GRADO P2 PROTECCION INTEGRAL DEL CONJUNTO DEL EDIFICIO 1 Aplicación de la calificación

Test fuels were stressed inside a reactor bomb at 250°C for 24h at a pressure of 10 atm. The temperature was selected to fall within the range of temperatures at the tip of a diesel injector [78], while the reactor vessel was charged with oxygen to facilitate the deposition process. A charging pressure of 10bar was selected because it was sufficient for the duration of the experiment, i.e. there would still be oxygen present in the reactor bomb after the fuel degradation process. Below are images of reactor bomb vessels as well as their lids.

7.2 Visual observations

Figure 7.1: Deposits derived from closed bomb degradation of commercial diesel at 250 °C for 24h at a pressure of 10bar: left) the reactor lid vessel body and b) the reactor lid

Commercial diesel formed very little deposits on its reactor surfaces (see Figure 7.1). Fouling on both the reactor lid and the reactor vessel body was less than observed for any of the other fuels. Not only was the quantity of deposit reduced, but the deposits were visibly lighter in colour. This result shows that even at elevated temperatures and the addition of a metallic surface, commercial diesel still displayed the highest thermo-oxidative stability.

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CHAPTER 7|CLOSED BOMB REACTOR DEPOSITS|2013

7.2.2 EN590 diesel

Figure 7.2: Deposits derived from closed bomb degradation of EN590 diesel at 250 °C for 24h at a pressure of 10bar: left) the reactor lid vessel body and b) the reactor lid

Figure 7.2 shows the emptied vessel (after the stressed liquid fuel had been removed) and sealing lid of a reactor bomb, in which EN590 was reacted for 24h at 250°C in the presence of 10 bar oxygen. It is apparent that carbonaceous deposits formed on the surfaces of the reactor vessel as well as the reactor lid. In the reactor vessel the deposits primarily formed in bottom half of the reactor. This is not surprising as the fuel resided and occupied the bottom half of the cylindrical reactor vessel and as such readily deposited on the adjacent vessel walls. Deposition on the sealing lids likely results from cracked fuel components where the lid provides a condensation surface for the gaseous components. Keck et al. [48] provide a mechanism to explain deposit formation in diesel injector tips. Their proposed mechanism is likely to be similar to the mechanism that governed the formation of deposits inside the reactor bomb walls.

7.2.3 RME20 and SME20

As can be seen in Figure 7.3 and Figure 7.4, fouling on reactor vessels of both RME20 and SME20 was significantly worse than commercial diesel. Comparison with Figure 7.2 suggests similar type of deposits to EN590 diesel. These experiments were repeated several times and similar deposits were observed.

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CHAPTER 7|CLOSED BOMB REACTOR DEPOSITS|2013

Figure 7.3: Deposits derived from closed bomb degradation of RME20 at 250 °C for 24h at a pressure of 10bar: left) the reactor lid vessel body and b) the reactor lid

Figure 7.4: Deposits derived from closed bomb degradation of SME20 at 250 °C for 24h at a pressure of 10bar: left) the reactor lid vessel body and b) the reactor lid

7.3 Transmission electron microscopy

Deposits generated on the walls of the reactor after degradation of diesel fuels were scraped off, ultra-sonicated in an ethanol solution and then viewed under a TEM. The micrographs of deposits from each fuel are depicted below.

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CHAPTER 7|CLOSED BOMB REACTOR DEPOSITS|2013

Figure 7.5: TEM micrographs of deposits formed from stressing commercial diesel in a closed bomb reactor; left) lower magnification image and right) higher magnification image Figure 7.5 illustrates that the deposits formed from commercial diesel had no regular structure. Figure 7.6 shows two TEM micrographs of EN590 diesel deposits at different magnifications. The microstructure of deposits formed in the bomb reactor appears to be similar to EN590 diesel deposits, formed in the flask reactors. The structures appear to be amorphous with no regular diffraction patterns visible [10].

Figure 7.6: TEM micrographs of deposits formed from stressing EN590 diesel in a closed bomb reactor; left) lower magnification image and right) higher magnification image

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CHAPTER 7|CLOSED BOMB REACTOR DEPOSITS|2013

The microstructure of RME20-derived deposits are shown in Figure 7.7. The microstructure of deposits from both these fuels produced familiar amorphous hybrid deposits with physical characteristics akin to EN590 diesel bomb reactor deposits.

Figure 7.7: TEM micrographs of deposits formed from stressing RME20 in a closed bomb reactor; left) lower magnification image and right) higher magnification image

Figure 7.8: TEM micrographs of deposits formed from stressing SME20 in a closed bomb reactor; left) lower magnification image and right) higher magnification image

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CHAPTER 7|CLOSED BOMB REACTOR DEPOSITS|2013

SME20, on the other hand, produced deposits with a very different microstructure. Closer inspection of Figure 7.8 reveals that SME20 deposits have smaller primary particles when compared to particles of other fuels. Diameters are less than 100 nm. Furthermore these particles configure into agglomerates in a manner that is similar to carbonaceous soot. Figure 7.8b reveals the presence of diffraction patterns as can be seen in the particle on the right. The patterns, however, are not perfectly circular suggesting a disordered structure. These are similar to those for HDPI deposits, reported by Venketaraman and Eser [10].