The first step in the process of adapting our work truck to run on fuels other than gasoline involved the chore of getting the truck restored to good operating conditions. If you haven't read that article, just click here. The truck is twenty-five years old and before it can be used as a reliable test platform, most of its components needed to be repaired or replaced in order to eliminate any potential problems that could interfere with or diminish its performance on alternate fuels. We started the process by installing a remanufactured engine, a task which was soon followed by a rebuild of the exhaust system. With those two improvements accomplished, it was time to install the hardware needed to enable the truck to run on both gasoline and propane. Since that was work that none of us had done before, we took the truck to a friend' shop and watched closely as he assembled the specialty parts and made the conversion. Since we were paying by the hour, we just wanted him to do the basic work, leaving the detail work for us to attend to later. This past week "later" finally rolled around.
Bi-fueling the work truck
July 29th update
When you purchase a rebuilt engine, the practice is to removed all the exterior components from the old engine and move them over to the "new" engine: examples, would include the generator, starter motor and the carburetor. We'd installed a new starter and flywheel during the process of installing the rebuilt engine, but we were still making do with the old carburetor. What triggered this current round of work on the truck was the realization that the carburetor's float valve was sticking, thereby causing the engine to flood; i.e. to get too much gasoline which is not only wasteful, but it fouls the plugs and makes the engine run poorly. So it was clearly time to upgrade thcarburetoror, and after a bit of research we decided on an Edlebrock after-market carb that was designed to go with the Chevy 350 V-8 engine we're using. The 350 is arguably the most common work engine out there, so whatever we learn will have the potential for broad application, which is one of our key goals for this project. Installing the Edlebrock was pretty straight forward except that the manner in which the fuel line is attached to the carb is notably different. Okay, that just gave us a good reason to rework that part of the system. When you're dealing with a truck that's twenty-five years old, it's always good to go through a system from one end to the other in order to insure that there aren't any wear or aging related defects to trip you up later on in the process.
In this case, we drained and dropped the main fuel tank, replaced the fuel line and installed an electric pump. The original installation of the propane system included an electric selenoid valve that cut off gasoline from mechanical fuel pump from getting to the carburetor when you were running on propane. The main problem there was that the point where the selenoid had to be mounted was up against line that carried hot exhaust gas through the choke. As the engine warmed up, the exhaust gas got hot, heated the bi-metal spring in the choke and caused it to rotate to the open position. In this case, the exhaust line was heating the choke and the selenoid -- not a good idea. The upshot is that we installed an electric fuel pump down near the gas tank (you want to put an electric fuel pump at the low point of the system since it pushes gas much better than it sucks, especially on a hot day when the gas wants to vaporize anyway. When someone says that they've "vapor locked," they're describing a situation in which their fuel pump is sucking vapor instead of liquid, and an engine won't run on the piddling amount of vapor getting through to the engine.
Now, instead of coming around the front of the engine and having to pass by the choke heater, the fuel line now enters the carb at the back, and the electric pump renders the selenoid valve redundant since when you shut off the electricity to the pump, the flow of gasoline to the carb stops. We took the truck into town yesterday to pick up a load of pea gravel for the aquaponics tanks, and the improved fuel system worked perfectly. Indeed, the process of changing over from gasoline to propane via shutting off the electric fuel pump is working much better than when we were relying on the selenoid. At this point, I'm considering the process of converting the work truck to multi-fuel vehicle to be successfully completed -- the next step will be to add pressure tanks to store synthesis gas made from pyrolysing wood chips.