The Uncertainties of Creosote
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Divergence in Sptcification Due to Origin and Prooess, Choice of Type of Engine for its Consumption, Paradoxical Attitude of Authority
Pri-IERE are at least three uncertainties with which the 1 patriotic: and enthusiastic:, experimenter in alternative fuels has to contend when he accepts the invitation of an encouraging G-overnn1ent to tackle creosote. They are the structure of the fuel as expressed by its specification, the method of utilization and the official control of supplies. In. January of this year, as.we know, transport operators were enjoined to use creosote as an alternative fuel; it was not definite whether the exhortation was addressed only to operators of compression-ignition engines or whether it
• included those running petrol-engined vehicles.
Turning up the back numbers of " The Commercial Motor" as we all did, to ascertain what, if anything, had been done in the past, we found that several municipalities, among other operators, bad experimented with creosote in recent years and had done a good deal of useful work.
„. Following up our investigations, we were considerably impressed by the fact that not one of those Municipalities or other users was employing the fuel to-day. Proceeding farther, we discovered that one or two people who had supplied atomizing equipment, for those experiments were totally unenthusiastic; a barge pole was a thing mentioned • with which one of them was totally unwilling to touch creosote.
The six-month period allowed by the Government for experimental engine revision has now run out and is renewed. Enthusiasm does not appear to be renewed along with the renewal of the fuel period.
In the beginning of the enthusiasm (if any) the fleet operator sent off his order for fuel and immediately discovered that it was necessary' to obtain a licence to buy creosote. This' was not part of his original understanding of the. Government encouragement, and rather annoying. By the time the "passed to you please" game was played out by the various parties 'concerned in preventing the recotenended fuel from being obtained, much time was lost, and the six-month experithental period was ticking itself out. In one case it took five, months to get the licence.
Operators' Disheartening Experiences
Having got it, the fleet operator rubbed his hands, and sent off the order again. " Sorry," came the reply, " no creosote available." " But there was when I first sent the order." " Ah! yes, but . . . " and a lot of indefinite talking which wqg neither yes nor no, but there was definitely no creosZte to be had. The suppliers had apparently "had the yellow" as the air raid wardens (don't) say, but nothing came through to the prospective users.
From careful enquiries it was eventually elicited that the creosote was wanted for more urgent war purposes than poor road transport. It was to be used under boilers in conjunction with or to replace fuel oil for steam raising and other heating purposes—quite legitimately, of course, but why then recammend it for road transport? / Creosote is a most complex substance and there are therefore many variations in its specification dependent upon the differing quantities of its constituent compounds, such as anthracene, naphthalene and phenols. It is itself a distillate of tar, which in turn is a distillate of coal.
There are coals of widely differing specifications, ranging from -anthracite of low volatile content to high-volatile bituminous coals used for gas making. Among the gasmaking coals the specifications differ considerably, and these differences are translated into the constitution of the tars distilled from them and on into the ta!r derivatives.
Besidesthe constitution of the raw material, coal, there are also two main systems of carbonization the resulting products of which possess widely differing proyerties. These are low-temperature carbonization, carried out • at 400 .degrees C. and 11-gh-temperature carbonization at 1.100 degrees C. The tars of these two systems differ, and their products on distillation reflect-the differences; creosotes
from the disiiHates .possess distinctive variations due to these processes.
There are.further differences due to the types of retort used in the carbonization processes; horizontal and vertical ' retorts produce, respectively, different qualities 'of tar. Coke-oven tars are different again, as also are blast-furnace tars.
Through all these differing•Itinds of tar and the distillates, the differences of raw coal, plant and process are carried, and must be reckoned with in attempting to make use of any of them as fuel, particularly for internal-combustion engines. It was this variation in resulting tar-derived fuels that caused the failure of the creosote experiments carried out during the past decade.
As an \instance of the effect of these differences upon the motor-fuel creosote may be mentioned the case of a municipality which, after long experimenting, arrived at satisfactory operation on creosote of 25 public-service vehicles. Then suddenly, and for no apparent reason, everything went wrong. Eventually the trouble was traced to a change in the coal used by the gas works producing -the creosote; it had saved a penny a ton on the coal by buying
it from a, different source. . • Continental Research Well Ahead The Germans knew all about these difficulties as far back as 1935 and beyond; in that year they reported results of 'experiments on creosote in their Technical Press, extracts of which were published in this country. These experiences appear to have diverted their researches into different channels.
Two different specifications suitable for light creosote to be used as motor fuel are given below:—
A basic difficulty in the utilization of creosote as a fuel for engines is the liability of naphthalene to separate out and to clog tanks, pipes and carburetters of fuel systems. The higher the percentage of naphthalene the greater is',
the trouble. Low atmospheric temperature is the cause, as will' be deduced from the above . specifications. Tars from vertical-retort distillation contain less naphthalene
than those from horizontal retorti. Tars from lowtemperature carbonization are more suitable than those
from high-temperature, but, as low-temperature carbonization is not in use .to anything like the extent of hightemperature, these tars are scarcer.
It is more difficult to utilize creosote in petrol engines • than in oil engines. Both heat and a high degree of atomization are necessary. Starting, of the former type,. must always be done on petrol, as also must slow running. In some cases a thermostatic control automatically meters creosote and petrol according to the engine demand under changing soad, conditions. In the compression-ignition engine the type using a precombustion chamber appears to give the best results, owing to the possibility of producing greater turbulencewith this design. Increased compression ratio is reported as Gerntan practice for these conditions. Owing to the ignition temperature of creosote being much higher than that of petroleum oils (400-500 degrees C. compared with 260-280 degrees C.) difficulty of starting, poor combustion. and " diesel knock " are liable to be experienced.
Whilst 'some operators have failed in satisfactorily blending creosote and paraffinic oils for internal-combustion engines, others appear to have succeeded, but much care has to be exercised in doing this to prevent naphthalene from being depOsited. Blending accelerates the deposit of naphthalene in pipes and tanks, and the blended fuel is sometimes put through centrifuges to take out as much of the deposit as possible before putting it into use. The blended fuel should stand for 24 hours so as to become thoroughly mixed before centrifuging. Blends containing up to 25 per cent, of creosote appear, to be possible under favourable conditions and specifications of creosote.
The tar acids in creosote give rise to irritating fumes on combustion. They can be separated out in order to prevent this trouble by washing, which reduces the volume of creosote by up to about 20 per .cent. The washed product consists of neutral hydrocarbons, and is referred to as neutral oil. Its ignition temperature is 50 degrees C. lower than that of the unwashed oil, thus improving ignition conditions.
For petrol engines several carburetters were made for creosote when there was a certain amount of actiVity some years ago. Suitable instruments are of quite a special nature to meet the peculiar requirements. Little is being done now, however, except in a few isolated places, chiefly because of the difficulty in obtaining creosote for the purpose under consideration. The physical condition of different creosotes ranges from a fairly thin liquid to a jelly not far removed from the solid. This indicates the great variation in what is generally referred to as "creosote," the reasons for which have been given in the foregoing; it also demonstrates the need for a specificatidn which will ensure the suitability of the fuel for internal-combustion engines.
With such extensive differences it is difficult to procure the right wit, as the limitations necessary for use in engines cut. down severely the possibn sources of supply! -further, if the operator has to become also the refiner in order to use this new fuel, he will probably consider that he has already enough troubles, of his own without taking on, in addition, those of someone else, so the fuel 'goes without' trial. Nor do I think he can be blamed for that attitude.