattern and also help cool the cylinder thus transferring less heat to the injector and help it last longer.

Well that's my theory behind it which has worked for me keeping missfires and knock at bay thus far.
 

Torgus

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Just wanted to make sure.

So from 275 aka 35 degrees in freedom units to 440F, is that graph...wide range. Fuel line temp hits 107 after heat soak in the images on the last page taken with a Flir. So everything after 315k on the graph ignore in theory because the whole thread hinges on the fact not only the vc heating up the fuel lines but most importantly that the 2 INCH LONG fuel lines will heat up the fuel going through them in a measurable way(which we don't have and logic says next to no heating is occuring at WOT). I have yet to see actual fuel temps at the injector, just external readings of lines etc.

Everyone should reread from page 1.

So if cold fuel helps to prevent knock, then thermally insulating the fuel rail from the heat of the engine should help to prevent knock.
What is the proof cold fuel prevents knock again?

No one is talking about insulating the fuel rail. The phelonic spacers just decouple part of the fuel rail from the engine. Not the part that matters aka the injector which lives physically connected to the head and sits in the combustion chamber which is a better conductor of heat than the fuel rail to valvecover which has an air gap or fuel line mounting points to the head. All of this is covered on page 1 of this thread.



Anywho the point of this thread was already proven:

The vc does not heat up the fuel lines

The m18 vc is equal in terms of the vtt vc in terms of heating up the fuel lines unlike what the vtt fan boy claimed with no data.


TLDR: insulate your fuel lines! <-- This is a JOKE!
 
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wheela

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Just wanted to make sure.

So from 275 aka 35 degrees in freedom units to 440F, is that graph...wide range. Fuel line temp hits 107 after heat soak in the images on the last page taken with a Flir. So everything after 315k on the graph ignore in theory because the whole thread hinges on the fact not only the vc heating up the fuel lines but most importantly that the 2 INCH LONG fuel lines will heat up the fuel going through them in a measurable way(which we don't have and logic says next to no heating is occuring at WOT). I have yet to see actual fuel temps at the injector, just external readings of lines etc.

Everyone should reread from page 1.


What is the proof cold fuel prevents knock again?

No one is talking about insulating the fuel rail. The phelonic spacers just decouple part of the fuel rail from the engine. Not the part that matters aka the injector which lives physically connected to the head and sits in the combustion chamber which is a better conductor of heat than the fuel rail to valvecover which has an air gap or fuel line mounting points to the head. All of this is covered on page 1 of this thread.



Anywho the point of this thread was already proven:

The vc does not heat up the fuel lines

The m18 vc is equal in terms of the vtt vc in terms of heating up the fuel lines unlike what the vtt fan boy claimed with no data.


TLDR: insulate your fuel lines!
This is essentially it. I think the biggest question mark is the actual temp of the fuel and fuel lines. If they're being measured with IR pyrometer (ie Flir camera, or hand-held optical pyrometer) - those measurements are only accurate for materials who's emissivity matches the settings of the camera. Good ones can be adjusted, but I believe the default values are generally set for reading temps from a theoretical black body (emissivity = 1.0), or very close to a true black body (emissivity = 0.95). The emissivity of a shiny metal fuel line is not a good representation of a black body (emmisivity is much less than 1.0) so the indicated temps of the fuel line are likely being under reported if using IR pyrometer. How much, I can't say - it's probably still ball park accurate, but we should be aware of the limitations.

I also suspect that the amount of fuel line exposed by the m18 cover is negligible regarding addition heat transfer to the fuel in the lines over a different valve cover design. By this, I mean I doubt enough heat could be transferred here via convection or radiation to have a meaningful impact on fuel temp rise across this short section of line. The emissivity of the lines is low (shiny metal) so they won't absorb much radiant heat, they have no fins on either side, so they'll be a poor heat exchanger for convection. And the overall exposed length is relatively short.

Playing devil's advocate, if we assume convective heat transfer on this section of fuel line IS significant, what is the ambient temp of the air under the hood interacting with this line which now acts as a heat exchanger? Heat flows from high temp to low temp. If the air temp is higher than the fuel temp at the beginning of this line, then additional airflow around the line will increase the convective coefficient of the line (which is now a heat exchanger) and therefore transfer more heat to the fuel than if there wasn't air flow around the lines. So if we assume convective heat transfer here IS significant (I suspect it isn't), then the valve cover offering more air flow over the lines could actually heat the fuel in the lines more, depending on the under-hood air temps relative to fuel temps at the beginning of the exposed section of line.
 

martymil

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Just wanted to make sure.

So from 275 aka 35 degrees in freedom units to 440F, is that graph...wide range. Fuel line temp hits 107 after heat soak in the images on the last page taken with a Flir. So everything after 315k on the graph ignore in theory because the whole thread hinges on the fact not only the vc heating up the fuel lines but most importantly that the 2 INCH LONG fuel lines will heat up the fuel going through them in a measurable way(which we don't have and logic says next to no heating is occuring at WOT). I have yet to see actual fuel temps at the injector, just external readings of lines etc.

Everyone should reread from page 1.


What is the proof cold fuel prevents knock again?

No one is talking about insulating the fuel rail. The phelonic spacers just decouple part of the fuel rail from the engine. Not the part that matters aka the injector which lives physically connected to the head and sits in the combustion chamber which is a better conductor of heat than the fuel rail to valvecover which has an air gap or fuel line mounting points to the head. All of this is covered on page 1 of this thread.



Anywho the point of this thread was already proven:

The vc does not heat up the fuel lines

The m18 vc is equal in terms of the vtt vc in terms of heating up the fuel lines unlike what the vtt fan boy claimed with no data.


TLDR: insulate your fuel lines!

You proved nothing, as I said all alloy valve covers will transfer heat into the fuel lines but some will do in worse than others, the only one that will not is the factory plastic unit.

I've done my testing and saw the difference, run boiling hot ass fuel if you wish as I don't care.
 
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SlowE93

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This is essentially it. I think the biggest question mark is the actual temp of the fuel and fuel lines. If they're being measured with IR pyrometer (ie Flir camera, or hand-held optical pyrometer) - those measurements are only accurate for materials who's emissivity matches the settings of the camera. Good ones can be adjusted, but I believe the default values are generally set for reading temps from a theoretical black body (emissivity = 1.0), or very close to a true black body (emissivity = 0.95). The emissivity of a shiny metal fuel line is not a good representation of a black body (emmisivity is much less than 1.0) so the indicated temps of the fuel line are likely being under reported if using IR pyrometer. How much, I can't say - it's probably still ball park accurate, but we should be aware of the limitations.

I also suspect that the amount of fuel line exposed by the m18 cover is negligible regarding addition heat transfer to the fuel in the lines over a different valve cover design. By this, I mean I doubt enough heat could be transferred here via convection or radiation to have a meaningful impact on fuel temp rise across this short section of line. The emissivity of the lines is low (shiny metal) so they won't absorb much radiant heat, they have no fins on either side, so they'll be a poor heat exchanger for convection. And the overall exposed length is relatively short.

Playing devil's advocate, if we assume convective heat transfer on this section of fuel line IS significant, what is the ambient temp of the air under the hood interacting with this line which now acts as a heat exchanger? Heat flows from high temp to low temp. If the air temp is higher than the fuel temp at the beginning of this line, then additional airflow around the line will increase the convective coefficient of the line (which is now a heat exchanger) and therefore transfer more heat to the fuel than if there wasn't air flow around the lines. So if we assume convective heat transfer here IS significant (I suspect it isn't), then the valve cover offering more air flow over the lines could actually heat the fuel in the lines more, depending on the under-hood air temps relative to fuel temps at the beginning of the exposed section of line.
What my associate said 👆🏾
 

SlowE93

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Just wanted to make sure.

So from 275 aka 35 degrees in freedom units to 440F, is that graph...wide range. Fuel line temp hits 107 after heat soak in the images on the last page taken with a Flir. So everything after 315k on the graph ignore in theory because the whole thread hinges on the fact not only the vc heating up the fuel lines but most importantly that the 2 INCH LONG fuel lines will heat up the fuel going through them in a measurable way(which we don't have and logic says next to no heating is occuring at WOT). I have yet to see actual fuel temps at the injector, just external readings of lines etc.

Everyone should reread from page 1.


What is the proof cold fuel prevents knock again?

No one is talking about insulating the fuel rail. The phelonic spacers just decouple part of the fuel rail from the engine. Not the part that matters aka the injector which lives physically connected to the head and sits in the combustion chamber which is a better conductor of heat than the fuel rail to valvecover which has an air gap or fuel line mounting points to the head. All of this is covered on page 1 of this thread.



Anywho the point of this thread was already proven:

The vc does not heat up the fuel lines

The m18 vc is equal in terms of the vtt vc in terms of heating up the fuel lines unlike what the vtt fan boy claimed with no data.


TLDR: insulate your fuel lines!
TLDR is what I understood.

My associates always make good points.
 
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martymil

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This is essentially it. I think the biggest question mark is the actual temp of the fuel and fuel lines. If they're being measured with IR pyrometer (ie Flir camera, or hand-held optical pyrometer) - those measurements are only accurate for materials who's emissivity matches the settings of the camera. Good ones can be adjusted, but I believe the default values are generally set for reading temps from a theoretical black body (emissivity = 1.0), or very close to a true black body (emissivity = 0.95). The emissivity of a shiny metal fuel line is not a good representation of a black body (emmisivity is much less than 1.0) so the indicated temps of the fuel line are likely being under reported if using IR pyrometer. How much, I can't say - it's probably still ball park accurate, but we should be aware of the limitations.

I also suspect that the amount of fuel line exposed by the m18 cover is negligible regarding addition heat transfer to the fuel in the lines over a different valve cover design. By this, I mean I doubt enough heat could be transferred here via convection or radiation to have a meaningful impact on fuel temp rise across this short section of line. The emissivity of the lines is low (shiny metal) so they won't absorb much radiant heat, they have no fins on either side, so they'll be a poor heat exchanger for convection. And the overall exposed length is relatively short.

Playing devil's advocate, if we assume convective heat transfer on this section of fuel line IS significant, what is the ambient temp of the air under the hood interacting with this line which now acts as a heat exchanger? Heat flows from high temp to low temp. If the air temp is higher than the fuel temp at the beginning of this line, then additional airflow around the line will increase the convective coefficient of the line (which is now a heat exchanger) and therefore transfer more heat to the fuel than if there wasn't air flow around the lines. So if we assume convective heat transfer here IS significant (I suspect it isn't), then the valve cover offering more air flow over the lines could actually heat the fuel in the lines more, depending on the under-hood air temps relative to fuel temps at the beginning of the exposed section of line.

Ducted air will never heat up fuel lines as it will never reach 320k even in extreme situations it might only reach 325k, this is much lower than the fuel lines when stationary as even mine will reach 350k or more and won't drop till the car is moving or ducted airflow is present like I did with a dyno fan to measure the drop.

This is why we also cut the HVAC tray to extract as much heat and as fast as possible at speed which helps with high flow and speed of ambient air over the top of the motor when the hood is closed, thus hindering under bonnet aero. LOL what a joke that thread was.

Good airflow over the top of the motor is essential when running an alloy cover with good circulation and then we get to the rest of the issues.

The first step is to insulate the fuel rail from the head as that is the biggest fuel temp drop, then going one step further and doing a special heat dissipation coating that extracts heat out and reflects any radiating heat from entering it.

Also I powder coated the rocker cover to prevent heat transfer to coils, injectors and wiring that sits in the valley of the head, i could have done
the heat dissipation coating too but it doesn't come in any other color than black and is easily scratched so a decent ceramic coating will do the job to a point but no where near as good but it helps.

I went one step further and ducted ambient air over the top of the motor to help cool the fuel rail, lines and injectors to extract as much of the heat as you possibly can and haven't seen temps go any higher than 325k on the dyno at full throttle in a heat soaked engine bay.

Before it use to hit into late 300 and early 400's without all the work, I can tell you ducting air over the fuel lines has seen a significant drop.

Thats why I never made a cover to hide all wiring and coils as it traps heat, hot coils are bad for spark, hot injectors are bad in lots of ways like spray pattern, cylinder cooling and shortened lifespan, to what extent, I don't know but I was not going to spend any more money but it stopped timing pull and misfires so it did what I wanted to achieve.

If one want's to run hidden lines and covers on their rocker covers and run super heated fuel be my guest, this is how far one has to go
in extreme conditions to protect the n54 from failure which most of you will never experience.

You don't need a science degree to work this out but common sense and a bit of ingenuity which most lack and try to discredit in the name of fanboyism for all the work being done and shared to help others, but go for it and hide your heads in the sand.
 
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