106 



GASCONY 



GAS-ENGINE 



persevering, and make capital soldiers. This is 

 especially true of the Gascons in the Gers depart- 

 ment ; the peasants of the Landes, living in mud- 

 huts, are extremely ignorant and rude in their 

 manners, but yet are honest and moral. 



Gascony derived its name from the Basques or 

 Vasques, who, driven by the Visigoths from their 

 own territories on the southern slope of the Western 

 Pyrenees, crossed to the northern side of that 

 mountain-range in the middle of the 6th century, 

 and settled in the former Roman district of Novem- 

 populana. In 602, after an obstinate resistance, 

 the Basques were forced to submit to the Franks. 

 They now passed under the sovereignty of the 

 dukes of Aquitania (q.v. ), who for a time were in- 

 dependent of the crown, but were afterwards con- 

 quered by King Pepin, and later by Charlemagne. 

 Subsequently Gascony became incorporated with 

 Aquitaine, and shared its fortunes. 



See Monlezun, Histoire de la Gascogne (6 vols. Audi, 

 1846-50) ; Cenac-Moncaut, Litterature populaire de la 

 Gaacoffne (Paris, 1808); and J. F. Blade, Contes populaires 

 de la Gascogne (3 vols. Paris, 1886). 



Gas-engine* Gas-engines are heat-engines of 

 a type in which the fuel is combustible gas, which 

 is burned within the engine itself. In all heat- 

 engines there is a working substance, which is 

 alternately heated and cooled, and does work by 

 alternate expansion and contraction of its volume, 

 thereby converting into mechanical form a portion 

 of the energy which is communicated to it as heat. 

 In most heat-engines the combustion of the fuel 

 which supplies heat to the working substance goes 

 on outside of the vessels within which the working 

 substance is contained : the steam-engine is a char- 

 acteristic example of this class. Gas-engines, on 

 the other hand, belong to the internal combustion 

 class : the working substance is made up of the fuel 

 itself before and after combustion along with a 

 certain quantity of diluting air. Internal com- 

 bustion engines have the enormous advantage that 

 there is no heating surface of metal through which 

 the heat must pass on its way to the working sub- 

 stance. The existence of a heating surface in the 

 external combustion engine imposes practically a 

 somewhat low limit upon the highest temperature 

 to which the working substance may be raised. In 

 gas-engines a far higher temperature is practicable, 

 and the result is that it becomes possible to convert 

 a larger fraction of the heat into work. The theory 

 of Thermodynamics (q.v.) shows that even the most 

 efficient conceivable heat-engine can convert into 

 work no more than a certain fraction of the heat 

 supplied to it a fraction which is increased by 

 increasing the range through which the tempera- 

 ture of the working substance is caused to vary. 

 This range is much greater in the gas-engine than 

 in the steam-engine, and the ideal efficiency that 

 is to say, the fraction of the heat convertible into 

 work is consequently greater. In practice, although 

 the gas-engine as yet falls short of its ideal effici- 

 ency to a much greater extent than does the steam- 

 engine, it is actually the more efficient of the two. 

 A pound of fuel converted into gas and used in 

 a modern gas-engine gives a better return in 

 mechanical work than if it were burned in the 

 furnace of a steam-engine of the most economical 

 type. For small powers the gas-engine has the 

 great practical merit, as compared with the steam- 

 engine, of dispensing with the attendance which a 

 boiler and furnace would require. This considera- 

 tion has made it in many thousands of cases an 

 economical motor even when the gas it uses is of 

 the comparatively costly kind supplied for illum- 

 inating purposes. 



From the year 1823 onwards a number of pro- 

 posals were made by Brown, Wright, Barnett, and 



others for the construction of engines to work by 

 the explosive combustion of gas. Although in some 

 instances these inventions anticipated later success- 

 ful engines, and although the details were often care 

 fully elaborated, no practical success was attained 

 till 1860, when an effective gas-engine was brought 

 into public use by M. Lenoir. 



Lenoir's engine resembled in appearance a single- 

 cylinder horizontal steam-engine. As the piston 

 advanced it drew in an explosive mixture of gas 

 and air. About nri< J stroke this was ignited by an 

 electric spark, and for the remainder of the stroke 

 work was done through the pressure of the hot 

 products of the explosion. During the back-stroke 

 these products were expelled to the atmosphere, 

 while on the other side of the piston a fresh ex- 

 plosive mixture was being taken in and exploded at 

 mid-stroke as before. To keep the cylinder cool 

 enough to admit of lubrication it was surrounded 

 by an external casing within which cold water was 

 caused to circulate. This water-jacket has con- 

 tinued to be a feature of nearly all modern gas- 

 engines. An indicator-diagram from Lenoir's engine 

 is shown in fig. 1. From A to B the gas and air are 



Fig. 1. Indicator-diagram of Lenoir's Engine. 



being sucked in. The rapid rise of pressure from B 

 to C is due to the ignition of the mixture. After C 

 the hot products of combustion go on expanding to 

 the end of the stroke, D, and the pressure diminishes 

 although ( as recent investigations have shown ) the 

 process of combustion is to some extent continued 

 into this stage. The back-stroke, DA, expels the 

 burned gases at atmospheric pressure. 



Lenoir's engine used about 95 cubic feet of gas 

 per horse-power per hour, which is about five times 

 the quantity required by the best gas-engines of 

 the present day. Its poor economy was mainly 

 due to the small amount of expansion which the 

 hot gases underwent after the explosion. Another 

 drawback was that the average pressure upon the 

 piston was so low as to make the engine bulky 

 in proportion to the work performed by it. 

 These defects are remedied in modern gas-engines 

 by compressing the mixture before it is ex- 

 ploded, so that a greater range of expansion is 

 required to reduce the burned gases to the atmo- 

 spheric pressure at which they are expelled. This 

 secures greater efficiency, while at the same time 

 the higher mean effective pressure of the work- 

 ing substance permits an engine of a given size 

 to have more power. Compression or the ex- 

 plosive mixture had been proposed by Barnett as 

 early as 1838, and was a feature in several later 

 patents ; but its advantages were first practically 

 realised in the well-known and highly successful 

 engine of Otto, which dates from 1876. 



Nine years earlier (in 1867) a gas-engine had 

 been commercially introduced by Otto in conjunc- 

 tion with Langen which, although now obsolete, 

 deserves mention both on account of the success 

 which it achieved and the peculiarity of its action. 

 The Otto and Langen engine was of the free-piston 

 type ( originally proposed by Barranti and Matteucci 

 in 1857). There was no compression of the ex- 

 plosive mixture ; it was taken in during the early 

 part of the up-stroke of a piston which rose in a 

 vertical cylinder. Then the mixture was ignited 

 by being brought into momentary contact with a 



