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
Archaic humans In this case the standard taxonomy is used, i.e. "Homo rhodesiensis", or "Homo neanderthalensis". The evolutionary dividing lines that separate modern humans from archaic humans and archaic humans from "Homo erectus" are unclear. The earliest known fossils of anatomically modern humans such as the Omo remains from 195,000 years ago, "Homo sapiens idaltu" from 160,000 years ago, and Qafzeh remains from 90,000 years ago are recognizably modern humans. However, these early modern humans do possess a number of archaic traits, such as moderate, but not prominent, brow ridges. The emergence of archaic humans is sometimes used as an example of