In non-diesel internal combustion engines, gasoline direct injection (GDI), also known as petrol direct injection, direct petrol injection, spark-ignited direct injection (SIDI) and fuel-stratified injection (FSI), is a variant of fuel injection employed in modern two-stroke and four-stroke gasoline engines.

The overall equivalence ratio of the in-cylinder mixture maintains at 0.75 in all the cases. And it is observed that, the turbulent kinetic energy and tumble ratio are more sensitive to the engine speed than to other parameters also The fuel injection play a vital role in obtaining combustible.

Thanks for your answers Baboo

There is big difference between global equivalence ratio and local equivalence ratio. Partly the reason why stratified mode is used. (maintaining combustion while have a very lean environment)

Generally, it is like what you said near the spark plug. We want it to be slightly rich, but not too rich.

The max and min global equivalence ratio might not make that much impact on the flame formation because it is the local PHI near the spark plug which matters most.

Optimum size of the kernel for achieving an efficient flame propagation depends on the engine operating conditions (T, P), fuel type, local PHI, spark plug gap, spark plug operation strategy and etc. According to Pischinger & Heywood and available literature the optimum radius of flame (constant flame thickness) for gasoline PHI~1.2 condition can be between 1-1.5mm. The optimum kernel size can be analysed by investigating CO2 formation trajectory, as an indication of completed combustion product, during high temperature reactions.