THE THERMODYNAjMICS OF THE MARINE OIL ENGINE. 79 



made in the present engine but the cycle is unchanged, so that results obtained in 

 these early tests are at least indicative of what is obtained in the present engines. 

 This shows that the friction is practically constant at all loads, and would rather 

 seem to bear out the contention that the friction is toll taken out of both the com- 

 pression and working strokes. With the compression pressure constant the sum of 

 the compression work and expansion work would vary but little for a great varia- 

 tion in the net work done in the cylinder. However, the sum of the compression 

 and working strokes would vary greatly if the compression pressure were decreased. 



Air is compressed and then expanded. The air in itself does nothing. All the 

 work put into compression of the air will be given up in the expansion except the 

 losses. Now if the quantity used per stroke be reduced the losses per stroke will 

 be reduced by this same amount. Unnecessary compression of air is an extrava- 

 gance. It is needless to compress more than is required for the proper combustion 

 of the fuel. 



We will next consider the problem of extreme slow speed. 



In order to reduce to an extreme slow speed care must be taken to obtain a 

 maximum temperature at the end of the compression stroke. Cards 9, 10 and 11, 

 Plate 25, show the efl'ect of cooling at the end of compression. For moderate speeds 

 with a falling horse-power the amount of air compressed per stroke in the cylinder 

 can be varied. Under present conditions there is a limit to the speed of the oil en- 

 gine. At this limit the ignition will be uncertain. To go beyond this limit in the 

 present engines the air should be heated before it enters the cylinder and the tem- 

 perature of the jacket water should be raised. It might be even wise in an emer- 

 gency to cut out the circulating water entirely. 



This need for this slow speed was painfully evident when the Diesel-engined 

 ship Christian X fell in with a disabled ship in mid-ocean. Her speed range was 

 from 80 to 140 revolutions per minute according to published data. It was also 

 stated in the press at the time that the Christian X repeatedly passed tow-lines to 

 the disabled ship only to as often part them. The press report of this meeting was 

 not very full. However, presumably the best that could be done would have been 

 to keep starting and stopping the engines in the hope of gradually accelerating 

 their tow to the point where the line would stand the lowest possible speed of the 

 engine. 



A steam vessel under the same condition would have run her engine very 

 slowly just enough to give steerage way until she had taken up the slack of the tow- 

 line and then would have increased her revolutions gradually until the desired num- 

 ber was obtained. This is manifestly impossible in the present oil engine. In the 

 plant proposed at the end of this paper the motive power would be steam. Like the 

 steam engine, the proposed engine would start a few turns per minute with steam 

 from her economizing boilers. These would have energy sufficient to run the vessel 

 for an hour at least without the use of fuel. In addition to the speed under the 

 use of steam in the cylinders, by the use of steam in the jackets the radiation loss 

 for the compression stroke should be cut down. If in a low-pressure type of en- 



