January 9, 1903.] 



SCIENCE. 



61 



Moreover, the smoothness of action is 

 greatly retarded with this form of engine, 

 especially if the governing is controlled by 

 the 'hit-and-miss' method, in which the 

 regulation is effected by varying the fre- 

 quency of the explosions, thus causing 

 great variations in the driving torque. 



Various expedients have been employed 

 to overcome these defects, such as the use 

 of multi-cylinders and different methods of 

 control, but the size and cost of engine 

 have been increased rather than decreased. 

 Notwithstanding these well-recognized de- 

 fects in the four-cycle type of engine, it 

 constitutes by far the largest class in use 

 to-day of what may be called successful 

 gas-engines. 



More recently very satisfactory results 

 have been obtained in the construction of 

 two-cycle engines. In some of these we 

 find separate pumps employed to compress 

 the charge of gas and air, which ignites and 

 burns as it enters the cylinder. Higher 

 compression is thus obtained without fear 

 of pre-ignition, and this permits smaller 

 clearance spaces with attendant advan- 

 tages. 



If the engine is single-acting, an impulse 

 is obtained every revolution, which thus 

 insures better speed regulation, as well as 

 double the power for a given sized cylinder. 



The highest thermal efficiency yet at- 

 tained, namely 38 per cent., has been se- 

 cured with a two-cycle type of engine which 

 compresses the air and gas in separate 

 pumps to a nominal pressure of eight or 

 ten pounds ; the air under this pressure be- 

 ing used to scavenge the cylinder toward 

 the end of expansion. After the uncon- 

 sumed products of combustion have been 

 forced out by the fresh air, the cylinder 

 walls having been cooled thereby, a charge 

 of gas is admitted and compressed to a 

 pressure of 150 to 175 pounds per square 

 inch and then exploded, as in the usual 



method. This engine is double-acting and 

 receives a charge each side of the piston; 

 thus two impulses are received each revolu- 

 tion, in a manner precisely similar to that 

 of a steam-engine. 



Whether these engines will be as satis- 

 factory for small motors remains to be seen. 

 It is possible that the greater complication 

 of details in the two-cycle types, as com- 

 pared with the simpler four-cycle engine. 

 will cause the latter to continue to give the 

 greater satisfaction, at least for the smaller 

 sizqs. 



At the last meeting of the British Asso- 

 ciation, Mr. H. A. Humphrey gave some in- 

 teresting data concerning recent gas-en- 

 gines, and the record is both remarkable 

 and signifiean,t. The limiting size has 

 rapidly grown during the past two years, 

 as shown by the fact that one manufacturer 

 is now constructing a gas-engine of 2,500 

 horse-power and is prepared to build up to 

 5,000 horse-power. 



The development of the large gas-engine 

 is closely connected with the evolution of 

 the fuel gas processes, and it is noteworthy 

 that the first gas-engines in England above 

 400 horse-power were operated with pro- 

 ducer gas, while many of the large gas- 

 engines in Europe have been built for use 

 with blast furnace gas. 



In August of this year (1902) two 

 leading English manufacturers had de- 

 livered or had under construction over 

 fifty gas-engines varying in size between 

 200 and 1,000 horse-power ; but we have to 

 look across the Channel for still greater 

 achievements in this direction. 



Neglecting all engines below 200 horse- 

 power, we note that a classified list of gas- 

 engines in use or under construction shows 

 the remarkable total of 327 gas-engines 

 capable of supplying 182,000 horse-powei'. 

 This gives an average of about 560 horse- 

 power per engine. 



