The position for this tube is defined by the manufacturer so that at the time of greater compression the explosive mixture is forced into the tube and ignited.
The Burner.—To obtain satisfactory ignition, the platinum tube must be heated to a red heat. This is effected by a small Bunsen burner placed directly underneath. The burner consists of a small tube or 'stem' easily detachable from the petrol supply, in which is inserted a wick, composed of cotton rolled up in a sheath of fine brass gauze. The upper extremity of the stem is provided with a removable nipple, in which is drilled a minute hole. The burner is completed by a cowl, with a slot at the top which directs the flame on to the ignition tube. The burner is on the well-known Bunsen system, taking in air through holes at the foot of the cowl, the air being carried upwards with the jet of petrol coming through the small hole in the nipple.
Although there are numerous designs of burners on the market, they differ little from one another save in small details of appearance.
Petrol Supply to Burners.—There are two methods of feeding the burners with petroleum spirit:—
(1) By allowing the spirit to flow by gravity from a small tank fixed in an elevated position—this is known as 'gravity feed.'
(2) By forcing up the spirit from a tank frequently the main supply—placed in a convenient position under the car by means of artificial pressure. This system is known as 'pressure feed.'
The advantages of gravity feed are its greater safety and perfect reliability. A good system of gravity burners will run for months without attention. The flame from a burner should be a bright blue, and directed lengthways on to the ignition tube.
Note.—In small Panhard cars the flame should be across the tube.
