Although biodiesel is drawing increasing attention from automakers, policymakers and farmers, there is another biofuel that can be used in diesel engines: straight vegetable oil, or SVO.
The two approaches, although apparently similar, are operationally and philosophically quite different. Broadly stated, you can either modify (refine) plant oil to create biodiesel to run in an unmodified diesel engine, or you can modify an engine system to allow it to use unaltered vegetable oil.
Journey to Forever, a terrific resource on multiple aspects of sustainability, puts it this way:
Does the SVO option work? Yes—IF you go about it the right way. It’s not quite that simple a choice. For one thing, if you want to use waste vegetable oil, which is often free, you’re going to have to process it anyway, though less so than to make biodiesel. And it still might not be a very good fuel.
The main problem is that vegetable oil is much more viscous (thicker) than conventional diesel fuel. It must be heated (thinned) so that it can be properly atomised by the fuel injectors. If it’s not properly atomised, it won’t burn properly, forming deposits on the injectors and in the cylinder head, leading to poor performance, higher emissions, and reduced engine life.
Nonetheless, experience is showing that SVO systems are a practical proposition with a lot of advantages to offer, not least of all that using SVO can be cheaper than turning it into biodiesel and uses less energy than making biodiesel does.
But you have to be willing to take on the modifications. For those inclined to a D-I-Y project, there are a number of resources and kits available.
I will start including SVO on the site, including product news and lifecycle and emissions studies.
A few SVO links and online resources