PARAFFIN AS A FUEL-ITS RESS AND POSSIBILITIES.
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IN CONNECTION with an article published recently by us and .dealing with a device which would permit the use of heavy oils as fuel for petrol engines, we entered rather deeply into the question of the methods of conserving our fuel supplies. In this article, therefore, which deals with the possibilities of employing paraffin in what are practically ordinary petrol engines, we shall, in order to avoid repetition, refer only to a few general points, the chief of these being that the world's supply of liquid fuel is mainly composed of fractions which require the application of considerable heat to ensure complete vaporization; consequently, unless special provision be made, only the lighter and comparatively rare fractions -can be employed in the petrol engine, and to obtain these in suitable form the heavier oils have to be subjected to expensive distillation processes and cracking often resorted to in order -to increase the available supply.
With light fuels of high volatility, not only is the loss by evaporation heavy, but fire risk, where large quantities have to be stored, is considerable. Quite' apart, from these points, there is the question of price. Even with the present demand there is a liability to constant fluctuation, and at the moment this shows an upward tendency, and as the con
sumption steadily increases by a large amount every year, and there is no guarantee that the fuel supplies can continue to in crease in the same ratio, there is always the eventuality of increasing prices to be considered. On the the other hand, if the heavier fractions, such as paraffin, could be ' em
ployed to a greater extent,
not only would the cost of distillation be reduced,, but the quantities available
from a given amount of crude oil would be in creased. Even now, the
cheaper grades of paraffin can be purchased at from 7d. to Ad. per gallon, as against twice this amount for petrol, and although the importance of fuel cost may not be so great when considering private cars and the lighter types of commercial vehicle, yet in the heavier models, which may not be obtaining more than four or five miles to the gallon of petrol, this cost has to be looked into most carefully if economy is to be obtained. Let us consider what is being done to improve the situation. So far as the user is concerned; we may say definitely that very little is being done in this country, despite the fact that several satisfactory devices for the vaporization of paraffin have been placed on the market. Overseas the matter is receiving greater attention, for paraffin is often available where petrol is practically unobtainable, and in hot climates the factor of evaporation is even larger than at home, Many commercial vehicles purchased by the Crown Agents for the Colonies have been running satisfactorily on paraffin during several years and are continuing so to do, and it is our opinion that many commercial firms would save large sums of money per annum if they ran their vehicles on paraffin, providing that the correct type of apparatus be employed and that a due rneed of attention
be given to the very important matter of oil dilution in the crankcase. It is not economy blindly to fit GOVERNOR CONTROLLED. VALVE AND INROTTLE AUTOMATIC AIR VALVE & MIXING CHAMBER '
The successful Thornycrof AB4 and BB4-type engim chamber which
a paraffin vaporizer of an unsatisfactory type which may save a few pounds in fuel cost and yet involve a much heavier expenditure for engine repairs. This question of crankcase dilution is one of the chief difficulties facing the designer of a vaporizer, and it is unfortunate that it occurs more in an engine with a wide range of speeds than in stationary types operating at practically a constant speed. The trouble is not only due to incomplete vaporization, but to condensation of the fuel particles through after-cooling, and with certain exhaust-heated types running for anything beyond very short periods at low speed results in cooling the vaporizer to such an extent that when rapid acceleration is required the mixture entering the cylinders may be saturated, and the paraffin, passing between the rings and the walls of the cylinders, in the case of a wet-sump en gine mixes with and dilutes the engine oil.
Many efforts have been made to use paraffin in a standard engine by the employment o f some atomizing device ; as a matter of fact, it is quite possible to run the engine without a vaporizer if it be kept hot and the exhaust valves and jackets he kept well water-cooled, but it is almost impossible by this method to obtain any considerable range of power and speed. The great secret appears to be to maintain the heat of the mixture and always to provide the correct amount. of air to give practically perfect combustion, for if too rich a mixture be employed the formation of carbon deposit and sootwill be excessive, and there will also be a foul exhaust. Itmay be said that., as a
general rule, it is better to employ a weak mixture than one too rich.
An engine running on paraffin is always more prone to knock than one running on lighter fuels. It is for this reason that, in some cases, compressions have been lowered, or, in other cases, resort made to the employment of water vapour. In one well-known type, which we will describe in greater detail later, the products of combustion from a vaporizing lamp are employed as a mixture diluent.
It appears that it is far more important to obtain a correct balance of the mixture when using paraffin than when using petrol ; consequently, means for adjusting the proportions of air and fuel without difficulty must be provided. In the actual engine construction, the use of narrow rings of special type, such as that use& for preventing undue oil consumption, is also advantageous in that it assists in preventing paraffin from passing, but it is of far greater importance to prevent liquid fuel from entering the cylinders. The experience gained in connection with the testing of various vaporizers in use on many types of engine have shown that the power losses when using paraffin are inconsiderable, seldoin amounting to more than ten per cent. and in most cases being much under this figure.
Curiously enough, the consumption of paraffin as compared with petrol is often considerably less, tests having shown economies in the actual volume of fuel used of as much as 30 per cent., so that the actual gain is more than that shown by the difference in price between petrol and paraffin. We will now deal with specific instances of the use of paraffin and with typical vaporizing devices. The Albion Motor Oar Co., Ltd., for example, have for many years past sold considerable numbers of chassis equipped with vaporizers, these being particularly for the export market, as it has been found that an efficient paraffin vehicle is greatly appreciated by users in tropical and semi-tropical countries where the price of petrol is relatively inflated owing to wastage, etc., in transport. They manufacture, two sizes of engine which may be fitted with paraffin carburetters, these being a 24 h.p. and 32 h.p. respectively. Both these are fitted with the Albion-Murray lubrication system, which is peculiarly suitable for use in paraffinengines, because with it each bearing and each cylin der receives a small supply of entirely fresh and uncontaminated oil for so many revolutions of the crankshaft. Arrangements are also made whereby on a heavier load the late of feed can• be increased above the normal. The oil, once having been fed through the bearings, big-ends or cylinders, drains to the bottom of the crankcase and is removed from there daily. This oil is not again returned to the engine, but may be filtered and used for less im portant lubrication work. It has been found that the oil so removed after a single test run on the road is so heavily contaminated with paraffin that its viscosity is greatly reduced and it smells strongly of the fuel.
Both sizes of Albion engine referred to are fitted with the company's paraffin carburetter, which con sists primarily of a Zenith instrument, the mixture from which passes through a steel pipe totally enclosed in a special exhaust manifold, the flames from the exhaust playing ...directly on the outside of this pipe and transforming the wet mixture into an almost perfect gas. This gas is then led through the governor valve to the inlet ports, an extra-air valve being situated at a convenient place between the exhaust manifold and the governor valve and controlled from the driver's seat.
The effect of this system is that the paraffin engines will idle continuously with an almost clear exhaust, and under load the exhaust is practically invisible.
Petrol is used for starting purposes, being contained in a two-compartment tank fitted with a change-dVer cock. Actually, however, once the en gine is hot it is unnecessary to switch back to petrol before stopping, since a restart on paraffin can be made, even after a considerable period of idleness.
The compression ratio of these engines is slightly reduced and there is a corresponding slight reduc tion in b.h.p. This, however, can easily be compensated for by a lower back-axle ratio. Even with the lower ratio, the mileage per gallon is normally as good as that given by the same vehicles on petrol fuel.
The Thornycroft vaporizing system has behind it many years of experimental work ; in fact, the com pany were awarded a diploma by the Army Council for the successful results obtained with one of their vaporizers in the Royal Automobile Club Commercial Vehicle Trials of 1907.
e34 Since then Thornycroft vehicles so equipped have been supplied to many clients in various parts of the world. The Crown Agents for the Colonies have bought them for use in Africa and large numbers have been sent to New Zealand, Ceylon and elsewhere.
The Thornycroft apparatus is ' simple but efficient. It is of the exhaust-heated type, but does not merely rely on a small area for the heating, but has a separate casing with an inner chamber and a third chamber within this. The paraffin passes through the second chamber, whilst the exhaust gases are circulated round the exterior of this chamber and through the innermost compartment, so that the fuel is heated both by the outer an inner surfaces of the passage. On the 40 h.p. engine, petrol is introduced into the vaporizer by means of a carburetter similar to that fitted to the standard vehicles, but on the 30 h.p. and 50 h.p. types special carburetters are fitted, also automatic air valves with hand adjustment are provided. Should paraffin at any time be unavailable and it be necessary to run continuously on petrol, this can be effected merely by altering the sizes of the jets. One of the most interesting of the controls or adjustments on the apparatus is that for the amount of heat supplied. There is a by-pass valve which permits either a whole or a portion of the exhaust gases to pass through the vaporizer, any not so passed being short-circuited into the exhaust pipe. Care must be taken that the vaporizer is not permitted to become bob cold or free paraffin will pass into the cylinders ; in fact, it is better to run with the vaporizer too hot than otherwise.
For starting purposes, the use of petrel is recommended, the fuel tank being divided for this purpose, and, if necessary, when petrol be not available the vaporizer can be heated by means of a blow-lamp. Playing the flame for 10 minutes into the vaporizer body will make it hot enough to start direct on paraffin.
Another vaporizing device which has shown considerable potentialities and which presents the great advantage that it enables the engine to be started from cold on paraffin without any external source of
An Albion engine equipped with a paraffin vaporizer of the same make. The paraffin duct is thoroughly jacketed by exhaust gases, and the special system of lubrication obviates dangers through oil dilution. • heat is that which was originally produced by Southey Gas Producers, Ltd., but which is now controlled by Mr. E. Thomas, 57, Leagrave Road, Luton, Beds. Five sets of this vaporizer have recently been supplied to the Japanese Government, and it is interesting to note that Mr. Thomas has recently had a number of orders from commercial-vehicle and engine manufacturers in the United States of America, whilst inquiries have been received from France, Italy, Germany, etc. We also understand
that an important French manufacturer is at present carrying out comprehensive tests with this device with various grades of fuel.
This paraffin gas producer, as it is termed, has the advantage that it is a self-contained unit, weighs very little more than the average petrol carburetter and requires no structual alterations in the engine. The average economy of fuel, as against petrol, is shown to be from 10.5 per cent. to 30 per cent., and with a power practically the same as that obtained with petrol. No alteration of compression is required.
The apparatus is of that type in which the fuel is gasified by heat applied internally. It bolts direct to the induction pipe as close to the cylinders as possible, and the fuel feed is the same as that to an ordinary carburetter. f
Features of a Novel Device.
The main feature of the vaporizer is a small lamp provided with a number of wicks, and with a separate jet for supplying a limited quantity of fuel to these. The wicks are of asbestos and are in a carrier, which also forms the air-distributor sleeve.
Air to support combustion is drawn through two rows of holes, one row being immediately above a baffle resting on the air-distributor sleeve, the other row leading direct into an annular chamber between this sleeve and the main casing. The latter, row, the air supply through which is controlled by the number of tapped holes which are allowed to remain open in the lower half of the air-filter cover, provides air to support combustion in that portion of the lamp below the baffle.
The main flame from the lamp passes through a port connecting the lamp chamber with the vaporizing chamber. Flame is also drawn through holes in the baffle and into the upper chamber, where it mixes with air drawn through the holes above the baffle, in this manner forming an oxidizing flame which is drawn down a central tube leading to the main fuel jet. The flame which passes into the vaporizing 'chamber is 'drawn by the suction of the engine round the edge of a cone-shaped chamber and into direct contact with the sprayed fuel, which it completely vaporizes.
The advantage of dividing the flame in this manner is that the proportion of inert gas may he controlled.
It ilI be understood that the strength of the mixture permits only a very limited .combustion of the fuel issuing from the main jet, actually unburned vapour, Mixed with• a small percentage of products of combustion which, as we have previously mentioned, assists in the prevention Of knocking, enters the cylinders.
The gas and air-controlling valves are intereonfleeted in a special manner, which eeables the "mixture automatically to be increased in strength while the engine is idling, whilst giving economy over a wide range of throttle and a gradual increase in strength at the fully open position in order to obtain
maximum power. _ Immediately above the wicks of the vaporizing lamp is a sparking plug with a single electrode, whilst in one of the wicks immediately below the sparking plug is an earthing wire. The sparking coil operated from a battery provides the means for igniting paraffin in the lamp. After the fuel supply is turned on it is necessary to remove the cover to which is attached the baffle, open one or both of the air ports to assist combustion and switch on the ignition for a moment. Then the lamp is alio fed to buacn freely for two to three minutes, after which th7 cover and baffle are refitted and the air ports closed, when the suction draws in sufficient air for maintaining combustion.
With the special coil and time switch which can he provided if required, it is only necessary to switch on the coil, when this gives sparks for 'half a minute and then cuts out, for when the engine ia
running steadily the lamp remains alight. In case it be extinguished at any time, say, by a back-fire, it is necessary only momentarily to switch on the special ignition to re-ignite it. If everything is in order a slight roar can be heard in the vaporizer. If this be not so, it is a sure sign that the lamp ignition is not working satisfactorily and that the wicks are not alight. When the engine is once warm it is unnecessary to open the lamp, unless the engine has been stopped for more than one hour in winter or two hours in the summer. It is only necessary to switch on the lamp ignition and immediately to crank the engine.
Some very successful _experiments were recently carried -out with an interesting type of vaporizer known as the Saunt. This apparatus is not now made specifically for paraffin, but has been still further developed for the-utilization of gas oils and even heavier fuels, but can, of course, be employed quite easily with paraffin.
This apparatus is provided with a cold-starting burner, and although water injection was used on the original device it is now found unnecessary; also the same compression as for petrol is proving quite satisfactory. The fuel is pre-heated, and the power is nearly the same as is obtained with petrol, whilst • the flexibility is said to be quite am good. Even with Mex fuel oil or any grade of gas oil, the consumption is about the same as with petrol. We are not yet able to give fel details of the device but hope to be able to do so shortly. It is handled by Mr. T. W. Saunt, Tyklefield, Leigh-onSea, Essex.
We must not conclude without referring to another remarkable vaporizer, which was described by us in 1921, and was made by F. W. Rowlands and Co., of Seacombe, Cheshire, although it is to be regretted that this company are not at present doing anything with the device, as the demand was so small after the large reductions in the price of petrol which took place about that time.
The chief feature was the use of an external source of heat for the vaporization, this taking the form of burning charcoal, which was contained in a special chamber of cast-iron, oti the outer surface of which were cut spiral gutters, the fuel being admitted at the highest point and trickled along the heated metal, being, Of course, completely isolated from the burning charcoal.
Special attention was naid to the prevention of oil dilution, drains being provided in the manifold and vapour pipe, any recondensed fuel being removed by a small drainage pump driven by a chain or belt from the engine.
Igniting Fleavy..fuel Mixtures.
An invention which, whilst it can hardly be referred to as a vaporizer, may assist in the complete combustion of fuels heavier than petrol, has been developed. by Mr. F. A. Smith, Brasted Motor Works, Brasted, Kent. This device, which we illustrate, is known as a super-igniter ; it works on the principle of projecting the flame resulting from the combustion of a very small volume of petrol and air mixture into the mixture of heavier fuel and air, and has been used with success even when gas oil was the chief fuel employed.
We understand that this igniter is now being considered with a view to its rdoption on certain aeroplane engines.
We have by no means exhausted the list of paraten and heavy-oil vaporizers which, as a matter of fact, consists of dozens of different types, although not all of these have proved satisfactory ; we have also refrained from dealing with the Vapour Oil device, as this . was described in detail by us a few weeks ago. At the same time we believe that we have shown that there are possibilities in paraffin which should not be overlooked.