OPINIONS and QUERIES
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Progress with the Oil Engine.
The Editor, THE COMMERCIAL MOTOR.
[3265] Sir,—I notice with interest that Mr. Price has given, in your issue of November 11th, some remarkable results obtained with an all-British Blackstone oil engine, in which the fuel is admitted to the cylinders without pressure in the fuel pipes. Some of my researches have also gone in that direction, and I feel sure that it is the right line towards the future successful compression-ignition engine for general transport purposes. Ifs the case of my Paragon design, no fuel pumps or high-pressure nozzles are needed ; this simple engine will operate on my new compoundcombustion cycle, the fuel being delivered at atmospheric pressure only.
I am still of the opinion that your excellent editorial advice is the best which can be given to heavy-vehicle manufacturers while the commercial application of the compression-ignition engine is in its present state of undevelopment Now in regard to Major Goddard's remark concerning terminology, my views are the result of the legal and other opinions, resulting from my patent litigation in the German courts. The question was raised at the time whether Dr., Diesel was the inventor of the compression-ignition systdm of starting combustion; learned counsel were informed that the principle of compression-ignition of combustibles had been in use by the Asiatic people for many centuries before Dr. Diesel saw the light of day.
In 1872 Brayton put this principle to work in his famous oil and gas engines in America; these were afterwards made in quite large numbers at Nottingham.
Major Goddard refers to Dr. Diesel's first engine, but I can assure him that this was an utter failure, and that it was not until he was rightly advised to use oil as the fuel that his Asiatic engine was made a success.
The compression-ignition method of combustion is exceedingly ancient; it was indeed one of our early ancestors who was the real inventor of basic principles under which both the Diesel and the Paragon oil engines are thermo-dynamically operated. Dr. Diesel was the first to have the common sense to improve on the more ancient methods by using a Wast of separately compressed air to deliver the oil for combustion purposes, and therein laid the commercial foundation of his very brilliant researches. The heat cycle used in the road-Vehicle compression-ignition engines which I have seen,4 both in this country and in many parts of Europe, all differ from Diesel's heat cycle, principally by reason of the fact that they have hydraulic injection and have higher maximum pressures than do compression-ignition engines using pneumatic injection.
The thermo-dynamic efficiency of the real Diesel engine has long since been surpassed, particularly in connection with the Paragon cycle.
I have had many years' practical experience in the development of prime movers and can assure Major Goddard that, in my opinion, the two-stroke cycle has never been given a proper chance to prove its superior ability. It is surely not essential always to take German views as the last word in matters which are decidedly English by inspiration and practice.
The two-stroke-cycle engine is the offspring of English research and technical development, whilst the four-stroke engine is, I suppose, the legacy of the Otto or German constructional development. A properly designed two-stroke-cycle engine operating on the Paragon heat cycle can always beat any four-strokecycle engine in thermal as well as in mechanical efficiency.
' There is one thing which must not be forgotten; that is the danger from fire. I have known oil to be fired by coming into contact with the exhaust pipe of an oil engine; here again the advantages of the extra expansion obtained by use of the Paragon cycle comes in; the temperature of the exhaust is so low that HO ignition oefuel can take place; the temperature of a recently tested engine operating on the Paragon cycle was so-low as 160 degrees F. within 6 ins, of the cylinder outlet. I refuse to believe that the sixcylindered 3,000 r.p.m. engine is hardly the type of machine which the Ministry of Transport or Scotland Yard is likely to look on with exceptional favour for general use in the streets of London.
I should like to take this opportunity for offering my sincere congratulations to Mr. Dicksee on his new oil engine, as• it is evidently a well-thought-out prime mover. It remains to be seen what effect the six-cylinderecl two-cycle engine, spinning like a turbine, will have on public, as well as on technical opinion.
London, S.E.5. .Wxu,i,ti P. DEHTNALL.
Parcels Delivery by Commercial Sidecar.
The Editor, THE COMMERCIAL MOTOR.
[3266] Sir,—I have a commercial sidecar with a capacity of 5 cwt., with which I intend to commence a parcels-delivery service. Would this be suitable for the job? The service would be four times daily and one complete round would be 18 miles. What should I charge for different weights of parcels? How much capital should I require to commence? If this outfit be not suitable for this service, what class of work should I undertake?—Yours faithfully, M.M.
Glasgow.
LYour weekly mileage will be from 360 to 400, and the cost per mile in those circumstances will be about 21d., or 3s. 9d. per round trip. You should make at least (is. per trip for the business to be worth while. As you cannot count on your sidecar being more than half full on the average, that means you must obtain 6s. per 2 cwt. per 18 miles, which is equivalent to gs. per cwt. per 18 miles. The difficulty is, however, that your parcels will most likely be bulky rather than heavy and, in any case, it is almost impossible to scheme out a list of prices without some experience of the sort of work you are going to get. I think you should commence by charging an average rate for all distances up to the complete round, and your rates should be 2d. per small parcel, 4d. per medium-sized parcel, Od. per largo parcel, and is. per very large parcel. Run that rate for a week or two and keep an exact and careful note of the business you do. If you will do that I will go into the matter with you once more.—S.T.R.] c30
Carrying Passengers Free.
The Editor, THE COMMERCIAL MOTOR.
Is267] Sir,—Since January, 1930, I have maintained a bus service between one point in the county borough of Rotherham to a colliery which is situated in the rural district of Rotherham—two different licensing bodies.
The rural district council granted me licences to ply for hire in its area, but the Rotherham Corporation refused my applications. To get over this difficulty I used return tickets issued in the rural district. During September last I received a letter from the town clerk of Rotherham stating that under a new Bill which Rotherham Corporation had just got through Parliament this practice was illegal and amounted to plying for hire.
The same Bill gives the corporation a complete monopoly within the county borough boundaries.
Now, if I pick up my passengers and carry them out of Rotherham free of charge, does this amount to plying for hire? I would be grateful for your expert opinion on this question.
May I take this opportunity for thanking you for the "Weekly articles on the position of passenger vehicles under the Road Traffic Act, 1930, I would also like to thank " S.T.R." for the way...in which he goes for the rate-cutters ; may he keep it up. C. ROGERS.
Rotherham [You cannot get over the need for a licence to /Ay for hire in any particular area by carrying passengers free of charge within that area. A decision to this effect was given by the High Court in 1908.
Our solicitor understands that a new Rotherham Corporation Act has recently come into force, but copies are not at present obtainable. Presumably, the effect of the Act is that the rural district has been incorporated within the urban district, and there is, therefore, one licensing authority for the whole borough.—En.]
Oil-engined Transport Vehicles.
The Editor, THE COMMERCIAL MOTOR.
[32681 Sir,—The oil engine is now making rapid strides forward in road transport. A great deal of experience has been gained during the past few months and some most useful information collected. Particularly one can mention a very recent experience which conclusively proves that the direct-injection engine is more economical on fuel than one designed with precombustion chambers, or with "pockets." The difference in fuel consumption is approximately 12 per cent. in favour of the direct-injection system. With a fleet of vehicles this is a very considerable item in a year's work. The engine itself is, of course, much simpler, less bulky and cheaper to build.
Another important discovery is that high-speed oil engines, when allowed to run ungoverned up to whatever speed they will attain, fall away badly in consumption after the critical speed of combustion, as well as fall away in torque and mean effective pressure. The exact critical speed required varies, of course, somewhat with different types of engine, and this variation may be due to different injection pressures, shapes of piston crown, size and direction of jets and other contributory causes, but it can be noticed that the output curves of all three engines rise steadily to about 1,400 r.p.m. and that the best fuel consumption appears to be around about 900 r.p.m. to 1,200 r.p.m. in all cases. The direct-injection engine has the best consumption, being under 0.4 lb. per bh.p.-hour from 800 r.p.m. to 1,100 r.p.m.
The pre-combustion-chamber engine has a similar curve, but with a higher consumption. The ungoverned engine follows closely this latter up to about 1,400 r.p.m., and then rises gradually as the speed increases to .2,500 r.p.m., where it reaches 0.58 lb. At this high speed the b.m.e.p. falls away to 67 lb. from a maximum of 83 lb. at 1,400 r.p.m. The highest m.e.p. is that of the pre-combustion-chamber engine, which is 97 lb. ; the direct-injection engine records about 90 lb. It therefore appears to be clear that these engines must be
c40 governed, and the governor should cut out at somewhere about 1,400 r.p.m. to 1,600 r.p.m., if we are to keep the consumption within proper limits.
When we come to consider the reasons for this limit it becomes clear why it must, be so. The injection of fuel starts about 10 degrees before top dead centre and lasts until about 15 or 20 degrees after. Thus we have only this 25 or 30 degrees, or, say, one-twelfth of the crank circle, in which to mix the oil spray and air. In the petrol engine we have practically the whole circle for the same operation. Thus, if the oil engine does its work of combustion completely at 1,500 r.p.m., it is doing remarkably well as compared with a petrol engine at 3,000 r.p.m.
The oil engine is from the combustion point of view an entirely different proposition, and to get the best results from it we must study its characteristics and alter not the engine, but the transmission, to get the same results on the road as we get with petrol engines. The power is there, and plenty of it, but it is compressed into a shorter range of speed, and this is the important point to bear in mind. Not only is the power there, but the powerful-torque at low speeds and the great economy in fuel at fractional loads, if properly used, will produce a far better road-vehicle engine than the petrol engine can ever be.
Within the past few weeks a test has been carried out with a six-cylindered direct-injection engine fitted to a heavy lorry, with a pay-load of 8 tons and a gross weight of 12 tons 11 'cwt. The result was most remarkable, and gave the extraordinarily high figure of 150 gross ton-miles per gallon and 96 net ton-miles per gallon ; the lorry also climbed a 1 in 4-1 gradient.
For fuel economy these results conclusively prove that the direct-injection design is ahead of other types. Only 12 months ago the writer predicted that the precombustion-chamber design would probably be the engine of the future—and, indeed, at that time experience seemed to point that way. The experience of the past seven or eight mcintlis has completely changed the position, the reasons-being that in fuel economy, starting by hand from dead cold without any auxiliaries whatever, and simplicity of design, the direct-injection engine is superior. However, we have a long way to go yet, and the race is still on. Both types of engine have good points and only the hard test of some years of constant work will indicate the eventual winner.
The most important line of research is that of fuel pumps and injection systems, and there is undoubtedly a great deal yet to be learned in this direction. One point seems to be definitely established, and that is that each individual type of engine requires its fuel-pumb camshaft specially designed to suit its characteristics.
W. M. GODDARD, A.M.I.Mech.E.
Licensing Contract and Express Carriage.
The Editor, THE COMMERCIAL MOTOR.
[3269] Sir,—With reference to the new Road Traffic Act, will it be possible to license a vehicle as a contract carriage and as an express carriage? If not and I license it as a contract carriage, should I be able to advertise a trip from our garage to the seaside, etc., for separate fares on vacant dates, also could we license it as a stage carriage to run a regular -Sunday morning
service to a church three miles away? T. OWEN. Salop.
[The Road Traffic Act provides that the holder Of a licence to use a vehicle as a stage carriage may use it as a ' contract' carriage, or, subject to any condition attached to his road-service licence, as an express carriage, and that the holder of a licence to use a vehicle as an express carriage may use it as a contract carriage.
A vehicle licensed as a contract carriage cannot be used as an express carriage for trips to the seaside, etc., at separate fares, unless it be also licensed as an express carriage. A vehicle used for a regular Sunday morning service to a church should be licensed as a stage carriage, even though all the fares are less than 1s. for a single journey, because the vehicle would come within the concluding words of the definition of stage carriage.—En.]