Introduction: Waste Vegetable Oil Conversion for Diesel Bus

About: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output devices. His detailed drawings of traditional Pacific I…'s bus can get halfway across the country on a single fill of waste vegetable oil ( WVO ).
They get their fuel from the used oil tank behind restaurants.
All processing of incoming oil takes place right on the bus, mostly while it's in motion. That means heating, water separation and filtration. They get about 10 mpg on veggie oil, which is about the same as they do on diesel.

This bus is a VEGGIE DIESEL bus, that can burn straight vegetable oil, as well as regular diesel or biodiesel.
It's a "two-tank" system, which means the bus has a small tank of biodiesel (or diesel) to start the engine, and then they switch to straight vegetable oil when the engine is hot.

For the uninitiated, Biodiesel is veggie oil that's been subjected to a chemical process so it's thin and runny (lower viscosity) all the time and can be run in unmodified diesel engines. This bus runs on straight veggie oil, no reaction needed. It only requires biodiesel or diesel fuel except for starting and shutting down the engine.

Check out ['s website] for the history of how their methods have evolved.

Here Ethan Burke shows the pre-filters.

In another side compartment is the collection hose. They park next to the restaurant's waste tank, dip the end of their collection hose into the top, and start pumping oil into their storaage tanks.

They dip a piece of cardboard into the oil and do other connoisseur stuff to see if they want that restaurant's oil or not.
They don't want the oil at the bottom of the waste tank because that's where water and dirt settles. Their collection hose has a screen on the end to filter out bits of french fries, dead leaves, etc.

Step 1: Storage Tanks

These three 55 gallon oildrums are strapped under the rear of the bus.
The incoming oil goes here. The transfer pump can empty either of the side tanks into the center tank.
The center tank is heated.

Step 2: Water Separation

Hot coolant from the engine is piped to a coil of copper tubing in the middle tank.
That heats the vegetable oil.
After heating it up and letting it cool down water separates out and sinks to the bottom.
Then they drain out the water at the bottom of the tank.

Step 3: Transfer Pump

This is the main pump. It runs on 110volts from the inverter. The valves let them pump into or out of any of the three oildrums, out to the main fuel tank after passing through some filters, or in from a waste oil container at restaurants.

Step 4: Pre-Filters

On the way from the rear drum to the main fuel tank the hot oil goes through these filters.

These filter housings are available at any hardware store or plumbing supplier.
They contain one-micron nominal bag filters.
"nominal" means the average pore size is one micron. They don't block everything larger than one micron. A lot of multi-micron sized chunks still get through.

The pressure guages on the top are to check when the filters are clogged and need to be replaced.
When there's too much pressure across the filter, it means its clogged.
These filters are in parallel, in other words some oil goes through one and some goes through the other.

Ethan intends to change this so oil goes through three filters in series for finer filtration. He expects his screw on fuel filters in fuel injection system will last longer that way.

They look for very clean oil that won't clog their filters.
Their best oil came from the Falafel fryer at an Arab restaurant.
Chinese restaurants often have good oil.
Oil from frying chicken, any oil with animal fat in it is harder to filter and clogs the filter sooner.

After going through this filter the fuel goes into the main fuel tank. That's the regular stock fuel tank that came with the bus. I don't have any pictures of it. It wouldn't look like anything anyway.

Step 5: The Engine Compartment

It's a stock diesel engine, stock injector pump, stock injectors, the same as when it was bussing kids to school.
A bunch of additional plumbing has been added to heat and filter the veggie oil.
The next few steps will explain in more detail the function each add-on part.

Heated fuel line
starting fuel pump
Heated screen filters
heated final filters
temperature sensor
various hot hoses.

Step 6: Heated Fuel Line

A hot coolant hose from the engine goes back to the main fuel tank. It runs into 30 feet of PEX brand tubing coiled up in the tank. That heats up the fuel in the tank.
PEX is a type of heat-resistant plastic tubing available at hardware stores.

Inside another hot coolant hose is the aluminum fuel line.
That way the fuel is kept hot all the way to the engine.
Here's the T fitting where the fuel line comes out of the hot coolant hose.

This instructable has more details on how to make hose-in-hose heated fuel lines.

Step 7: Heated Screen Filters

The heated fuel line carries the fuel through these two heated screen filters with a 20 micron asbolute rating. Unlike the sock filters seen earlier, this micron size actually means there won't be any particles in it larger than 20 microns.
They are Volkswagen motor oil coolers from a junkyard. Each unit has a water hose in and out and a fuel line in and out, so there are plenty of hoses to delight the senses.In the original car, the hot engine coolant is cooler than the hot motor oil, meaning the heat exchanger in this case will heat the engine cooant and cool the motor oil.
In this case, the hot engine coolant exchanges heat with the cooler vegetable oil, raising the vegetable oil temperature as it passes through the metal screen filters.
They work great for that.

The filters are plumbed in parallel to decrease resistance, that is some fuel goes through one filter and some through the other.

The first photo shows a filter with the can removed.
These pleated screen filters seen here are handmade and intended to be used for motor oil.

Step 8: Elsbett Heat Exchanger and Filters

Our bean-squeezins journey now takes it into the main heat exchanger where it's once again heated by hot coolant. Then it goes through a 8 micron "nominal" filter.

This is an Elsbett brand unit from Germany. There's a temperature sensor on top.
Next to it is a mysterious black dingus.
Ethan says: "The black thing is a primer pump in case you want to pull fuel into the fuel filter before starting the engine and getting air inside. We havent even used it."

Step 9: Temperature Sensor and Starting Fuel Pump

This bus starts on diesel or biodiesel when the engine is cold. There is a separate small fuel tank for the starting fuel. I don't have a picture of it. It's a 20 gallon red plastic tank strapped under the bus.

Once the engine and veggie oil have heated up to 170 farenheit this temperature sensor switches to the other fuel pump and the engine runs on veggie oil.
There's a manual fuel selector switch in the cab also. When shutting down the engine they switch back to the starting fuel tank for a few minutes before turning off the engine. That way there's no cold veggie oil in the engine or injection system the next time they start it.

When veggie oil is cool, it can put pressure on the fuel pump, doesn't atomize well, doesn't burn completely, and can leave carbon deposits in the engine.

Also it's too thick for the fuel injection pump to move it. In the former inadequate heatling and filtering system that came with the bus when they bought (which has since been replaced by the one being described). Their injector pump broke and had to be replaced once because the veggie oil going into it wasn't hot enough.

Step 10: Roof Rack

The bus has many other ingenous systems and features, but for now, here's the roof rack.
It's a really simple and good design.

So that's it, a proven veggie diesel system for a large vehicle.
Get good veggie oil, heat it, and filter it.
Make sure it's good and hot before entering the injector pump.
Start up and shut down your engine on something else, either diesel or biodiesel.

For more info or to buy a shuttle bus ticket from SF to Burningman, check out their website.