GAS ENGINES


| May/June 1997



Barnett Igniting Cock

Fig. 4.Barnett Igniting Cock

The following is the second in a series of articles from the 1923 edition of Modem Mechanical Engineering, on the subject of gas engines. The original articles were sent to us by Jan van der Gugten, 2633 Ware Street, Abbotsford, B.C., Canada V2S 3E2, who thought our readers would find them of interest.

GAS ENGINES

CHAPTER III: Methods of Ignition

In the evolution of the gas-engine, ignition was for long a source of trouble, and the solution of the problem of igniting the charge with certainty and regularity proved long and difficult.

In the earliest non-compression of low-compression engines, as, e.g., those of Street (1794) and Wright (1833), a crude 'touch-hole' flame method was used. The piston near the commencement of its working stroke uncovered a small hole through which an external flame was sucked, thus exploding the fresh charge; the hole was sometimes so small as to cause no perceptible loss of pressure on explosion, or was fitted with a valve closed by the rise of pressure in the cylinder or ignition.

In engines compressing their charge before explosion this simple method was obviously inapplicable; but in 1838 W. Barnett introduced the celebrated 'Barnett Igniting Cock', which successfully solved the problem of ignition by flame in compressing engines, and was extensively used from that date down to about 1892. An illustration of this igniting cock is given in Fig. 4. It comprises a hollow open-ended single-ported plug (A) ground into a casing (B) containing two ports (C) and (D), of which (C) communicates with the atmosphere and (D) with the engine cylinder. A gas-jet (E) burns continuously outside the cock, while (F) is a gas-pipe terminating in a small burner within the hollow plug (A). The plug (A) is rotated by the engine in working, and in the position illustrated the external flame (E) ignites the jet within the plug. The rotation next causes the plug port to register with the port (D), whereupon the charge within the cylinder is immediately exploded; the explosion extinguishes the jet in the plug, but when next it opens to the atmosphere it is relighted by the flame (E) in readiness for the next explosion; the action is thus positive and regular. The later improved flame-igniting devices of Hugon, Otto and Langen, and Dr. Otto were based upon the principle of the Barnett cock.

In 1799 Lebon proposed to use a machine worked by the engine to produce electric sparks for exploding the charge; in 1850 Stephard suggested the use of a magneto-electric machine for this purpose; in 1860 Lenoir employed a Bunsen battery, Ruhmkorff coil, distributor, and sparking-plug, substantially as was largely used in automobiles between 1898 and 1908; the art of constructing reliable coils and plugs was, however, but little developed in Lenoir's day, and great trouble was always experienced with the ignition of his engines. In Hugon's Lenoir-type engine an important improvement was the replacement of the electrical ignition by a flame device of modified Barnett type. Ignition by magneto-electric machines is now all but universal in gas engines, but the unfavorable impression created by the early Lenoir arrangement probably retarded its development in Great Britain.

A method that has been very largely used since about 1883, and is even now (1922) not quite obsolete, particularly in small gas-engines of up to about 10 b.h.p. is that known as 'hot tube' ignition.