l8 PKKSIDENTIAL ADDRESS SKCTION A. 



quite a large number of inventors occupied themselves with this 

 form of heat engine. It remained for Otto to overcome all 

 difficulties and embody all the theories of his distinguished pre- 

 decessors in a reliable and practical engine. 



Otto and Langen's first engine — a free piston engine — was 

 exhibited at Paris in 1857; but it was not until 1876 that Otto 

 produced an engine which was the real precursor of all modern 

 gas engines. Otto's work occupied 22 years, and is a record of 

 extraordinary industry and perseverance. The successful engine 

 of 1876 embodied the four-stroke cycle principle now universal 

 in all automobile and aeroplane engines, and in most stationary 

 gas and oil engines. This cycle had. however, been suggested 

 by Beau de Rochas as far back as 1862. but the })rinciple upon 

 which it is based, the compression of the explosive charge in the 

 cylinder, was in the minds of several engineers about that time, 



The four-stroke, or Otto cycle, is so called because four 

 strokes of the reciprocating piston in the cylinder are required 

 to complete the series of (j])erations. These are as follows : — 



Firstly : The induction stroke, during which the explosive 

 charge is drawn into the cylinder. 



Secondly : The compression stroke, during which the charge 

 is compressed into a small volume. 



Thirdly : The explosive stroke, during which the gases are 

 expanded. 



Fourthly : The exhaust stroke, during which the products 

 of combustion are expelled from the cylinder. 



The development of the " Otto " gas engine ])roceeded 

 steadily, mainly in the hands of British manufacturers, from 1880 

 onwards, the improvement being most marked during the last 

 twenty years of the last century, and during this period of 

 development the indicated thermal efficiency increased from 

 about 16 per cent, to yj P^'" cent. This increase was mainly 

 due to the steady advance in compression pressures adopted, 

 which rose from approximately 30 pounds per square inch to 

 over 200 pounds per square inch. All the earlier engines worked 

 on ordinary town illuminating gas, but later on ])roducer gas 

 and waste gases from blast furnaces were largely used, more 

 especially in engines of larger sizes, developing as much as 2,500 

 brake horse-power and over, but in all cases the very high 

 thermal efficiency has been maintained. 



The modern gas engine is. as regards thermal efficiency, 

 greatly superior to the steam engine, and is consequently a much 

 more economical prime mover. It has many other points in its 

 favour, amongst which are rapid starting, less space occupied, 

 and the small engines require less skilled attention than in the 

 case of steam engines. The development of large engines work- 

 ing on blast furnace gas has had the most far-reaching effects in 

 the iron and steel making industries, and is now utilising vast 

 quantities of energy which, for generations, have been wasted. 



