234 



NA TURE 



[August 19, 1909 



RECEKT IMPROVEMEXTS IN THE IXTERXAL- 



COMBUSTION EXGLXE.' 



III. 



"VVTE have now to consider the way in which the recent 



' great practical improvements in the design and 

 operation of gas engines and gas-producing plant have 

 come about, and how they are connected with the 

 theoretical considerations referred to in the previous 

 articles. 



Despite the multitudinous ways in which the internal- 

 combustion engine is employed, there is a general assort- 

 ment into three main groups, which may be described 

 thus : — 



(a) Large gas engines for gas blowing, for the genera- 

 tion of electric power or other power purposes, the size 

 being usually more than looo horse-power. 



(fc) Smaller gas or oil engines used for workshop 

 driving, in sizes up to about 500 horse-power. 



(c) Petrol engines for road transport, for marine work, 

 and for aeroplanes, the sizes being usually less than 100 

 horse-power. 



With class (a) are associated pressure gas producers, 

 frequently worked with by-product recovery plant, and 

 schemes for the utilisation of the waste gases of coke 

 ovens and blast furnaces. The gas engines in class {b) 

 usually derive their gas from suction gas producers, which 

 are practically always of smaller size than the 500-horse- 

 power unit, though attempts are now being made to work 

 with the larger units suitable to marine work. H.M.S. 

 Rattler is one of the very first instances of the application 

 of the suction gas producer to marine purposes, and it has 

 been remarkablv successful. Looming in the distance is 

 the prospect of using suction gas producers and gas engines 

 in smaller units for road transport, but the difficulty of 

 finding space on the present type of motor-car for the 

 whole of the plant is a great one. On the other hand, 

 the considerable economy in fuel to which this develop- 

 ment would lead is an inducement to proceed with the 

 endeavour to overcome these difllculties. 



By far the most numerous class of internal-combustion 

 engine is that of class (c), which includes the thousands 

 of motor-cars and cycles now in use in all civilised 

 countries. The fuel used is not invariably petrol, as 

 successful attempts have been made to run on alcohol, 

 benzol, and the heavier elements in the paraffin series. 

 Ordinary commercial paraffin has recently been used with 

 extraordinary success, particulnrlv in tropical cotmtries, 

 and it is even reported from Uganda that the combination 

 there of altitude with high temperature enables paraflfin 

 to be used as a fuel in small engines without any change 

 in the usual petrol carburettor as used in this country. 



Improvemeiils in Class (a). 



The chief direct practical improvements in this class are 

 the better proportioning of parts, so as to avoid cracking 

 by unequal heating, and the better general design of the 

 fly-wheel effect in conjunction with such an arrangement 

 of cylinders as to produce a more even turning moment, 

 and therefore less cyclic irregularity. The former is 

 evidenced by the greater trustworthiness to-day of the big 

 engine, and the latter is abundantly illustrated bv the 

 following extract from Messrs. Andrews and Porter's 

 recent paper ^ before the Institution of Electrical 

 Engineers : — 



" The large gas engines at the Bruckhauser, Home- 

 comb and Heinitz installations visited by English engineers 

 in .-August last are all provided with fly-wheels to main- 

 tain a cyclic irregularity within i '250. ' The two former 

 are single tandem engines, and the latter twin tandem, 

 but no appreciable difference in the parallel running was 

 noticeable." 



The information derived from recent experimental work 

 on piston and wall-temperatures will probablv lead to still 

 further improvements in the mechanical design of details, 

 as once_ the conditions of the heat flow are known a proper 

 proportioning and subdivision of parts is rendered possible. 

 The recent improved trustworthiness of operation is shared 



^ Continued fr'>m p. 20^. 



- " The Use of Large Gas Engines for Generating Electric Power. ' Read 

 before the Institution of Electrical Engineers, 1909. 



NO. 2077, VOL. Si] 



equally by the two-cycle engines (such as the Oechol- 

 hauser, Koerting, and others) and the four-cycle engines, 

 and it is very diflicult to say that either type is gaining, 

 ground at the expense of the other. By-product recovery 

 work is becoming better understood, although there is 

 always the difliculty that the bj'-products, when produced, 

 have to be sold, and one has therefore to take into account 

 the efl'ect upon the market price should a largely increased' 

 output result from the extended use of such plant. The 

 utilisation in gas engines of the waste gases of coke ovens- 

 and blast furnaces is now very usual. This is especially 

 so in Germany and Belgium, where a great deal of work, 

 has been done in this direction ; in the United States there- 

 has been a rapid increase in the adoption of this process,, 

 whilst in this country matters have moved appreciably, 

 although, owing to the low cost of fuel in England, there 

 is not the same economic pressure to make the change. 

 On Tyneside an excellent plan is in operation, whereby 

 engines running on waste gases are made to generate- 

 electric power, which is then supplied to. and paid for 

 bv, the central electric generating station. By this method' 

 of pooling the current, which, of course, cannot be 

 economically stored, but has to be used as fast as it js 

 produced, the complicated questions as to its utilisation are 

 avoided. 



A notable recent irnprovemcnt in the ignition of gas 

 engines of all sizes is the adoption of the electric system- 

 with either low-tension or high-tension currents. On the 

 whole it seems likely that, as with motor-cars, the latter 

 will in the end become the most used, though at present 

 the low-tension system with moving contacts inside the 

 cylinder seems to be the most popular. 



Improvements in Class (b). 



In both this class and class (a) it is noticeable that the 

 engines designed on the Continent are more complicated' 

 in appearance than those designed here. The British' 

 desire for simplicity doubtless is, at the root, a good one. 

 One of its most noticeable illustrations in modern life is 

 the steam railway locomotive. -As applied to the gas 

 engine, this desire takes efl'ect in the much simpler method' 

 of governing. The usual English plan is to govern on the 

 " hit-and-miss " principle, that is to say, when the engine 

 runs up to too fast a speed the cylinder for one or more 

 cycles will get no charge of gas at all, or else (which 

 comes to the same thing) the ignition will be cut off and' 

 no explosion take place (this, though a very simple means 

 of governing, is wasteful in fuel). "The average Continental' 

 design provides for the throttling (as in a steam engine or 

 by varying the lift of the inlet valves) of the entering 

 charge, so as to cause a less intense explosion. This tends 

 towards a steadier speed, but on the other hand leads to 

 a constant lowering of the compression ratio, and there- 

 fore to a diminished therrnal efiiciency and an increased 

 rate of fuel consumption.' In England the difficulty of 

 speed fluctuation, to which the adoption of the hit-and-miss 

 principle leads, is met by increased fly-wheel effect or by 

 dividing the power between a number of cylinders, but 

 several well-known English makers are now governing 

 by throttling the inixture. 



The standard of achieved thermal efficiency is continu- 

 ally rising, although the amount of the improvement is 

 the less easy to state on account of the very optimistic 

 way in which certain experimental readings seem to have 

 been taken. Much depends upon the ratio of compression, 

 and many attempts have been made to permit of a high 

 compression pressure without pre-ignition. This has been 

 successfullv attempted in several wavs, viz. bv the method 

 of water injection, so lowering the compression tempera- 

 ture corresponding to a given pressure, or else by the 

 ?-nethod of supercompression, which consists of causing the 

 in-coming charge to be at a pressure of from ., lb. 

 to 10 lb. above the atmosphere, so that here also a 

 higher pressure corresponds to a lower temperature, and' 

 sometimes by the method of decreasing the proportion of 

 hvdrogen present, and so raising the temperature at which 

 the mixture would be liable to pre-ignition. In the usual 

 form of suction producer, the proportion of hydrogen pre- 



1 In a specific case the reduction of the compression pressure from 170 lb. 

 to ISO lb. led to an increase in the ther.-iial units used per horse-power from- 

 95C0 to 11,500. 



