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Aviation History
1927
1927 - 0885.PDF
NOVEMBER 17, 1927 CORRESPONDENCE The Editor does not hold himself responsible for opinions expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters intended for insertion in these columns. COMPRESSION-IGNITION ENGINES [2165] Many I.C. Motor Research workers like myself were disappointed with the paper read by Mr. H. B. Taylor on the above subject. We attend such meetings to receive enlighten- ment. Instead the audience was served with information known to most of us over 15 years ago. A shroud of mystery and secrecy was cleverly thrown over the meeting regarding this " hush hush " motor, by some able official speakers, but those of us " in the know " could clearly see it was the usual official window dressing and whitewash, backed by nothing interesting or original. As a research worker for over 16 years, and a patentee of numerous types of valve gears for I.C. motors, and having spent over two years at Farnborough during the war, and having been in close touch with Govern- ment experts in all the fighting services almost continuously ever since, I claim to know something about the mentality of the official expert, and the huge sums of money squandered at Farnborough, and in other departments of "the fighting services on white elephants. In reading Mr. Taylor's paper and studying the drawing of the experimental motor used, I have no hesitation in saying that the Air Ministry is pursuing a greater phantom than the famous phantom Salmon rotary valve motor built at Farnborough during the war, which was going to revolutionise flying, but which I laid low in the technical Press when the experiments were started. The experiments were, however, carried on for a considerable time with disastrous consequences to the taxpayers. In criticising this paper, I will not go into the many difficulties Mirrounding fuel injection, etc., at high speed, they are well known to practical engineers. I will confine my remarks to the overhead valve gear fitted. Most of us are agreed that the aero engine of the future must be able to function for days and weeks at high speed without stopping, like a marine engine, further, the overhaul and repair bill must be on a par with it. Mr. Taylor's position at Farnborough must make him con- versant with the serious, excessive; and rapid wear dev- eloped on the exhaust valves, guides, rocker arms, push rods, etc., due to side thrust, caused by the radial movement of the rocker arms, and lack of perfect lubrication. Sticky and broken exhaust valves are also a source of trouble, and cause great loss of life, especially in motors fitted with domed combustion chambers (as illustrated in his experimental engine) which distort due to the coal gas being taken in at one side of the cylinder and the red-hot exhaust being expelled at the other side. A 12-cylindcr 650 h.p. motor fitted with this type of cylinder has over 450 pieces m its valve gear alone. Is it to be wondered at that the Air Force'requires a great number of ground men to keep such motors in running condition ? Is this type of motor suitable for rapid overhaul in war time ? The experimental motor shown cannot be classed as a clean simple, business-like proposition. It gives one the impression of being a crude copy of the type of compression ignition motor in use many years ago. It did not surprise me to hear the lecturer say that it broke down many times. Away back in 1907 and 1908, when experimenting with and selling model motors for aeroplanes, I found it comparatively easy to get good results with single-cylinder engines of large bore, but when testing engines of small bore, 1 found them trouble- some to keep running perfectly, due to sensitive carburation. Mr. Taylor will find the same trouble when he comes down to .-.mailer bores, which he will have to do, as the present size he is using is excessive. The type of valve gear shown is wrong in theory and practice for effectively vapourising heavy fuels for high-speed aero engines, and the sooner the engine exjx-rts at the Air Ministry wake up to this fact, the sooner the perfect heavy fuel motor will be evolved. It is un- scientific practice to draw the cool air and vapour through a cool port and expel the flaming exhaust through a red hot port, the order should be reversed ; this can only be done by making one small positively operated valve per cylinder control the two ports. In considering the question of a heavy fuel motor. I see no difficulty in vapourinsing the fuel perfectly through a special carburettor, provided a new type of valve gear and cylinder head are fitted which will utilise about 55 per cent, of the heat energy now thrown away in the exhaust of the present type. This is within the bounds of possibility, and I would suggest to Mr. Taylor that he first solve the problem of reclaiming this heat energy (which I have done) then he will find it a simple matter to vapourise heavy fuel with this reclaimed heat, at a compression ratio of 9 to 1, without injection, and fire the charge like a petrol motor with a special type of sparking plug and coil. As is well known, this cannot be done with poppet or sleeve valve motors because the vapour is drawn upwards from the carburettor through cold ports, and as the fuel is heavier than air it quickly separates itself from the air and takes the shortest route which is along the bottom of the passages, reaching the cylinders in unequal quantities, this causes roughness in running. With the valve gear I have designed and patented, the vapour is drawn downwards directly from the carburettor into an expansion box extending the full length of the motor and is always at a constant temperature. It is then distributed equally to each cylinder from this box. This simple system of reclaiming lost heat energy- introduces the possibility of running an ordinary petrol motor on shale oil with a modified carburettor, valve gear, detachable head and ignition system. The motor need not be built heavier to run at this higher compression ratio because the strains will not be as great as the strains on a poppet valve motor when it is pre-igniting. In 1915, I fitted a De Dion car with a single-cylinder motor of this type. It ran perfectly either on petrol or workshop paraffin, price Qd. per gallon. The motor was fitted with an ordinary No. 30 Zenith petrol carburettor without heating the inlet. It gave off no moisture or smoke from the exhaust. With this encouraging result, I intended to proceed further with my experiments, but the War Office thought I would be better employed doing fatigue duty in the workshops at home and abroad. When I returned from France in 1919 and got demobilised, I found the garage proprietor had gone, also my experimental car ; since then I have not been able to continue my experiments. The Air Ministry are conversant with my motor, but as they are afraid to take risks with anything new, they play for safety by following other experi- menters when doing research work, as is evident from Mr. Taylor's paper. This appears to me to be a retrograde policy. Should not a well thought out simple scientific design be given more consideration even if it has not emanated from the highbrows at the Air Ministry, especially as it is acknow- ledged by two leading British research chemists on motor fuels to be the solution for pre-ignition, detonation and carbon monoxide gas in the exhaust. Further, a 700 h.p. 12-cylinder vertical parallel geared motor built to this design has only 52 pieces in its positively operated valve gear, and as the valves and combustion chambers temperatures are never excessive, high speeds equalling the recent Italian seaplane record of 313 m.p.h. could be kept up indefinitely, an im- possibility with a poppet valve motor, the exhaust valves of which are quickly destroyed by high velocity exhaust gas. I am not in agreement with Mr. Taylor that the two-cycle compression ignition motor presents possibilities for high speed aero engines. Assuming the speed of the engine to be about 1,200 r.p.m., how does he propose to open and close the fuel injection valve 1,200 times per minute while the crank pin travels through 80" ? At this speed will not the compression in the cylinder tend to blow the fuel back before the fuel valve closes ? Inertia forces and wear on such a high speed sensitive injection valve will become serious problems to solve. Further, the power stroke of a two-cycle motor is not effective for more than half a cycle whereas the power stroke of a well designed four-cycle motor fitted with a scientifically designed positively operated large ported valve gear is effective for over three-quarters of the cycle. When Mr. Taylor has seriously considered the above points, I do not think he will be so enamoured with his high speed two- cycle proposition. In 1915, I patented a two-cycle aeroplane engine working on fuel injection but when I came up against the above problems I abandoned it for my present type of four-cycle motor. West Hampstead. WILLIAM COCHRANE November 14, 1927. French Magazines for Sale A HEADER of FLIGHT wishes to dispose of the war issues, 7« in all, of La Guerre Aericmw, all in good condition, as well as 10 issues of Documents de I'Armee. Will any reader interested in these please communicate with the Editor, who will forward all enquiries to the owner of the documents ? 801
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