In case you haven’t noticed, Campus Progress isn’t paying me to cover this road trip because of my extensive automotive expertise. Nonetheless, I’m going to take a stab at explaining just how the bus runs on vegetable oil.
There are two hurdles to overcome with straight veggie oil before you can combust it: first, you usually get it unfiltered. If you’re picking up your fuel at a less FDA-friendly restaurant, you can find all kinds of gross stuff floating around in their veggie oil; rat poo, for example. Needless to say, you don’t want that in your engine.
As a result, Anne Marie’s fuel system has a whole bunch of anti-rat poo mechanisms in place. The first is that when we collect the fuel from the tanks, we use a suction wand which we place a couple inches below the surface of the oil–since crap (both literal and figurative) either floats to the top or sinks to the bottom, the center is the clean part you want to collect from.
If our day tank is already full, we dump that fuel into the bulk tank for use later. Both the bulk tank and the day tank have filters in place, so as it passes from one to the other it gets more and more refined. So the filtering problem is taken care of.
The next problem, fortunately, isn’t quite as gross; it’s an issue of viscosity. Veggie oil is too viscous to be processed effectively by a diesel engine, so its viscosity needs to be lowered to a level roughly equivalent to diesel fuel. This is done by heating it while it’s pumped towards the engine. Once it’s less viscous, it’s then filtered even more, before finally reaching the engine. And like in a normal diesel engine, any leftover fuel is pumped back around towards the tank.
One more cool thing about the fuel system: you’ll notice in some of the photos and video that there’s a complicated-looking instrument panel the bus driver has to fiddle with before beginning to drive. That’s because the diesel and veggie systems actually operate independently of one another. If there’s an emergency with the veggie oil system, that means we can always switch back to old-fashioned fossil fuel if necessary.
The two systems both connect to the engine at the supply line (where fuel gets pumped in) and the return line (where excess fuel is pumped out). So in order to start running on veggie oil, the driver needs to hit three switches: he starts the pump which will send veggie oil to the engine, then hits switches for the two valves controlling the supply line and the return line, so that only veggie oil enters and returns from the engine.
And then–voila–you get yourself some veggie oil-fueled motion.
