Chemical species tomography of sprays of volatile hydrocarbons

We report an All-Opto-Electronic tomography system that is sensitive to hydrocarbon vapour distribution, or liquid spray distribution, with temporal resolution of over 3,000 frames per second. A tomography system comprising 32 channels has been built and tested. For chemical sensitivity, we exploit the principle of Near Infra-Red (NIR) absorption at 1700nm, using laser diode sources whose technology is based on that of the communications industry. We report on the performance of the system for purely gaseous subjects, and for subjects containing vaporising liquid sprays. Images are obtained from a laboratory set-up, and the performance of an 8-channel prototype system on a running Gasoline Direct Injection (GDI) engine is reported. Testing on a GDI system has shown the difficulty in performing concentration measurements of the gaseous fuel in the liquid spray. However, it has been found possible to image the liquid spray cone using attenuation of the reference beam. These images correlate well with other techniques (Allen 1998).

In engine tests, the electronic noise immunity of the system is excellent. For early injection, good concentration path integrals are obtained (through the vaporised fuel) during the compression stroke. This augurs well for application of a many-channel system for tomographic imaging in an engine in this or related conditions. When the spray injection occurs during the compression stroke, the sprayrelated degradation of the light signals is severe. Means to overcome this effect are discussed.