921 research outputs found
Flame front propagation velocity measurement and in-cylinder combustion reconstruction using POET
The objective of this thesis is to develop an intelligent diagnostic technique
POET (Passive Optical Emission Tomography) for the investigation of in cylinder
combustion chemiluminescence. As a non-intrusive optical system, the POET system
employs 40 fibre optic cables connected to 40 PMTs (Photo Multiplier Tube) to
monitor the combustion process and flame front propagation in a modified commercial
OHV (Over Head Valve) Pro 206 IC engine.
The POET approach overcomes several limitations of present combustion
research methods using a combination of fibre optic detection probes, photomultipliers
and a tomographic diagnostics. The fibre optic probes are placed on a specially
designed cylinder head gasket for non-invasively inserting cylinder. Each independent
probe can measure the turbulent chemiluminescence of combustion flame front at up to
20 kHz. The resultant intensities can then be gathered tomographically using MART
(Multiplicative Algebraic Reconstruction Technique) software to reconstruct an image
of the complete flame-front. The approach is essentially a lensless imaging technique,
which has the advantage of not requiring a specialized engine construction with
conventional viewing ports to visualize the combustion image. The fibre optic system,
through the use of 40, 2m long thermally isolated fibre optic cables can withstand
combustion temperatures and is immune from electronic noise, typically generated by
the spark plug.
The POET system uses a MART tomographic methodology to reconstruct the turbulent combustion process. The data collected has been reconstructed to produce a
temporal and spatial image of the combustion flame front. The variations of lame
turbulence are monitored by sequences of reconstructed images. Therefore, the POET
diagnostic technique reduces the complications of classic flame front propagation
measurement systems and successfully demonstrates the in-cylinder combustion
process.
In this thesis, a series of calibration exercises have been performed to ensure
that the photomultipliers of the POET system have sufficient temporal and spatial
resolution to quantitatively map the flow velocity turbulence and chemiluminescence
of the flame front. In the results, the flame has been analyzed using UV filters and blue
filters to monitor the modified natural gas fuel engine. The flame front propagation
speed has been evaluated and it is, on average, 12 m/s at 2280 rpm. Sequences of
images have been used to illustrate the combustion explosion process at different rpm
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Novel cardiovascular magnetic resonance phenotyping of the myocardium
INTRODUCTION
Left ventricular (LV) microstructure is unique, composed of a winding helical pattern of myocytes and rotating aggregations of myocytes called sheetlets. Hypertrophic cardiomyopathy (HCM) is a cardiovascular disease characterised by left ventricular hypertrophy (LVH), however the link between LVH and underlying microstructural aberration is poorly understood. In vivo cardiovascular diffusion tensor imaging (cDTI) is a novel cardiovascular MRI (CMR) technique, capable of characterising LV microstructural dynamics non-invasively. In vivo cDTI may therefore improve our understanding microstructural-functional relationships in health and disease.
METHODS AND RESULTS
The monopolar diffusion weighted stimulated echo acquisition mode (DW-STEAM) sequence was evaluated for in vivo cDTI acquisitions at 3Tesla, in healthy volunteers (HV), patients with hypertensive LVH, and HCM patients. Results were contextualised in relation to extensively explored technical limitations. cDTI parameters demonstrated good intra-centre reproducibility in HCM, and good inter-centre reproducibility in HV. In all subjects, cDTI was able to depict the winding helical pattern of myocyte orientation known from histology, and the transmural rate of change in myocyte orientation was dependent on LV size and thickness. In HV, comparison of cDTI parameters between systole and diastole revealed an increase in transmural gradient, combined with a significant re-orientation of sheetlet angle. In contrast, in HCM, myocyte gradient increased between phases, however sheetlet angulation retained a systolic-like orientation in both phases. Combined analysis with hypertensive patients revealed a proportional decrease in sheetlet mobility with increasing LVH.
CONCLUSION
In vivo DW-STEAM cDTI can characterise LV microstructural dynamics non-invasively. The transmural rate of change in myocyte angulation is dependent on LV size and wall thickness, however inter phase changes in myocyte orientation are unaffected by LVH. In contrast, sheetlet dynamics demonstrate increasing dysfunction, in proportion to the degree of LVH. Resolving technical limitations is key to advancing this technique, and improving the understanding of the role of microstructural abnormalities in cardiovascular disease expression.Open Acces
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