Over the last few decades, in-cylinder visualization using optically accessible engines has been an important tool in the detailed analysis of the in-cylinder phenomena of internal combustion engines. However, most current optically accessible engines are recognized as being limited in terms of their speed and load, because of the fragility of certain components such as the elongated pistons and transparent windows.
To overcome these speed and load limits, we developed a new generation of optically accessible engines which extends the operating range up to speeds of 6000 rpm for the SI engine version, and up to in-cylinder pressures of 20 MPa for the CI engine version.
The main reason for the speed limitation is the vibration caused by the inertia force arising from the heavy elongated piston, which increases with the square of the engine speed. To compensate for the inertia force associated with the elongated piston, we used two opposing balancing pistons, in a configuration which is perfectly balanced.
The maximum in-cylinder pressure of current diesel engines exceeds 15 MPa. To enable the study of such high in-cylinder pressures, the elongated piston of the diesel version was designed and optimized using finite element method (FEM) calculation.
This paper describes the details and features of the newly developed optically accessible engines and provides some examples of in-cylinder visualization.
