Mineral Fuels for Gas-producer Vehicles.
Page 24
If you've noticed an error in this article please click here to report it so we can fix it.
lirANY industrial motor vehicles JILequipped with gas-producer plants have now secured a permanent position amongst the users in France, the numerous trials that have been held having demonstrated that the design and construction have been so perfected that they may be relied upon to give satisfactory results. Hitherto, attention has largely been devoted to the use in the producers of vegetable fuels, such as dry timber, ordinary charcoal, patent fuel with a charcoal base and a semi-coke obtained from peat. in some quarters, however, fears are being expressed that too much reliance is being placed on vegetable fuels and that as a result of the steadily increasing demand, those who control the supplies may so increase their prices as to remove any advantage to be gained by the use of home-produced fuel in place of Imported petrol.
Following a resolution of the French Office National des Combustibles Liquides, the authorities of a number of collieries, particularly those in the Sarre district, have been enquiring into the use of mineral fuels in gas-producers, and an interesting and instructive contribution on the subject was recently prepared by M. Sainte-Claire Devine, the chief engineer of the Laboratories Centraux de In Sarre.
The author first puts the question as to what are the qualities which a good fuel for gas-producers must possess. Among these, a leading requirement is that the sulphur content must be low. as its existence in the fuel gives rise to sulphuric acid which quickly exercises a deleterious effect on gas-producers, the C40
associated piping and even on the engine. A fuel with a sulphur content exceeding 0.75 per cent, is regarded by the author as being entirely unsuitable for the purpose under review.
Apart from what may be termed chemical considerations there ere certain points in the use of mineral fuels to be regarded from the practical point of view. For one thing the density must not be too low as, otherwise, too frequent recharging of the producer furnace will be necessary. The shape and size of the fuel have also to be considered, so that it shall combine the properties of complete combustion with sufficient permeability for the flow of the gas.
With certain fuels a tendency has been experienced for the formation of zones within the producer and for the gas to pass off in independent small streams instead of in bulk, the passage then taking place too quickly for the necessary reactions to occur, with the result that the quality of the gas suffers. Other fuels have been found to be sube ject to the formation of arches or bridges within the producer, which prevent the steady generation and passage of the gas.
Again, the fuel must not be of too friable a character, otherwise, however well chosen the original shape and size, It will be pounded to dust by the jolting and vibration of the vehicle on which it is being used. Finally the fuel when gasified must not leave too much cindcr or ash or give rise to any slag, etc., that may block up the furnace bars and so interfere with the draught.
Notwithstanding all these varied desiderata, M. Sainte-Claire Devine considers that there are mineral fuels which can be advantageously and satisfactorily utilized in gas-producers. To begin with, he entirely rules out raw coal and coke carbonized at a high temperature. On the one hand, according to him, coal contains too high a content of tar, whilst coke, having been completely deprived of its volatile contents, gives off gas of but a very poor quality. The author, therefore, selects as a suitable fuel what he terms semi-coke, which is the residue of coal carbonized at a low temperature. This fuel, whilst having all the tar contents removed, still contains a high percentage of a mixture of hydrogen, methane and other gases, which provides for the explosion chambers of the engine a gas that can he readily fired and one with a high calorific value. Its sulphur content, although 0.70 per cent, is not regarded as excessive, whilst the fuel meets quite satisfactorily the requirements as to density and sizing. Furthermore, it is able to withstand transport over rough roads without breaking up.
The most difficult problem with regard to the use of semi-coke, in M. SainteClaire Deville's opinion, is that of the ash content, but as a result of experiments in the Central Laboratories of the State Mines, it has been found possible to produce a semi-coke from commercial washed coal, having an ash content of only 5 per cent. The laboratory work has also included the production of a patent fuel made of semi-coke with a 5 per cent, addition of paraffinic-breeze which has given satisfactory results in gas-producers.