Assaad Masri

ABSTRACT Introduced in this paper is a Bayesian model for isolating the resonant frequency from combustion chamber resonance. The model shown in this paper focused on characterising the initial rise in the resonant frequency to investigate the rise of in-cylinder bulk temperature associated with combustion. By resolving the model parameters, it is possible to determine: the start of pre-mixed combustion, the start of diffusion combustion, the initial resonant frequency, the resonant frequency as a function of crank angle, the in-cylinder bulk temperature as a function of crank angle and the trapped mass as a function of crank angle. The Bayesian method allows for individual cycles to be examined without cycle-averaging—allowing inter-cycle variability studies. Results are shown for a turbo-charged, common-rail compression ignition engine run at 2000 rpm and full load.

... 9, CF 3 + CF 2 = CF 3 −CF 2, 13.0, 0, 0.0, 15.4, 0, 214.5, estd. 10, CH 2 F−CF 3 = CH 2 F + CF 3, 17.0, 0, 373.6, 13.6, 0, −0.3, estd. 11, CH 2 F−CF 3 = HF + CHF:CF 2, 13.4, 0, 296.2, 11.2, 0, 180.3, 4. 12, 2CH 2 F = CH 2 F−CH 2 F, 13.5, 0, 0.0, 17.3, 0, 351.4, estd. ...

The kinetics of the high-temperature oxidation of CâFâ by O(³P) have been studied by experiment, using a single-pulse shock tube, and by kinetic modeling. The O atoms were generated by the thermal decomposition of NâO. Three mixtures, each diluted in argon, were studied: 0.6 mol % of CâFâ with 1.5 mol % NâO; 6.2 mol % of CâFâ with 0.6

Abstract This paper introduces a new class of transient turbulent flames as a new benchmark case for studying turbulent combustion. It also brings together the latest high-speed laser imaging experiments with large-eddy simulation (LES)/probability density function (PDF) to advance the calculations of transient processes in the newly introduced test cases. The otherwise steady jet flames are subjected to a pulse of inflow velocity such that the flow experiences sequentially increased local extinction, the formation of upper ...

Received 26 May 2005; accepted 10 November 2005 Abstract. Measurements of mean velocity components, turbulent intensity, and Reynolds shear stress are presented in a turbulent lifted H2/N2 jet flame as well as non-reacting air jet issuing into a vitiated co-flow by laser ...

... Stability characteristics and flowfields of turbulent non-premixed swirling flames Yasir M Al-Abdeli1 and Assaad R Masri School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia E-mail: alabdeli@aeromech.usyd.edu.au ...

This paper reports measured stability limits and PDF calculations of piloted, turbulent flames of compressed natural gas (CNG) partially-premixed with either pure oxygen, or with varying levels of O2/N2. Stability limits are presented for flames of CNG fuel premixed with up to 20% oxygen as well as CNG–O2–N2 fuel where the O2 content is varied from 8 to 22% by volume. Calculations are presented for (i) Sydney flame B [Masri et al. 1988] which uses pure CNG as well as flames B15 to B25 where the CNG is partially-premixed with 15–25% oxygen by volume, respectively and (ii) Sandia methane–air (1:3 by volume) flame E [Barlow et al. 2005] as well as new flames E15 and E25 that are partially-premixed with ‘reconstituted air’ where the O2 content in nitrogen is 15 and 25% by volume, respectively. The calculations solve a transported PDF of composition using a particle-based Monte Carlo method and employ the EMST mixing model as well as detailed chemical kinetics. The addition of oxygen to the fuel increases stability, shortens the flames, broadens the reaction zone, and shifts the stoichiometric mixture fraction towards the inner side of the jet. It is found that for pure CNG flames where the reaction zone is narrow (∼0.1 in mixture fraction space), the PDF calculations fail to reproduce the correct level of local extinction on approach to blow-off. A broadening in the reaction zone up to about 0.25 in mixture fraction space is needed for the PDF/EMST approach to be able to capture these finite-rate chemistry effects. It is also found that for the same level of partial premixing, increasing the O2/N2 ratio increases the maximum levels of CO and NO but shifts the peak to richer mixture fractions. Over the range of oxygenation investigated here, stability limits have shown to improve almost linearly with increasing oxygen levels in the fuel and with increasing the contribution of release rate from the pilot.

... The concept of edge flames being influential in the stabilization process has also received some experimental and numerical support [1111. Phillips, H. 1965. ... Balachandran, R., Ayoola, BO, Kaminski, CF, Dowling, AP and Mastorakos, E. 2005. ...

The mean structure of turbulent bluff-body jets and flames is presented. Measurements of the flow and mixing fields are compared with predictions made using standard turbulence models. It is found that two vortices exist in the recirculation zone; an outer vortex close to ...

Laser diagnostic and flow visualization techniques have previously been applied to several reacting and isothermal swirling jets. Resolved flow features include the presence of vortex breakdown and unsteady behavior. As such, turbulent flames stabilized on the present (laboratory scale) burner bear similitude to those in larger (industrial) swirl combustors. With this in mind, the impact of vortex breakdown and unsteady behavior on flame stability continues to require further study. Such understanding can be gained through applying non-intrusive laser diagnostics to flow conditions covering a broad range of flame stability characteristics. This paper presents the results of one such investigation. Laser Doppler Velocimetry (LDV) measurements are acquired (along the centreline) to ascertain the presence of time periodicity and downstream recirculation. Unsteady behavior is identified through the spectra of axial velocity data whilst negative axial velocities delineate vortex breakdown. This information is augmented with observations of visible flame length and discussed in relation to established flame stability characteristics. Findings indicate that swirl numbers, over which improvements in flame stability occur, coincide with conditions leading to unsteady behavior and shorter flames. Because downstream flow reversal is not resolved at all such conditions, information available indicates flow unsteadiness is a clearer contributing factor, compared to vortex breakdown, on the observed stability characteristics. Shorter flames coupled with improvements in flame stability have significant implications on the design and operation of swirl combustors.

A burner with a hybrid bluff body swirl design, incorporating a central jet surrounded by a swirling annulus, is applied to the investigation of turbulent isothermal swirling jets. Nonswirling flows stabilized on this burner form only one stagnation zone on the face of the bluff body. Such a far upstream recirculation zone is typical of those formed behind solid obstructions