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OPINIONS and QUERIES
Page 96
Page 97
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The Pros and Cons of Pie-combustion and Direct-injection Oil Engines. A Plea to Hauliers for Action
The Editor invites correspondence on all subjects connected with the use of commercial motors. Letters should be written on only one side of the paper. The right of abbreviation is reserved and no responsibility for views ex pressed is accepted.
Keeping Accounts for Long-distance Haulage. Coloured Lights for Buses. More About the Economy of Steamers
Pre combustion versus Direct injection Oil Engines.
The Editor, THE COMMERCIAL MOTOR.
[3904] Sir,—Mr. Goddard's letter in your issue of October 28 is most interesting as regards the records of vehicles in service, but I feel that his consideration of the direct-injection oil engine, as against the precombustion-chamber type, is somewhat one-sided. In the first place, he speaks of the latter as though it were an antiquated system which had been ousted by the "modern" direct-injection method.
Admittedly the earlier oil engines were of the precombustion-chamber type, but they lacked several essential features on which the modern type depends. Admittedly, also, there are many pre-combustionchamber (hereinafter P.C.) engines on the market which are dismal failures, but there are also one or two which have set a new standard in performance.
The success of the direct-injection (D.I,) engine is not due to its type but more to the sound manufacture it has enjoyed and the entire lack of any reasonable competition. I have endeavoured below to give a fair view of the true case:—
Without doubt the main claim of the D.I. engine is Its ability to start from cold without preheating. As regards fuel consumption, the saving on this score is negligible when taken over a year's working. 'Cold starting is at first sight an advantage, but apart from odd conversion jobs it has not any great value. In these days of better batteries and electrical equipment the tendency is to do away with hand-starting, involving, as it does, considerable risk to the man (or men!) Involved.
Hand-starting not only involves wastage of human energy, but it also has a detrimental effect on the engine. On starting, the combustion is very incomplete and it does not become normal until the engine has been under load for some time. This means that a considerable quantity of fuel is unburnt, and is sprayed on to the cylinder walls, washing away the lubricating oil and penetrating to the sump. This is proved by the fact that the sump of a D.I. engine will always be found to contain a quantity of fuel oil, necessitating frequent changes. The penalty for this is wear on cylinders and bearings, and however good the materials used, this is bound to take place to a greater extent than in the ease of a P.C. engine.
In the case of the engine in which I am interested, combustion is complete almost at once, owing to the air-spaced pre-combustion chamber with its recessed hot plug. Any drop of fuel which is unburnt is accumulated in the hot body and burnt before reaching the cylinder space. It is an established fact, with this type, that no flame or fuel oil ever comes in contact with the cylinder walls, resulting in a perfectly maintained lubricating-oil film.
The D.I engine has already reached, and possibly overstepped, the limit of its revolutions. This is evident from the noise when running at high speeds, also from the sharply dropping brake mean effective pressures. No doubt, when forced, it could run up to 2,000 r.p.m., but power would be falling off and the noise excessive. The type of engine before mentioned is capable of running efficiently at 3,000 r.p.m. and of producing over 16 b.h.p. per litre at this speed. The demand in the future will be for an engine directly comparable with the petrol engine as regards specific output and revolutions. Another drawback to the D.I. engine is that it necessitates the use of fine-hole injectors, which may at any time become blocked by minute particles of dirt. The P.C. engine can use a pintle-type injector which has such a large aperture as to avoid any chance of blockage.
Finally, the P.C. engine is far more flexible and lively to handle, owing to its ability to adapt itself more rapidly to varying conditions of load and speed. It is also capable of a far higher output for a given capacity and is therefore much lighter per b.h.p. Below are set out in brief the relative advantages of the two types. Unbiased consideration should make it clear which type of engine we are to look to in the future:—
DIRECT-INJECTION TYPE.
1. Can start from cold without hot plugs.
2. Slightly lower fuel consumption (about 6 per cent.).
PRE-COMBUSTION-CHAMEER TYPE.
1. Higher power output from a given capacity, therefore lower weight per b.h.p.
2. Absence of crankcase dilution.
3. Ability to use pintle nozzles.
4. Reduced Diesel knock and generally quieter running.
5. Ability to run at high speeds.
6. Ability to adapt itself more rapidly to varying conditions of load and speed.
C. G. TANGYE, Director, for Tangyes, Ltd. Birmingham.
The Goods Haulage Industry Must Put its Own House in Order.
The Editor, THE COMMERCIAL MOTOR.
[30051 Sir,—I have read with great interest the articles by Capt. E. H. B. Palmer which have appeared in your journal, and which dealt with the urgent need for unanimity of action on the part of the road transport industry in the present crisis. He is undoubtedly a man with distinctly advanced views and a wide experience of the haulage problem,
and I think he should be invited to contribute a further article, setting out in more detail the practicable scheme that he has already outlined, giving due attention to the case of the owner-driver.
It is always comparatively easy to indulge in destructive criticism, hut the suggestions he puts forward define a constructive policy and, to my mind, form the nucleus of an organization which would put commercial road transport on a thoroughly sound basis, with a power behind it that would have to be seriously reckoned with.
At present it is an industry divided against itself, its very existence threatened from day to day, with "the Sword of Damocles" ever raised above its head.
It is only by putting into operation a similar policy to the one your able contributor outlines—with, of course, the usual saving clauses to meet exceptional cases—that this state of affairs can be altered and the further threatened legislation averted.
That it should be averted is not, I think, in serious doubt, for Government control, when applied to industry, is the cold finger of death and progress is impeded, if not actually paralysed, at the source. This is probably the one reason, more than any other, why the railways are so urgently pressing for it, because their real case, stated briefly but honestly, is that the clock should be put back 20 years in order that their obsolete methods and indifferent management natty be foisted on a helpless community for a further decade.
They have not the courage, of course, to state this in SO many words and therefore resort to subterfuge and misrepresentation of facts.
This can be effectively countered only by the road transport industry showing itself both willing and capable of putting its own house in Order, and to do this calls for big men of outstanding executive ability, above reproach and beyond suspicion.
The time has come to sound the clarion call and close the ranks ready for action!
London, S.E.4. R. CRAFTS SE{IPSIDE, Recording Costs for Long-distance Haulage.
The Editor, THE COMMERCIAL MOTbR.
[3906] Sir,—As I expect delivery of two new Leyland lorries for long-distance work, would you be good enough to inform me as to the best system of keeping a record of running costs, etc-, for these vehicles, also the account system you would recommend for haulage work?
Perhaps you could put me in touch with some firm of printers who would supply specimen sheets.
Alloa. rt. J. JOHNSTON.
[The Tables of Operating Costs, sent to you, should serve as a valuable guide in drawing up your system of account, ancy.
You should make provision for individual records of each vehicle after the following fashion: Obtain an analysis sheet ruled to cover the 10 items enumerated in The Commercial Motor Tables of Operating Costs, splitting that of maintenance into four, one for repairs mate-. rials, one for repairs labour, one for general maintenance labour and another tor general maintenance materials. The item wages, too, may also need to be divided to cover the various classes of insurance necessary in con nection with employees. There must also be a column for mileage, one for the vehicle, one for the date, and, at the end, one for cost per mile.
Each vehicle must have its own analysis sheet, which should be made up once per week.
Any local firm of stationers will provide you with analysis sheets suitable for this purpose. You need not have them specially printed, as you can write in the headings at the top of the columns yourself.—S.T.R.]
Indicating Particular Buses by Coloured Lights.
The Editor, THE COMMERCIAL MOTOR. [am] Sir,—As a regular reader of your paper, I notice that you give legal advice on matters pertaining to the commercial side of the motor trade. In this connection I would be obliged if you would advise me regarding the legality of carrying a green light above the destination board on the buses operated by me, as I have received instructions from a certifying officer that they must be taken down.
The reason that the green light is used is to distinguish the vehicle, as there are three other operators who run over part of the route. So far as I can ascertain there is no local rule regarding this point.
Bus OPERATOR.
[The regulations with regard to lights on motor vehicles are contained in the Road Transport Lighting Act, 1927, and the Road Vehicles Lighting Regulations, 1929, dated August 29, 1929.
With regard to lights on the front of a vehicle, we can find nothing to prevent the use of a green light for indicating the particular route or service; but the position -with regard to lights showing to the rear is not so clear. Sub-section (2) of section 2 ot the Act reads as follows:—
" No vehicle shall show any light other than a red light to the rear, but this sub-section shall not apply to lamps carried by vebicles for the purposes of the internal illumination thereof, or of illuminating a number plate, taximeter, or any device for giving signals to overtaking traffic, or, in the case of publicservice vehicles within the meaning of this Act for the purpose of illuminating boards, plates or devices indicating the route or destination of the vehicle."
Front this it appears to us that, in order to justify the use of a rear light, other than a red light, it is necessary to show that it is used for the purpose of illuminating a device indicating the route or destination, and that the use of a green light alone which does not illuminate any special device is not allowed. For example, it would be permitted to use green lights for illuminating a glass circle or cross which was used for indicating a particular route. —En.] Excellent Result from Steam Wagons.
The Editor, THE COMMERCIAL MOTOR.
(39081 Sir,—Having read with considerable interest "Criticisms of Our Costs for Steamers Answered," by " S.T.R.," may I, as a steamer user of 10 years' experience, make a few remarks? I respectfully beg to differ, and very considerably, from " S.T.R.," and all the figures I give I am prepared to substantiate in any way you wish.
I run two steam wagons with trailers, the first one I purchased seven years ago; it has to date covered 200,000 miles and still has the original piston rings and bearings throughout, the big-ends being first attended to after the wagon had covered 160,000 miles. The wagon completes a journey, 60 miles light and 60 miles loaded, with a 13-14-ton load, on 7 cwt. of coal, including ,raising steam and normal waits and stops for loading and unloading. Three months ago this wagon required a full set of solid tyres, so I decided to convert to pneumatics, and I venture to say this wagon is good for another seven years. The other steamer I have was rather heavy on solid tyres, so I had it converted to pneumatics in August, 1931. This wagon has completed 36,000 miles on the new tyres and will easily do a further 14,000 miles. Of course, I periodically change the tyres from wagon to trailer and vice versa.
The distance from here to South Wales is considerable, but I obtain my supplies of the very best smokeless steam coal, delivered to my station, for 35s. 7d. per ton, plus 2s. per ton cartage from station to garage if I'm too busy to do it myself.
Although I am a fairly busy person I am quite prepared to be cross-examined on my remarks and would very much like to discuss the points with " S.T.R.," not because I am steam biased but just because I cannot see how I eould possibly carry on during these times if I ran any other type of vehicle.
Thanking you for the valuable information and advice I have had through your journal, including that from " S.T.R." NOEL Holum,. Audlem.