302 



Mr. Dugald Clerk 



[Jan, 29, 



From these determinations it is possible to roughly estimate the 

 heat loss on the explosion line in an ordinary gas engine using the 

 most economical mixture and a maximum temperature of about 

 1800° C. With time of explosion y^'oth second under ordinary 

 compression, a 3 per cent loss may ])e expected. 



It was long ago observed by Hirn, Bunsen, and others, that the 

 rise of temperature in gaseous explosions could not be calculated from 

 the then assumed specific heat of the constituent gases and the known 

 calorific value of the inflammable gas. The deficit of temperature 

 was found to be about 50 per cent, and many attempts were made to 

 explain this deficit, Hirn advocating the theory of heat loss on the 

 rising line and Bunsen supporting the idea of a limit to temperature 

 due to dissociation. Later, the French observers ]\Iallard and 

 Le Chatelier maintained that at least part of the deficit could he 

 accounted for on the assumption of increase of specific heat of the 

 gases. Investigations of the Members of the Committee have dealt 

 not only with the points which have been here discussed, l)ut with all 



Fig. 29. 



these questions— heat loss on the rising line, specific heat of the 

 constituent gases, heat loss on the falling line, and dissociation of the 

 combining gases. Specific heat work has been in progress by Clerk, 

 by Callendar and his pupil Swann, and much of this work has not yet 

 been published. Dissociation has been discussed by Dr. J. A. Barker, 

 Professor Smithells and Dr. Bone, and both internal energy and 

 dissociation have been discussed by Hopkinson. Ignition tem- 

 peratures of gases have been dealt with by Professor Harold Dixon, 

 and Dr. Watson has studied the nature of the exhaust gases from the 

 petrol engine. Many experiments, too, have been made on the law 

 of cooling and heating of gases under compression in cylinders by 

 Hopkinson, Dalby, Callendar, and Clerk. As a result of this work 

 the conclusion has been arrived at that so far as explosions in internal 

 combustion engines are concerned dissociation has but little to do 

 with the limit reached. This limit is partly due to increased specific 

 heat at high temperatures, to heat loss to the walls, aud to radiation 

 from the explosion. Varying specific heat and increasing radiation 

 account for most of the deficit. Alio wine for all these things. 



