Question

Compare stratified charge engine and conventional petrol engine

Answer 1

A stratified charge engine is a type of internal combustion engine, usually SI engine that is used in automobiles, in which the fuel is injected into the cylinder just before ignition. This allows for 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 and fuel necessary for a 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 lean mixture with a homogeneous charge results in unstable combustion; this impacts on power and emissions, notably increasing nitrogen oxides or NOx.