In this work the changes necessary to make optically accessible a commercial spark ignition and direct injection engine (GDI), operating in stratified charge condition, have been designed trying to keep as much as possible its operational characteristics. To this aim it was decided to design two optical accesses which would interfere as little as possible with the combustion chamber, that is a key condition in the formation of stratified charge, creating an "optical" 4-cylinder engine, versus the classic single-cylinder, so as to leave unchanged the thermo-fluid dynamics configuration of the real engine and so its emissions and fuel consumption. A first optical access has been achieved in the piston head and a second by inserting an endoscopic fiber probe in the header. Both combinations allow a complete analysis of the injection and combustion in an engine whose features are nearly similar to the standard one
