Coal is considered one of the major fuels alternative to petroleum. The possibility of its use in combustion engines is particularly great in marine engines, and its use could reduce fuel costs considerably. This paper presents the engine performance and exhaust gas emissions with Coal Oil Mixtures (COM; in the experiment carbon black was used instead of coal slurry) and Solvent Refined Coal-II (SRC-II) as diesel fuel substitutes. Properties of the fuels when blended with diesel fuel and their spray characteristics are also presented. The results of the experiment show that specific heat consumption and exhaust smoke were improved when 5w-% carbon black or 25v-% SRC-II were blended with the diesel fuel. However engine noise and NOx emissions increased with the increase in the carbon or SRC-II ratio in the fuel. The analysis of the indicator diagrams show that these fuels result in larger premixed combustion and shorter combustion duration compared with conventional diesel fuels. Both COM and SRC-II have higher viscosity than diesel fuels; the paper shows their viscosities in empirical formula as a function of the blending ratios. In spite of the higher viscosities, the spray atomization of these alternative fuels was better than diesel fuel.
The erosion at cylinder liners or cylinder blocks in water cooled diesel engines is considered to be due to the collapse of cavitation bubbles attributed to the cylinder liner vibration. In this study, using a model equipment and an actual engine, the behavior of cavitation bubbles grown in a water jacket is observed continuously under the several liner vibration conditions by taking direct microscopic photographs with high speed drum camera. In case that the vibration velocity of the cylinder liner is small, gaseous cavitation bubbles caused by dissolved air or contaminated air are generated. These gaseous bubbles stay for a long time more or less independent of transient change in the water pressure fluctuation. And the cooling water pressure fluctuation is assessed from the vibration velocity of the cylinder liner employing a water hammer equation. As the liner vibration velocity is increased, vaporous cavitation bubbles are generated because the cooling water pressure fluctuation reaches to the water vapor pressure. And the critical vibration velocity of the cylinder liner is revealed in term of generation of these vaporous bubbles. These vaporous cavitation bubbles are initiated as small bubbles, grow up to about 200-300μm in diameter, and a shock wave is took place in the instant of bubble collapsing after the life time about 150μs.
A small sized, high speed, direct injection, naturally aspirated Diesel engine and eight kinds of fuel have been used to investigate the influence of fuel qualities on soot, deposit, piston ring wear and deterioration of lube oil. A 30 hours running test of the Diesel engine was carried out for each fuel. Main items measured included soot emission rate, smoke density, deposit on combustion chamber wall and the vicinity, piston ring wear, n-pentane insoluble in lube oil, total base number of lube oil and viscosity of lube oil. The test results indicated that soot emission rate increased with the increase of carbon residue and sulfur content in fuel oil, and that high soot emission rate promoted piston ring wear and deterioration of lube oil, and that high sulfur fuel oil lowered rapidly total base number of lube oil.
Various kinds and types of energy saving systems such as waste heat recovery system, shaft driven auxiliaries, etc., have been developed and employed into most of motor ships. Design conditions of those systems are getting severer, and in some of heat recovery cases, close to almost available limit, then, there are lot of points to be checked and considered when applying and outfit-designing them. This paper presents such points, based on actual operation results and experience, that were gathered and discussed by Machinery Plant Committee III.