IGNITION SPARK.

Press, Volume LXIII, Issue 19150, 5 November 1927, Page 9

IGNITION SPARK.

AUTOMATIC CONTROL. It is not surprising that an increasing number of car makers is taking tlio control of the ignition spark out of the hands of the car 'driver,'and making the advance and retard operations automatic. For tho spark lever is probably one of tho least used filaments on a motor vehicle. Many drivers allow the lover to remain in the fully advanced position! irrespective of speed, road conditions, or grades. Others leave it where it happens to be when they take' the wheel, while a minority use the lever intelligently, and get more efficient operation of the engine.

In effect, the spark lever enables the driver to adjust the spark to coincide with piston speed and the class of fuel used. There is no hard and fast rule regarding ignition timing, owing to the fact that piston speed and tho degree of inflammability of the mixture of petrol and air are 'variable factors. Economy of fuel and a, better delivery of power will result if the engine is run with the greatest amount of spark "advance" it will take without knocking.

The explosive mixture comprising petrol and air is comparatively slow burning, although the fact does not seem to be generally recognised by motorists. The mixture takes a definite period of time from when the spark occurs until it gives its full driving power. This period depends upon the strength, quantity, and degree of compression of tho mixture. It follows, then, that- at any given piston speed (engine revs.) there must be a definite point m the stroke which is the most favourable for the piston to take the full power of the explosion. The timing lever, which operates a simple piece of mechanism on the magneto, or in the ease of coil ignition on the distributor, allows the inai; at' the wheel to control the spark so that it will take place at the most favourable position of the stroke. When the piston is travelling at high speed the spark should be sent on ahead, so that the full force of the explosion will be available precisely at the right moment. The spark, of course, occurs at some point before ton dead centre, and by experience a driver learns just how the spark should be timed for all running conditions.