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

Abstract

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 influence on fuel efficiency and emissions. We report the development of a fiber-based near-infra-red absorption tomography system, to measure the distribution of hydrocarbons in cylinder. It has been successfully applied to transient gas injections. The technique exploits the specific (but weak) hydrocarbon absorption of 1.7 μm radiation, which wavelength has only recently become accessible by availability of solid-state all-optoelectronic components. A standard telecommunications laser was also deployed to measure reference information. The measurement space is sampled by 32 dual- wavelength fiber-coupled measurement paths. The logarithm of the ratio of the two measurements 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 readily calibrated for temperature and pressure effects, over the region 70–150 °C 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. © 2001 SPIE and IS&T.