Document Details

Document Type : Thesis 
Document Title :
Laser Spark Ignition: Theoretical Study of the Breakdown Threshold Intensity of Laser Induced H2 Combustion
اشعال شرارة الليزر : دراسة نظرية لعتبة شدة الاستضاءة اللازمة للانهيار في احتراق الهيدروجين المحث بالليزر
 
Document Language : Arabic 
Abstract : This research presents a numerical study for investigating the effect of laser wavelength on threshold intensity required to produce a spark in molecular hydrogen over a wide range of gas pressure. A modified electron cascade model previously developed by Evans and Gamal (1980) is applied to investigate the experimental measurements that carried out by Phuoc (2000) to determine the threshold intensity for spark ignition in molecular hydrogen combustion. A Nd: YAG laser source operating at its fundamental and second harmonics with wavelengths 1064 nm and 532 nm respectively of pulse duration 5.5 ns is used to irradiate the gas. The model depends on the numerical solution of the time dependent Boltzmann equation for the electron energy distribution function (EEDF) and a set of rate equations that describe the change of the formed excited molecules population. The model takes into account set of physical processes that expected to occur in the interaction region, where it considers the inverse Bremsstrahlung process as a main process responsible for the electron energy gain from the laser field. These electrons can accumulate enough energy to ionize the gas through inelastic collisional processes reaching finally to a spark ignition. In this model the main electron energy loss takes place through vibrational excitation. This process is treated in two energy regions. On the low energy region (< 3 eV), the electrons lose their energy through elastic collisional processes, while on the high region (> 3 eV) this process is considered as an inelastic collisional process. In addition electron loss processes such as diffusion of electrons out of the focal volume, electron dissociation are also c considered in this model. The results showed good agreement between the calculated threshold intensities for spark ignition and those experimentally measured by Phuoc (2000). It is noticed from this result that the thresholds corresponding to 532 nm lie above those refer to 1064 nm over the whole pressure range .This indicates the different physical processes responsible for laser spark ignition at the two wavelengths. This result is confirmed by studying the EEDF and its parameters at different values of the gas pressure for the two wavelengths. It is found that at the short wavelength ionization proceeds via multi-photon ionization process, where a fast increase of the electron density can be achieved during the early stages of the laser pulse. At the long wavelength the rate of this process decreases and ionization occurs by collisional process beside the photo ionization one. The increase of the electron density at the short wavelength increases the rate of electron loss through diffusion out of the focal volume. These losses are more pronounced at the low pressure region. At high pressure electrons lose their energy via vibrational excitation of molecules. Dissociation of the molecules is found to have a negligible contribution under the tested experimental conditions. 
Supervisor : yosr eaz alden gamal 
Thesis Type : Master Thesis 
Publishing Year : 1433 AH
2012 AD 
Number Of Pages : 185 
Added Date : Thursday, May 22, 2014 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
جملا منيف الدليحيaldalbahy, jamlaa munifInvestigatorMaster 

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