Stratified charge engine

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A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, 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 cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.

Conventionally, a 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 NO_x.

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.