The effects of re-entrant combustion chambers on emissions of particulates and unburned hydrocarbons were investigated in a high speed small direct-injection diesel engine. From our study, it has been already suggested that the fuel or the fuel-air mixture can become an important origin of unburned hydrocarbon emissions when they intrude into the narrow space between the piston and the cylinder head. In this work, especially noticing this point, the trends of THC and SOF were examined changing the injection timing and the top clearance.
The results show that the re-entrant combustion chamber reduces THC emissions, but increases SOF emissions compared with the deep bowl chamber at the advanced injection timing. On the other hand, at the late injection timing, THC and SOF are simultaneously reduced. When the injection timing and the top clearance are optimized for the re-entrant combustion chamber, it is possible to reduce not only smoke and NOx but also THC and SOF.

View full abstract

The relation between soot and NOx exhaust characteristics becomes an important problems which oppose each other.
It is difficult to reduce simultaneously those components. The method for attaining those purpose are tried by added water into flame whose method is proved to be most effective. The theoretical prediction of the local soot and NO concentrations together with the flame structure are needed to obtain better understanding of the local conditions for controls of the soot and NO formation in the flames. In the present study, the added methods of water are made by high humidity in the combustion air and addition into fuel, the detailed characteristics for soot and NO reductions are investigated based on the influence of the gas temperature, various species and local equivalence ratio by the addition of water.

View full abstract

Alminum revolving disks are immersed in the sea to measure the change of the moment coefficient of them with growth of barnacles in 3 different term. These term, about one month respectively, settled during from the middle of May to middle of August in 1989 and 1991. Because the temperature of the sea become gradually higher in this season, with the result that the marine growth become actively.
The formula of prediction tendency is calculated with multiple regression analysis from the result after the calculation of the increase of the coefficient by friction between 4×10^-5 and 10×10^-5 of Reynold's number every week. Then the valiables are the lapse of days and the increment of the sea water temperature from immersion and the sea water temperature when the coeff. of disks are measured. The regression expressions of each term and the period added all term are respectively available to use, because all multiple correlation coeff. are about 95% or over, the coeff. of determination are about 90% or over and the F-destribution ratios are higher than the value of 0.1% significanece level.

View full abstract

The last investigation (The Issues of Japan Marine Diesel Engine Society of 1992, Vol.27 No.11) concerning the actual circumstances of wear of slow speed, long stroke 2 cycle marine diesel engines, showed that generally the wear on cylinder liners improved, on the contrary, excessive wear of piston ring resulted similarly on A type, B type, and D type.
This report describes the analysis results of wear condition as to the types discussed in the last investigation, based on the three years data (April 1989-March 1992)
1. Wear Rate Analysis of the Cylinder Liners
Liner wear circumstances of A, B and C type has stabilized since the previous investigation.
2. Wear Rate Analysis of Piston Rings
Generally speaking, the ring wear condition of the engine of each type (A, B and D) with small bore cylinders is stabilizing, however the engines with large bore cylinders continue to wear excessively.

View full abstract