Spark-ignition means relating to a gasoline-fueled engine or other engines with a spark plug (or other sparking device) and with operating characteristics significantly similar to the theoretical Otto combustion cycle. Spark-ignition engines usually use a throttle to regulate intake air flow to control power during normal operation.
40 CFR § 94.2
The definitions of this section apply to this subpart. They also apply to all subparts of this part, except where noted otherwise.