This is the first car I converted to run on used fryer fat. It is a 1980, five cylinder, three litre diesel Mercedes Benz. The conversion was done in late 2000 and has been driving an average of 1000km per week ever since.
The car actually runs more quietly on fat and has the same power and economy as standard fossil fuel diesel. The extra lubrication offers lower engine wear and longer life. Exhaust emissions have no sulphur content, less than half the NOx content, much reduced soot and smells much better (like a BBQ). The fuel itself is non toxic (it is after-all, a food), far less flammable than fossil fuels and fully renewable.
The vehicle runs on all sorts of cooking oils from new highest-grade canola oil to well used beef fat.
The basic principle is very simple. Just replace standard diesel fuel with vegetable and/or animal fat. Rudolf Diesel actually designed his engine to run on peanut oil long before crude-oil based diesel fuel was made. The biggest problem is that modern diesel engines are designed to run on fuel with a relatively low viscosity and low flash point. Vegetable oil is quite thick and animal fats are solid at room temperature. The easy way to overcome this is to heat it up, around 50 degrees celsius seems to work well depending on the fat make-up.
Since the fat will cool and be useless as a fuel we need to start the engine on normal diesel and use the engine’s waste heat to warm the fat. Once the fat has become liquid we can switch the fuel supply over to fat, switching back again before turning the engine off. In practice the fat stays liquid for about four hours after turning the engine off so there is no need to switch back to diesel if the vehicle is to be used within that time.
So the idea is to install a second, heated fuel tank for the fat and have a dash-mounted switch for selecting the fuel source.
Total cost if you used all new materials is about $500 excluding labour. The most difficult job is fabricating a fat tank and fitting it. The reason I chose the Mercedes was because of the extra space available in the engine compartment. I have made up a 20 litre tank fitted with a heat exchanger and plumbed this directly into the vehicle’s cooling system. A solenoid valve selects which fuel source is fed to the injector pump. A digital thermometer gives the driver a read-out of the fat temperature.
In practice I start the car in the morning and let it idle for about 10 minutes. This heats the fat to over 30 degrees and from then on I drive on fat. If I plan to leave the vehicle during the day for more than a couple of hours I will switch back to diesel for a couple of minutes before turning the engine off.
Since converting the car in December 2000 I have driven it 1000km per week without too many problems. As the weather has cooled down I have made a few alterations to the heat exchanger setup but so far nothing major.
In March 2001 I converted another Mercedes for my wife. The conversion on this one is much tidier and the improved heat exchanger design means that the fat heats up more quickly. This car has barely done a quarter of a million kilometers and runs much better than the other vehicle. This vehicle drives about 800km per week.