: ii 
ON GASEOUS EXPLOSIONS. 957 
the eiid of the stroke. The cylinder was charged with 4 mixture of gas 
and air, the piston being placed so that the port was closed, and sufficient 
time was allowed for complete diffusion to take place. The mixture, 
which was at atmospheric pressure and temperature, was then fired, the 
pressure generated forced out the piston, which opened the port at a 
period yarying from 0:11 to 0°23 second from the moment of ex- 
plosion, thus liberating the gases. The gases escaped through the port 
and through a passage packed with cold wire gauze C by way of a 
small slide-valve D into a collapsed gas-bag E. The gauze checked any 
chemical action going on in the gases, which were subsequently removed 
from the bag into which they had been exhausted and analysed. In 
each of eight experiments, three of which were made with a mixture of 
1 volume of coal gas to 7 of air, and five with a 1 in 10 mixture, a 
certain proportion of unburnt fuel was found in the exhaust. The 
quantity of carbon ranged from 2 to 4°3 per cent. by volume and the 
quantity of hydrogen from 0°8 to 3°7 per cent. by volume. These ex- 
periments seem to prove that from some cause combustion continues 
even in the explosion of a strong mixture for some little time after the 
attainment of maximum pressure. 
In the petrol motor as ordinarily used the air is insufficient to burn 
the petrol completely. Under these conditions the efficiency of the 
engine, reckoned on the actual consumption of petrol, is of course much 
reduced, since the exhaust contains CO and other substances of consider- 
able heating value. Hopkinson and Morse, however, pointed out two 
years ago’ that if the efficiency were calculated on the heating value of 
the chemical changes which actually took place in the engine, 
it remained nearly constant over a wide range of mixture 
strength, as was to be expected from theory. The effect of mixture 
strength on the efficiency of a petrol motor has been exhaustively 
investigated by Watson during the past year. Some of his results are 
given in the following table :— 
Indicated Thermal Efficiency calculated on 
Air : 3 F 
atchl by calorie Nene aoe ; 
P : '  correspondin ercentage o 
pufent Whole Calorific | “the Chemical Heat of Fuel 
ue Changes which liberated 
actually take place 
14 248 | 251 99 
13 235 . 264 89 
12 220 278 79 
11 204 287 71 
10 185 289 64 
Fig. 4 gives curves showing change of thermal efficiency with ratio 
of air and petrol by weight, beginning with a mixture having so little 
experiments ; indeed, I should have been rather surprised if he had not obtained 
such evidence. Some years ago, working on the combustion of dense hydrocarbons 
in a Diesel engine, I found a considerable ‘‘ disappearance’ of both carbon and 
hydrogen, which was at once explained when the water condensed from the exhaust 
gases was found to give very strong aldehydic reaction.’ 
* Engineering, August 9, 1907. 
1909. . 8 
