Modelling Of Gas Temperature Using Nitric Oxide As A Tracer

Author : Mohd Kamal Muhajir Kamarudin
Supervisor : Dr. Zeyad Alwahabi

Aim and Objectives

• To model the internal states for nitric oxide (NO) for different temperature range
• To predict the best strategy for temperature measurements in reactive flow using NO as a tracer gas

Background theory

• A suitable temperature measurement technique in reactive flow is using planar laser-induced fluorescence (LIF) method
• In LIF method, laser sheet is beamed across the flow causing molecules at the corresponding quantum number to the laser wavelength, to the excited
• Excited molecules will emit fluorescence when returning back to ground state from the excited state
• NO molecule is chosen to be excited (tracer) in the reactive flow as NO have excellent molecular thermometry in the internal states
• The formula for temperature measurement using LIF method is

Modelling Methodology

• Temperature calculation formula required a pair of fluorescence intensity values in order to calculate the temperature hence the developed model should be able to predict the suitable pairing quantum number to obtain two fluorescence intensity values.
• The fluorescence intensity is directly related to the molecular population at the excited quantum number.
• The molecular population can be expressed in relative molecular population and fractional molecular population, shown respectively below

and

• The equations showed that the fractional molecular population is dependent on the quantum number, J and temperature, T
• The theoretical molecular population is calculated for every quantum number and every temperature, and the data is tabulated
• Molecular population relationship with quantum number and temperature are studied by plotting the tabulated data for molecular population versus quantum number at constant temperature and molecular population versus temperature at constant quantum number
• The study showed that fractional molecular population is more suitable representation for the molecule internal states
• Molecular population data showed quadratic-like relationship with quantum number for a given temperature
• Molecular population data have either constant or changing relationship with temperature for a given quantum number
• Sensitivity of molecule at certain quantum number to a certain temperature range is determine using the molecular population relation with temperature at the quantum number
• The suitable pairing of quantum number is concluded to be between quantum number that is least sensitive (constant relation) and the most sensitive (largest change) for any given temperature range
• The quantum number that is least sensitive with temperature is determine by setting the differentiating the fractional molecular population equation with temperature, setting it to 0 and solving it to find the J at average temperature in the range
• The most sensitive quantum number is determine by looking up the quantum number that have the most absolute changes in the molecular population in the given temperature range
• The laser sheet in LIF method will be set so that the laser wavelength will correspond to the two quantum numbers

Programming Development

• The NO internal state model is used to develop computer programming using Microsoft Excel and Borland C
• The computer programs follow the modelling methodology steps to produce the suitable quantum number pairing for temperature measurement in a given temperature range
• The sensitivity test for the programs showed;
  1. Both program give exact results of quantum number pairing
  2. The pairing produced sufficient fluorescence intensity (more that 50% of maximum theoretical fluorescence intensity)
  3. The accuracy of the quantum number pairing is low for large temperature range

Further Work

• The quantum number pairing result should be tested experimentally to determine the accuracy of the computer program
• The effect of seeded NO in reactive flow should be taken into consideration in order to find the suitable NO concentration that should be added to the flow
• The model can be tested using different types of molecules