1915] on Gaseous Explosions 281 



through a passage into the mass of inflammable mixture, and thus 

 adding to the rate of ignition the mechanical disturbance produced 

 by the entering flame. He has succeeded by this means in producing 

 maximum pressure in one-hundredth part of a second in a space 

 containing 20(» cubic inches. This rate of ignition is too rapid, and 

 would not give the engine time to take up the slack in bearings, 

 connecting-rods, etc. But by firing a mixture with varying amounts 

 of mechanical disturbance almost any time of ignition can be obtained 

 between one-hundredth and one-tenth of a second. It does not 

 matter whether the mixture used is rich or weak in gas ; the rich 

 mixture can be fired slowly and the weak one rapidly, just as may be 

 required. The rate of ignition of the strongest possible mixture is 

 so slow that the time of attaining complete inflammation depends 

 on the amount of mechanical disturbance permitted." 



From this it will be seen that even in 1882 it was known that 

 mechanical disturbance was necessary in order to get the maximum 

 pressure in the time required for running an engine effectively. It 

 was then known that the rate of ignition was slow even in a strong 

 mixture, and that the time of attaining complete inflammation 

 depended upon the amount of mechanical disturbance permitted. It 

 was known that the rate of spread of flame was much greater in 

 engines than in closed vessels. In experiments made by the author 

 at that time he found that mechanical disturbance could be caused by 

 means of a projection of flame through a passage into the mass of 

 the mixture ; and it was supposed that the higher rate of flame 

 propagation in ordinary internal combustion engines was due partly 

 to this flame disturbance and partly to the higher temperature of 

 compression before ignition. 



The examination of indicator diagrams from gas engines and 

 petrol engices has shown that the rate of flame propagation varies in 

 different engines, from 35 to 100 feet per second. Experiments made 

 with a horizontal gas engine 22 inches diameter and 34 inches stroke 

 running at IGO revolutions per minute with Mond gas, suction gas, 

 and town gas, all at 160 revolutions per minute, show that with Mond 

 gas the explosion period required 45 degrees of the circle, with 

 suction gas 40 degrees, and with town o:as 25 degrees. The respective 

 times of explosion were aV^h, ^jth, ^^^th of a second, and the respective 

 flame velocity as well 47, 54, and 85 • 5 feet per second. In these 

 experiments the maximum flame temperatures were nearly the same, 

 but of the different gases used Mond gas had the slowest ignition and 

 town gas the fastest. In this particular engine the inlet velocity of 

 the charge through the valve throat was 160 feet per second. In 

 another horizontal gas engine of 9 inches diameter by 17 inches 

 stroke running at 200 revolutions per minute the charge velocity was 

 about loo feet per second. In this engine 25 degrees crank angle was 

 required for explosion. The time of explosion was 4Vth second, and 

 the rate of flame propagation was 37 J feet per second. 



