232 



NA TURE 



;[ApRIL 2 2, 1909 



M' 



PRODUCER GAS FOR ENGINES.' 

 II. — Tests and Efficiencies. 

 'R. DUGALD CLERK had careful tests made with a 

 30-B.H.P. plant and a 40-B.H.P. plant of the type 

 shown in Fig. 2 of the article published last week, and 

 found that the heat efficiency of the former gas was 83 per 

 cent, and that of the latter as high as 90 per cent., both 

 with hot starts." In Table A, I give the results obtained 

 with the last-named suction plant, and for comparison the 

 results with a steam-jet pressure_ plant of the same power, 

 and the average of results with seven other pressure plants 

 of different sizes : — 



Table A. 

 Comparison of Suction and Pressure Plants. 



pli'nT 

 40 B.H.P. 

 (hot start) 



e)- 



by 



Fuel used ... 



Composition of gas (per cent, by i 



Hydrogen 



Methane 



Carbon monoxide 



Carbon dioxide 



Oxygen 



Nitrogen 



Total combustible gases (per 



volume) 



Calorific power (higher scale)— 



Calories per cubic metre 



B.Th.U. per cubic foot 



Air required for combustion of unit 



Yield of gas— 



Cubic metres per kilo, of fuel 



Cubic feet per ton of fuel 



Approximate power civen by an engine 

 which will give loo H.P. with gas of 

 Column 3 



Pressure 



plant 



40 B.H.P. 



(hot start) 



Anthracite 

 9-8 



0-74 

 56-24 



Pressure 



Average of 



7 plants 

 (hot start) 



Anthracite 



i7'36 



=S'S5 

 5'77 

 0-30 



The practical outcome of many tests made with engines 

 worked wilh suction plants is that with a full load, or 

 nearly full load, the consumption when running is a little 

 under i lb. of anthracite, or about ij lb. of gas-coke per 

 B.H.P. -hour. This is exclusive of the fuel burnt when 

 starting and during the stand-by hours. The consumption 

 of fuel and water in the small plants (about 20 B.H.P.), 

 tested at Derby in 1906 on behalf of the Royal Agri- 

 cultural Society was as follows :— 



i> /Tull load ... i-i lb. per B.H.B.-hour, including fuel for starting and 

 'o I banking during the night. 



Sj Half load ... I'S lb. per B.H.P. -hour." including fuel for starting and 



- I banking during the night. 



^ Water ... i gallon per B.H.P.-hour at full load. 



u ^^ J ■ „ ,, half „ 



■^ j Full load ... 1-3 lb. per B.H.P.-hour, including fuel for starting. 



UlWater ... I's gallons per B.H.P.-hour at full load. 



1 had an interesting test made with a 250-8. H.P. engine 

 and suction plant, working night and day for 123 hours 

 without a stop. The engine worked a dynamo, and read- 

 ings were taken every half-hour of the current generated. 

 The general result was that the consumption of small 

 anthracite, including all sources of waste, was only 1.23 lb. 

 per kilowatt-hour. On the assumption that the efficiency 

 of the dynamo was 90 per cent., this corresponds with 

 0.82 lb. per B.H.P.-hour. 



Close attention is usually given to the consumption of 

 fuel per H.P. -hour, sometimes to the thousandth of a 

 pound, and it is not a little remarkable that a separate 

 account is seldom taken of the consumption of fuel while 

 the steam or gas plant is standing with a fire in it. The 

 stand-by loss of a boiler is much greater than that of a 

 gas producer, and the explanation is not far to seek ; for 

 a given H.P. the producer is much smaller, and has far 

 less radiating surface than a boiler; it has no water In it 

 to be heated, and it can be worked up to its maximum 

 production in about fifteen minutes, after standing almost 

 any length of time. With a boiler, except in the vertical 

 or portable tjpe, there is a large amount of external brick- 



* Continued from p. 203. 



2 For full details of these trials see "Producer Gas," 2nd edition 

 (Longmans). 



NO. 2060, VOL. 80] 



work to be heated, and there is a considerable quantity 

 of water, even in the tubular type. When the boiler is 

 standing the water and the brickwork lose heat, and not 

 only more time, but more fuel, is required to make up 

 this loss than in the case of a gas producer. Doubtless 

 the heat efficiency of a good boiler is high when it is 

 working to nearly its full capacity, but the reverse is the 

 case when it is standing. Table B gives some comparative 

 results : — 



Table B. 

 Consumption of Fuel in Stand-by Hours. 



On this basis, if a 200-B.H.P. steam plant works eight 

 hours and is standing sixteen hours, and if it consumes 

 2.5 lb. per B.H.P.-hour, the stand-by loss will be more 

 than 20 per cent, of the total fuel consumed in twenty- 

 four hours. Under like conditions, if a gas plant of the 

 same power consumes i lb. per B.H.P.-hour, the stand-by 

 loss will be under 4 per cent. With a 500-B.H.P. plant 

 the stand-by loss with steam will be about 15 per cent., 

 and with gas under 2 per cent. If we take the percentage 

 of the stand-by loss on the fuel consumed during the work- 

 ing hours, we have the following results : — - 



200 B.H.P. 500 B.H.P. 



Steam power 26"S per cent. ... i7"y percent. 



Gas power ... ... ... 3'8 ,, 20 ,, 



The accompanying Figs. 3, 4, 5, and 6 show at a 

 glance the relative heat efficiencies of a steam boiler and 

 steam engine, and of a gas plant and gas engine of the 

 same power; Figs. 3 and 4 are each for 250 B.H.P., and 

 Figs. 5 and 6 are for 40 B.H.P. The blank space at the 

 top of each column represents the number of heat units 

 (100 calories or B.Th.U.) in the fuel consumed to produce 

 the same amount of useful work. For the 250-B.H.P. 

 steam plant I have taken 80 per cent, as the heat efficiency 

 of the boiler, and for the 40 B.H.P. 75 per cent. ; for the 

 condensation in pipes, driving feed-pumps and other usual 

 losses, I have taken lo per cent, of the total heat 

 lor the larger plant and 5 per cent, for the smaller one. 

 For the larger steam engine I have assumed a heat 

 efficiency of 15 per cent., and for the smaller one 10 per 

 cent. For the 250-B.H.P. gas power I have assumed that 

 the gas plant is of the steam-jet pressure type, and that, 

 including its small boiler, the heat efficiency is 80 per 

 cent. For the 40-B.H.P. gas power I have assumed that 

 the gas plant is of the suction type, and that its heat 

 efficiency is 85 per cent. With gas plants there are no losses 

 from condensation or other causes beyond those allowed 

 for in the above percentages. For the gas engines I have 

 assumed a heat efficiency of 28 per cent., and in all the 

 diagrams I have taken the friction of the engine as 15 per 

 cent. The figures given for the fuel consumed correspond 

 approximately with the following consumptions of fuel of 

 average quality : — ■ 



goo grams (2 tb. ) per B.H.P.-hour for 250 B.H.P. steam power 

 450 ,, (lib.) ,, ,, I, ,, gas power (pres- 



1350 ., (3 lb.) ,, ,, 40 „ steim power 



400 ,, (o'9 lb. ) ,, ,, ,, ,, gas power (suction 



plant). 



In Fig. 3, 1 120 heat units are absorbed in the boiler, 



and of these 224 are taken as lost in ashes, radiation, flue 



1 Exclusive of raising the steam pressure from go lb. lo 120 lb. 



