Editing Stratified charge engine (section)

{{Short description|Type of internal combustion engine}}
{{More citations needed|date=February 2012}}

A '''stratified charge engine''' describes a certain type of [[internal combustion engine]], usually spark ignition (SI) engine that can be used in trucks, [[automobile]]s, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the [[Engine cylinder|cylinder]] or enters as a fuel rich vapor where a spark or other means are used to initiate [[combustion|ignition]] where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher [[compression ratio]]s without "[[Engine knocking|knock]]," and leaner [[Air-fuel ratio|air/fuel ratio]] than in conventional internal combustion engines.

Conventionally, a [[Four-stroke engine|four-stroke]] (petrol or gasoline) [[Otto cycle]] engine is fueled by drawing a mixture of air and fuel into the [[combustion chamber]] during the intake stroke. This produces a '''homogeneous charge:''' a homogeneous mixture of air and fuel, which is ignited by a [[spark plug]] at a predetermined moment near the top of the [[compression stroke]].

In a homogeneous charge system, the air/fuel ratio is kept very close to [[stoichiometric]], meaning it contains the exact amount of air necessary for complete combustion of the fuel. This gives stable combustion, but it places an upper limit on the engine's efficiency: any attempt to improve fuel economy by running a much leaner mixture (less fuel or more air) with a homogeneous charge results in slower combustion and a higher engine temperature; this impacts on power and emissions, notably increasing nitrogen oxides or [[NOx|NO<sub>x</sub>]].

In simple terms a stratified charge engine creates a richer mixture of fuel near the spark and a leaner mixture throughout the rest of the combustion chamber.  The rich mixture ignites easily and in turn ignites the lean mixture throughout the rest of the chamber; ultimately allowing the engine to use a leaner mixture thus improving efficiency while ensuring complete combustion.