Petrol engine has good full load power characteristics but poor part load efficiency. Diesel engine has good part load efficiency but poor full load characteristics. Both have poor emission characteristics because of high peak temperatures. Fuel efficiencies of both the engines are very much lowered in actual operation because of stoichiometric F/A mixture ignition.

Therefore there is need to develop an engine which combines the advantages of both SI and CI engines and simultaneously avoids the possible disadvantages a stratified charge engine is an attempt in this direction. The stratified charge engine offers solutions to most of the problems mentioned above. Despite the attempts made by the engineers to develop stratified engines, it has suffered several drawbacks as high hydrocarbon omission part loads.

The stratification means to provide different A/F mixture at various places in the combustion chamber of SI engine. A rich mixture near or around spark plug and lean mixture A/F in the rest part of combustion chamber. The whole A/F mixture is distributed in layers with different A/F mixture in the combustion chamber while the overall mixture is rather lean.

This segregation in mixture formation may be obtained either by carburetor or fuel injection. Rich mixture near spark plug helps to establish a strong flame kernel with accelerated growth which spreads into lean mixture and consumes it completely. This technique paved the way to run the engines with lean mixtures which was not possible earlier in conventional spark ignitions engines. This system saves the fuel and reduces emission.