Image reconstruction for Chemical Species Tomography with an irregular and sparse beam array

Application of Chemical Species Tomography (CST) inside the combustion chamber of an automotive engine entails the introduction of many optical beams into a complex and hostile environment. Optimization of the number of beams and their spatial arrangement is a potentially difficult process, being subject to many mechanical constraints. In the IMAGER project, we have installed 27 optical paths in one cylinder of a multi-cylinder engine. Optimization of the beam array for near-uniform cross-sectional sensitivity results in an irregular arrangement, i.e. beams are not arranged in conventional parallel- or fan-beam projections. This has necessitated novel approaches to image reconstruction, advanced versions of which are reported and discussed here. This work reports on successful laboratory tests used to assess the spatial performance of the IMAGER system. The resulting measurements of gas concentration path integrals have been used to reconstruct images with good fidelity.