The limitations posed by the use of vegetable oils in some typologies engines, in particular those that require auto traction, due to the high viscosity of the combustible, can be overcome by the transformation of oils into bio-diesel, which is obtained by the esterification process (this will be analysed in detail in the par. 2.4.3, Chapter 4). Vegetable oils are mainly made of triglycerides and their viscosity (median of 40 mm2/s) is higher than that of fuels of fossil origin (diesel has a viscosity equal to 3 mm2/s). The transformation into bio-diesel is due to the conversion of the triglycerides into methylic esters which reduces the prod­uct’s viscosity. The mixture of methylic esters, called bio-diesel, has a viscosity of 5 mm2/s which is similar to that of diesel. Bio-diesel can be produced even from saturated cooking oils. These substances must be purified before the esterification process. The esterification process involves the use of alcohol, mainly methanol, and it yields glycerine as a by-product (which is re-sold to the chemical and phar­maceutical industry as a raw material) [1, 2]. Consequently, by using bio-diesel, on one hand, an improvement in the invested capitals is achieved (compared to that necessary to start the spinneret which aims to produce energy using vegetable oils); on the other hand, there is a noticeable increase in the possible use scenarios. From Table 12 we can see that bio-diesel shows some characteristics which are similar to diesel.

The substitution of diesel for auto traction in vehicles equipped with diesel engines and the feeding of boilers for electricity generation are the main uses of bio-diesel as an energy product. The recent interest shown by the European Com­mittee (Directive 2003/30 of the European Parliament and of the Council, 8 May 2003) in the development of the biocombustible spinneret and in view of the fact that it is already theoretically possible to feed diesel engines which are present in the market with a mixture of diesel and bio-diesel make the use of bio-diesel as a fuel for auto traction particularly interesting.

Directive 2003/30 of the European Parliament and of the Council, 8 May 2003, on the promotion of bio-fuels and other renewable fuels in the transport sector, stipulates that each member state should fix its target for bio-fuel usage relative to the bio-fuel quotation available in the market. Such targets must be based on the

reference levels as per the Directive: 2% of the total fuels (petrol and diesel) that are available in market by 31 December 2005 and 5.75% by 31 December 2010. Legislative Decree 120/2005 acknowledges Directive 2003/30 at a national level and for Italy it establishes the target of 1% by 31 December 2005 and 2.5% by 31 December 2010.

Currently, in Italy, the use of bio-diesel for auto traction is limited to the realiza­tion of mixtures with diesel only up to 5%. Studies conducted by German and Austrian experts demonstrated the possibility of using bio-diesel in mixtures up to 30% without making any modifications in the engine. To use pure bio-diesel, on the contrary, it is necessary to substitute the rubber rings with other compatible materials (copper, carbon steel, brass, fluorinated rubbers, etc.).

Bio-diesel, pure or as a mixture, can also be used in diesel burners by making only modest remedial interventions (regulation of the air/fuel ratio, modification of the atomization nozzles’ slant, etc.) [2, 14, 24].

The main advantages of bio-diesel compared to the use of the traditional diesel are [24]

• high number of cetanes (higher flammability in diesel cycles);

• high lubricant capacity;

• absence of sulphur;

• high percentage of oxygen (high stability of combustion, lower production of PM10, lower volatile organic residuals);

It is useful to remember that bio-diesel production is an option for the agricultural cultivation of the abandoned or rotated soils after intensive cultures. Figure 18 shows the historical trends of bio-diesel production in Europe.

The statistical almanac on bio-diesel production, edited by the European Bio-diesel Board (EBB), describes the highly positive bio-fuel production situation in 2005. Particularly in Europe, an increase in production equal to 65% of the production in the previous year was observed. This increment was a result of the involvement of 15 member states of the European Community, of whom Germany again affirmed itself as the leader in bio-diesel production with 1.6 millions tons produced in 2005. Although the scenario is positive, the target of 2% of the biocombustible production as per European Directive 2003/30 has not yet been achieved [26].