Measurement of gaseous hydrocarbon distribution by a near-infrared absorption tomography system

The spatial distribution of chemical species can be a critical determinant of chemical reactor performance. The spatial variation of air-fuel ratio in a combustion chamber of an internal combustion engine has significant infl uence on fuel efficiency and emissions. We report the development of a fibe r-based near-Infrared absorption tomography system, to measure the distribu tion of hydrocarbons in cylinder. It has been successfully applied to trans ient gas injections. The technique exploits the specific (but weak) hydroca rbon absorption of 1.7 mum radiation, which wavelength has only recently be come accessible by availability of solid-state alloptoelectronic components . A standard telecommunications laser was also deployed to measure referenc e information. The measurement space is sampled by 32 dual- wavelength fibe r-coupled measurement paths. The logarithm of the ratio of the two measurem ents yields the path Integral of the hydrocarbon absorption, and hence, of concentration. The path integral is measured with typically 28 dB signal-to -noise ratio. Single-channel characterization shows that the technique is r eadily calibrated for temperature and pressure effects, over the region 70- 150 degreesC and 1-10 bar. Tomographic reconstruction of different gaseous hydrocarbon flows has been achieved with spatial resolution of the order D/ 5, where D is the vessel diameter. Temporal resolution of about 1000 frames /s is demonstrated. (C) 2001 SPIE and IS&T.