All About Engines

188 All About Engines coil accumulators are necessary, and they must be kept charged or a duplicate set must be held in readi- ness. For large engines, where the cost of acces- sories is less important, the arrangement devised by Sir Oliver Lodge is frequently used. This gives a very powerful spark, which is certain and effective in its action. By whatever method the electricity for the spark is generated, it is produced inside the cylinder between the ends of two wires fixed in a sparking plug. This is easily removable for cleaning or renewal. The gas engine needs to be governed just as a steam engine does, or it would “ race ” when the load was decreased or removed. The governor itself is practically the same as a steam engine governor, but the method by which it controls the speed of the engine may differ. Many of the early gas engines were fitted with a “ hit and miss” governor. Be- tween the cam and the gas valve spindle was a small rod which when the engine ran too fast was lifted out of the way. When this occurred the gas valve did not open, no charge entered, and no explosion occurred. Missing a whole explosion is rather a drastic method of reducing the speed, especially when there is only one explosion in two revolutions; and the modern practice is to employ a “ throttling ” gover- nor, which controls very delicately the quantity of gas drawn into the cylinder on each occasion. One of the neatest devices for effecting this is that adopted by Messrs. Crossley Bros., and shown in Fig. 112.