BTL-FT diesel is a renewable fuel of excellent quality compared to both fossil — derived diesel and first-generation biodiesel produced via the transesterification of vegetable oils. BTL-FT synthetic fuel consists mainly of linear paraffinic hydrocarbons with almost zero aromatics and sulphur compounds. The physical properties of BTL diesel presented in Table 19.5 (Rantanen et al, 2005) demonstrate its very high cetane number that can reach up to 75, much higher than conventional diesel. The big advantage of BTL diesel is that it is directly usable in the present day in transportation sector, and furthermore, it may be suitable for future fuel cell vehicles via on-board reforming since it is free of sulphur. It is fully blendable with conventional diesel and compatible with current diesel

engines and with common materials used in the tank system and the engine components. This constitutes a great plus, as the fuel can be used today using the current distribution and retail infrastructure.

Due to its bio-origin, the BTL diesel has much lower CO2 emissions than fossil — derived fuels. Moreover, it shows considerably improved emission behaviour. BTL diesel fuels have been tested by Volkswagen AG and DaimlerChrysler AG in modern, state-of-the-art passenger cars, as part of the EU-funded IP RENEW project that explored technology routes for the production of B TL fuels (RENEW, 2008). The vehicles were equipped with different types of exhaust gas after­treatment system, oxidation catalytic converters (oxycats), which reduce CO and hydrocarbon emissions and are the most common technique in the existing fleet and additional diesel particulate filter (DPF), the after-treatment technology of future diesel passenger cars. The reductions of the different emissions with the BTL diesel compared to conventional diesel are summarized in Table 19.6. Great emission reductions were achieved with no special adaptation of the engine. The BTL diesel causes a significant reduction of CO and hydrocarbon emissions, a medium reduction of particulate emissions and only a slight reduction of NOx (nitrogen oxides) emissions. The next lines of the table present emission reductions with different after-treatment technologies and optimization of the engine operation with special software. It can be generally seen that a further reduction of particulates or a significant reduction of NOx can be realized. In general, the BTL diesel manages to reduce not only CO2 but also the emissions of most air pollutants. What is also important is that the BTL fuel exhibited at least the same fuel consumption as conventional fuels when compared on an energetic basis (RENEW, 2008). With adapted engines, the improved combustion process could also lead to better efficiency and thus reduced fuel consumption.