Pre-ignition Pre-ignition Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events. The phenomenon is also referred to as 'after-run', or 'run-on' or sometimes dieseling, when it causes the engine to carry on running after
Mesoamerican Archaic period differed regionally. Most Archaic sites are not very well preserved or visible, which hampers archaeologists' ability to discover and study Archaic period sites. As a result, not many Archaic sites have been identified, although major sites like Guilá Naquitz and Colha have been explored by archaeologists. Most known Archaic sites are in the Mesoamerican highlands or along the coasts, though there are sites throughout the region. During the Archaic period, Mesoamerican peoples slowly changed from being nomadic hunter-gatherers to semi-sedentary or sedentary foragers and farmers. Based on research at sites on Mexico's gulf coast, central highlands, and coasts, it seems