Controversial Topic

[Steve G.]

Re: Controversial Topic

Again, my original post was just a reflection of observed differences between 110 octane and Ethanol blend fuel in a single FI C1. I have way to many "hot day" stories about 60' dying or failing to restart when I was using 91-93 Ethanol blend. All I am saying is that when I got rid of the Ethanol and started the VP fuel my operation reliability went to 100% and that has been over the past 1 & 1/2 years. I am not trying to convince anyone to use hi-octane leaded fuel in a C1 however, for those of you who are experiencing operation difficulty in the Summer this might be a solution worth considering.

I can certainly understand your frustration and then relief at finding some kind of solution. It seems, however, that not everyone experiences these problems when running pump gas. And that causes me to think that the fuel change may be a compensation for a treatable problem. Especially given the fact that you are also only getting 10 mpg.

Personally, I wouldn't want to be tethered to a racing gas outlet and carry extra fuel in the trunk. Especially at 10 mpg. But if it works for you, that's all that matters.

Steve

[Jim L.]

Re: Controversial Topic

How do you know it's boiling in the spider? What tests are performed to determine this? It seems to me that it would be unlikely for an fi engine, with no heat riser or crossover to reach the 200 F threshold required for the fuel to boil, given that measurements taken on lines and fuel bowls sitting on engines with heat risers and crossovers were only recorded in the 150-180 range. And that's the temp of the containers, not the fuel in them.

I'm unclear where/how you developed the notion that motor fuel doesn't boil until it reaches 200F. Its various components will vaporize at a broad spectrum of temperatures many of which are well below 150F

In well controlled experiments, I've observed Rochester FI systems going lean at idle due to fuel perc at nozzle line temperatures between 135F and 140F. This is with summer fuel. With winter fuel, the lean idle due to perc can happen with nozzle line temperatures as low as 110F.

The correlation between nozzle line temperatures (which logically have to be related to fuel temperatures) and idle air/fuel ratios is inarguable.

Jim

[Steve G.]

Re: Controversial Topic

I'm unclear where/how you developed the notion that motor fuel doesn't boil until it reaches 200F. Its various components will vaporize at a broad spectrum of temperatures many of which are well below 150F

In well controlled experiments, I've observed Rochester FI systems going lean at idle due to fuel perc at nozzle line temperatures between 135F and 140F. This is with summer fuel. With winter fuel, the lean idle due to perc can happen with nozzle line temperatures as low as 110F.

The correlation between nozzle line temperatures (which logically have to be related to fuel temperatures) and idle air/fuel ratios is inarguable.


Jim

Well Jim, for one, the chart posted in one of my threads above. Published by the fuel people and inserted into the thread I started entitled Gasoline Distilation charts. According to the fuel industry evap fuel loss in the carb doesn't even start until 150. It further identifies 200 as being the threshold for vapour lock and percolation issues.

Secondly, those numbers are referencing fuel in a vented bowl, not under pressure in an enclosed tube,

Thirdly, as Peter Stout identifies in his contribution, the boiling point of the component everyone is blaming for the problem, ethanol, is 173.

In addition to that, the fuel temp is not the same temp as the tube. There is a relationship, but they are not the same. The lines are the source of the heat to the fuel. It's like measuring the temp of the pot that you are heating something on the stove.

Furthermore, If, huge if, the fuel were actually boiling in the lines, why would it matter? The fuel has already been metered. Air fuel ratios that we talk about are actually by weight of the air compared to the weight of the fuel. Whether the fuel is liquid or vapour you still have the same amount of fuel and it's going the same place. Contrary to what Jerry was eluding to, it does not escape up the vent in the nozzle box. At idle 40% of the air going into the engine for combustion is entering through those vents. It is designed that way to improve atomization and vaporization of the fuel. Whatever goes into the top end of those tubes comes out the bottom, and the constant flow from a positive displacement pump ensures that.

The top of the nozzle with the tiny hole is the end of the pressure system. It sprays into the nozzle chamber from there and it's pressure is reduced. Just like an expansion valve in an AC system. From there engine vacuum pulls it and the air coming through the vents into the intake stream. Combining the atomized fuel with air breaks it down further and aids it's evaporation.

But the point is, whatever fuel is metered and sent into the spiders ends up in the cyls. Where it vapourizes isn't as important as if it vapourizes.

If it were me looking at this problem I'd be more inclined to look at fuel not properly vapourizing.

Think about this. All the liquid fuel that is metered is accounted for. It all makes it into the cyls. Can't go anywhere else. But sometimes you have a lean condition and sometimes you don't. Fuel that doesn't vapourize does not burn. It might as well not be there. Incomplete vaporization of the fuel results in a lean condition. The fuel companies tell us that perc and vapour lock are less of a problem than it was in the 80's. Could that be because today's fuels don't vapourize as well as they did in the 80's? Could it be related to the fact that these trouble temps identified in the chart are actually higher than they used to be?

I don't know about the science used to determine the boiling fuel in the spiders, but I've seen lots of bad science.

Steve

[John D.]

Re: Controversial Topic

Jerry, Your comments are always most welcome and most appreciated.
Back to work. John

[Jim L.]

Re: Controversial Topic

Steve, your lack of understanding about how a Rochester FI system works coupled with an equivalent lack of understanding of fluid physics is insurmountable. Many bright, knowledgeable FI people have patiently tried to explain the errors in your assumptions and thought processes, all to no avail, apparently. I see no value in making another attempt to point out where you continue to be wrong in your thinking.

Jim

[Steve G.]

Re: Controversial Topic

Steve, your lack of understanding about how a Rochester FI system works coupled with an equivalent lack of understanding of fluid physics is insurmountable. Many bright, knowledgeable FI people have patiently tried to explain the errors in your assumptions and thought processes, all to no avail, apparently. I see no value in making another attempt to point out where you continue to be wrong in your thinking.

Jim

Jim,
I deal with fuel systems far more complex than this, high pressure injection systems with pressures roughly 100 times and tolerances much tighter than what you see here. This isn't rocket science. I have been a journeyman for almost 40 years and between what I was taught and what I picked up along the way, I know enough to tell when someone's piddling in my ear and trying to tell me it's raining.

Instead of explaining how hopeless I am, for the sake of the curious minds out there, why don't you take a stab at answering some of the questions the experts weren't able to.

The expert 's take on how this system works is that the nozzle doesn't atomize the fuel, it has to squirt a liquid stream to get it across the chamber and hit a hole on the other side to work. In as much as there is no heat riser and crossover heating the induction air to vapourize the fuel like a carb has, and the nozzle doesn't atomize the fuel like a current technology common rail system injection nozzle does, what vapourizes the fuel? Or does an engine fitted with a Rochester FI not need to have it's fuel vapourized to burn.

And perhaps you can also explain the 63 factory service manual's error. It says the vent in the nozzle chamber is letting air in, not venting it out as is described by the expert as the exit passage for the fuel vapour. 40% of the air the engine is consuming at idle coming through that hole and yet the percing fuel vapour makes it around it and somewhere outside the intake system.

Perhaps with that you could also explain how the nozzle vent, and those fumes escaping through it, are able to do that in opposition to the vacuum at the other port of the nozzles. You know, the one the liquid stream needs to bullseye for the fuel to flow.

Explain to all of us how the chart posted above by the fuel industry is all wrong.

When you finish these I've got a lot more that the "percing" disciples have not been able to answer.

Jim, it's probably best not to assume everyone has your understanding of the operation of your fuel system. But it certainly explains why some of these run the way they do.

Steve

[Gary C.]

Re: Controversial Topic

Gentlemen, enough. Need I remind everyone that no disbaragement of members is not permitted.

This thread is closed