15 research outputs found
CSTNet: A Dual-Branch Convolutional Network for Imaging of Reactive Flows using Chemical Species Tomography
Chemical Species Tomography (CST) has been widely used for in situ imaging of
critical parameters, e.g. species concentration and temperature, in reactive
flows. However, even with state-of-the-art computational algorithms the method
is limited due to the inherently ill-posed and rank-deficient tomographic data
inversion, and by high computational cost. These issues hinder its application
for real-time flow diagnosis. To address them, we present here a novel
CST-based convolutional neural Network (CSTNet) for high-fidelity, rapid, and
simultaneous imaging of species concentration and temperature. CSTNet
introduces a shared feature extractor that incorporates the CST measurement and
sensor layout into the learning network. In addition, a dual-branch
architecture is proposed for image reconstruction with crosstalk decoders that
automatically learn the naturally correlated distributions of species
concentration and temperature. The proposed CSTNet is validated both with
simulated datasets, and with measured data from real flames in experiments
using an industry-oriented sensor. Superior performance is found relative to
previous approaches, in terms of robustness to measurement noise and
millisecond-level computing time. This is the first time, to the best of our
knowledge, that a deep learning-based algorithm for CST has been experimentally
validated for simultaneous imaging of multiple critical parameters in reactive
flows using a low-complexity optical sensor with severely limited number of
laser beams.Comment: Submitted to IEEE Transactions on Neural Networks and Learning
System
Relative Entropy Regularised TDLAS Tomography for Robust Temperature Imaging
Tunable Diode Laser Absorption Spectroscopy (TDLAS) tomography has been
widely used for in situ combustion diagnostics, yielding images of both species
concentration and temperature. The temperature image is generally obtained from
the reconstructed absorbance distributions for two spectral transitions, i.e.
two-line thermometry. However, the inherently ill-posed nature of tomographic
data inversion leads to noise in each of the reconstructed absorbance
distributions. These noise effects propagate into the absorbance ratio and
generate artefacts in the retrieved temperature image. To address this problem,
we have developed a novel algorithm, which we call Relative Entropy Tomographic
RecOnstruction (RETRO), for TDLAS tomography. A relative entropy regularisation
is introduced for high-fidelity temperature image retrieval from jointly
reconstructed two-line absorbance distributions. We have carried out numerical
simulations and proof-of-concept experiments to validate the proposed
algorithm. Compared with the well-established Simultaneous Algebraic
Reconstruction Technique (SART), the RETRO algorithm significantly improves the
quality of the tomographic temperature images, exhibiting excellent robustness
against TDLAS tomographic measurement noise. RETRO offers great potential for
industrial field applications of TDLAS tomography, where it is common for
measurements to be performed in very harsh environments.Comment: Preprint submitted to IEEE Transactions on Instrumentation and
Measuremen
Chemical species tomographic imaging of the vapour fuel distribution in a compression-ignition engine
This article reports the first application of chemical species tomography to visualise the in-cylinder fuel vapour concentration distribution during the mixing process in a compression-ignition engine. The engine was operated in motored conditions using nitrogen aspiration and fired conditions using a gasoline-like blend of 50% iso-dodecane and 50% n-dodecane. The tomography system comprises 31 laser beams arranged in a co-planar grid located below the injector. A novel, robust data referencing scheme was employed to condition the acquired data for image reconstruction using the iterative Landweber algorithm. Tomographic images were acquired during the compression stroke at a rate of 13 frames per crank angle degree within the same engine cycle at 1200 r min−1. The temperature-dependent fuel evaporation rate and mixing evolution were observed at different injection timings and intake pressure and temperature conditions. An initial cross-validation of the tomographic images was performed with planar laser-induced fluorescence images, showing good agreement in feature localisation and identification. This is the first time chemical species tomography using near-infrared spectroscopic absorption has been validated under engine conditions, and the first application of chemical species tomography to a compression-ignition engine