Posted by Krzysztof Lis on March 24, 2008
Straight vegetable oil is a good fuel for most diesel engines, but it can be used safely only if the engine is modified a bit. The viscosity of this fuel is far more greater than the viscosity of petrodiesel. Because of that, the injection nozzles will not atomize the fuel enough — the fuel droplets will be larger than if petrodiesel is used. Those droplets will vaporize slower and may not vaporize completely. Because of that, the fuel may not be burnt fully, which will lead to soot formation inside the cylinder, on the injection nozzles, and so on.
The vegetable oil’s viscosity is reduced when it’s heated. For trouble-free operation in most older diesel engines it’s enough to warm the SVO to 70-80°C (158-176°F). But how to get that result? What modifications are required?
First of all, you need to use some heat exchanger. It’ll use warm fluid from engine’s cooling system to heat the vegetable oil. Depending on who manufactured the set used to modify the engine, shell and tube or plate heat exchangers are used.
The second important thing to install in your VO-powered car is second fuel tank. Until the engine is warm enough to heat the vegetable oil to the required level, you need to fuel it with petrodiesel. So you can’t pour the vegetable oil directly into car’s fuel tank. You need a second tank. In some cases, this tank is equipped with second heat exchanger to speed up the heating of the oil.
The third device you need is three-way walve, to be precise – two such valves. In most cases they’re electrically-driven, so when the engine is warm enough you simply press some button and the car from that moment uses fuel from the second tank. The second valve is required to drive excess fuel from injection pump back to the right tank. You don’t want the vegetable oil to be mixed with petrodiesel in car’s main fuel tank.
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