What is Homogeneous Charge?

Homogeneous charge, as it relates to internal combustion engines, is a thoroughly and completely mixed (so that every molecule is evenly distributed) charge of air and fuel across the combustion chamber. This absolute mixing occurs well before the start of ignition. The idea behind homogeneous charge is to create an easily ignitable fuel mixture that is easy to manage and burns smoothly and evenly across the entire combustion chamber. It does this well, but at the expense of excessive NOx build-up that must then be captured and processed by the vehicle's catalytic converter.