High-speed chemical species tomography in a multi-cylinder automotive engine

High-speed continuous imaging of fuel distribution and mixing within the combustion cylinders of automotive engines has been a high-priority goal for engine designers and combustion scientists for many years. We report here the first application of Chemical Species Tomography (CST) of gaseous hydrocarbons in a multi-cylinder automotive engine.

A measurement grid consisting of 27 dual-wavelength optical paths has been implemented in one cylinder, using a unique OPtical Access Layer (OPAL) carrying embedded optical fibres and collimators. The OPAL provided adequate performance on many beams for more than 2 hours of fired engine operation. To improve sensitivity and to cope with fuel spray injection directly into the cylinder (in future applications), a second-generation low-noise opto-electronic system has been developed, with laser intensity modulation at frequencies up to 600 kHz. Dual-wavelength measurements are recorded on each channel at 100 kSPS, prior to off-line processing that typically reduces the frame rate to 3000-4000 fps, dependent upon engine speed.

The measured data and processing schemes are discussed and examples of tomographic images are presented. The concept is readily extendable to further species of interest. This research has demonstrated that CST offers considerable promise to penetrate the fundamentals of many dynamic chemical reaction processes.