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 fibre-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 fibre-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 28dB signal-to-noise ratio (SNR). Single-channel characterisation shows that the technique is readily calibrated for temperature and pressure effects, over the region 70-150°C and 1-10bar. 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 1,000 frames per second is demonstrated.

Optimisation of a tomography sensor for imaging of temperature in a gas turbine engine

“…is known as the model resolution matrix. If we consider that the error in the solution is probably dominated by a lack of measurement data as opposed to measurement noise (which is likely to be true with an estimated dB signal-to-noise ratio typical of diode laser absorption measurements [21]), we can neglect the measurement noise term. Subtracting from both sides and taking the norm gives an approximation of the Tikhonov error:…”

Three–Dimensional Water Vapor Visualization in Porous Packing by Near-Infrared Diffuse Transmittance Tomography

“…5 Nevertheless, optical techniques are increasingly cited in both open and industrial literature, being boosted by rapid developments in tunable lasers and single or 2D array detectors and leading to experiments being performed at high spatiotemporal resolutions. 5,6 In the present work, two experimental procedures based on spatially resolved NIR imaging are presented; their capabilities are demonstrated by observing water vapor (H 2 O v ) flow subjected to entrance effects, to tube to particle aspect ratio, and to nonisothermal conditions. The first technique, which involves the use of NIR broadband light, interference optical filters centered on absorbing and nonabsorbing wavelengths of H 2 O v , a Vidicon NIR camera, and single back-projection of collected images, is applied to 2D imaging of gas−solid fluidized bed reactor with a low aspect ratio of tube to particle diameters (D t /d p ).…”

Imaging of Chemical Processes via Electrical, Optical, and Ultrasonic Tomography

“…Electrical and optical methods provide tomographic images in excess of several thousand frames per second [3][4] and can monitor dynamic processes. This technology provides unique data about the structure of multiphase materials over a wide range of length scales.Optical tomography has been used in research engines to monitor distribution of hydrocarbons at the flame front during internal combustion cycles [3]. Optical fibers and collimation lenses are used to launch infrared light along 32 paths (at 4 separate angles) through the wall of a combustion chamber.…”

“…This data is used to reconstruct cross-sectional or full volume images of the distribution or concentration of the component phases in side the process vessel. Electrical and optical methods provide tomographic images in excess of several thousand frames per second [3][4] and can monitor dynamic processes. This technology provides unique data about the structure of multiphase materials over a wide range of length scales.…”

“…Optical tomography has been used in research engines to monitor distribution of hydrocarbons at the flame front during internal combustion cycles [3]. Optical fibers and collimation lenses are used to launch infrared light along 32 paths (at 4 separate angles) through the wall of a combustion chamber.…”