. Automotive industries . curve. It has sometimes been said that an engine which willknock badly with a single spark will cease knocking whentwo sparks are applied by plugs in different parts of thecylinder. This is true within certain limits, but fromtests made at the Bureau it becomes evident that the de-termining factor in this respect is in reality what maybe termed the effective spark advance. Suppose, forexample, that in the case of the engine referred to de-tonation occurs with a single spark at a point in. be-fore center. (Fig. 1.) Using two sparks at this poinlwill in effect advan
. Automotive industries . curve. It has sometimes been said that an engine which willknock badly with a single spark will cease knocking whentwo sparks are applied by plugs in different parts of thecylinder. This is true within certain limits, but fromtests made at the Bureau it becomes evident that the de-termining factor in this respect is in reality what maybe termed the effective spark advance. Suppose, forexample, that in the case of the engine referred to de-tonation occurs with a single spark at a point in. be-fore center. (Fig. 1.) Using two sparks at this poinlwill in effect advance the spark and cause more violentdetonation. If, however, the engine is knocking badlywith an advance of in. on a single spark, and 2sparks are applied, knocking will cease, due again tothe earlier effective advance. Hence it is clear that theeffective advance is the controlling factor and not themere occurrence of one or two sparks. 754 AUTOMOTIVE INDUSTRIESTHE AUTOMOBILE April FILM ON DRUM DRIVEN ATCONSTANT SPEED. Apparatus tised in study of flame propagationphenomena This is further illustrated in Figs. 2 and 3. Under theconditions obtaining in Fig. 2, it will be noted that withone spark detonation does not occur, the range of maxi-mum pressure, from cycle to cycle, varying as shown bythe bracket from about 240 to 350 lb. per sq. in., whilewith two sparks, and the same actual advance, maximumpressures due to detonation, as shown by the bracket,run from about 370 to 450 lb. per sq. in. On the otherhand when the spark advance is increased and ignitionoccurs nearly 1 in. of piston travel before center (seeFig. 3), violent detonations resulting in occasional maxi-mum pressures (as- shown again by the bracket) of 600to 800 lb. occur, whereas, when two sparks fired simul-taneously occur at the same advance, the maximum pres-sures are much less, although detonation is not entirelyabsent. Other tests made with varying ratios of air to gas indi-cate that the detonation is also
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