Stuart C. Murray

Toward in-cylinder absorption tomography in a production engine

Design requirements for an 8000 frame/s dual-wavelength ratiometric chemical species tomography system, intended for hydrocarbon vapor imaging in one cylinder of a standard automobile engine, are examined. The design process is guided by spectroscopic measurements on iso-octane and by comprehensive results from laboratory phantoms and research engines, including results on temporal resolution performance. Novel image reconstruction techniques, necessary for this application, are presented. Recent progress toward implementation, including details of the optical access arrangement employed and signal-to-noise issues, is described. We present first cross-cylinder IR absorption measurements from a reduced channel-count (nontomographic) system and discuss the prospects for imaging.

Absorption measurement of methane gas with a broadband light source and interferometric signal processing

The relationship between methane concentration and second-harmonic output of a particular optical methane-detection system is derived. The system uses a broadband source and a comb filter with its transmission peaks matched to the R-branch absorption lines of methane. An optimal modulation index is obtained, and a noise-limited detection resolution of 0.02% lower explosive level (3-s time constant) is estimated.

Source-noise limitation of fiber-optic methane sensors.

The effect of source (LED) noise on the sensitivity of fiber-optic methane sensors is discussed. Once the source is dominant, the system sensitivity cannot be improved by increasing the source power further.

Performance limitation of a D-fiber evanescent wave methane sensor due to interference effects

We model interference effects in a D-fibre evanescent wave methane sensor and predict its influence on the performance of the system. System sensitivity in terms of minimum detectable methane concentration is expressed as a function of birefringence and spectral transmission characteristics of the D-fibre, polarisation dependent loss occurring after the sensing D-fibre, and polarisation and coherence characteristics of the light source. The sensitivity is calculated for various system arrangements and is found to agree with experimental results.

Multimode approach to optical fiber components and sensors

The evanescent field coupling from a single-mode optical fiber, side polished close to the core, to a high index (> core index), multimode, planar waveguide overlay has been investigated as a means of realizing in-line components such as modulators, wavelength filters, and sensors without interruption of the fiber. Such structures offer considerable advantages in terms of fiber-to-device interfacing and ruggedization over other component technologies such as integrated, bulk, or micro optics. The results reported here confirm the technical feasibility of manufacturing rugged, low loss, all solid state devices of this nature, and the measured or projected performances are realistic in terms of application requirements.

Parameter optimization in a methane detection system using a broadband source and interferometric signal processing

A D-fiber evanescent field methane sensor has been reported by Culshaw et al., where a sinusoidally modulated Fabry-Perot interferometer was used for signal processing. To optimize the sensitivity, it is essential to establish a relation between output signal, methane concentration, and certain other key parameters. Previous work with open-path cells, which use a sawtooth driven Fabry-Perot interferometer, shows a noise-limited detection level of +/- 0.003% methane (1s time constant). However, no analytic expression has been reported to relate the key parameters in the system. In this paper, we report such a relation and calculate the optimal values of some key parameters.

Application of Chemical Species Tomography in a Standard Production Internal Combustion Engine

Chemcial Species Tomography (CST) can be used to provide information on the spatial distribution of a target species by reconstruction from multiple independent optical absorption measurements taken in the measurement space. In this paper, we describe how CST can be used to capture the spatial and temporal distribution of the fuel-vapour mixture within an internal combustion engine, thereby providing invaluable data to engine designers in their quest for reduced emissions and improved fuel economy. We further report on the first application of CST to a standard, multi-cylinder production engine, which involved the design and fabrication of a custom OPtical Access Layer (OPAL), which provided 27 independent, collimated optical channels in one cylinder of a 4 cylinder, 2.0 litre gasoline engine

Optical sensors for smart structures applications: A small company experience

AOS Technology is a UK-based SME which develops advanced optical solutions to challenging measurement and communication problems. Operating across the development spectrum from concept to consumer, the Company manufactures a range of products including a significant portfolio of complete and sub-systems for its clients. Active in the area of smart structures since its inception in 1996. AOS has recently released its GRATIS family of multi-channel, Bragg grating interrogation systems, capable of low drift, high resolution and high accuracy measurements and fast sensor update rates. AOS has also announced a commercial partnership with the FBG manufacturer, AOS GmbH, which will enable both companies to provide turnkey transducer and interrogation system packages.