Two-fuel Carburetters and Fittings.—XV.
Page 4
If you've noticed an error in this article please click here to report it so we can fix it.
An Ingenious Device Invented by a Motorist, Who Combines Racing Experience on Road and Track, and Engineering Training, With Practical Knowledge of the Difficulties Attendant on the Use of Paraffin In Petrol Engines.
On grounds both of cleverness of conception and neatness of execution, the Pullin carburetter is particularly worthy of notice. , The inventor, Mr. Cyril Pullin, is well-known in the motor-cycling and touringcar world.,, He was successful in winning.the highlyesteemed Tourist Trophy which is competed for each year in normal times by motorcyclists in the Isle of Man. From the point of view of the commercial user, it is perhaps more important to know that he has had several years experience of a paraffin carburetter and of the difficulties attending1 its use. The theory' on which the design of his carburetter and vaporizer is based is ingenious. It may be more easily explained When the reader has grasped the de tails of the construction of the carburetter This primary object be attained by a. Perusal of the following text, read in conjuiiction'with' the drawings which we reproduce at the foot of this pad. •Of these drawings, that sectional elevation, which apPears at the left-hand top -corner of the illustration, gives the best idea Of the arrangement. The passage • of the fuel may be traced.froni the float chamber through the three-way cock (whichis.shown in section) along the inclined jet into the throttle barrel, which is designed so that the requisite folurne of air is drawn past the jet at right-angles to it, and causes thorough atomization of the liquid fuel. It passes thence-through a tube, which is taperin 'form, being smaller at the bottom end than at the top. This, choke tube—and, by the way, there are three of them with a jet and passage in the throttle valve s, contained in an exhaust-heated vaporizer. Above the vaporizer is a pipe which serves to collect the gas issuing from these three tubes and to deliver it to the inductiol -pipe, in which it is conveyed to the cylinders. The three-way cock connects the three jets to one or other of the two float chambers, one of which serves ',for petrol, the other for paraffin. A reference to the sectional plan at the right-hand top corner of the drawing will enable the reader to understand how this is effected.
" The supply of paraffin to the three-way cock is regulated by means of a screw-down valve ; this may be arranged so as to be operated from the dashboard. The'supply to each jot is also capable of being regulated by a similar valve. In the central portion of our illustration, which shows the carburetter dismantled, is depicted the combined throttle valve and choke tubes. This throttle valve is cylindrical and is made in three parts, which are adjusted before the carburetter is sent out so that the jets, Nos. 1, 2 and 3, come into operation in turn; an additional slot in the throttle valve also allows of No. 1 being used as a pilot jet for "ticking over" or slow running. We have not space to deal at length with the theoretical considerations which led the inventor to this design of carburetter. It will be sufficient if we state that the tapering tubes are calculated as to their sizewith reference to any type of engine for which the carburetter may be intended, the object being to ensure, so far as possible, that gas of practically atmospheric pressure and at a stated temperature enters the cylinders. By this means, packing of the cylinders with mixture at high temperature—and therefore liable to pre-ignition—is avoided. Attention is also directed to the peculiar shape of the vaporizer. This "dog's hind leg" path along whichfthe exhaust gases are forced to travel, causes them to impinge with greater frequency upon the vertical tubes containing the mixture. This necessarily brief description of the carburetter will be willingly supplemented by Mr. Pullin, the patentee and manufacturer, if application be made to him at the Thomas Auto-Coach Building Co., Beavor Lane, Hammersmith.