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 seasonally by largely mobile peoples in the Early and Middle Archaic periods. Based on the presence of specific plants, the rock shelter was inhabited during the wet season from July to September, then in the Archaic period, around 4700 BCE, from May to October. Some of the earliest known villages appear along sea coasts, specifically the Chiapas and Caribbean coasts. It is likely that the abundant sea and lagoon resources could easily support long-term, year-round settlements, leading people to settle first in these areas. Shell mounds in these areas are highly visible, which likely aided in their identification by scholars.