3.1 Use of rapeseed SVO in diesel engines

Rapeseed oil can be used as fuel in diesel engines. Other vegetable oils can also be used as SVO to fuel diesel engines because they have similar properties. In Table 2 the properties of different oils are shown. The differences in the oil properties are small. However, to replace diesel fuel, some modifications are required to adjust the physical properties of the oil to be pumped to the engine and pulverized in diesel common injectors.

The modifications are aimed to heat the rapeseed oil to reduce its viscosity and density. During start-up, the vehicle runs with diesel to avoid the engine working at low temperatures with straight vegetable oil. Once the engine has warmed, it will be able to heat and use SVO. Note that the engine shouldn’t be stopped for a long time when using SVO, otherwise it will be complicated to cold start the engine with SVO.

The components that need to be installed in the fuel supply system:

— an additional deposit for the start-up diesel

— a water-oil heat exchanger

— a temperature sensor

— two solenoid valves to select the fuel to be used

— filters for oil and diesel fuels

The use of vegetable oil as fuel started long ago. Rudolf Diesel used peanut oil to run a diesel engine at the World Exhibition in Paris in 1900 (Baquero et al., 2010). He also suggested that vegetable oils could be the future fuel for diesel engines, but diesel fuel from oil substituted vegetable oil due to its abundance and price.

The use of SVO in diesel engines carries also some difficulties, namely:

— difficulties in operating the motor itself because of the different ignition temperatures of the two fuels. These difficulties can be solved just by preheating the vegetable oil.

— problems of engine durability due to deposit formation in the combustion chamber and mix of the vegetable oil with the engine lubricating oil. The first problem is solved by increasing the vegetable oil temperature, so it decreases its viscosity and density, which allows a correct injection and burning of the vegetable oil. The second problem is solved by reducing the life of the engine lubricant, (Agarwal et al., 2008; Vaitilingom et al., 2008). Despite these difficulties, it is noteworthy that both fuels have very similar energy content: 34.42 MJ/l for rapeseed SVO and 35.81 MJ/l for diesel fuel. This makes the engine performance and consumption very similar for both fuels. If we compare the performance of both fuels in the same engine, experimental results show that the performance of a vehicle running on diesel is optimal at low loads, whereas working with vegetable oil is optimal at high loads.