The Technology of Converting to Biodiesel or SVO

Converting an engine to run on biodiesel, or even vegetable oil, is much simpler than converting a gasoline engine to run on ethanol. In fact, depending on your vehicle, you may not have to do any conversion work at all. Since petroleum diesel has been the norm for a century and change, and the infrastructure for petroleum-based fuel is basically everywhere, a certain mystique has risen up around the idea of biodiesel, but the situation is actually a lot simpler than many people think.

One of the most attractive things about the diesel engine is that it doesn’t have to run on diesel fuel. That is to say, diesel engines were originally designed to run on a wide variety of different fuels, and it was only later that petroleum diesel became the norm. Today, biodiesel is becoming more prevalent with each passing year, and people are also turning to other alternative fuels, like vegetable oil, to run in their diesel engines.

The Difference Between Diesel, Biodiesel, and Cooking Oil

Although diesel engines can technically run on a huge variety of different fuels, the three most common options are diesel made from petroleum, biodiesel made from plant and animal products, and straight vegetable oil or animal fat.

  • Diesel, or petrodiesel, is the fuel most commonly available from gas stations, and it’s what modern diesel vehicles are designed to run on. It is a petroleum product, just like gasoline, which makes it a fossil fuel.
  • Biodiesel, unlike regular diesel, is made from renewable plant oils and animal fats. Under ideal circumstances, it’s functionally the same as petroleum diesel, so you can run it in virtually any diesel engine with little to no conversion process. The main caveat is that pure biodiesel doesn’t do so great in cold weather, which is why it’s often sold as a blend with conventional diesel. For instance, B20 consists of 20 percent biodiesel and 80 percent petrodiesel. There are other issues with running straight biodiesel in some engines, but we'll touch on that later.
  • Straight vegetable oil (SVO) and waste vegetable oil (WVO) are exactly what they sound like. SVO is new, unused vegetable oil, and WVO is typically cooking oil obtained from a restaurant. Although it’s possible to run a diesel engine on fresh cooking oil bought from a store, it’s much more common—and more cost-effective—to obtain used oil from restaurants. The oil must then be strained before it can be used as fuel. Some level of modification is typically also required before you can safely run a modern diesel engine on cooking oil.

Converting an Engine to Run on Biodiesel

In most cases, you don’t have to do any kind of conversion or add any additional tech to your car to run it on biodiesel instead of conventional diesel. Mixtures ranging from B5, with 5 percent biodiesel, to B100, with 100 percent biodiesel, are commonly available, but you’ll want to check the fine print in your warranty before you fill up. Some manufacturers will now warranty engines that have been run on B20 or less, meaning 20 percent or less biodiesel, but it varies from one OEM to the next.

The one major factor to be aware of when converting over to biodiesel is that biodiesel can contain traces of methanol, which is a solvent that can destroy any rubber hoses or seals in your fuel system. So if your vehicle uses any rubber in the fuel system, it’s important to switch over to components that won’t fall apart when you fill your tank up with biodiesel.

Converting an Engine to Run on Cooking Oil

The easiest way to convert a diesel engine to run on cooking oil is to buy a kit that’s specifically designed for your vehicle, but there are two major factors that need to be addressed. The first issue is that cooking oil tends to get very thick when it’s cold, and the other is that used cooking oil contains a lot of impurities and particulates.

The first issue is addressed in two ways: starting and stopping the engine on conventional diesel or biodiesel, and pre-heating the vegetable oil prior to combustion.

With that in mind, SVO and WVO conversion kits typically come with an auxiliary fuel tank to hold the cooking oil, fuel lines and valves, filters, heaters, and other components necessary to perform the conversion process.

The other issue is primarily dealt with by pre-filtering the cooking oil, which means that you need to filter the oil manually after obtaining it from a restaurant. After the oil has been manually filtered and added to the auxiliary fuel tank, it will typically be filtered at least one more time through an in-line filter that you need to install in the system.

Turning Cooking Oil Into Biodiesel

If converting an engine to run on biodiesel by changing out a few fuel lines sounds like a better idea than installing a total conversion kit, but the idea of free fuel from local restaurants is too good to let go, then the possibility of turning cooking oil into biodiesel may be of interest.

While it is possible to make your own biodiesel at home out of SVO, the process is not simple, and it involves toxic materials like methanol and lye. The basic idea is that methanol as a solvent, and lye as a catalyst, are used to crack the triglyceride chains in the SVO and create a reasonable facsimile of biodiesel. When properly synthesized, the resulting product can be used like regular biodiesel. However, it’s important to remember that traces of methanol may remain, which can and will damage any rubber components in the fuel system.

Converting to Biodiesel or Straight Vegetable Oil

The prices of diesel and biodiesel fluctuate, but there are plenty of other non-economic reasons to convert an engine to run on biodiesel or straight vegetable oil. Whether the idea is to run a more sustainable fuel, use free fuel from local restaurants, or even get ready for when the SHTF, the great thing about diesel engines is that converting to run on biodiesel or vegetable oil is something that just about anyone with the right tools and inclination can do in their own backyard.

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