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cated surfaces, a disadvantage from which the steam turbine is entirely immune. Compounding the Diesel | Engine N THE case of the gas engine at- tempts carried out some 20 years ago at compounding failed, and there are no new developments that would lead us to assume that it would meet with any success if applied to the heavy oil engine of today. In his original treat- ise Diesel spoke of pressures such as are developed in guns but it did not take much experimental work to dem- onstrate that the moderate pressures now in use were all that could be eco- nomically employed, a limitation that was dictated by the purely mechanical reasons already stated. As far back as 1912 a laboratory en- gine was in existence giving a _ fuel consumption of about -.38 pound per brake horsepower per hour, which is approximately better than that realized by the majority of large engines now in operation. It is, however, becoming more common in both large and small engines but the fact stands out that all the oil engine designer has been able to accomplish in nearly twenty years of effort has been to commercial- ize this laboratory achievement. An- other noteworthy and _ disconcerting feature is that the fuel consumption does not improve with increase in di- mensions, the reverse being more often the case. There are engines of 10 brake horsepower per cylinder giving as good results as many of 1000 brake horsepower per cylinder. On the other hand, the steam engine shows a progressive decrease in fuel consumption with each increase in size, because more fuel saving refinements can be introduced and powers are now being approached at which the thermal efficiency will be about equal to the large oil engine which will then have to fall back on its other advantages to keep up the struggle. In a small cyl- inder the whole of the air can be effec- tively and economically attacked by 28 Motorship Rangitiki. Built in 1929; 16,698 Gross Tons. one jet. In a large cylinder penetra- tion to the remote parts is extremely difficult and proper mixing can only be attained in the region of the injector and before the jets have commenced to spread. The best result is obtained by dividing the combustion chamber up into a number of small combustion chambers and fitting an injector in each, which is in effect equivalent to considering the large cylinder as made up of a number of small cylinders. This is a complication but it has been found necessary to bring the fuel con- sumption in line with that realized in small engines. Maintenance Costs Not Available O DEFINITE maintenance cost | te of large oil engines are available for publication. It is known that in some cases they have been high, but as it is still in its youth these may be looked upon as develop- mental charges due mainly to the big steps that had to be taken in a short time in order to enter into the compe- tition for large passenger’ vessels which up to a few years ago were all steam driven. Just as advances in pressures and temperatures are sure to bring about increased maintenance charges in the case of the steam engine, so does in- crease in size of the oil engine bring about a similar state of affairs. Liner and piston ring wear have always been a source of worry and whilst they are Se Sulzer Two-Cycle Single Acting Diesels, 9300 B.H.P. Me ee shee a now considered to be within reasonable limits, there is still room for im- provement. The fact that all the wearing parts of an oil engine can be easily renewed as required is distinctly in its favor and there is, therefore, practically no end to its life. It is a signfiicant fact that the engne of the first ocean going mo- tor ship, namely, the VULCANUS, is as good today as the day it was installed, whereas the hull is about finished and the owners will have to consider plac- ing this 21-year-old engine in a new home. In the case of high pressure MARINE REVIEW—September, 1931 steam plants replacements are not so easy and nothing less than the pros- pect of re-boilering the whole outfit may have to be faced. This, however, is a matter that will take some time to determine on account of the com: parative infancy of the best high pres- sure steam plants. Lubricating Oil Consumption HIS is a small item in the case of dase plants, since it is impossible for any lubricating oil to reach the furnaces, which, in the case of the oil engine, adds to the apparent economy of the plant. It is known that for simi- lar powers the oil engine is much more extravagant, since all the oil used for cylinder lubrication is entirely lost. It is either discharged into the exhaust system or the more volatile fractions are evaporated and consumed as fuel, leaving residues of carbon that collect at the bottom of the pistons or in the various elements comprising the ex- haust system and which have to be removed periodically. It is known that a good oil engine will run on lubricaing oil as a fuel and some of the published tests should be examined bearing this point in mind. It would appear that for a true comparison of fuel consumptions a combined figure including the lubri- cating oil used for the pistons should be considered. In the case of cross- head type engines having the pistons entirely outside the crank chamber the piston lubricating oil consumption can be definitely determined, but with trunk piston engines in which the pis- tons operate in the crank chamber, some notice must be taken of the crank chamber lubricating oil consumption, since a fair amount is splashed on the cylinder walls and lost in the exhaust system or consumed in increasing the power output. Lubricating oil is an expensive fuel and any gain in power that it may give is far outweighed by the increase in running costs. The consumption for both main and auxiliary engines may be anything from five to ten times the amount for an equal steam plant. Oil Engines or Steam N ENDEAVOR has been made to present in an unbiased fashion the relative merits and demerits of the two types of propelling machinery. It is of course, impossible to generalize the position as a whole, but the main characteristics have been outlined and the few special cases constituting the exceptions may be left to the reader’s imagination. At the present time and for powers up to about 3000 brake horsepower, the oil engine is supreme in all but coal producing countries. In Italy, Scandi- navia, Belgium and Holland it has practically no competitor, the construc- tion of steam tonnage being almost negligible. In the first named coun- try the Fiat company alone had 160,- 000 brake horsepower of engines either going through their shops or on order at the end of last year.