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Modeling of Spark to Ignition Transition in Gas Mixtures

Akram, Muhammad (1996)
Abstract (Swedish)
Popular Abstract in Swedish

Den här avhandlingen behandlar modeller för studier av gnist-urladdningar i kemiskt icke-reagerande gaser. Modellerna är härledda från grundläggande principer inom ramen för kontinuums mekanik. De processer som sker under övergången från en gnista till en flamma kan delas upp i fysikaliska och kemiska processer. Denna studie är inriktad på de fysikaliska processerna. Plasmat i gnistan betraktas som ett material bestående av en enstaka substans. En och två-demensionella modeller har utvecklats. Transformeringen av elektrisk energi till termisk energi hos gasen och dess redistribution i tid och rum, tillsammans med utvecklingen av plasma- kanalen har studerats i tidsområdet mellan 10 nanosekunder... (More)
Popular Abstract in Swedish

Den här avhandlingen behandlar modeller för studier av gnist-urladdningar i kemiskt icke-reagerande gaser. Modellerna är härledda från grundläggande principer inom ramen för kontinuums mekanik. De processer som sker under övergången från en gnista till en flamma kan delas upp i fysikaliska och kemiska processer. Denna studie är inriktad på de fysikaliska processerna. Plasmat i gnistan betraktas som ett material bestående av en enstaka substans. En och två-demensionella modeller har utvecklats. Transformeringen av elektrisk energi till termisk energi hos gasen och dess redistribution i tid och rum, tillsammans med utvecklingen av plasma- kanalen har studerats i tidsområdet mellan 10 nanosekunder och 40 mikro- sekunder. I fallet med ultrasnabba gnistor, inkluderas utbredningen av shockvågen, samt reflektion från en vägg. Influensen av elektrodernas form, samt deras inbördes avstånd, har visat sig vara en dominerande faktor på strukturen hos gasflödet. Det har observerats att gasflödet som har uppkommit under det tidiga skedet, i stort sätt kvarstår under senare skeden och kraftigt påverkar formen och utvecklinen av den varma kanalen. Elektrodernas geometri och konfiguration är ansvariga för utvecklingen av gasflödet. Styrkan hos de virvlar som bildats i gasflödet påverkas av effektinladdningen i elektrodgapet och den plats där de bildas är bestämd av elektrodernas form och konfiguration. I fallet med ultra- snabba gnistor domineras värmeöverföringen efter 2 mikrosekunder av konvektion och diffusion. Den kraftiga gasomblandning som uppkommer pga hydrodynamiska effekter, samt elektrodernas geometri, tyder på att den magnetiska pinch-effekten kan vara försumbar. Denna modell kan producera realistiska startvillkor för studier av antändningsprocesser i brännbara gaser, till exempel i förbränningmotorer. Slutligen presenteras en modell för gaser med multipla komponenter. En kemisk reaktionsmekanism för dissociation och jonisation har introducerats. De preliminära resultaten tyder på att dissociations och jonisationsprocesser, och även bildningen av NO, kan studeras vid ett tidigt skede av en urladdningsprocess. Denna modell kan ytterligare utveklas för studier av flaminitiering och utbredning i en bränsle-luft blandning genom att introducera en lämplig kemiskt reaktionsmekanism. (Less)
Abstract
This thesis pertains to the models for studying sparking in chemically inert gases. The models are derived from the basic principles and framework in continuum mechanics. The processes taking place in a spark to flame transition can be segregated into physical and chemical processes. This study is focused on physical processes. The plasma is regarded as a single-substance material. One and two-dimensional models are developed. The transfer of electrical energy into thermal energy of the gas and its re-distribution in space and time along with the evolution of a plasma kernel is studied in the time domain ranging from 10 nanoseconds to 40 microseconds. In the case of the ultra fast sparks, the propagation of the shock and its reflection... (More)
This thesis pertains to the models for studying sparking in chemically inert gases. The models are derived from the basic principles and framework in continuum mechanics. The processes taking place in a spark to flame transition can be segregated into physical and chemical processes. This study is focused on physical processes. The plasma is regarded as a single-substance material. One and two-dimensional models are developed. The transfer of electrical energy into thermal energy of the gas and its re-distribution in space and time along with the evolution of a plasma kernel is studied in the time domain ranging from 10 nanoseconds to 40 microseconds. In the case of the ultra fast sparks, the propagation of the shock and its reflection from a rigid wall is presented. The influence of electrode shape and the gap size on the flow structure development is found to be a dominating factor. It is observed that the flow structure that has developed in the early stage, more or less prevails at later stages and strongly influences the shape and evolution of the hot kernel. The electrode geometry and the electrode configuration are responsible for development of the flow structure. The strength of the vortices generated in the flow field is influenced by the power input to the gap and their location of emergence is dictated by the electrode shape and configuration. The heat transfer after 2 microseconds in the case of ultra fast sparks is dominated by convection and diffusion. The strong mixing produced by hydrodynamic effects and the electrode geometry give the indication that the magnetic pinch effect might be negligible. This model can produce a realistic initial condition for the study of ignition processes in combustible mixtures, for example, in internal combustion engines. Finally, a model for a multicomponent gas mixture is presented. The chemical kinetics mechanism for dissociation and ionization is introduced. The preliminary results indicate that dissociation and ionization processes as well as formation of NO can be studied at an early stage of the discharge process. This model can further be extended for the study of flame initiation and propagation in an air-fuel mixture by introducing the proper chemical kinetics. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof. Peters, Norbert
publishing date
type
Thesis
publication status
published
subject
keywords
Spark ignition, Spark discharge, Fluid dynamics, Physics, Plasma dynamics., Fysik, Fysicumarkivet A:1996:Akram
pages
120 pages
defense location
Sal B, Fysiska Institutionen
defense date
1996-10-10 10:15
external identifiers
  • other:ISRN: LUTFD2/TFCP--24--SE
ISSN
1102-8718
ISBN
91-628-2204-7
language
English
LU publication?
no
id
fd82c919-74f4-4b36-9639-a66bdf9696cc (old id 28710)
date added to LUP
2007-06-13 09:47:01
date last changed
2016-09-19 08:45:00
@phdthesis{fd82c919-74f4-4b36-9639-a66bdf9696cc,
  abstract     = {This thesis pertains to the models for studying sparking in chemically inert gases. The models are derived from the basic principles and framework in continuum mechanics. The processes taking place in a spark to flame transition can be segregated into physical and chemical processes. This study is focused on physical processes. The plasma is regarded as a single-substance material. One and two-dimensional models are developed. The transfer of electrical energy into thermal energy of the gas and its re-distribution in space and time along with the evolution of a plasma kernel is studied in the time domain ranging from 10 nanoseconds to 40 microseconds. In the case of the ultra fast sparks, the propagation of the shock and its reflection from a rigid wall is presented. The influence of electrode shape and the gap size on the flow structure development is found to be a dominating factor. It is observed that the flow structure that has developed in the early stage, more or less prevails at later stages and strongly influences the shape and evolution of the hot kernel. The electrode geometry and the electrode configuration are responsible for development of the flow structure. The strength of the vortices generated in the flow field is influenced by the power input to the gap and their location of emergence is dictated by the electrode shape and configuration. The heat transfer after 2 microseconds in the case of ultra fast sparks is dominated by convection and diffusion. The strong mixing produced by hydrodynamic effects and the electrode geometry give the indication that the magnetic pinch effect might be negligible. This model can produce a realistic initial condition for the study of ignition processes in combustible mixtures, for example, in internal combustion engines. Finally, a model for a multicomponent gas mixture is presented. The chemical kinetics mechanism for dissociation and ionization is introduced. The preliminary results indicate that dissociation and ionization processes as well as formation of NO can be studied at an early stage of the discharge process. This model can further be extended for the study of flame initiation and propagation in an air-fuel mixture by introducing the proper chemical kinetics.},
  author       = {Akram, Muhammad},
  isbn         = {91-628-2204-7},
  issn         = {1102-8718},
  keyword      = {Spark ignition,Spark discharge,Fluid dynamics,Physics,Plasma dynamics.,Fysik,Fysicumarkivet A:1996:Akram},
  language     = {eng},
  pages        = {120},
  title        = {Modeling of Spark to Ignition Transition in Gas Mixtures},
  year         = {1996},
}