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Surface ignition may be initiated by one of two mechanisms: mechanical hot spots or combustion-chamber deposits. Conditions determining whether or not surface ignition occurs and the surface ignition resistance of fuels are different for each mechanism. The occurrence of surface ignition may be detected by changes in engine noise, time of peak pressure, rate of pressure rise, or flame front propagation time. Surface ignition may cause decreased engine power, increased heat rejection, and, in severe cases, component physical damage and ultimate failure. Increased compression ratio, speed, and specific output all increase the tendency of an engine to experience surface ignition. The composition and additive treatment of both gasoline and crankcase oil have large effects on the surface ignition tendencies of accumulated combustion-chamber deposits.