Measurement of Wall Film Thickness in the Intake Manifold of a Standard Production SI Engine by a Spectroscopic Technique

This paper reports on a non-intrusive method for measuring the liquid fuel film thickness in the intake manifold of a series production SI engine with multi-point fuel injection.

The technique is based on laser-induced fluorescence. The optical set-up uses a bifurcated optical fibre bundle for transmission of the laser light for excitation of the fluid and for detecting of the fluorescence light. Due to the special design of the optical probe head it is highly sensitive for thin film measurements and it allows the accurate determination of the fuel film thickness even between a few and 100 μm. Special emphasis is placed on the selection of an adequate tracer added to the iso-octane fuel to achieve the correct film thickness even under vaporizing conditions, and on a detailed study of the parameters influencing the evaluated film thickness.

Crank angle resolved measurements of the wall film thickness at different locations in the intake manifold and at different engine speeds and loads demonstrate the capability of the technique and even allow the estimation of the total fuel mass stored in the wall film.