NA TURE 



[April 15, 1909 



leave the steam-raising apparatus at a higher temperature 

 than that of the steam, and there is still a considerable 

 loss of heat when the gas is cooled for use in an engine. 

 There is also the loss due to radiation from the producer. 

 Other conditions which have to be considered are the depth 

 of fuel, its porosity, the size of the pieces used, and the 

 velocity of the air blast — all are interdependent ; for ex- 

 ample, the depth of fuel required to give the best results 

 will depend on the nature of the fuel, its size, and the 

 velocity of the currents passing through it. It is obviously 

 desirable that this velocity should not be excessive, and 

 the producer should have a sectional area large enough for 

 a given ma.ximum rate of production. 



The fuel consumption and the cost of repairs with a 

 gas engine worked with a pressure plant, as shown 

 m Fig. I, have been much lower than can possibly be 

 obtamed with the best steam engines and boilers of the 

 same horse-power ; but in recent years the modification 

 called a suction plant has given even better economical 

 results for moderate powers. In some of the early 

 gas producers for furnace work air was drawn into the 

 producer by suction, instead of being forced in under 

 pressure, and the idea of working the producer by suction 

 has been reverted to in connection with gas engines. In 

 i8b2 Dr. Jacques Arbos, of Barcelona, patented a com- 

 bmation of gas plant and gas engine in which the latter 

 drew gas direct from the producer. It was not a very 

 practical arrangement, and the charge of gas and air was 

 not compressed before ignition, but it deserves to be men- 

 tioned as one of the early suction plants devised. The 

 first to give effect to this idea in a practical wav, in a com- 

 pression engine, was M. L^on Bonier, of Paris. His first 

 patent was in 1891, and he afterwards took out others- 

 the engine had a suction pump by ' 



the side of the motor cylinder, and 



this pump was connected by a pipe %.^^.r 



with the outlet of the g.is plant. 

 As soon as the fire was lighted it 

 was blown up with a hand-power 

 fan, and when the gas was good 

 enough to work the engine the latter 

 was started. The pump on the 

 engine then drew gas from the pro- 

 ducer and forced it into the motor 

 cylinder. This suction of gas from 

 the producer lowered the pressure in 

 the latter, and as a consequence air 

 from the outside flowed in. Steam 

 was produced in the apparatus and 

 mixed with the air, so that both 

 steam and air were drawn together 

 into the fire. By suitable adjust- 

 ments the volume of air drawn in 

 varied with the rate at which gas 

 was consumed in the engine; in 

 other words, the rate of producing 

 the gas was governed automatically 

 by the engine itself, and the gas- 

 holder and the independent boiler 

 used in a pressure plant were dis- 

 pensed with. As this plant, and 

 those of which it is the type, work 

 by suction, they are now generally 

 known as suction plants, to dis- 

 tinguish them from- pressure plants worked by air and 

 steam at pressure. 



The results obtained with this combination of gas plant 

 and engine were disappointing, and the fuel consumption 

 with a full load was greater than with a pressure plant; 

 with a low load it was relatively worse. The gas was 

 poor in quality compared with that made in a pressure 

 plant, and there were other drawbacks ; but the idea was 

 an ingenious one, and it was seen that the working of a 

 plant by suction, in combination with an engine, would 

 have distinct advantages if the practical details could be 

 worked out satisfactorily. Several engineers gave their 

 attention to the subject, and the next step of importance 

 was to do away with the pump on the engine and to use 

 the suction of the engine itself, i.e. the suction caused by 

 the out-stroke of the piston in the motor cylinder, to draw 

 gas from the gas plant. This reduced appreciably the loss 



NO. 2059, VOL. 80] 



from friction. Various methods have also been devised 

 for producing the steam required and for removing the 

 clinker formed in the producer, as those adopted by M. 

 Bf5nier were not satisfactory. In Fig. 2 we give a typical 

 example of a modern suction plant. 



The production of the steam required to make gas of 

 good quality and to keep the temperature of the fire low 

 enough to prevent the formation of an excessive amount 

 of clinker, presents many difficulties. Steam at pressure is 

 not needed, and some makers have a water vapouriser 

 inside the producer, sometimes near the bottom of the fire, 

 but more often near the top. They heat it by the fire or 

 by the hot gas which leaves the fire, and in some cases 

 both these sources of heat are used. On the other hand, 



Fig. 2. — Suet 



z, starting fan ; b. gas produ 

 scrubber with water seal ; /^ 1 



, water vaporiser ; d, waste cock and pipe ; 

 sprayer ; g-, gas outlet. 



some makers prefer to have the vapouriser outside the pro- 

 ducer, and to heat it by the sensible heat of the gas after 

 it has left the producer. The latter system has the 

 advantage of cooling the gas more, but the amount of 

 steam raised is less than in other systems, and there is 

 the risk that gas will not always be hot enough to make 

 the full quantity of steam required. This not only affects 

 the percentage of hydrogen, &c., in the gas, but has an 

 important bearing on the formation of clinker. 



Apart from producing a sufficient quantity of steam when 

 the maximum volume of gas is required, there is the 

 further necessity for regulating the quantity of steam 

 drawn into the fire when the load on the engine is variable. 

 By some it has been supposed that when less gas is pro- 

 duced, i.e. when less air is drawn into the fire, the lower- 

 ing of the temperature which follows causes less steam 

 to be produced, and that in this way the quantity of steam 



