20 PRESIDENTIAL ADDRESS SECTION A. 



With engine reliability came its adaptation to need of 

 aviation, and aviation practice developed a new species of 

 motor engine, in which economy in petrol and oil consumption 

 was, to a considerable extent, sacrificed to minimise weight per 

 horse-power and extreme reliability. As regards the weight per 

 horse-power, the first stationary petrol engines made in the year 

 1880 weighed about 1,110 lbs. per horse-power. Six years later 

 Daimler, in his early motors, had reduced this weight to 88 lbs. 

 per horse-power, and during the evolution of the motor engine 

 this figure was rapidly reduced. In modern motor-car engines 

 the engine weight, including the heavy fly-wheel, ranges from 

 18 to 24 lbs. per nominal brake horse power. 



In aeroplane motors the weight has been cut down to a 

 wonderful degree, and engine weights per rated B.H.P. are 

 given as varying from 21 lbs. to 1.8 lbs. This last figure is 

 claimed for the 14-cylinder, 123 H.P. rotary Gnome engine. In 

 the 7-cylinder Gnome engine the weight is only 3^ lbs., and 5 to 

 6 lbs. per rated H.P. is comparatively common in good engines. 



Another type of internal coml)Ustion engine of comparatively 

 recent origin is the Diesel engine. This engine works on what 

 is known as the continuous or slow combustion principle, whereas 

 all gas engines, petrol engines, etc., work by explosion, that is to 

 sav. by comlnistion at approximateh' constant volume. From 

 the point of view of thermal efficiency, an engine on the slov/ com- 

 bustion principle is more efficient than one working on the explo- 

 sion principle. The slow combustion principle was first used by 

 Bray ton in America in 1872, but it was not until 1893 that the 

 late Dr. Diesel published his ideals defining the proper principles 

 on which a heat engine should be designed in order to ensure 

 its working with a maximum economy. Diesel's ideas were 

 embodied in a patent taken out in 1892, and the manufacture 

 was taken up by two important engineering firms in Germany, 

 and the highly successful modern Diesel engine stands to the 

 credit of the Germans — Augsberg engineering firm. 



The principle of this engine is to produce the highest tem- 

 perature of the C3^cle before combustion of the charge takes 

 place, and this high temperature is obtained solely by the com- 

 pression of air, which is efifected in a separate air compressor, 

 and not, as in the usual four-stroke cycle, by a compression 

 stroke of the piston. The initial compression of the air is very 

 great, reaching as high as 500 lbs. per square inch. At the 

 commencement of the expansion stroke liquid oil fuel is injected 

 into the charge of compressed and highly-heated air, and com- 

 bustion of the mixture immediately takes place at more or less 

 constant temperature. 



This engine immediately showed itself to be the most 

 economical internal combustion so far as fuel consumption was 

 concerned, and it was adapted to use low grade heavv oil fuels, 

 such as crude petroleum and heavy vegetable oils, which could 

 not be used in other types of internal combustion engines. This 



