. Scientific news for general readers; a popular illustrated weekly journal of science . lly for the treatment of thegas with which theengine is to be worked. The theoretical efficiency of a gasengine, considered as a heat engine, depends on the dif-ference between the initial temperature produced in thecylinder when the charge is ignited, and the final tempera-ture of the products of combustion escaping through theexhaust. The greater the difference between these tem-peratures the greater the efficiency. With this in viewMr. Clerk shows that by compressing the mixture of gasand air before ign
. Scientific news for general readers; a popular illustrated weekly journal of science . lly for the treatment of thegas with which theengine is to be worked. The theoretical efficiency of a gasengine, considered as a heat engine, depends on the dif-ference between the initial temperature produced in thecylinder when the charge is ignited, and the final tempera-ture of the products of combustion escaping through theexhaust. The greater the difference between these tem-peratures the greater the efficiency. With this in viewMr. Clerk shows that by compressing the mixture of gasand air before ignition, its temperature is raised by reasonof the work done upon it, and consequently there is agreater difference between the initial and final temperatures,and a corresponding increase in efficiency. In the Lenoir pressed the molecules of gas are brought closer together, andare then more readily ignited ; also that when so compressedthey are exposed to less cooling surface in the of these are important considerations, and should notbe lost sight of. ] ^^Exh oust Vali/e. Fig. 2. Mr. Clerk describes other engines, and gives useful detailsof their mechanical parts, but those we have selected may betaken as typical of the first gas engine used for practicalpurposes, and of the best modern engine now made. Wehave already seen that in the Lenoir engine there is no com-pression of the gas and air before ignition. The action SCIENTIFIC NE\VS. [March 1st, 18&7. will be readily understood by referring to Fig. 2. In theOtto engine (Fig. 5) A is the water-jacketed cyhnder ; Bthe piston when at the end of its in-stroke; and C a con-tinuation of the cylinder forming a chamber in which thecharge is compressed before ignition. On the out-stroke ofthe piston, gas and air are drawn into the cylinder throughthe port I, and on the return of the piston the charge iscompressed, and then ignited through a little port or touch-hole in the slide M. As soon as the ignition takes placether
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