The term spark-ignition is normally used to refer to [[internal
combustion engine]]s where the fuel-air mixture is ignited with
a spark. The term contrasts with compression-ignition engines,
where the heat from compression alone ignites the mixture.
Spark-ignition engines can be either two-stroke or four-stroke,
and are sometimes referred to as "gasoline engines." However,
this nomenclature is not preferred, since spark-ignition engines
can (and increasingly are) run on fuels other than gasoline,
such as methanol[], ethanol[] , CNG[] , hydrogen[] , and
nitromethane[] . A four-stroke spark-ignition engine is an Otto
cycle engine. Until recently, a major distinction between spark-
ignition and compression-ignition engines has been where the
fuel is mixed - spark-ignition engines mix fuel outside the the
cylinders and compression-ignition engines mix fuel inside the
cylinders. However, both two-stroke and four-stroke spark-
ignition engines are increasingly being designed with direct
injection, eliminating this di