GAS-ENGINE 



GA8KELL 



109 



by the application to gas-engines of the regenera- 

 ti\i- principle which hat* done HO much t<> promote 

 e.-o iiniiiy of IK-HI in metallurgical operations. It 

 was proposed by Siemens to use a separate com 

 l>u-tion chaiulwr, which, being distinct from the 

 working cylinder, might be kept always hot, and 

 in |>ii*g the outgoing gases through a regenerator, 

 which would take til) their heat and give it hack to 

 tin- incoming air. Much the same end was aimed 

 at hy Fleeming Jenkin, who tried to adapt the 

 regenerative engine of Stirling (see AIR-ENUINK) 

 to sen i- fur the internal combustion of gas. These 

 at i fin | its have hitherto failed, and the gas-engine 

 still falls far short of the limit of thermodynamic 

 efficiency which its high range of temperature 

 .shows it to be theoretically capable or. The 

 greatest ideal efficiency of any heat-engine is 



measured by the fraction * ~ 2 , where TJ is the 



T i 



highest (absolute) temperature at which it can 

 receive heat, and TJ is the lowest (absolute) tem- 

 perature at which it can reject heat. The highest 

 temperature in the combustion is, as we have seen, 

 about 3000 F., and the lower limit of the range 

 is the atmospheric temperature, or say 60 P. 

 Substituting these values in the formula, we have 

 0'85 as the highest ideal efficiency ; in other words, 

 it should be, from the thermodynamic point of view, 

 theoretically possible to convert 85 per cent, of the 

 heat-energy of the gas into work. The greatest 

 efficiency hitherto realised is about 0'22, or little 

 more than one-fourth of the ideal efficiency. It 

 must not be supposed that under any imaginable 

 practical conditions it could be possible to reach 

 the ideal limit, but it may be confidently expected 

 that the gas-engine of the future will approach it 

 much more closely than does the gas-engine of to- 

 day. The comparison serves to show how much 

 room there is for invention in the direction of 

 obviating what is essentially preventable loss. 



It is instructive in this connection to compare 

 the efficiency of gas-engines with that of steam- 

 engines. In a large steam-engine the efficiency is 

 about 0'15; in other words, the engine converts 

 into work only some 15 per cent, of the heat-energy 

 supplied to the steam, and the figure would be 

 greatly less if one stated it as a fraction of the 

 whole heat of combustion of the fuel. In steam- 

 engines small enough to be fairly comparable with 

 actual gas-engines, the efficiency is rarely more, 

 and generally a good deal less, than 0*1. Con- 

 sidered as a thermodynamic machine, the gas- 

 engine, imperfect as it admittedly is, is already 

 not far from twice as efficient as the steam-engine. 

 It is in fact the most efficient heat-engine we 

 possess. 



Experiments show that the consumption of gas 

 in practice in a small gas-engine (indicating 10 

 horse-power or more) may, in favourable cases, be 

 l>'-> than 20 cubic feet per hour per indicated 

 horse-power, including the gas which is consumed 

 in maintaining the igniting fiame. Of the indi- 

 cated horse-power about 85 per cent, is available 

 for doing mechanical work outside of the engine 

 itself. The cost of the fuel is necessarily high so 

 long as the gas supplied to the engine is the puri- 

 fied coal-gas used for lighting. Thus, with gas cost- 

 ing 3s. per 1000 cubic feet, the supply required for 

 each indicated horse-power per hour will cost about 

 three-farthings, whereas the coal bill of a steam- 

 engine for each horse- power hour need not exceed 

 a fifth of a penny, and may be even less. In such 

 cases the advantage of the gas-engine lies in its 

 compactness and convenience, in the saving of 

 charges for attendance, and in the ease and 

 economy with which it can be applied to do 

 intermittent work. Economy in the cost of fuel 

 may, however, be secured by supplying the engine 



with a cheaper kind of go*, a gan suitable for heat- 

 ing though not suitable for illumination. The late 

 Sir William Siemens pointed out that a compara- 

 tively cheap gas of the kind required might ! go* 

 by separating successive stages in the distillation 

 or coal, and advised supplying of towns with nucli 

 a gas for heat and power through distinct muiim. 

 Another gas for gas-engines in that produced by 

 Mr Emerson J)o\\ son's process of blowing a mix- 

 ture of air and steam through a bed of red-hot 

 anthracite or coke. The product contains 22$ per 

 cent, of hydrogen and the same quantity of car- 

 bonic oxide, mixed with much nitrogen and a 

 small quantity of carlionic acid, and is said to 

 cost about 2id. per 1000 cubic feet.* The engine 

 requires about four times as much of it as it would 

 require of illuminating coal-gas. When Dowson 

 gas is used, the fuel needed for a gas-engine is 

 not more than H lb. of coke or anthracite per 

 horse-power per hour as compared with the 4 or 

 5 lb. burned in a steam-engine or corresponding size. 



Gas-engines have recently been applied with 

 great success on the Continent to the propulsion of 

 tramcars, which carry compression -cylinders. The 

 gas from the mains is driven by pumping-engines 

 into a compression-reservoir : the car runs up out- 

 side the station, and the reservoir is connected with 

 the car cylinders, which promptly become refilled 

 under a high pressure : the stopcock is closed, the 

 connecting-tube removed, and the car is again 

 ready. 



A notice of gas-engines would be incomplete 

 without a reference to oil-engines using petroleum 

 as fuel, which is vaporised and then exploued along 

 with air. In Priestman's engine the petroleum, 

 which is a safe oil with a flashing-point higher than 

 75 F., is injected in the form of spray, by a jet of 

 compressed air, into a chamber which is heated by 

 means of a jacket through which the hot gases of 

 the exhaust pass. There the spray is raised to a 

 temperature of about 300, and is completely 

 vaporised. From the hot chamber the vapour is 

 drawn, along with more air, into the working 

 cylinder, where the cycle of operations is essentially 

 the same as in Otto's engine. In some types, only 

 1 lb. of oil is burned per brake horse-power per hour. 

 The compactness and smoothness of working of 

 these oil-spray motors has made it possible to adapt 

 them to vehicles, from tramcars to tricycles ; and 

 innumerable types of 'auto-cars' or 'motor-cars' 

 have been perfected, and since 1896 (see TRACTION 

 ENGINES ) nave become familiar even on the roads 

 of remote country districts. 



See worka by D. Clerk (1886), W. MacGregor ( 1885), 

 and Bryan Donkin ( 1894) ; Professor Perry, The Steam- 

 Enniiu, and Gas and Oil Engines ( 1899) ; and numerous 

 papers in Engineering magazines. 



Gaskell, MRS, novelist, was born at Cheyne 

 Row, Chelsea, 29th September 1810. Her maiden 

 name was Elizabeth Cleghorn Stevenson, and her 

 father was in succession teacher, preacher, farmer, 

 boarding-house keeper, writer, and Keeper of the 

 Records to the Treasury. She was brought up by 

 an aunt at Knutsford the Cranford which she 

 was yet to describe with such truthful patience ; 

 was carefully educated, and married in 1832 

 William (lask'ell (1805-84), a Unitarian minister in 

 Manchester. In 1848 she published anonymously 

 her Mary Barton, which at once arrested public 

 attention. It was followed by The Moorland Cottage 

 (1850), Cranford (1853), Ruth (1853), North and 

 South (1855), Round the Sofa (1859), Right at Last 

 ( 1860), Sylvia's Lovers ( 1863), Cousin Phillis ( 1865), 

 and Wives and Daughters (1865), a series of novels 

 that have permanently enriched English literature, 

 and almost lifted their authoress into a rank repre- 

 sented alone by Jane Austen, Charlotte Bronte', and 



