**1. Introduction**

Petroleum is still the major source of energy in the world; petroleum-based fuels are used to various combustion devices, such as automotive engines, gas turbines and industrial furnaces. Combustion of petroleum-based fuels generates undesirable exhaust emissions (e.g. unburnt hydrocarbons, NOx, soot particles), and exhaust emissions from combustion devices cause serious problems to the environment and human health. Adjustment of the properties of the fuels is an effective way to improve the combustion characteristics so that minimize pollutant emissions. Basic knowledge of relationship between the fuel properties and practical combustion performances is necessary to make effective adjustments corresponding to the ongoing diversification of fuels, such as newly-introduced crude oil, sulfur-free fuel, and synthetic fuel (Iwama, 2005).

It is well known that combustion characteristic of liquid fossil fuels vary by fuel properties, such as distillation characteristics and hydrocarbon components (Kök & Pamir, 1995). Especially in the case of diffusion combustion, soot emission is strongly affected by fuel properties (Kidoguchi et al., 2000). Diffusion combustion is widely applied to various combustion devices, but the influence of fuel properties on diffusion combustion is not fully understood. Moreover, when combustion devices are used for a long time, deposits gradually accumulate on the parts of the device that are exposed to high temperatures, such as the fuel nozzle and the combustion chamber wall (Zerda, 1999). Accumulation characteristics of deposits are also strongly affected by changes in the properties of the fuel used. Since excessive deposit accumulation can cause malfunctions of combustion devices, such as decreased output and degradation of exhaust emissions, understanding of the relationship of fuel properties to deposit accumulation is important.

The effects of fuel properties on diffusion combustion and deposit accumulation are described in this article. Several types of kerosene fraction, which have different fuel properties, were used as the test fuels. A wick combustion burner was used to form a stable laminar diffusion flame of liquid fuel; the difference of diffusion combustion characteristics was investigated. Moreover, the effects of fuel properties on deposit accumulation were investigated through deposit accumulation on wick during wick combustion.

Effects of Fuel Properties on Diffusion Combustion and Deposit Accumulation 3

Technology, DH-534-18F-03), which was oriented perpendicular to the laser beam direction. The LIF and LII images were obtained by averaging 20 laser shots. For the PAHs-LIF measurement, the Nd: YAG laser was used to pump the dye laser (Rhodamine 590), producing a beam at 563 nm, and the doubling unit was used to double the dye laser output to produce 281.5 nm radiation. For the LII measurement, second harmonic generation (532

Burner

Nd: YAG laser

Six types of fuel, with different distillation and compositional properties, were used. The physical properties of the test fuels are shown in Table 1. The calorific value of each fuel was same level, because the difference of net calorific value between test fuels was within 2.5%. Regarding fuel F, its smoke point (>50 mm) implies that the sooting tendency of fuel F was much smaller than that of the other fuels. Distillation characteristics indicate that fuel C was light, whereas fuel D was heavy in the test fuels. Fuel F was comparatively light, and fuel A, B and E had similar distillation characteristics. Influence of sulphur and nitrogen compounds on combustion was negligibly-small, because the contents of sulphur and

Table 2 shows the results of the composition analyses of the test fuels. Although content of n-paraffin was not much difference between test fuels (28.6~34.4 vol%), there was considerable difference of i-paraffin content such as the fuel F (57.8 vol%) and fuel C (12.1 vol%). Content of naphthene hydrocarbons was low in fuel F (12.4 vol%) and comparatively low in fuel A (23.5 vol%). Aromatic hydrocarbons were much contained in fuel C (23.3 vol%), and were little contained in fuel E (9.9 vol%). Fuel F did not have any aromatics. Most of the aromatic components of the test fuels were one-ring aromatics;

Doubling unit

*PAH*=281.5nm

**3. Effects of fuel properties on diffusion combustion** 

λ

Fig. 2. Schematic of laser diagnostic system

Dye laser

Computer

ICCD camera

Delay generator

nm) of the Nd: YAG laser was used.

Cylindrical lenses

Prism

λ

**3.1 Test fuels** 

nitrogen were extremely low.

two-ring aromatics were very rare.

*LII*=532nm
