1915] on Gaseous Explosions 271 



Broadly the rate of pressure rise becomes slower as the air 

 proportion increases. The time elapsino^ between the beginning- 

 of pressure rise and the attainment to maximum pressure is termed 

 the time of explosion ; and with a mixture of four of air to one of 

 gas it is 0*045 second, and with eleven of air to one of gas 0*29 

 second. These experiments Avere made in an explosion vessel 7 inches 

 diameter and 7 inches long. The pressure rise is caused by the 

 formation of flame at the ignition point — in this case an electric 

 spark— and the spread of this flame throughout the vessel increases 

 the temperature of the gaseous contents and thus increases the pressure, 

 as in a closed vessel the volume remains constant. The rate of 

 pressure rise is thus, broadly, the measure of the rate of the travel 

 of the flame througli the mass ; and if it be assumed that maxi- 

 mum pressure is attained when the whole vessel is filled with flame, 

 then it is possible to determine the flame velocity by these measure- 

 ments. 



In this case the electric ignition points were placed in the centre 

 of the cover at one end of the cylinder, and so a travel of 7 inches is 

 necessary to practically flU the whole vessel w^ith flame. Calculated in 

 this manner the flame velocity for the weak mixture is 2 feet per 

 second, and for the strong mixture 13 feet per second. Other experi- 

 ments at the Massachusetts Institute of Technology, Boston, and also 

 at the Royal College of Science, London, give very similar results. 

 Ordinary internal combustion engines of the stationary type, when 

 adjusted for the highest economy, usually draw into the cylinder a mix- 

 ture of 9 volumes air to 1 volume coal gas, and the flame velocity for 

 this mixture, as tested in the closed vessel, is found to be about 4 feet 

 per second and the time of explosion 0*155 second. If a large ex- 

 plosion vessel be used and iguition be started at one end of the cylinder, 

 it is obvious that the flame must travel a longer distance in order to fill 

 the vessel, and consequently the time of explosion will be increased. 

 By experimenting with vessels of different dimensions this has been 

 found to be true. For example, Prof. Hopkinson, of Cambridge, has 

 made experiments with a large vessel 23*4 inches diameter and 28*5 

 inches in length, having a capacity of 6 * 2 cubic feet, which show 

 for a mixture of air 9 and gas 1 a flame velocity of 5 feet per 

 second and a time of explosion of * 26 second. The time of explosion 

 is thus 0*26 second for the large vessel and 0*155 second for the 

 small. In the large vessel experiments, ignition w^as started at the 

 centre of the vessel. These experiments were made with an initial 

 pressure atmospheric, but tests with similar mixtures by Messrs. 

 Bairstow and Alexander at 34 J lbs. per square inch above atmosphere 

 show no material change in velocity. Prof. Petavel, too, has made 

 tests at the very high initial pressures of over 1000 lbs. per square 

 inch, rising to between 9000 and 10,000 lbs. per square inch after 

 explosion, and he found the rate of inflammation to be about 10 feet 

 per second for a mixture of 6 gas and 1 air. Within wide limits it is 



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