100 octane leaded aviation gasoline question?---?

Question

What additive is used to raise the boiling pt. of this fuel to counter vapor lock conditions and how is this fuel inspected to insure operational quality after delivery to the field?

Answer 1

There is no additive to prevent vapor lock. Vapor lock comes from a fuel pump mounted higher then the fuel tank a boost pump of some kind is needed to keep the positive pressure in the fuel lines so as not to allow vapors to form. Some planes have a system for cooling the fuel. Some use something that looks like a radiator witch passes fuel through and is cooled by ram air. Others use cool air from the Environmental Control System and some use a combo of the two to help keep fuel below its boiling point. 100 Octane AVGAS is a stable fuel for high power and high compression engines that operate at or near thier maximum power setting for long periods of time. A fuel sample is taken from the aircrafts external fuel sample ports and is collected in a glass jar then visually inspected for water and other forigen objects then that sample can be forwarded to the fuel distribusion plant for further testing such as flash point.

Answer 2

The octane rating of hydrocarbon fuels is a measure of it's flash point. This is the temperature and pressure conditions required for the fuel to combust. Higher octane ratings mean higher flash points. High performance gasoline engines typically have higher compression cylinders, which require a high octane fuel to prevent pre-ignition or pinging.

Diesel fuel is just the opposite. The flash point of diesel fuel is much less then gasoline. That is why mixing these fuels in different engines can damage an engine.

There are octane additives you can but but they don't just add up like you think. The best way to get 100 octane is buy it from the pump. The octane level is more reliable that way. Unless you can measure the specific gravity of gasoline.

Adding glycerol to water, like in engine coolant, will raise it's boiling point.

Answer 3

Octane is not about vapor lock- it is about temperature at which auto-ignition, also called detonation, will occur. This allows higher compression ratios and better efficiency; or at lower compression, a cooler running engine.

Aviation 100 octane fuel is called Low Lead but still has some lead.

I doubt it is inspected post delivery other than for water or other contaminants.

Answer 4

Not sure about the vapor lock part.

When I was an assistant airport manager, we did a density check on the fuel as it was delivered from the truck (and before we let him put the fuel in the tanks). Then, daily, we had to take a sample of fuel from each of our two 100LL tanks to check that the pump was working properly and to inspect for any contamination in the fuel, such as water or dirt.

EDIT:
I guess I should clarify that I mean the in-ground fuel tanks for the fuel farm, not the plane's tanks.

Answer 5

Fuel boiling in the lines is what causes vapor lock, so I assume there is an additive to lower the boiling point. Where I worked, no tests except in the tanks of our planes. If we got a bad batch, they found out right away and it was replaced.

Answer 6

There should be a section in the Pilots Operating Handbook / Flight Manual / owners manual of each plane you fly that tells you exactly what fuels are approved and can be safely used, so you should refer to that. In the USA, the chance of you encountering anything other than 100LL (blue) is very slim. If you ever do encounter the 100 octane leaded variety (green), it is perfectly safe to use in your Cessna 150 / 172. By the way, the answer above regarding lead fouling missed an important point. While lead does not burn, it is adequate EXHAUST SCAVENGING that is a major factor in preventing lead fouling of the spark plugs. For proper scavenging (purging unburned exhaust residue from the engine), one needs to keep the idle speed on the ground above 800 rpm and reduce ground running time as much as possible. Older aircraft (such as my 1959 C-172) are particularly prone to fouling, even on 100LL.

Answer 7

Lead content in grams of lead per gallon:

100LL = 2
80/87 = 0.5
Regular Auto Fuel = 0.1
Unleaded (Premium or Regular) = .001