Ignition was provided by capacitor discharge ignition (CDI). Each cylinder has its own miniature ignition coil. Power delivery is tapered through manipulation of the throttle butterfly and ignition and fuel cuts. The fuel is altered to change its self ignition temperature. A cetane number is a measure of the delay of ignition of a diesel fuel. Rocket engine ignition systems are especially critical. Gasoline engines combine homogeneous charge (HC) with spark ignition (SI), abbreviated as HCSI. These work by sensing that the engine is running by detecting ignition pulses. Diesel engines rely solely on the heat of compression for ignition. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is . Fire prevention is intended to reduce sources of ignition. Experimental engines with laser ignition have been built. A backup cue is the time elapsed from booster ignition. Gremlins included standard electronic ignition developed by Prestolite. Misfires are usually caused by inadequate ignition.