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.

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.

Vegetable oil can be used as an alternative fuel for your car in one of three ways:

• after chemical altering to biodiesel,
• mixed with petrodiesel,
• as single fuel.

In each of the above, all the engine parameters, e.g. power, torque, and fuel consumption, remained on the same level as for petrodiesel. It is worth mentioning, that the first diesel engine ever was fueled by peanut oil, not by petrodiesel!

Using vegetable oil as a single fuel requires some engine modification. It is very viscid, much more than diesel fuel. Because of that standard diesel fuel injector doesn’t spray vegetable oil to small enough droplets. This means that it’ll vaporize slower, and will not become burned completely. Some residual oil will then be collected inside the cylinder and by engine oil.
To overcome the high viscosity, the vegetable oil needs to be heated before it can be sprayed by injection pump and injector nozzle.

The vegetable oil must be heated to at least 70°C (158°F). At this temperature level viscosity of is comparable to viscosity of cold diesel fuel. Because of that, engine must be started on petrodiesel. When it achieves required temperature, warmed vegetable oil from second fuel tank is fed to injection pump. Vegetable oil is heated inside heat exchanger with heat from water in engine’s cooling system. In some cases, the fuel tank itself is heated, in some engines heated fuel filters are installed.

You can buy on the internet some kits that allow you to change your diesel engine into one that’s fueled with vegetable oil. Those kits consist of heat exchanger and electrovalves. Those valves allow driver to switch the fuel without leaving his seat, as fast as cooling water heats itself to required level. Some kits have also fuel tanks and some additional equipment.

The engine should be started and stopped on petrodiesel. The vegetable oil if left in fuel lines or anywhere else in engine for cooling would make starting this engine more difficult or even impossible.

Vegetable oil as fuel additive

If you don’t want to change anything in your car, consider using vegetable oil as fuel additive. Addition of 15-20% od vegetable oil to your fuel tank does not affect engine’s work and doesn’t require installing heat exchanger to heat the fuel. If you’d like to use more vegetable oil, up to 75% of total fuel, you would need to mix it with DFX additive. You add it in 1:320 proportions, one litre of DFX costs about $25-30.

Is vegetable oil safe for engine?

There are many engines fueled with vegetable oil out there. Some of them are grouped in vegetable oil fuel database. This database consists of 340 vehicles, of which:

• 32% have two engine tanks,
• 49% have some kind of fuel heating,
• 38% use waste vegetable oil,
• 93% work just fine!

Using vegetable oil means that engine works a bit quieter than on its standard fuel. It also uses a little more fuel, since vegetable oil’s heating value is only 96% of the heating value of petrodiesel.