Switch 22hp gas to 18hp diesel, will it be less powerful?

[Superduper]

T the fuel return line back to the feed hose from the tank... If it has an electric or mechanical fuel charge pump to lift fuel to the injector pump, make sure the return T is on the suction side ( tank side ) of the fuel charge pump. You will essentially be dumping unused fuel back to the feed line from the tank..

soundguy

Wow, now why didn't I think of that? And all this time, I was trying to figure out the easiest method to install a bulkhead fitting into the tank. But is this an appropriate method for a return line? It seems so easy that the question needs to be asked, why then does everyone go to all the trouble to plumbing the return line back to the tank?

 

[Superduper]

Quote:
Originally Posted by JSharp
The 2 cycles are "governed" too. By port timing and fuel/air flow...

Hey hey hey now, let's not bring that back up!

jb

I'd almost forgotten the circuitous route this thread had taken prior to getting back on track.

 

[ciderman]

Wow, now why didn't I think of that? And all this time, I was trying to figure out the easiest method to install a bulkhead fitting into the tank. But is this an appropriate method for a return line? It seems so easy that the question needs to be asked, why then does everyone go to all the trouble to plumbing the return line back to the tank?

Return fuel can become "aerated" by the agitation of the injection pump. It also gets hot. By returning it to the tank, the air bubbles out and the fuel cools somewhat.

If you can find the space, you might be able to install a small (1 qt.?) return tank, which then can be tee'd into the suction line.

 

[Matt_Jr]

Wow, now why didn't I think of that? And all this time, I was trying to figure out the easiest method to install a bulkhead fitting into the tank. But is this an appropriate method for a return line? It seems so easy that the question needs to be asked, why then does everyone go to all the trouble to plumbing the return line back to the tank?

The reason the fuel is returned back to the tank is because the fuel pump supplies more fuel pressure and volume than the engine needs to run. If you did not have a return line the engine wouldn't run because too much fuel will make it run too rich. That fuel has to go somewhere. If it doesn't go back into the tank then it will go into the engine. If it goes back into the supply line before the pump it will cause cavitation of the fuel, or as Ciderman said, cause aeration, unless the only pump is on the rail. then the fuel will never be pulled out of the tank. It will just go in circles if not just pump air. All fuel injected vehicles have a fuel pressure regulator that keeps the fuel supply line at the pressure needed under changing loads. If manifold pressure increases (under load) then fuel pressure goes up and less goes down the return line. When manifold pressure goes down (idle or engine braking) then more fuel goes down the return line. That applies to gasoline engines. Many diesels don't have throttle plates, therefore don't have low manifold pressure(vacuum) but the fuel pressure is still regulated and the fuel not used goes back into the tank. This also allows the fuel pressure change properly according to engine load, pass through the filter several times, keeps sediment off the bottom of the tank, lowers moisture content in the tank and cools the fuel, like Ciderman says.

 

[IXLR8]

Wow, now why didn't I think of that? And all this time, I was trying to figure out the easiest method to install a bulkhead fitting into the tank. But is this an appropriate method for a return line? It seems so easy that the question needs to be asked, why then does everyone go to all the trouble to plumbing the return line back to the tank?

The "T" worked for a friend of mine when he put fuel injection in his airplane. I tried it when I upgraded the engine in my airplane to a fuel injected one. His worked fine, in mine, the fuel got too hot and 'boiled', causing fuel starvation. Glad I found the problem during taxi testing and not in flight. I had to run the fuel back to the main tank for everything to work properly. I think the key for my setup not working was the fact that my fuel injection system ran at twice the pressure as his, more heat buildup. I would think diesel would be less of a problem, but it might depend on the injection pressures. You might want to run a longer copper line back to your "T" to provide some cooling, if you go that route. I would give it a try, much simpler. If ended up putting it back into the fuel tank, could you make up something simple to go in the fill cap?

 

[Matt_Jr]

IXLR8, Your airplane. I'm sooooooo jealous ........It could work if a cooler was installed before the "T" fitting and the flow and pressure wasn't too high or the T was closer to being "Y" shaped. Another interesting topic-fluid dynamics. We need a machinist to make a cone shaped "Y" fitting.

 

[Superduper]

You guys just bursted my bubble! Seriously, I thought it might be too easy to be true. My understanding is that the fuel pump which I'll be adding before the engine is merely a low pressure fuel transfer pump. The actual diesel injection pump is mounted on the engine and I don't know if the fuel return is from surplus fuel after the injection pump or not. I'll take another look when I unwrap the motor after the weather gets better.

 

[ciderman]

You guys just bursted my bubble! Seriously, I thought it might be too easy to be true. My understanding is that the fuel pump which I'll be adding before the engine is merely a low pressure fuel transfer pump. The actual diesel injection pump is mounted on the engine and I don't know if the fuel return is from surplus fuel after the injection pump or not. I'll take another look when I unwrap the motor after the weather gets better.

Sorry SD, don't want to sound discouraging. I want this to work for you.
You are correct that you'll need a low pressure lift pump to supply the injection pump. Concentrate on diesel not gasoline injection. Also, check your nozzles. Most, but not all, diesels also return fuel from the nozzles to the tank. This cools and lubes the nozzle. If the return from the nozzles is plugged, the nozzles will hydrostaticly lock. Bear in mind my experiance is fom running a Bacharach test stand at a Mack Truck branch, and may not apply to smaller diesels.

Is your existing fuel tank metal or plastic? I've added fittings to plastic tanks by cutting a hole in the top of the tank, installing the fitting, the reattaching with a plastic welder I got from Eastwood
Eastwood Co. - TPO, TEO & PP Plastic Welding Kit

Metal tanks can be trickier. If it has a sending unit, sometimes you can remove the sender to get enough room to work inside the tank.

 

[john_bud]

It sounds like an o-ring sealed "bulkhead" fitting swagelock or similar is what you need. Just drill a hole put in place with the back up nut. Uh, you can get a back up nut in there, right?

Ok, if you have man sized hands how about adding a nipple to the gas cap?

jb

 

[Superduper]

It sounds like an o-ring sealed "bulkhead" fitting swagelock or similar is what you need. Just drill a hole put in place with the back up nut. Uh, you can get a back up nut in there, right?

Ok, if you have man sized hands how about adding a nipple to the gas cap?

jb

Is your existing fuel tank metal or plastic? I've added fittings to plastic tanks by cutting a hole in the top of the tank, installing the fitting, the reattaching with a plastic welder I got from Eastwood
Eastwood Co. - TPO, TEO & PP Plastic Welding Kit

Metal tanks can be trickier. If it has a sending unit, sometimes you can remove the sender to get enough room to work inside the tank.

Well, the tank is plastic. Getting a backup nut in there might not be so easy as the filler is at an angle (not straight down) and the gascap mod is not practical. Because the cap unscrews, how would you remove it if there is a fuel line attached to it? Ciderman: cutting and rewelding sounds interesting but I have zero experience with a plastic welder and a fuel cell might not be something I'd like to start experimenting on. In the past, my attempts to weld with something other than the correct tool results in nothing more than making ugly holes in plastic. Seems plastic likes to shrink. Oh, BTW, the tank is one of those fitted/molded plastic tanks that looks like it was blow molded in place, flat pancake shape. Need to remove, rear seat, fenders which wraps around and the foot rests, etc to get at it. Will take another look later. Thanks guys for all the great info. A collection of brains is always better than a single one.