HI William, Nice job...thorough and easy to understand. We all appreciate your efforts to educate us.
The potential I see in unleaded gasoline, is the potential of the growth of algas in the system. I experienced this when using Amoco 93 octane unleaded fuel. Successfully for many years....One time the normally clean smell of Amoca 93 Ultimate gas had a different smell...oily, like deisel fuel. My thought was "no Problem"...tho recognizing the fuel had been contmainated by deisel, or fuel oil, I felt because my engine was certifed on 73 Octane gasoline, there should be no problem......HA, HA, HA, was I fooled ! This was a time when I was flying very infrequently, leaving the same fuel in my tanks for weeks. Aa I drained the tanks on prefliight, I not only removed accualated water, but it was GREEN ! Evidently I was growing algae in my tanks. To correct this, I drained all fuel from my Coupe, and replaced the fuel with fresh fuel, and added some PRIST aditive used by the airport to treat jet fuel. This was used to prevent Algae growth in jet fuel ( now added at the refinery, as I understand). While this helped cure the algae growth, much dead algae black reidue remained in the tanks.... What a mess to clean out ! Foolishly, as I am quite stingy, I took the drined home and put it into of my autos.......bad decision !!!!, Within a day or so, both vehiclkes gad guages failed........I quickly recognized that the algae was eating on the copper wiring in the guage float system.... ON one vehicle that I used frequently, and refuled ofter, the problem cured it self in about two weeks....after adding PRIST... BUT, on the other car, I didn't act fast enough, and the guage no longer works ! :( I then began to wonder, why don't autos running on lead free gas have this problem ??? I then recognized that for over 15 years, autos have sealed systems, and carbon flters, not allowing water condensation, and thus potential algae growth. Also, recognizing that tetra ethyl lead in old auto fuels, and in Aviation fuels which contained lead, prevents the growth of algae, even if we get condensatioin water in out tanks....thus avoiding algae growth! I doube that alcohol addition would also prevent algae growth...maybe even engourtage it ! So, we surely must have a problem in finding a suitable fuel that is lead free, but also algae free....maybe just add PRIST to all Aviation un-leaded fuels ???? as is done to jet fuel at the refinery???? This May be the simple solution... Thought to consider :) Fly Safe - Have Fun Harry Francis N93530 ________________________________ From: William R. Bayne <[email protected]> To: [email protected] Sent: Fri, August 13, 2010 5:20:10 PM Subject: Re: [ercoupe-tech] Mogas Vapor Lock? Our "gascolator" is a combination fuel strainer/sediment bowl, and I have heard that the screen in it is of a size that will pass gasoline but not water. Presuming this true, If all water is not removed from the fuel system before flight and the gascolator bowl becomes filled with water fuel will cease to flow to the carburetor. Such in-flight power loss would NOT be "vapor lock", but the pilot tasked with suddenly having to select a suitable place to land really doesn't care. From the standpoint of risk management, however, the distinction is worthwhile. The EAA's "Firewall Forward" book states that "Gascolators are susceptible to the effects of heat from the co-located engine and exhaust components, which can cause fuel vapourization in the gascolator and vapour lock problems. This usually manifests itself as a partial power loss in cruise flight." Our "gascolator" is a combination fuel strainer/sediment bowl. When it is mounted on or adjacent to the carburetor there is no "high point" where vapor lock can occur. When it is mounted low on the firewall, as is the case with F1A, Alon and M10 fuel systems, the carburetor float bowl becomes a "high point" in the fuel system. Fuel vapourization in the gascolator could ultimately cause the float chamber in the carburetor to partially or completely drain, causing fuel starvation in the engine. Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine. Wikipedia has, in part, this to say: "Gravity feed fuel systems are not immune to vapor lock...if vapor forms in the fuel line, its lower density reduces the pressure developed by the weight of the fuel. This pressure is what normally moves fuel from the tank to the carburetor, so fuel supply will be disrupted until the vapor is removed, either by the remaining fuel pressure forcing it into the float bowl...or by allowing the vapor to cool and re-condense. Vapor lock has been the cause of many[quantify] forced landings in aircraft. That is why aviation fuel (AVGAS) is manufactured to far lower vapor pressure than automotive gasoline (petrol). In addition aircraft are far more susceptible because of their ability to change altitude and associated ambient pressure rapidly. Liquids boil at lower temperatures when in lower pressure environments." If fuel vapor entering the carburetor float bowl is vented via the intake system, the mixture is, in effect, enriched; creating a mixture control issue. Wikipedia also, in part, had this to say: "Vapor lock was...common in older gasoline fuel systems incorporating a low-pressure mechanical fuel pump driven by the engine, located in the engine compartment... Such pumps were typically located higher than the fuel tank, were directly heated by the engine... Fuel was drawn under negative pressure from the feed line, increasing the risk of a vapor lock developing between the tank and pump..." In our systems, such "vapor lock" would not interrupt gravity flow of fuel to the carburetor from the fuselage tank, but would only intermittently disrupt the fuel pressure long enough to briefly decrease the rate of replenishment of the fuel level in the fuselage tank by the fuel pump. Our fuel systems allow such fuel vapor delivered into the fuselage tank to condense back to the liquid phase, either in the fuselage tank or in the process of excess fuel entering the return standpipe and returning back to the wing tank(s). "Vapor lock" of this sort would not affect our engine's operation. Perhaps others can shed more light on this subject? Regards, William R. Bayne .____|-(o)-|____. (Copyright 2010) -- On Aug 12, 2010, at 23:24, Wayne Woollard wrote: > > > Oftentimes with the F1's,A2's, and models with the larger gascolator mounted >lower on the fire wall, a vapor lock is misinterpreted as the culprit when >just >plain old air gets into the system after carburetor work, fuel leak repairs >and >running the header tank out of fuel. Air can be purged from the fuel system >by >bleeding fuel at the input to the carburetor. > > I have had it happen on more than 1 occasion so I know it to be true. > WW > D. Wayne Woollard CPBE > o--iii--( >
