**5. Conclusions**

14 Fossil Fuel and the Environment

one of the aromatics, more naphtheno benzenes may be contained in the aromatic-rich fuel. It is well known that naphtheno benzenes are more susceptible to thermal decomposition at lower temperatures than other hydrocarbons; thus, pyrolysis and polycondensation of naphtheno benzenes would be performed within the wick. Finally, naphtheno benzenes were transformed into tar-like deposits. Conversely, because the pyrolysis of aromatics was difficult to perform due to their high thermal stability, initial aromatics contained in the fuel transformed into heavy molecules and tar-like deposit without pyrolysis. Note that the sooting tendency became stronger with increasing aromatic content in the fuel; soot adherence to the wick possibly affected the results shown in Fig. 12. Although the deposits did not necessarily originate from aromatics and naphtheno benzenes, the deposit accumulation ratio of fuel K was extremely low and no correlation was found between the bromine number, diene value, and deposit accumulation ratio. These results suggested that most of the deposits originated

Deposits that accumulated on the wick were extracted by diethyl ether and chloroform solutions and dried after evaporation of the solutions. The collected deposits were then analyzed with a simultaneous thermogravimetry/differential thermal analysis (TG-DTA) instrument (TA Instruments, SDT2960). Analysis was performed by the following steps: 1. The sample was held at room temperature for 5 minutes and then heated to 250 °C.

Table 5 shows the mass loss of the deposits in each step. Considering the boiling point of hydrocarbons, the mass loss of each step corresponds to (1) the kerosene fraction, (2) the heavy kerosene component and light polycondensation products of low molecular weight, and (3) the heavy polycondensation product. The residue was considered to be a carbonized

Mass loss G H I J K

(N2) [wt%] 15.0 12.5 12.5 15.1 14.2 250~550C (N2) [wt%] 22.2 23.2 18.0 21.4 26.4 550C (air) [wt%] 49.5 51.1 61.4 62.8 60.0 Residue [wt%] 13.4 13.2 8.1 0.8 0.0

The results of TG-DTA analysis suggested that most of the deposit components were heavy polycondensation products formed by thermal decomposition and polycondensation of the fuel within the wick. Residues of fuel G, H and I, which contained higher amounts of aromatics and naphtheno benzenes, were higher than that of the other two fuels; this result

[heating rate; 50°C/min]

2. The sample was held at 250 °C for 10 minutes and then heated to 550 °C.

from the naphtheno benzenes and/or aromatic hydrocarbons.

(atmosphere: N2, flow rate: 100 mL/min)

(atmosphere: N2, flow rate: 100 mL/min) 3. The sample was held at 550 °C for 20 minutes. (atmosphere: air, flow rate: 100 mL/min)

Room temp.~250C

**4.3 Deposit analysis** 

deposit and soot particles.

Table 5. Results of TG-DTA analysis

In this chapter, effects of fuel properties on diffusion combustion and deposit accumulation were studied experimentally. Obtained results could contribute to a design of fuel properties for reduction of the pollutant emissions from diffusion combustion of fossil fuels, and for suppression of the deposit accumulation within a combustion device.
