Technical Papers
Current Studies on Stability and Combustibility of Marine Fuel Oil*
Kazuo Shimizu**, Jun Uehara**, Toshraki Hayashi**
Developing techniques to evaluate fuel stability and combustibility is essential to ensure the quality of marine fuel oil.
Experimental research was performed to determine the combustion performance of marine fuel using the thermogravimetry-differential thermal Analysis (TG-DTA) and the fuel droplet combustion method and the fuel ignition Analyzer (FIA-100).
The results made it possible to distinguish between normal fuel and fuels which caused combustion problems.
Compatibility of fuel oils follows solubility theory. The solubility of asphaltene can be predicted by the Scatchard-Hildebrand equation. This paper describes how to apply the solubility theory to evaluate fuel stability of marine fuel oil.
1. Introduction
“Degradation” of marine fuel oil has been discussed for a long time, and discussions on the introduction of the international standard on the quality of marine fuel oil are still continued. During that time, the studies have been made on the relationship between the sludge problems or combustion problems and the property of marine fuel oil in the oil industry. In this paper, the stability (heat, storage, blend) and the combustibility, which are the quality items not clarified in the general properties, are high-lighted as the problem on the quality of marine fuel oil, and the outline of the laboratory evaluation device to evaluate these items, and its basic concept are mainly reported.
2. Quality Index desired for marine fuel oil
The important quality as the petroleum fuel, not limited to marine fuel oil, must satisfy the items specified in Fig. 1 as the quality in the use in addition to general properties including the viscosity and sulfur content. As for the fluidity, the viscosity at 50℃ or at 100℃ is an important quality item in C oil etc. which is predicated on the storage or use in the heated condition. However, for A oil which is not heated during the storage, the index value such as the low temperature fluidity including the fluidity point and the low temperature plugging point is also important. The viscosity - temperature relationship of the fuel oil (including kerosene to C oil) has an approximately constant gradient (Fig. 2). The relationship can be expressed by the formula as follows.
Viscosity-temperature characteristic:
loglog(v+0.7) = A-B･longitudinal(273.15+t) where,
v = dynamic viscosity (mm2/s),
t = temperature(℃),
A, B = constant
Fig. 1 Important quality as petroleum fuel
However, this gradient may be different even for C oil like the residual oil under reduced pressure in which heavy oil is diluted with only light cutter (generally, referred to as “dumb bell fuel”, or like the residual fuel oil which is extremely cracked. That is, troubles are experienced that the viscosity is not dropped to the specified value even when the oil temperature rises, and it is thus necessary to grasp the viscosity-temperature characteristic of a special case at site.
3. Method for evaluating combustibility
The approach for evaluating the combustibility of the fuel includes the method to use the actual combustion equipment and the method to use the simplified device for evaluation on the laboratory scale. In the combustiontest by the actual engine like a large marine diesel engine, the data itself is greatly influenced by the equipment, and it is often difficult to judge the effect of the fuel.
* Translated from Journal of MESJ . 34, No. 4 (Manuscript received Nov. 12, 1998)
** Nippon Mitsubishi Oil Co., Ltd. (Naka-ku. Yokohama City)
