June 8, 1888,] 



SCIENTIFIC NEWS. 



533 



THE PRIESTMAN PETROLEUM 

 ENGINE. 



IN gas engines the power is derived from the explosion 

 of successive charges of gas and airin the cyHnder, and 

 many attempts have been made to work engines of this 

 type with vapour of petroleum instead of gas. At first 

 sight it would appear comparatively easy to do this, but 

 in reality the difficulties are considerable. In the first 

 place the oil must be vapourised before being admitted 

 to the cylinder, for ifitbenot in a very fine state of divi- 

 sion it will not thoroughly mix with the air required for 

 its combustion. The usual speed of such an engine is 

 about 160 revolutions per minute, and to insure uni- 

 formity of power it is necessary to have an explosion 

 every revolution, or at least every alternate one. Seeing, 

 therefore, that at best there is only the eightieth part of 

 a minute in which the gas or vapour can mix with air 

 before the charge is ignited, it is evident that only an 

 attenuated vapour can be used instead of gas. For 

 instance, the ordinary petroleum of commerce, such as is 



the heavier oil can be used without danger, whereas the 

 light oils are so volatile that very special precautions 

 have to be taken. 



To start the engine, the retort is first heated by a 

 lamp, and after the engine has been run a short time 

 the retort is heated by the waste products of combustion 

 from the exhaust. 



Sir William Thomson and others have tested the 

 engine, and he reports that the quantity of oil used (of 

 gravity about '800) was at the rate of 171 pints, or i'6g 

 pounds per brake horse power per hour. He also states 

 that this engine does not use the lighter portion of the 

 oil only, but consumes the whole of the oil put into the 

 tank, without leaving a residuum. He adds further that 

 the piston requires no oiling, as the vapour admitted 

 into the cylinder lubricates it sufficiently. All these 

 points are of great importance, and we are very pleased to 

 have so high an authority for them. At the same time 

 it is clear that if i'6g lb. of oil are required per 

 effective horse power per hour, the working cost 

 of an engine of this type will be much greater than 



lillp' 



used for lamps, etc., has not hitherto been used, because 

 it does not vapourise readily, and because its vapour so 

 soon condenses. The best result? hitherto attained have 

 been with a light petroleum spirit, such as gasoline, 

 having a specific gravity of "650 to '670 ; but in most 

 countries its price is almost prohibitory, and it is seldom 

 used, except for little engines of half or one-horse power. 

 Attempts have been made to use rather heavier oils in 

 the form of fine spray produced by an air injector, but 

 the results have not been very encouraging, and again 

 the cost of the oil is great. 



In the Priestman engine (made under the several 

 patents of Priestman, Humes, and Etfeve) a new feature 

 has been introduced which promises very well. A small 

 pump attached to the engine, and shown on the front of 

 our illustration, forces air into an oil receiver, and causes 

 a very fine jet of oil to enter a little retort, in which the 

 oil is at once vapourised. The oil vapour, mixed with 

 a suitable proportion of air, then enters the cylinder, and 

 is exploded by an electric spark. In this way ordinary 

 petroleum, with a specific gravity of about '800, and with 

 a high flashing point, can be used. This is not only im- 

 portant from an economical point of view, but because 



with a good steam engine, or with a gas-engine driven 

 by Dowson gas requiring only the same weight of coal 

 per horse power per hour. In countries where suitable 

 oil is low in cost, the advantages of the Priestman engine 

 will be more apparent, but in Great Britain or other 

 countries where coal is much cheaper than oil, we fail 

 to see how the latter can be used with economy. The 

 expert's reports give only the brake horse power deve- 

 loped during the trials, and not the indicated power, but 

 it would have been interesting to know the actual power 

 absorbed by the pump and other working parts of the 

 engine. The theoretical dynamic effect of a pound of 

 oil is very great, and if we knew the consumption off oil 

 per indicated horse power per hour, i.e., the gross power 

 actually developed in the cylinder without reference to- 

 the friction of the mechanical parts, we could determine 

 the efficiency of the machine as a heat engine. 



Apart from questions of strict economy, there are 

 many cases of engine power being required for isolated 

 houses, etc., where there is no gas, and where coals are 

 expensive and difficult to obtain. In such cases, the 

 ease with which the engine and oil apparatus can be 

 worked are doubtless well worth consideration. 



