I had a 3.# litre deisel Ford farm tractor engine in a boat. The fuel pump had a glass cover. A blockage in the pipe from the tank reduced power, and showed vapour in the pump, which disappeared when the engine was shut down. I eventually found a wad of fibre in the inlet to the pump.
Red deisel has a much lower VP than Avgas, which is itself lower than the EN228 I buy from Tesco.
LeSving wrote:
…It has much more than nothing to do with temperature.
However, you can’t really control the temperature. I have seen ISA-10 and I have seen ISA+20 or so. Also you can’t really control the temperature of all parts of the fuel system; e.g. the parts passing under the cockpit will be warmer, and parts in the engine compartment could be a lot warmer.
An interesting point is that the IO540 engine driven fuel pump has a cooling duct going to it. It may be that was done for this reason.
Yes, but lower the temperature, and you suddenly will not get any vapor forming. It has much more than nothing to do with temperature.
LeSving wrote:
That doesn’t sound right. Vapor forming is a function of pressure AND temperature.
Why not? You don’t necessarily need both. A pressure drop at constant temperature could be enough.
ChuckGlider wrote:
This had nothing to do with temperature and was all to do with the pressure drop caused by the suction of the pump.
That doesn’t sound right. Vapor forming is a function of pressure AND temperature.
Maoraigh wrote:
Would the suction of the pumps increase the possibility of vapour lock in the gascolator?
I recall reading an article in the EAA magazine many years ago about vapour lock. Piper had built a test rig of the fuel system for one of their models, I forget which, but built entirely from transparent materials so they could see what was going on. The most reliable place for vapour to form was on the supply side of the fuel pump. This had nothing to do with temperature and was all to do with the pressure drop caused by the suction of the pump.
My own little 50 year old machine, low wing, single fuel tank ahead of the panel, is entirely gravity fed, downhill to the filter and downhill again to the carb. Gravity has never been known to fail.
As to the possibility of vapour lock stopping an engine at higher altitudes and the pilot draining the battery attempting a restart, for many (most?) engines I’d say not very likely. Disregarding takeoff from a high altitude field and therefore low height above ground, the pilot will (a) have a lot of height to play with and (b) very probably not be faced with a stopped prop so no battery drain necessary. I have seen this demonstrated and very aggressive action was required to stop the prop.
LeSving wrote:
Sonex themselves recommend using only avgas though, probably due to vapor lock reasons. According to them, the more gadgets you can do without, the more reliable and trouble free the aircraft is.
I’m afraid the use of AVGAS itself might cause problems. It doesn’t do any good in a Rotax (the lead settles everywhere and reduces the maintenance intervals) and I can imagine it doesn’t in an AeroVee (VW-conversion) neither. Hence I doubt, that the usage of AVGAS contributes to a more reliable and troublefree aircraft(engine) other than avoiding vapour lock.
BTW the lifetime of the electric fuel pump in a car normally exceeds the lifetime of the car.
I think it is upstream of gascolator, but I’m not sure. I live 80 km from the hangar, and haven’t been there for weeks, as the one-piece wing is off and away for wood repair and recovering.
Maoraigh wrote:
Would the suction of the pumps increase the possibility of vapour lock in the gascolator?
Was the electrical pump also placed downstream the gascolator, inside the cowling? If so, that seems very counter productive to me regarding preventing vapor lock.
