Diesel Engines or Heavy-oil Vaporizers.
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VOlt many ydars various investigators have. endeavoured -to employ fuels heavier than commercial motor spirit in the cylinders of petrol engines, either in normal form or equipped with some special. vaporizing, device, in the former case the vaporization being effected outside the cylinders; but all sorts of difficulties have attended their efforts.
The trouble is that the vaporization points of the constituents of heavy oils cover a wide range, and according to a technical expert of a well-known German maker some of these go beyond 680 degrees Fahr., whilst when She compression pressure is comparatiVely high the ignition point occurs at a teinperature at which a large portion of fuel would not have been vaporized. This results in liquid fuel either being depositedon the walls and, subsequently, diluting the lubricating oil or in causing afterburning, ivhich leads to high temperatures in the exhaust gases and an increased fuel consumption.
The designer of engines working upon the ordinary cycle who wishes to employ heavy oil is thus faced with a great initial difficulty. In View of the high vaporization point it is almost essential to utilize a high compression; on the other hand, the low-ignition point practically demands a comparatively low compression—hence he is straightaway confronted with diametrically opposed requirements, whereas all these difficulties are overcome in the case of the Diesel engine.
Other difficulties, we know, are introduced in producing Diesel motors, and 'the slovenly methods which could be employed in the case of a. mixture of vapour and air must, in the Diesel unit, be changed into a high degree of exactitude.
Then there is the question of obtaining the additional strength necessary to withstand the higher pressure and greater stresses upon the working parts without adding unduly to the weight as expressed in l. per b.h.p. It is stated by the expert to whom we have already referred that in a Diesel engine with combustion pressures up to 42 atmospheres the weight of the connecting rods must be increased by about 21 per cent., and that of the crankshaft about 5 per cent, over those of a corresponding petrol engine. Cylinders, cylinder heads, pistons and crankcases are usually so heavy (because of the difficulties of casting and manufacture) that they need not be increased in weight, whilst the means for fuel injection can be quite light, and in the end a Diesel engine will weigh only 10 per cent. to 15 per cent. more than the petrol engine.
A particular feature of the Diesel engine which will commend itself to users is that the torque rises considerably as the speed falls ; in actual tests a speed drop of about 20 per cent, gives a torque increase of some 10 per cent.
As regards engine control, it has been noted that the response to a change in throttle position is extremely rapid. This is for the reason that practically the same weight of air is available for each stroke and the power developed corresponds to the quantity of fuel injected, and as the control is usually by fuel supply only there is no lag of the air, as happens with the ordinary throttle control of the petrol engine.
It is on hills that the Diesel-engined vehicle gains a real advantage, and it can usually climb more rapidly and steadily than a petrol engine nominally of rather greater power, although the petrol engine will probably make up speed on the level, but from many points of view it is more satisfactory for a commercial vehicle to be able to keep up a good, steady speed than to progress in a series of spurts.
In a test carried out a short time ago in New York City traffic, with a vehicle having a useful load capacity of five tons and a fairly powerful, engine, the consumption of fuel oil was a gallon per ten miles, and in a test run of 1,200 miles with a load of two tons the same vehicle averaged 11.6 m.p.g. (These are, of course, American gallons, which are slightly less than Imperial gallons, making the consumption, when the English scale is employed, appear still more economical, the Increased mileage being something like 20 per cent. on the figures given.) Testing the engine only, it was found that from half-load to full-load the fuel consumption was almost constant, averaging .45 lb. per b.h.p..hour.
• The Friction Clutch Behind the Gearbox.
A LETTER from a correspondent in a recent issue referred to our comments on a Patent recently published, in which we stated that the difficulty irie•connection with the use
of a friction clutch behind the gearbox to facilitate gear-changing was that no clutch had yet been made that will transmit the torque of the low gear. This statement our correspondent 'characterized as "hardly in accordance with facts." ,
We probably take considerably more care in .the preparation of these abridgements of -recent Patents than any other technical Journal. They are prepared for us. not by a patent agent, but by. an engineer of long experience in the commercial industry, whose remarks on the patents described are always well considered. Our abridgements are prepared from the actual Patents and are not copies of the abridgements to be found in the official journal. In many an instance we actually make new drawings where we feel that, by so doing, we shall make the aim of the inventor plainer.
Having regard to all the care taken by us in this matter and in any remarks relating to the effect any patents may have upon the. Industry,. we cannot allow our correspondent's remark to go unchallenged when he says that our statement is "hardlye in accordance with facts." We think that if he will again read the resume to which he refers, he will see we in no way infer that it La impossible to construct a clutch which will transmit the torque of the low gears. We said that "such a dud% has not vet been made."
The difficulty we see is not one of heat, as suggested by our correspondent, for h clutch employed to facilitate gear-changing would not be required to slip for sufficient time to generate any objectionable heat. Our correspondent says that if sufficient pressure can be brought to bear to induce the necessary friction to transmit the torque of the low gears, a clutch of ordinary pattern would answer the purpose. The difficulty in that case, howetrer, would be that the clutch pedal would require more power to operate it than would be convenient to the driver. On the other hand, if the number of Plates were multiplied until the necessary friction were obtained (about four times that of an ordinary clutch) the movement of the clutch Pedal which would be necessary to free such a number of plates would, when added to the movement of the ordinary clutch pedal, be equally inconvenient to the driver.
What we have endeavoured to point out is that some new form of clutch, probably of the self-energizing type, would have to be designed, as we feel sure that no mere adaptation of the ordinary clutch, as we know it to-day, will meet the situation. The want of success of all efforts in this direction that have been made in the. Past confirms our opinion on this matter.
close any ill-effects from the use of that spirit. There has never been any restriction on its use, merely on its sale. By the way, the inquiry here into the alleged ill-effects of handling and using ethyl petrol seems to have died a natural death
THE Scottish Motor _allow, to be held at Kelvin Hall, Glasgow, from _November 9th to 17th, will embrace commercial motor vehicles, and it DOW seems that the bommerciaavehicle section of that show will alternate with the Commercial Motor Show at Olympia. The next Scottish Show will, therefore, from the point of view of the heavy vehicle interests, assume a new importance, for any new models will be shown instead of being held back for the London exhibition.
IT will scarcely seem right not to see the name of a motor concern on the extensive buildings beside the London, Midland and Scottish Railway line at Adderley Park, for the name of Wolseley has been associated with the factory and its extensive developments for many years. Commercial vehicles have not been built there since the war, and now, under Mr. Morris's regime, the organization has been transferred to Ward Eild, Birmingham, The Adder ley Park works will probably be taken by the railway company, and may be used in connection with its projected road-transport activities.
AN inquiry came to the editorial desk the other day. "Could you kindly tell me whether we can get iuto touch with any London representatives of a French concern called Renalt? " (pronounced to rhyme with ' he-halt '). For the moment we were puzzled, and then we asked, "Oh ! do you mean R-R-Renault "—(rolling our Rs in the approved telephone manner)—" spelled R-E-N-A-U-L-T? " "Yes, I think that's it." Further conversation elicited the fact that the inquirer had been instructed by his governor to get the information "because we have had a lorry of that make for some years, and it has done so well the governor has decided to get another like it! "
THE Dunlop Guide to the roads of Great Britain has just appeared in its third edition in a rather smaller size, revised and considerably amplified. It is virtually indispensable to every road traveller, for it offers that fine detail of information which is so essential and important but is rarely obtainable by the traveller until he reaches his objective, and then its value is not always so great as if he had received it beforehand. With its maps and town plans, its information about garages, repairers and the towns and villages, it is the best five shillingsworth for the road user that we know.
FOR travel over Scottish roads only, there is a recent publication at one shilling called the " Scottish Motorists' Guide, Garage and Hotel Directory." It has a series of small-scale maps and is full of information additional to that conveyed by the title of the book.