Vegetable oil is an alternative source of fuel for running a diesel engine. It can be either converted to biodiesel and then used as a fuel, or it can be directly used to run a diesel engine. In the latter case, it is either straight vegetable oil (SVO), pure plant oil (PPO), or waste vegetable oil (WVO), i.e., the oil discarded after cooking. For running a diesel engine, it can be used alone or mixed with diesel or kerosene.
Using Vegetable Oil as an Alternative to Conventional Fuels
The history of using vegetable oil as a fuel dates back to the 1900s, when the Otto company demonstrated the diesel engine designed to burn mineral oil. Peanut oil was used as a fuel to run the engine. Later, Rudolf Diesel carried out an extensive investigation to explore its potential as a fuel, and predicted that in the course of time, the importance of vegetable oil would increase and reach the level of natural mineral oil and petroleum products.
Another factor that encouraged research on vegetable oil was the occasional shortage of petroleum faced by the world in the 1930s, 1940s, and again in the 1980s. In the 1970s, the first commercial enterprise was formed to use straight vegetable oil in automobiles. The Elsbett, a diesel engine invented by Ludwig Elsbett was specially designed to run on vegetable oil. However, the prices of petroleum went down in the 1980s, and subsequently, the pace of scientific research on vegetable oil slowed down. Only recently, researchers have been able to find out the required fuel properties for using this oil for running a diesel engine.
The main disadvantage of this oil is that it has higher viscosity than biodiesel or petrodiesel, which is why it is not completely combusted. Its incomplete combustion leads to the deposition of carbon, which in turn can damage the engine. However, it is possible to reduce the viscosity and the surface tension by preheating the oil. The usual method is to install a heat exchanger and two fuel tanks, one for the diesel or biodiesel, and the other one for vegetable oil. In this way, the engine can be started up on diesel. Once the engine warms up, it can be switched over to vegetable oil. Similarly, before turning off the engine, switching over to diesel is essential to make sure that no vegetable oil remains in the engine.
Rapeseed or canola oil is the main vegetable oil that is used in engines. However, some Pacific countries use coconut oil as well. Studies are also being conducted to explore the potential of using sunflower oil, especially in colder climates. Pure vegetable oil is derived from plants. On the other hand, waste vegetable oil can be obtained mainly from the restaurants. According to some estimates, the amount of excess waste vegetable oil produced by the snack food factories, fast food restaurants, and potato processing plants of USA was 11 billion liters.
The main advantage of using vegetable oil as a fuel is that it is cheaper and eco-friendly. In this age of global warming and increasing fuel prices, it can emerge as an efficient source of alternative fuel. So, if adequate measures are taken for its effective use, as well as the dilution of the drawbacks, vegetable oil can help reduce expenses and excessive dependence on fossil fuels.