In-Cylinder Velocity Measurements with a Mobile Fiber Optic LDA System

A fiber optic LDA is introduced which simplifies setup and alignment procedures for in-cylinder velocity measurements. The system is novel in its use of graded-index fibers excited in their fundamental mode for beam transmission, which also leads to a high degree of robustness and temporal stability of the alignment.

The system has been used to study velocity fields in a fired 4 stroke, single cylinder SI research engine with a pancake shaped combustion chamber operating at 1000 rpm. A window mounted in the cylinder head provided optical access and both the radial and swirl component of velocity could be measured, simultaneously with the cylinder pressure and crankangle. A spectral analysis of the acquired data is made possible by the high data rates achieved with the system.