JUNE 19, 1902] 
burning liquid fuel have always considered the possibility of its 
use becoming limited in certain circumstances, and all modern 
appliinces are so constructed that with slight trouble coal alone 
may be used in them to the best advantage. One of the great 
claims to be considered in favour of liquid fuel is the ease with 
which the burners can be extinguished and a coal fire sub- 
stituted, thus enabling consumers to take every advantage of 
fluctuations in the prices of both fuels. For marine purposes 
this is most desirable, since at many ports liquid fuel would be 
far more economical to ship for boiler use than a suitable steam 
coal, whilst a vessel trading from a port—such as Cardiff or 
Newport— would naturally replenish her bunkers with the steam 
coal at hand. 
Any liquid hydrocarbon of sufficiently high flash point may 
be used as a liquid fuel ; thus residues from many manufacturing 
processes may be utilised in an economical manner. Astatki, 
the residuum from petroleum distillation, has been extensively 
used in Eastern Europe, but tar oils and the oils from oil gas | 
plant are frequently employed. These oils are especially suitable 
for locomotive work, since most large railways make oil gas in 
considerable quantities for lighting purposes, and, moreover, 
have exceptional facilities for transporting gas tar from small 
towns on their lines where it can be obtained at a reasonable 
cost. On the Great Eastern Railway this form of liquid fuel is 
largely employed. Crude petroleum, which has been treated to 
remove the more volatile constituents and so bring its flash 
point above the imposed limit for use as fuel, is now being 
imported into this country. The various methods of burning 
liquid fuel have been classified by Aydon as follows :— 
(1) Lnjectiom with compressed air (W. Bridges Adams, 1863 ; 
Tarbutt, 1885. ) 
(2) Percolation through a porous bed (C. J. Richardson, 1864 ; 
Weir and Gray; St. Caire Deville), in which the liquid fuel 
percolates upwards through a porous bed, accompanied by 
heated air (and sometimes steam also). 
(3) Vaporzsation (Foote ; Simm and Barff, 1865-67), the oil 
being vaporised from a small retort heated in the furnace, or in 
some cases (Dorsett, 1868-69; Eames, 1875) by a special 
external heater for the retort. 
(4) Steam spray injection (Aydon, Wise and Field, 1865-67), 
in which the oil is sprayed into the combustion chamber by a jet 
of steam, whilst at the same time the burner is so constructed 
that air, heated if possible, is drawn in to supply the oxygen 
necessary for combustion. 
Such a classification does not include burning in open troughs, 
a method first introduced by Wittenstrom about the year 1884, 
and which for many purposes in stationary boilers, furnaces, 
&c., has met with considerable success; or the more recent 
method of Korting, by direct injection of heated oil at consider- 
able pressure. 
Excepting in a few special cases, the steam spray injection 
method has been universally adopted. Various extravagant 
claims have been made for the chemical action of the steam, 
but it is not easy to see from a theoretical standpoint that it has 
any advantage over injection by compressed air. From a practical 
point of view, however, the steam spray is the more simple, since it 
dispenses with the auxiliary apparatus necessary for the supply of 
the air blast. On alocomotive, where economy of space is of im- 
portance and suitable water for the boilers is readily obtainable, 
steam spray injection is universal. For marine boilers the choice 
formerly lay between steam and air injection, each having certain 
advantages. Using steam injection, the auxiliary apparatus 
necessary for the air-blast is done away with, thus giving 
economy of space, whilst it has the disadvantage of requiring 
more condensed water from the evaporators to replace the 
steam used. On the other hand, the extra steam necessary 
for the air-blowers can be condensed and returned in the usual 
way to the feed water-pipe, but of necessity extra machinery has 
to be employed. With the introduction of the Korting system 
referred to above, and the success which has attended its use, 
notably on the Hamburg-American Line steamers, the marine 
engineer now has the choice of another method, and everything 
seems favourable to the extensive adoption of this new system 
in the future. 
From the numerous estimations of the calorific value of 
different liquid fuels, we may approximately state that in centi- 
grade units it has a value of 19,500, whilst for good steam coal 
a value of 8000 to 8509 may betaken. It will thus be seen that 
the liquid fuel has a decided advantage. The usual calculations 
NO. 1703, VOL. 66] 
NAIURE 
187 
of the theoretical heating value of a fuel fail to take one 
important factor into consideration, namely, the physical con- 
dition of the fuel. Thus the determined calorific value of carbon 
is always that of solid carbon, the value for hydrogen being 
obtained experimentally for hydrogen gas ; but although in coal 
the carbon is in the solid form, it is certain that in liquid fuels 
it has undergone the first change in the passage of a solid to a 
gaseous condition, and consequently carbon in a liquid fuel will 
have a higher calorific value by just as much heat as would be 
required theoretically to raise solid carbon to the liquid condi- 
tion. Aydon has estimated that this is equivalent to an expen- 
diture of some 3500 calories. 
It is, of course, impossible even with the most perfect 
appliances to obtain anything like the full heating effect of a 
fuel in any boiler, and the only real test of the value of competing 
| fuels is their performance under similar conditions in practice. 
One is struck at the outset with the extremely contradictory 
figures which have been published to show the evaporative duty 
of liquid fuel, figures ranging from 46 lbs. of water per Ib. of 
fuel burnt to 14 or 16 Ibs. per 1b. It may be taken, however, 
that in modern practice an efficiency of 15 lbs. by steam injec- 
tion isa very fair result. Many comparisons have been made 
with coal in the same boilers and under the same conditions 
with results varying from 7 to 84 lbs. of water evaporated per lb. 
of coal consumed. A valuable series of tests made by the 
Engineers’ Club of Philadelphia in 1892 gave the following 
results :— 
I lb. anthracite evaporated ... 9°7 lbs. of water. 
I lb. bituminous coal IO'l4,, ” 
lb Rolls ORB. | jee ace 16 48,, a 
Icu. ft. of gas 20 C.P. 1:28 ,, » 
We are indebted to the carefully recorded results obtained by 
Mr. Urquhart on the Grazi and Tzaritzin Railway for probably 
the best published figures of the relative merits of solid and 
liquid fuels. In winter he found that liquid fuel was 41 per 
cent. in weight and 55 per cent. in cost better than anthracite 
coal; or, compared with bituminous coal, 49 per cent. by 
weight and 61 per cent. in cost better. This was under the 
worst climatic conditions, and, as might be expected, in 
summer better results still were obtained. It must be borne 
in mind that these figures were deduced from the work of a 
large number of engines, 
The Canadian Pacific Railway find that liquid fuel in use on 
their steamers effects a saving of 56 percent. on the cost of coal 
firing. 
+ In this country the pioneer of liquid fuel on our railways is 
Mr. James Holden and his company; the Great Eastern Railway 
has now more than sixty engines burning it, either alone or in 
conjunction with coal. Ina note presented at the International 
Railway Congress in 1900, Mr. Holden gives the following 
particulars of express trains running between Liverpool Street 
and Cromer. The distance of 138 miles is covered in 175 
minutes with a four minutes’ stop, on aconsumption of 14°4 lbs. 
of tar residues per train mile, and an equivalent of 5 lbs. per mile 
of coal, which is used in raising the steam necessary for starting 
the oil injectors. In the same paper it is stated that on railways 
working with wood fuel a saving of 50 percent. has been effected 
by burning liquid fuel. Through the kindness of Mr. Holden, 
the writer recently made a long run on an engine burning crude 
coal tar over a coal fire with the Holden steam injectors, and 
was impressed with the ease of maintaining a regular steam 
pressure and the freedom from smoke. 
The South Eastern and other railways are now fitting engines 
for this class of fuel, and an oil-fired engine is used for shunting 
on the Central London Railway. Boilers are also being fitted 
for liquid fuel at Woolwich Arsenal, and its use is extending 
amongst private firms. 
In the English shipping trade the pioneers have been Messrs. 
Samuel and Co., the managers of the Shell Transport Company, 
and a reference to the excellent performance of their vessel the 
s.s. Clam will be found in a recent number of Nature. An 
interesting account cf the record voyage under liquid fuel 
appears in the Shzpping Gazette of February 13, the vessel 
being the s.s. d/zex, also belonging to the Shell Transport 
Company. This ship arrived at Thames Haven from Borneo 
vid Singapore and the Cape on March 10, having steamed 
11,830 miles on a consumption of 800 tons of prepared fuel. 
