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Wednesday, April 14, 2021

Biodiesel versus SVO and WVO

Posted by Krzysztof Lis on November 11, 2011

A lot of people say that biodiesel is the future biofuel. You can pay to learn how to make biodiesel (or read it for free here) and buy an expensive biodiesel processor (or make your own for small fraction of the price). But is biodiesel really a good alternative to petrodiesel?

I believe not. I think that it’s better to use straight or waste vegetable oil, and not biodiesel.

Biodiesel is a fuel manufactured from vegetable oils or animal fats and methanol. You might say that this fuel is fully renewable, as both vegetable oils and methanol can be produced from plants: oils from soya, canola (rapeseed) or sunflower (or a lot of different plants) while methanol is a product of wood pyrolysis. The necessity of using sodium or potassium hydroxide as catalyst doesn’t change much.

But in my opinion it is better to use vegetable oil directly in the diesel engine, instead of producing biodiesel. Its production requires some energy input so that the oil can be transesterified into biodiesel. This makes the EROEI a bit smaller.

Of course to use the vegetable oil in engine you need some changes to the engine itself. This fuel has noticeably higher viscosity so that it is not easily sprayed by injection nozzles. Because of that, vegetable oil needs to be heated before it can be supplied to the injection pump.

Vegetable oil use in winter is very difficult, but biodiesel also gels in cold temperatures. Both those fuels are not suitable for colder climates and colder seasons.

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