Gasoline Distillation Curves

[Jim L.]

Re: Gasoline distillation curves as related to fuel injection

As soon as it gets to about 85 or above.......

The 65 fuel car is a bit different. At those same temps I will get percolation in the injector lines if I get caught in any type of traffic.

My own FI experience generally matches that of John Seeley..... fuel perc (with summer fuel) at idle when ambient temps are ~85F.

It wasn't always this way and the distillation curve does not make it clear as to why. Follow me....

My own effort at data gathering indicates that the onset of FI fuel perc will happen with summer fuel when the nozzle line temperatures reach 135 - 140 degrees. Looking at the distillation curves of modern E10 and of conventional gasoline, it seems the two curves are very similar in that temperature band, both suggesting about 15% evaporation.

This similarity would suggest that there should be little difference in the fuel perc behavior with either fuel. That doesn't match my experience, though. Thirty years ago, when all fuel was ethanol free (at least where I lived at that time), I remember fuel perc happening only when ambient temps were truly hot.... 90 - 95 degrees or so.

So something is different between the real gasoline then and E10 now and the distillation curves don't adequately explain it..... do they?

And keep in mind this relates to fuel injection only. I have no equivalent experiences with fuel perc in carbs.

Jim

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

My own FI experience generally matches that of John Seeley..... fuel perc (with summer fuel) at idle when ambient temps are ~85F.

It wasn't always this way and the distillation curve does not make it clear as to why. Follow me....

My own effort at data gathering indicates that the onset of FI fuel perc will happen with summer fuel when the nozzle line temperatures reach 135 - 140 degrees. Looking at the distillation curves of modern E10 and of conventional gasoline, it seems the two curves are very similar in that temperature band, both suggesting about 15% evaporation.

This similarity would suggest that there should be little difference in the fuel perc behavior with either fuel. That doesn't match my experience, though. Thirty years ago, when all fuel was ethanol free (at least where I lived at that time), I remember fuel perc happening only when ambient temps were truly hot.... 90 - 95 degrees or so.

So something is different between the real gasoline then and E10 now and the distillation curves don't adequately explain it..... do they?

And keep in mind this relates to fuel injection only. I have no equivalent experiences with fuel perc in carbs.

Jim

Jim,
I'd be more inclined to look to the low pressure side for the issues.

If you read the document that Duke's distillation chart comes from (I haven't studied it all, but read a bit of it) you will find that the heat perc issue is of little to no problem with current model vehicles for two reasons. One is that the fuel pump does not rely on suction, it is an immersed push pump and as such the vapor in the line can not cause the vapour lock condition generally associated with percing fuel and a suction pump (vapour lock). The other thing is that increasing the pressure on the fuel decreases the ability of the fuel to boil off. So in today's cars fuel is under pressure of about 65 psi from the tank forward, pretty much eliminating any chance of vapour issue. Similarily, your system is on the high pressure side.

On your system I would suspect that the high side delivery problem is due to vapour produced on the low side prior to the injection pump.

Additionally, I would take the distillation chart info with a grain of salt. It is a very small part of a very big picture. Looking at distillation curve in isolation from Vapour Pressure, Vapour-Liquid Ratio, Vapour Lock Index, Driveability Index, Volatility Specs..... etc is not going to give you any clear answers.

Steve

[Jim L.]

Re: Gasoline distillation curves as related to fuel injection

On your system I would suspect that the high side delivery problem is due to vapour produced on the low side prior to the injection pump.

Not true.

The reasons for fuel perc in Rochester FI units are well understood. There is no mystery. At idle, pressure in the fuel lines leading to the nozzles is too low to prevent the lighter components of modern motor fuel from vaporizing. This is just the nature of the design.

However, some property of modern motor fuels makes the old FI units more prone to fuel perc now than they were in the past.

I have two fuelies which I've been driving for 35+ years. Same cars, same engines, same engine temps, same fuel plumbing, same everything...... except for the fuel perc behavior and the properties of the fuel they use. Fuel perc is worse now than in the past and the only change has been to the motor fuel.

Jim

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

Not true.

The reasons for fuel perc in Rochester FI units are well understood. There is no mystery. At idle, pressure in the fuel lines leading to the nozzles is too low to prevent the lighter components of modern motor fuel from vaporizing. This is just the nature of the design.

However, some property of modern motor fuels makes the old FI units more prone to fuel perc now than they were in the past.

I have two fuelies which I've been driving for 35+ years. Same cars, same engines, same engine temps, same fuel plumbing, same everything...... except for the fuel perc behavior and the properties of the fuel they use. Fuel perc is worse now than in the past and the only change has been to the motor fuel.

Jim

As I said in an earlier post, I have no experience with this FI system. I have no idea what pressures runs at on the high side, but it's interesting that the vapourization problem happens on the high pressure side and not the low pressure side prior to the high pressure pump, very counter intuitive. Is the fuel exposed to higher heat on that side, is the high side idle pressure lower than the low side. Raising the pressure raises the boiling point. If the temp is equal on both high and low sides of the pump you would expect the vaporization problem to show up b4 the pressure increase. I'm sure there's a logical explanation for it, but as I said, I don't know the system.

As you say, this appears to be an issue all the FI cars are experiencing and from the sounds of it,someone has taken the time and effort to properly diagnose the problem and has determined it to be a fuel issue, having isolated it right down to where in the system and under what conditions it's happening.

Not so with the carbs on this forum. Age old complaint and symptoms are no longer found to be the result of the malfunctions that caused them for the last 80 years, instead being blamed on the fuel without even checking for the malfunctions historically known to cause the problems.

The more I read on the Chevron paper that Duke's chart came from the less relevance I believe the chart has. It's intent was not to indicate what temp your fuel is likely to be vapourizing in your lines. The paper explains the importance of having the different components vapourize off at diff temps. If it didn't we couldn't start our cars at all. As was said earlier, liquid fuel doesn't burn, only vapour burns. It is critical to have some vapour produced at low temps so the car will start. As the engine warms and charge air increases in temp it goes through the temp range that the lower components vaporize off at until it reaches a temp that all the fuel will vaporize, the top of the chart.

If you want to explore the issues with vapour lock and other hot fuel issues you need to keep reading. I'm not done yet. It's dry reading.

Steve

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

Should also point out that the article goes on to say that until the charge air reaches the temp where all the components will vapourize it will not all completely burn. And that's one of the roles of the heat risers and why it has a bi-metalic spring. To get the charge air up to temp quickly when the engine is cold. Another is to maintain a constant charge air temp once it gets there for a consistent AFR.

Steve

[Timothy B.]

Re: Gasoline distillation curves as related to fuel injection

I want to post a email message I received from Michael Hansen about this long winded thread. Steve, please read this because with respect to all people here, Mike has been around these cars since they were new and he can add to what others are saying about modern fuel and heat soak/ percolation on engines with carburetors and fuel injection.

I wish Mike was still here on the board, good to here from you, Mike..


From Michael Hansen,


The issue of heat soak/fuel boil is not new. It's been around for many decades but it became worse with the new alcohol enriched formula fuel. For a decade or more, it was at 5% but several years ago, it was increased to 10%. That's when the major issues with percolation/boil began.


So what's the problem? How does raw fuel manage to find it's way into the intake manifold? And in upper level heat situations, actually perc out of the carburetor bowl vent?
Here's what happens. The first sign of fuel dribbling into the carburetor bores is likely coming from the accelerator pump well. Because the check ball restricts reverse flow, expanding fuel has only one place it can go and that's out of the nozzle and into the bore of the carburetor.
As more heat is introduced and fuel in the bowl begins a mild boil, two things happen. The fuel level increases and eventually starts to drip from the booster and down the bore of the carburetor. That's not all though. At full boil, fuel will gush out of the bowl vents in the same exact manor as a coffee pot. Random surges of fuel perc out and eventually down the carburetor bores.
Also, fuel in the fuel line from the fuel pump to the carburetor will begin to boil and build more pressure. The carburetor float needle/seat would normally prevent this fuel from by-passing but something else is happening.
The buoyancy of the float is calculated to close the needle/seat when partially submerged in fuel. However, what is the buoyancy factor when the fuel is made up of 50% bubbles because the fuel is boiling? The float needle/seat can no longer hold back the pressure and it fails. That allows even more fuel to enter the bowl.
(more on this later but methane gas bubbles from the ocean floor and/or under sea earthquakes that cause vast amounts of bubbles to rise to the surface can actually cause a large ship to sink)
When fuel dribbles down the bores of the carburetor, most is temporarily held above the closed throttle plates and it will eventually run out along the throttle shaft. That's why some think that there's an external fuel leak.
But why didn't we have this strange problem when these 50's and 60's cars were new? Because the fuel that we used then was ethanol free. Pure gas boils at a higher temperature than E10.
Folks can argue all they want about this but the above is precisely what has been happening since the introduction of E10 fuel for older cars.

[Duke W.]

Re: Gasoline distillation curves as related to fuel injection

My own FI experience generally matches that of John Seeley..... fuel perc (with summer fuel) at idle when ambient temps are ~85F.

It wasn't always this way and the distillation curve does not make it clear as to why. Follow me....

My own effort at data gathering indicates that the onset of FI fuel perc will happen with summer fuel when the nozzle line temperatures reach 135 - 140 degrees. Looking at the distillation curves of modern E10 and of conventional gasoline, it seems the two curves are very similar in that temperature band, both suggesting about 15% evaporation.

This similarity would suggest that there should be little difference in the fuel perc behavior with either fuel. That doesn't match my experience, though. Thirty years ago, when all fuel was ethanol free (at least where I lived at that time), I remember fuel perc happening only when ambient temps were truly hot.... 90 - 95 degrees or so.

So something is different between the real gasoline then and E10 now and the distillation curves don't adequately explain it..... do they?

And keep in mind this relates to fuel injection only. I have no equivalent experiences with fuel perc in carbs.

Jim

The distillation curve gives a clue to vapor pressure at higher than the normal 100F or so that is measured and specified. As a liquid is heated its vapor pressure increases with temperature. The definition of boiling is when vapor pressure is equal to surrounding pressure, which is atmospheric pressure for a carburetor or the Rochester FI fuel bowl.

Above about 130F more of the E10 components are at or closer to their boiling points, so vapor pressure will be higher at any temperature above 130F than traditional non-ethanol fuel. This means vapor will be leaving the bowl vents at a higher rate; and after a hot soak so much fuel vapor may be inside the air filter, carburetor, and manifold that the mixture is too rich to ignite, so a lot of cranking is required. My recommendation is to use the flooded engine starting procedure if this occurs because the definition of flooded is a A/F ratio too fuel rich to ignite.

Actual percolation (boiling) of the fuel does not have to be occurring for hard hot starting and initial rough operation to occur.

Cranking speed fuel pressure of the Rochester FI system is only a few psi, so vapor bubbles can form in the spider, which means there is insufficient fuel delivery until the engine fires and you bring up the revs or drive off immediately to increase spider pressure which causes the vapor to condense back to liquid form, and the engine smooths out. In this case it's vapor lock in the spider that is causing the problem.

Duke

[William F.]

Re: Gasoline distillation curves

After reading all this 2 quotes come to mind: one from Shakespeare-"Brevity is the soul of wit. " the other from J.R. Ewing: "Darlin', there's bound to be a point around here somewhere."
My take away:
1. Today's gasoline is different from what is was when these older Corvettes were designed. That's a fact.
2. Steve, while a certain amount of heat is needed to vaporize gasoline, more is not better. Many times there's too much and it does cause problems.
3. Some probably do try to correct a problem without first going through a check list of possible causes; Float has pin hole or is set too high; warped carb parts or bad gaskets, etc. However, once these things are ruled out, appears to be a good idea to insulate fuel lines, block under carb heat passages in some manifolds (as GM did after problems emerged), use a carb heat shield if possible(as GM did on some engines), and make sure heat riser valve is not sticking.

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

I want to post a email message I received from Michael Hansen about this long winded thread. Steve, please read this because with respect to all people here, Mike has been around these cars since they were new and he can add to what others are saying about modern fuel and heat soak/ percolation on engines with carburetors and fuel injection.

I wish Mike was still here on the board, good to here from you, Mike..


From Michael Hansen,


The issue of heat soak/fuel boil is not new. It's been around for many decades but it became worse with the new alcohol enriched formula fuel. For a decade or more, it was at 5% but several years ago, it was increased to 10%. That's when the major issues with percolation/boil began.


So what's the problem? How does raw fuel manage to find it's way into the intake manifold? And in upper level heat situations, actually perc out of the carburetor bowl vent?
Here's what happens. The first sign of fuel dribbling into the carburetor bores is likely coming from the accelerator pump well. Because the check ball restricts reverse flow, expanding fuel has only one place it can go and that's out of the nozzle and into the bore of the carburetor.
As more heat is introduced and fuel in the bowl begins a mild boil, two things happen. The fuel level increases and eventually starts to drip from the booster and down the bore of the carburetor. That's not all though. At full boil, fuel will gush out of the bowl vents in the same exact manor as a coffee pot. Random surges of fuel perc out and eventually down the carburetor bores.
Also, fuel in the fuel line from the fuel pump to the carburetor will begin to boil and build more pressure. The carburetor float needle/seat would normally prevent this fuel from by-passing but something else is happening.
The buoyancy of the float is calculated to close the needle/seat when partially submerged in fuel. However, what is the buoyancy factor when the fuel is made up of 50% bubbles because the fuel is boiling? The float needle/seat can no longer hold back the pressure and it fails. That allows even more fuel to enter the bowl.
(more on this later but methane gas bubbles from the ocean floor and/or under sea earthquakes that cause vast amounts of bubbles to rise to the surface can actually cause a large ship to sink)
When fuel dribbles down the bores of the carburetor, most is temporarily held above the closed throttle plates and it will eventually run out along the throttle shaft. That's why some think that there's an external fuel leak.
But why didn't we have this strange problem when these 50's and 60's cars were new? Because the fuel that we used then was ethanol free. Pure gas boils at a higher temperature than E10.
Folks can argue all they want about this but the above is precisely what has been happening since the introduction of E10 fuel for older cars.

With all due respect to you and Mr Hansen, I've also been around these cars since they were almost new, circa 1970. I was trained in the field, certified, and worked on these in 70's and 80's. I made my living at it (if you could call it that back then). If you need to see it, I can scan my Interprovincial Journeyman's certificate and show you the date. We were a shop that did everything. I rebuilt carbs, alternators, transmissions, auto and manual, diffs.... We subbed out nothing. On a day to day basis, winter and summer, hot and cold, I dealt with driveability problems. I am not a school kid on my computer spouting theory based on articles and charts I've read on the internet. I was there and I had my hands on these things. And I am working on them again today. I have 8 carburated vehicles in my shop here right now, ranging from 1934 to 1975.

While I don't agree entirely with what Mr. Hansen wrote, even his explanation points to exactly what I've been saying all along. The roiling boil brings on the effect. Diagnosis of fuel perc causing the hard start without any of the classic signs of the roiling boil is a misdiagnosis.

Fuel perc has always been here, we all agree on that. What's changed is the temp at which it happens. Assumptions are being made that it happens at just about any hot engine temp (not ambient temp) and that it is pretty much always the cause of hot engine hard start and fuel dripping down the throat.

What hasn't changed, and Mr. Hansen's letter doesn't address, is what the visible symptoms of perc are and how they haven't changed. Perc never occurred without white fuel vapour exiting the bowl vent. Again, using Roberts case as the example, how can fuel perc be causing his problem with no other evidence of fuel perc. No splashing liquid fuel out the vents, no white vapour out the vents, take the sight plug out and no boil going on. Yet everyone is telling him his fuel is percing. Wire open the heat riser and insulate the carb. That is what is wrong here.

Where I don't agree with Mr. Hansen is on the theory of the float buoyancy in the boiling fuel. Just like the kettle of water, when fuel boils the liquid level goes down. Keep boiling your kettle and it will eventually go dry. When the fuel escapes out the vents as vapour , the liquid level drops, the needle opens and allows more fuel in until the level rises enough to close the needle again. And this happens only as long as there is residual pressure in the line because the engine is off. Once there is no more pressure in the line the needle will open, nothing more will come in and the level will continue to drop as long as the fuel is boiling away out the vent as vapour. The opening needle doesn't let fuel in continually until it over fills the bowl.

In fact, it's been reported that in the Q-jets with the return line in the filter, this boiling away of the fuel actually caused a hard start due to a lack of fuel. When the fuel bowled off in the bowl the level dropped, The needle opened, but there was no pressure in the line because of the return line. Additionally the return line provided a route for fuel to return to the tank. Because the needle and seat were below the level of the fuel in the bowl, with the needle opened, the fuel would drain from the bowl, back out the line and down the return line. When you went to start it the engine had to crank enough to fill the bowl enough to start the engine.

Additionally, fuel discharge from the accelerater pump nozzles associated with heat perc is not something that I've ever heard reported, or seen myself looking down the throat of a carb with percing fuel, but pump discharge check (not inlet check) is listed as one of the twelve possible cause of hard hot start in carb trouble shooting chart in the 1963 Corvette Factory service manual.

Tim, perc is real. I saw it with my own two eyes back then. I absolutely believe it still happens today. I don't doubt for a moment that it happens at a lower temp. What I don't agree with is that it looks different today than it did back then. I read the bulletins back then. I read about the symptoms and the engineering fixes. I saw it.

I also saw, on damn near a daily basis, cars come in with hard hot start, dripping carb issues that were not fuel perc. There is a list of twelve possible hot hard start check points in the trouble shooting charts. How did those become invalid?

And at the top of the carb trouble shooting chart in the manual in bold letters,

"Always check first:
Heat riser, intake manifold bolts, compression, ignition system, manifold heat valve"

I'm not sure what we were supposed to take from the chart that started this thread. Even Mr. Hansen's theory revolves around a point at which this roiling boil starts. Where is that on the distillation chart? How do you know at what temps this is supposed to occur. We believe it starts at a lower temp than it used to. How much lower? It was a high ambient temp problem. What outdoor temp have we determined that we should start to ignore all the other possible causes?
Steve

[Jim L.]

Re: Gasoline distillation curves as related to fuel injection

The distillation curve gives a clue to vapor pressure at higher than the normal 100F or so that is measured and specified.

How does it do this? I'm just not seeing it. What I'm seeing is that the Summer E10 curve and the traditional summer fuel curve are pretty near coincident at the approximate temperature at which fuel perc becomes detectable in a Rochester FI unit.

If there is some hint about vapor pressure embedded in those curves, I don't know how to extract it.

Above about 130F more of the E10 components are at or closer to their boiling points, so vapor pressure will be higher at any temperature above 130F than traditional non-ethanol fuel.

I don't disagree with this but that's only because it's consistent with what I've observed first hand. That said, how can one know what you've stated about the E10 fuel components from studying the distillation curves?

Cranking speed fuel pressure of the Rochester FI system is only a few psi, .....

In the '64-'65 Sting Ray FI units, cranking fuel pressure is generally whatever the engine-mounted fuel pump can deliver, maybe 4 - 7 PSI or so. However, for '63 and older (excluding '57 units), I doubt cranking fuel pressure is much over about 1 PSI. And for sure, at idle on ALL Rochester FI systems, fuel pressure is only about 0.1 PSI.

drive off immediately to increase spider pressure which causes the vapor to condense back to liquid form, and the engine smooths out.

This is true and it's the world's best kept secret for how to deal with fuel perc in a Rochester FI unit. Once the fuel pressure rises due to the engine being under a load, fuel perc stops instantly.

Jim

[Steve G.]

Re: Gasoline distillation curves

After reading all this 2 quotes come to mind: one from Shakespeare-"Brevity is the soul of wit. " the other from J.R. Ewing: "Darlin', there's bound to be a point around here somewhere."
My take away:
1. Today's gasoline is different from what is was when these older Corvettes were designed. That's a fact.
2. Steve, while a certain amount of heat is needed to vaporize gasoline, more is not better. Many times there's too much and it does cause problems.
3. Some probably do try to correct a problem without first going through a check list of possible causes; Float has pin hole or is set too high; warped carb parts or bad gaskets, etc. However, once these things are ruled out, appears to be a good idea to insulate fuel lines, block under carb heat passages in some manifolds (as GM did after problems emerged), use a carb heat shield if possible(as GM did on some engines), and make sure heat riser valve is not sticking.

William,

I'll try to keep it brief and maybe ask the question first.

Do you fully understand the purpose of the heat riser valve, the exhaust cross over in the intake and the exhaust passages found in the throttle plate of some of the carbs? If you fully understand the purpose of those items then there's no need for me to go into some long winded explanation of their importance. You already know why they shouldn't be disabled.

Yes fuel is different. Does that make everything that goes wrong the fault of the fuel?

There is a logical and methodical sequence to diagnosing fuel problems. Fuel perc can be identified very quickly as part of that diagnosis.We all agree, the fuel boils in the bowl. Whether you believe it causes a liquid drip or not, if you believe it to be the cause, check it out.

Just like water boiling in a kettle produces steam, fuel boiling in the bowl produces vapour. A whispy white vapour that's very easy to see. No steam coming out the kettle, it's not boiling. No plumes of white gas vapour coming out the bowl vents, likewise, it's not boiling. Move on with your diagnosis and find the problem.

And that's not how the diagnosis that I've observed since I joined have gone.

Symptom, dripping fuel and hard hot start. Diagnosis, heat soak. Fix, wire back the heat riser, insulate the carb and fuel lines re-engineer the timing management.

Had my 63 manual out today reading a bit on the fi. Found the diagnostic check chart for carbs on the prev. page. 12 check points for hard hot starts.

Steve

[Duke W.]

Re: Gasoline distillation curves as related to fuel injection

How does it do this? I'm just not seeing it. What I'm seeing is that the Summer E10 curve and the traditional summer fuel curve are pretty near coincident at the approximate temperature at which fuel perc becomes detectable in a Rochester FI unit.

If there is some hint about vapor pressure embedded in those curves, I don't know how to extract it.

You said problems begin at about 135 to 140F, but it could be the method or surface that you're trying to measure . The aspect ratio of my Harbor Freight IR gun is about 4:1, so if held four inches away from the surface it measures the average of a one-inch circle, so it's best to hold and IR gun as close to the surface as possible to avoid cooler surfaces that might be within its field of view. That can be done with the fuel meter, but the spider would be tough to get accurate readings. Most carburetor owners don't report significant problems until the carburetor body reaches about 150, and some have reported as high as 180.

The key to understanding is the following statement from that post:

As a liquid is heated its vapor pressure increases with temperature. The definition of boiling is when vapor pressure is equal to surrounding pressure, which is atmospheric pressure for a carburetor or the Rochester FI fuel bowl.

Thats' why E10 has lower vapor pressure at 100F than traditional straight gasoline on the Chevron graph because fewer of the E10 components are boiling (atmospheric vapor pressure) below about 130F.

Likewise, the the greater percentage of the fuel's components that are at their boiling temperature, which means their vapor pressure is at atmospheric pressure, the higher the average vapor pressure of the fuel blend. That's the implication of the difference in distillation curves of the E10 versus the traditional straight gasoline blend from about over 130-140, and the higher the vapor pressure of the blend the greater the rate of vaporization from the surface. The bulk liquid does not have to be boiling for a high surface a vaporization rate to occur, just as you see saturated steam rising from a heating pot of water before a roiling boil occurs.

Vapor pressure could probably be computed for any temperature if one had the vapor pressure curves for all of the several hundred hydrocarbon species that are in gasoline blends and the percent of each in each blend, but I don't have that data.

It would be easier to measure the vapor pressure every 5 or 10 degrees from room temperature to over 300, but don't try this at home.

Remember the "vapor pressure" that is measured and published for gasoline is at about 100F. I says nothing about what the vapor pressure is at higher temperature, but we can make reasonable relative inferences from the distillation curves.

Duke

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

You said problems begin at about 135 to 140F, but it could be the method or surface that you're trying to measure . The aspect ratio of my Harbor Freight IR gun is about 4:1, so if held four inches away from the surface it measures the average of a one-inch circle, so it's best to hold and IR gun as close to the surface as possible to avoid cooler surfaces that might be within its field of view. That can be done with the fuel meter, but the spider would be tough to get accurate readings. Most carburetor owners don't report significant problems until the carburetor body reaches about 150, and some have reported as high as 180.

The key to understanding is the following statement from that post:

As a liquid is heated its vapor pressure increases with temperature. The definition of boiling is when vapor pressure is equal to surrounding pressure, which is atmospheric pressure for a carburetor or the Rochester FI fuel bowl.

Thats' why E10 has lower vapor pressure at 100F than traditional straight gasoline on the Chevron graph because fewer of the E10 components are boiling (atmospheric vapor pressure) below about 130F.

Likewise, the the greater percentage of the fuel's components that are at their boiling temperature, which means their vapor pressure is at atmospheric pressure, the higher the average vapor pressure of the fuel blend. That's the implication of the difference in distillation curves of the E10 versus the traditional straight gasoline blend from about over 130-140, and the higher the vapor pressure of the blend the greater the rate of vaporization from the surface. The bulk liquid does not have to be boiling for a high surface a vaporization rate to occur, just as you see saturated steam rising from a heating pot of water before a roiling boil occurs.

Vapor pressure could probably be computed for any temperature if one had the vapor pressure curves for all of the several hundred hydrocarbon species that are in gasoline blends and the percent of each in each blend, but I don't have that data.

It would be easier to measure the vapor pressure every 5 or 10 degrees from room temperature to over 300, but don't try this at home.

Remember the "vapor pressure" that is measured and published for gasoline is at about 100F. I says nothing about what the vapor pressure is at higher temperature, but we can make reasonable relative inferences from the distillation curves.

Duke

When I first read this post I thought there was something about the temp of the fuel in the metering body being higher than the IR reading of the body itself. I'm not seeing it now, but I'll throw this in anyways.

One of the problems with making assumptions about the vaporization of fuel based on the temp of the vessel it's held in is that it does not take into account the removal of heat that results from the vaporization process.

It's the reason that no matter how much heat you apply to a pot of boiling water, the temp never exceeds 212F. And the rate of vaporization varies by the difference in the temp of the heat source and the boiling point of the liquid. You can boil water all the water out of a pot at 215F, but it takes a long time, much longer than a heat source of a constant 500F. It's the principle under which air conditioning works, its the reason we perspire.

I was at a friends house last weekend to see his still, a commercially made item for home distillers. What's interesting about the process is that for a small amount of liquid this is an all day process. The temp of the mash is being monitored during the process. Initially, you can not get the mixture to 212F. In fact, that's how you tell when you're done. When the mash temp hits 212f you know that all you are getting at that point is water vapour. The vapourization of the components with lower boiling points removes heat as they boil off which regulates the temp. And with the constant two burner propane heat source of a temp multiple times higher than that of the mash, it takes all day to do that, the temp gradually rising as as the lower boiling point components boil off.

Further, the rate of vaporization is greatly influenced by surface area exposed to atmospheric pressure.

Lacquer thinner vapourizes quite quickly at room temp. However, I can store it indefinitely at room temp with the lid on the can. Remove the lid, it will disappear, but not that quickly. Pour it into a large bowl, quicker yet. Pour it on the floor, still quicker. Spray it out an atomizer and now very quick.

When the chart says that for a given temp 40% of the compound is at or above it's boiling point it does not mean that at that temp 40% is now vapour. Besides the huge unknown of what the actual temp of the fuel is, as opposed to the vessel holding it, none of the other factors that affect the rate of vapourization have been taken into account. You only know the temp of the vessel and the distillation curve of the contents. That's a pretty incomplete picture.

Jim,
With the FI system and vapour in the delivery lines, is the situation that after shut down vapour bubbles backwards off the fuel surface (the open end of the line exposed to atmospheric pressure) and lodges in higher points in the line? Are the symptoms from that a rough idle after initial startup until the liquid fuel now being metered into the line displaces those bubbles?

Steve

[Steve G.]

Re: Gasoline distillation curves as related to fuel injection

Here's another point to contemplate.

"As distillation progresses, the concentration of the lowest boiling component will steadily decrease. Eventually the temperature within the apparatus will begin to change; a pure compound is no longer being distilled. The temperature will continue to increase until the boiling point of the next-lowest-boiling compound is approached. When the temperature again stabilizes, another pure fraction of the distillate can be collected."

In keeping with what I observed in my friends still. Per the fuel distillation chart, in order for the temp to rise to 130 we would have had to boil off the components with boiling points below that. In this case, roughly 10% of our fuel. That's a big loss.

The context of the article that the chart above was taken from was using it not to indicate levels at which perc might be an issue, but rather to explain the importance of having compounds come off at different temps. If they did not we would not be able to start the engine and if we were driveability through warm-up would be very poor.
With that in mind, it is the boiling point of fuel atomized into the air that is being heated by the exhaust cross over that is of interest.

Steve

[William F.]

Re: Gasoline distillation curves

Steve,
Reread my post. I stated that cause of problems should first be diagnosed in a logical fashion before making "fixes." But you seem to think the more underhood, manifold , carb heat the better. I, and many others disagree.Why did GM discontinue the under carb heat slot, install carb to manifold heat insulators/heat deflectors if we need so much heat? Why do we have cold air induction systems on many high performance engines? A heat riser is fine for cold starts but not so good after warmup in hot conditions. Are racers who uniformly block manifold heat passages wrong-at least from producing more horsepower point of view? This topic has been beat to death.