Notes from Windward: #66


Bi-fueling the work truck

Adding the ability to run on propane

the bi-fuel carb mounted on the engine
  

     One of Windward's longterm goals is to develop ways to utilize waste wood (especially forest waste) as an automotive fuel. Being able to power our vehicles with renewable fuels grown on our site will make Windward more sustainable, and show the way for others to lessen their dependence on foreign oil.

     Now, if that were an easy thing to do, then lots of people would be doing it. Well, actually back during World War II more than a million vehicles were powered by the on-board gasification of wood and charcoal, but that was a while back. Today, vehicles are more complex and few people are used to tinkering with them, so different approaches need to be developed.

     We're going to be using our work 3/4 ton Chevy work truck as our test platform, and had started the process of installing the gear needed to enable the engine to run on propane gas when we made the decision that the truck's engine was too worn out to serve as a viable working model. It was still running, but it was worn to the point where it produced notable amounts of smoke on start up.

     We didn't want people to think that the use of alternate fuels was causing the engine to have a smokey exhaust so we made the decision to hold off on going further with the conversion until after we installed a rebuild motor. That happened last January, and now that the engine has been broken in and is running fine, we're comfortable going forward with setting it up to run on either gasoline or propane.

the new carb set up and running
  

     The propane "carb" mounts on top of the standard carburator which functions in the usual way so long as it has gasoline delivered to it by the fuel pump, so the first step in switching over from gasoline to propane is to turn off power to the gasoline selenoid shut-off valve. The engine will keep running for a minute or so as it uses up the fuel still inside the carburator, and as it start to falter, power is switched over to the selenoid that controls the delivery of propane to the evaporator and from there to the engine.

     Depending on outside temperature, the propane in the fuel tank will be under between eighty and a hundren and fifty psi. As the liquid propane is drawn out of the fuel tank, it first passes through a selenoid valve that has to be powered on in order for fuel to flow through the valve to the regulator which will lower the pressure before the fuel is delivered to the evaporator.

     When a liquid evaporates it adsorbs energy from its environment (energy that's referred to as the heat of vaporization) which is why if you get liquid propane on your skin, you'll get a "freezer burn" as the liquid extracts heat from you in order to vaporize itself. If propane was being drawn off the fuel tank as a gas, the liquid remaining behind would become progressively colder until it froze into a solid hunk of propane, at which point it would have very little vapor pressure left, and your engine would die from a lack of fuel.

     To get around that, the propane is drawn off the fuel tank as a liquid and fed into an evaporator that's been spliced into the water line that feeds the car's heater. That provides a ready source of hot water which provides the heat of vaporization needed to vaporize the propane so that it can be delivered to the engine as a gas.

the propane shut-off selenoid / regulator and the evaporator
  

     The bi-fuel system is controled by a dash-mounted switch which allows the driver three options: propane on - gasoline off, propane off - gasoline on, and both propane and gasoline off. There no configuration of the switches which allow both propane and gasoline to flow to the engine at the same time, a condition which would "flood" the engine and shut it down.

     This is a good example of how we approach research projects, and the relevance of our name. An engine powered boat can head directly into the wind so long as it's fuel holds out and the engine keep running, but when it runs out of fuel or if the engine fails, it will have no choice but to drift with the wind while it awaits rescue.

     A sailboat doesn't have to worry about running out of fuel or having the engine fail since it uses the wind to propell itself to windward. The tradeoff is that it can't sail directly into the wind, but rather has to tack back and forth as it works its way into the prevailing wind first reaching to one side of the wind, and then coming about and reaching to the opposite side of the wind.

     Our ultimate goal is to be able to produce methanol (wood alcohol) from waste wood for use as a car fuel (most commonly used as M85, a blend of 85% methanol and 15% gasoline), but there are many steps that will have to come together before that comes on line. And so we proceed by breaking the task down into discrete steps that take us part of the way, that accomplish some incredmental part of the agenda before we "come about" and head off on the next tack.

     The next leg of this part of this research project will involve the installation of high pressure tanks in sides of the bed of the pick-up to hold producer gas. With that on-board, it will be a simple matter to route the producer gas through another selenoid valve and pressure regulator, and then tee it up with the line feeding gaseous propane to the engine.

     Note: the combustible gases given off by wood are referred to as "wood gas." It's a mixture of many compounds including the hydrogen and carbon monoxide that will power the engine, but it also contains notable amounts of wood tar and ash, two things that you don't want to get into your engine. Once wood gas has been processed to remove these problem causing impurities, it goes by the name of "producer gas" which is the gas that city people used a century ago to light their homes and street lights before the introduction of "natural gas" as a by-product of oil drilling and refining.

     There is also an immediate advantage to having the work truck set up as a bi-fueled vehicle in that we're now able to use which ever fuel is the cheapest. Right now, with regular gasoline at $3/gal, it makes all the sense in the world to run as much as we can on propane which we're able to buy from the wholesaler at $2/gal. We'd still rather be running on home-made renewable fuel, but in the meantime we'll be enjoying considerable savings while we work through the next leg of our journey down the road that leads to sustainability.


Notes From Windward - Index - Vol. 66