Malcolm Lawes - Academia.edu (original) (raw)

Papers by Malcolm Lawes

Combustion and Flame, 2015

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2000

ABSTRACT Some overall considerations for the optimization of the energy chain for the spark ignit... more ABSTRACT Some overall considerations for the optimization of the energy chain for the spark ignition engine are briefly discussed and figures given for the relative inhaled energies with different fuels. There follows a description of the nature of turbulent flame propagation in engines, showing the computed characteristics of the burning rate for stoichiometric and lean mixtures at different engine speeds. These reveal the factors influencing partial quenching and misfire. Flame instabilities are shown theoretically to become more important with increasing pressure. The associated flame wrinkling and cellularity increase the burning rate of both laminar and turbulent gaseous flames. Fundamental aspects of the present trend towards the direct injection of gasoline are discussed and the unique instabilities in aerosol combustion are shown to increase the burning velocity above that of the corresponding gaseous mixture. The degree to which evaporative cooling of droplets can enhance the volumetric efficiency is discussed. The onset of autoignition in an engine is calculated with recent shock tube data, which are also used to show that evaporative cooling can increase the knock resistance by about four octane numbers.

Combustion Science and Technology, 2012

ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependen... more ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependent upon the nature of the three dimensional (3-D) turbulence adjacent to the ignition source. The turbulence scales vary in 3-D from shot to shot, resulting in successive flame kernels developing differently and thereby causing cyclic variations in, for example, spark ignition engines. It is necessary to quantify the scales affecting the flame at any instant for the accurate measurement of burn rate of such flame kernels, which requires visualization of the flame surface in 3-D. The experiments reported here employ a multiple sheet mie-scattered light technique to successfully characterize a non-stabilized expanding turbulent flame kernel in 3-D. A novel algorithm was developed to construct the flame surface in 3-D which enabled accurate calculation of parameters such as flame surface density, reaction progress variables and turbulent flame thickness.

Combustion and Flame, 2000

Spherically expanding flames propagating at constant pressure are employed to determine the unstr... more Spherically expanding flames propagating at constant pressure are employed to determine the unstretched laminar burning velocity and the effect of flame stretch as quantified by the associated Markstein lengths. Methane–air mixtures at initial temperatures between 300 ...

Combustion and Flame, 2006

In an earlier mathematical model of laminar pulverized coal-air combustion, supported by added CH... more In an earlier mathematical model of laminar pulverized coal-air combustion, supported by added CH 4 , it was assumed that the volatiles from the coal consisted solely of CH 4 and HCN. A revised model is introduced with speciated devolatilization rate constants for tar, CH 4 , CO, CO 2 , H 2 O, H 2 , and HCN. It is assumed that these rate constants can also be applied to the devolatilization of the tar. In addition, it is assumed that the soot is predominantly carbon and is oxidized by the attack of O, H, OH, and O 2 , in the same way as the coal char. Because the devolatilization rate is strongly dependent on particle temperature, the latter has to be determined accurately from the momentum and energy equations of the particle. The model is one-dimensional, with axial radiative transfer. The introduction of soot formation and speciation of the volatiles results in much improved accuracy in the prediction of species and temperature profiles in subatmospheric combustion on a flat flame matrix burner. It is possible to derive an overall global devolatilization rate constant that agrees reasonably with the measurements. These computations suggest that the effective area of the assumed spherical coal char particles is four times greater than that of the assumed sphere. Modeling of atmospheric pressure flames suggests that in this case, the value of 4 should be reduced, probably because, as pressure increases, the diffusion flux of reactant is reduced. Subatmospheric pressure laminar burning velocities are predicted with satisfactory accuracy over the full range of overall equivalence ratios. Previous measurements of laminar burning velocity at atmospheric pressure are reviewed. However, the various means of supporting a stable coal flame and the associated uncertain geometries make it impossible to apply the present model to the different conditions. It is suggested that burning velocities measured on a flat flame burner, with a controlled amount of methane to support the combustion of a pulverized coal/air mixture, would provide a good test of the reactivities of different coals.

Iso-octane aerosols in air have been ignited with a focused Nd:YAG laser at pressures and tempera... more Iso-octane aerosols in air have been ignited with a focused Nd:YAG laser at pressures and temperatures of 100 kPa and 270 K and imaged using schlieren photography. The aerosol was generated using the Wilson cloud chamber technique. The droplet diameter, gas phase equivalence ratio and droplet number density were determined. The input laser energy and overall equivalence ratio were varied. For 270 mJ pulse energies initial breakdown occurred at a number of sites along the laser beam axis. From measurements of the shock wave velocity it was found that energy was not deposited into the sites evenly. At pulse energies of 32 mJ a single ignition site was observed. Overall fuel lean flames were observed to locally extinguish, however both stoichiometric and fuel rich flames were ignited. The minimum ignition energy was found to depend on the likelihood of a droplet existing at the focus of the laser beam.

Combustion and Flame, 2015

International Journal of Multiphase Flow, 2015

MTZ - Motortechnische Zeitschrift, 2000

Atomization and Sprays, 2006

ABSTRACT This study investigates the influence of the ambient turbulence on a pressure-atomized d... more ABSTRACT This study investigates the influence of the ambient turbulence on a pressure-atomized diesel-like spray in the well-characterized and controlled turbulence flow field of a fan-stirred experimental vessel. Injections were performed into nitrogen at 15 bar and 400 K under four turbulent conditions, with RMS velocities ranging from 0.5 up to 5.5 m/s. Mie scatter laser sheet and Schlieren techniques were applied to visualize the liquid and the vapor phase of the spray. With increasing turbulence, there was increasing formation of droplet clusters and ligaments, which resulted in a reduced detection of droplet vapor along the whole penetration length of the spray. From considerations of the Stokes numbers fir the droplet-turbulence interaction, it is concluded that the microlength scales of the ambient turbulence were the probable source of this droplet clustering.

Proceedings of the Combustion Institute, 2005

A new technique is reported for measuring burning velocities at high pressures in the final stage... more A new technique is reported for measuring burning velocities at high pressures in the final stages of two inwardly propagating flame kernels in an explosion bomb. The flames were initiated at diametrically opposite spark electrodes, close to the wall, in quiescent mixtures. Measurements of pressure and flame kernel propagation speeds by high-speed photography showed the burning velocities to be elevated above the corresponding laminar burning velocities as a result of the developing flame instabilities. The enhancement increased with increase in pressure and decreased with increase in Markstein number. When the Markstein number was negative, instabilities could be appreciable, as could the enhancement. For the iso-octane-air mixtures investigated, where the mixtures had well-characterised Markstein numbers or critical Peclet numbers at the relevant pressures and temperatures, it was possible to explain the enhancement quantitatively by the spherical explosion flame instability theory of Bechtold and Matalon, provided the critical Peclet number was that observed experimentally, and allowance was made for the changing pressure. With this theoretical procedure, it was possible to derive values of laminar burning velocity from the measured values of burning velocity over a wide range of equivalence ratios, pressures, and temperatures. The values became less reliable at the higher temperatures and pressures as the data on Markstein and critical Peclet numbers became less certain. It was found that with iso-octane as the fuel the laminar burning velocity decreased during isentropic compression.

Proceedings of the Combustion Institute, 2005

Hydrogen offers an attractive alternative to conventional fuels for use in spark ignition engines... more Hydrogen offers an attractive alternative to conventional fuels for use in spark ignition engines. It can 11 be burned over a very wide range of equivalence ratios and with considerable exhaust gas recirculation. 12 These help to minimise pumping losses through throttleless operation and oxides of nitrogen (NO x ) pro-13 duction through reduced temperature. Full understanding of hydrogen-fuelled engine operation requires 14 data on the laminar burning rate of hydrogen-air residuals under a wide range of conditions. However, 15 such data are sparse. The present work addresses this need for experimental data. Spherically expanding 16 H 2 -air flames were measured at a range of temperatures, pressures, and equivalence ratios and with vary-17 ing concentrations of residuals of combustion. Unstretched burning velocities, u l , and Markstein lengths, 18 L b , were determined from stable flames. At the higher pressures, hydrodynamic and diffusional-thermal 19 instabilities caused the flames to be cellular from inception and prohibited the derivation of values of u l 20 and L b . The effect of pressure on the burning rate was demonstrated to have opposing trends when com-21 paring stoichiometric and lean mixtures. The present measurements were compared with those available in 22 the literature, and discrepancies were attributed to neglect, in some works, the effects of stretch and insta-23 bilities. From the present measurements, the effects of pressure, temperature, and residual gas concentra-24 tion on burning velocity are quantified for use in a first step towards a general correlation. 25

Proceedings of the Combustion Institute, 2000

ABSTRACT A combined experimental and large eddy simulation (LES) study of flame kernel growth in ... more ABSTRACT A combined experimental and large eddy simulation (LES) study of flame kernel growth in isotropic, homogenous turbulence has been carried out. LES calculations using the combustion methodology of Weller were compared with experimental measurements from a fan-stirred bomb for iso-octane and propane air mixtures at various turbulence intensities and pressures. For the purpose of model validation, the mean radius evolution was compared with experimental measurements, obtained from Schlieren photographs. Initially, a small laminar flame kernel was produced that burned at an increasing rate as it grew and was wrinkled by the turbulent flow field. It was also observed that at atmospheric pressure propaneair flames demonstrated less variability between experimental realizations than did iso-octane air flames High-variability combustion events were associated with the convection of the flame kernel away from the spark plug during ignition. Good agreement between experiments and calculations was obtaiend for the full range of conditions investigated in this study, and the LES results were able to reproduce some of the observed variability between experimental realizations as a result of turbulent interactions with the small kernel during ignition. These results provided further validation of the combustion model, though the simple ignitiion treatment did not reproduce the full range of ignition variability due to strain sensitivity.

Proceedings of the Combustion Institute, 2011

A new technique is described for measuring turbulent burning velocities at higher pressures than ... more A new technique is described for measuring turbulent burning velocities at higher pressures than is usual in fan-stirred bomb explosions. Measurements are made during the final stage of inward propagation of two flames, initiated at diametrically opposite spark electrodes. Pressure records and schlieren high speed photography define the rate of burning and the smoothed area of the flame front. This implosion technique was validated at the lower pressures by the good agreement between the values of turbulent burning velocity it yielded and those obtained with the commonly employed central ignition. The new technique has the advantage of yielding values of turbulent burning velocity at pressures much closer to the safe working pressure of the explosion bomb. Subsequently, mixtures of ethanol–air and propane–air were investigated in the pressure range of 0.7–3.0MPa with a corresponding temperature range of 377–468K. For explosions with central ignition the maximum pressure was 1.2MPa.Findings over a wide range of conditions are generalised. Plots are presented of turbulent burning velocity normalised by the effective rms turbulent velocity, ut/u′k, against the Karlovitz stretch factor, K, for different strain rate Markstein numbers, a decrease in which, increases ut/u′k. At low values of K, ut/u′k is enhanced by flame instabilities, while at high values of K, it is gradually reduced due to increasing localised extinctions.

Proceedings of the Combustion Institute, 2007

Experimental and theoretical studies are reported of turbulent flame quenching, with premixed fla... more Experimental and theoretical studies are reported of turbulent flame quenching, with premixed flames of methane–air, iso-octane–air and hydrogen–air. Mixtures were exploded in a fan-stirred explosion bomb in which the rms turbulent velocity was varied by changes in fan speed. Influences of Markstein number, pressure up to 1.5MPa, and Karlovitz stretch factor, K, were studied. It was found that the ratio

Symposium (International) on Combustion, 1992

Accurate temperature measurement with the CARS technique is difficult when appreciable temperatur... more Accurate temperature measurement with the CARS technique is difficult when appreciable temperature gradients occur within the measurement volume. The problem is aggravated by the non-linearity of the spectral intensity with temperature. The paper reports on the results of steps taken ...

PLoS ONE, 2008

T-killer cells eliminate infected and cancerous cells with precision by positioning their centros... more T-killer cells eliminate infected and cancerous cells with precision by positioning their centrosome near the interface (immunological synapse) with the target cell. The mechanism of centrosome positioning has remained controversial, in particular the role of microtubule dynamics in it. We re-examined the issue in the experimental model of Jurkat cells presented with a T cell receptor-binding artificial substrate, which permits controlled stimulation and reproducible measurements. Neither 1-mM taxol nor 100-nM nocodazole inhibited the centrosome positioning at the``synapse'' with the biomimetic substrate. At the same time, in micromolar taxol but not in nanomolar nocodazole the centrosome adopted a distinct peripheral rather than the normally central position within the synapse. This effect was reproduced in a computational energy-minimization model that assumed no microtubule dynamics, but only a taxol-induced increase in the length of the microtubules. Together, the experimental and computational results indicate that microtubule dynamics are not essential for the centrosome positioning, but that the fit of the microtubule array in the deformed body of the conjugated T cell is a major factor. The possibility of modulating the T-cell centrosome position with well-studied drugs and of predicting their effects in silico appears attractive for designing anti-cancer and antiviral therapies. Citation: Baratt A, Arkhipov SN, Maly IV (2008) An Experimental and Computational Study of Effects of Microtubule Stabilization on T-Cell Polarity. PLoS ONE 3 (12): e3861.

Flow, Turbulence and Combustion, 2011

ABSTRACT

Combustion Science and Technology, 2012

ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependen... more ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependent upon the nature of the three dimensional (3-D) turbulence adjacent to the ignition source. The turbulence scales vary in 3-D from shot to shot, resulting in successive flame kernels developing differently and thereby causing cyclic variations in, for example, spark ignition engines. It is necessary to quantify the scales affecting the flame at any instant for the accurate measurement of burn rate of such flame kernels, which requires visualization of the flame surface in 3-D. The experiments reported here employ a multiple sheet mie-scattered light technique to successfully characterize a non-stabilized expanding turbulent flame kernel in 3-D. A novel algorithm was developed to construct the flame surface in 3-D which enabled accurate calculation of parameters such as flame surface density, reaction progress variables and turbulent flame thickness.

Combustion and Flame, 2015

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2000

ABSTRACT Some overall considerations for the optimization of the energy chain for the spark ignit... more ABSTRACT Some overall considerations for the optimization of the energy chain for the spark ignition engine are briefly discussed and figures given for the relative inhaled energies with different fuels. There follows a description of the nature of turbulent flame propagation in engines, showing the computed characteristics of the burning rate for stoichiometric and lean mixtures at different engine speeds. These reveal the factors influencing partial quenching and misfire. Flame instabilities are shown theoretically to become more important with increasing pressure. The associated flame wrinkling and cellularity increase the burning rate of both laminar and turbulent gaseous flames. Fundamental aspects of the present trend towards the direct injection of gasoline are discussed and the unique instabilities in aerosol combustion are shown to increase the burning velocity above that of the corresponding gaseous mixture. The degree to which evaporative cooling of droplets can enhance the volumetric efficiency is discussed. The onset of autoignition in an engine is calculated with recent shock tube data, which are also used to show that evaporative cooling can increase the knock resistance by about four octane numbers.

Combustion Science and Technology, 2012

ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependen... more ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependent upon the nature of the three dimensional (3-D) turbulence adjacent to the ignition source. The turbulence scales vary in 3-D from shot to shot, resulting in successive flame kernels developing differently and thereby causing cyclic variations in, for example, spark ignition engines. It is necessary to quantify the scales affecting the flame at any instant for the accurate measurement of burn rate of such flame kernels, which requires visualization of the flame surface in 3-D. The experiments reported here employ a multiple sheet mie-scattered light technique to successfully characterize a non-stabilized expanding turbulent flame kernel in 3-D. A novel algorithm was developed to construct the flame surface in 3-D which enabled accurate calculation of parameters such as flame surface density, reaction progress variables and turbulent flame thickness.

Combustion and Flame, 2000

Spherically expanding flames propagating at constant pressure are employed to determine the unstr... more Spherically expanding flames propagating at constant pressure are employed to determine the unstretched laminar burning velocity and the effect of flame stretch as quantified by the associated Markstein lengths. Methane–air mixtures at initial temperatures between 300 ...

Combustion and Flame, 2006

In an earlier mathematical model of laminar pulverized coal-air combustion, supported by added CH... more In an earlier mathematical model of laminar pulverized coal-air combustion, supported by added CH 4 , it was assumed that the volatiles from the coal consisted solely of CH 4 and HCN. A revised model is introduced with speciated devolatilization rate constants for tar, CH 4 , CO, CO 2 , H 2 O, H 2 , and HCN. It is assumed that these rate constants can also be applied to the devolatilization of the tar. In addition, it is assumed that the soot is predominantly carbon and is oxidized by the attack of O, H, OH, and O 2 , in the same way as the coal char. Because the devolatilization rate is strongly dependent on particle temperature, the latter has to be determined accurately from the momentum and energy equations of the particle. The model is one-dimensional, with axial radiative transfer. The introduction of soot formation and speciation of the volatiles results in much improved accuracy in the prediction of species and temperature profiles in subatmospheric combustion on a flat flame matrix burner. It is possible to derive an overall global devolatilization rate constant that agrees reasonably with the measurements. These computations suggest that the effective area of the assumed spherical coal char particles is four times greater than that of the assumed sphere. Modeling of atmospheric pressure flames suggests that in this case, the value of 4 should be reduced, probably because, as pressure increases, the diffusion flux of reactant is reduced. Subatmospheric pressure laminar burning velocities are predicted with satisfactory accuracy over the full range of overall equivalence ratios. Previous measurements of laminar burning velocity at atmospheric pressure are reviewed. However, the various means of supporting a stable coal flame and the associated uncertain geometries make it impossible to apply the present model to the different conditions. It is suggested that burning velocities measured on a flat flame burner, with a controlled amount of methane to support the combustion of a pulverized coal/air mixture, would provide a good test of the reactivities of different coals.

Iso-octane aerosols in air have been ignited with a focused Nd:YAG laser at pressures and tempera... more Iso-octane aerosols in air have been ignited with a focused Nd:YAG laser at pressures and temperatures of 100 kPa and 270 K and imaged using schlieren photography. The aerosol was generated using the Wilson cloud chamber technique. The droplet diameter, gas phase equivalence ratio and droplet number density were determined. The input laser energy and overall equivalence ratio were varied. For 270 mJ pulse energies initial breakdown occurred at a number of sites along the laser beam axis. From measurements of the shock wave velocity it was found that energy was not deposited into the sites evenly. At pulse energies of 32 mJ a single ignition site was observed. Overall fuel lean flames were observed to locally extinguish, however both stoichiometric and fuel rich flames were ignited. The minimum ignition energy was found to depend on the likelihood of a droplet existing at the focus of the laser beam.

Combustion and Flame, 2015

International Journal of Multiphase Flow, 2015

MTZ - Motortechnische Zeitschrift, 2000

Atomization and Sprays, 2006

ABSTRACT This study investigates the influence of the ambient turbulence on a pressure-atomized d... more ABSTRACT This study investigates the influence of the ambient turbulence on a pressure-atomized diesel-like spray in the well-characterized and controlled turbulence flow field of a fan-stirred experimental vessel. Injections were performed into nitrogen at 15 bar and 400 K under four turbulent conditions, with RMS velocities ranging from 0.5 up to 5.5 m/s. Mie scatter laser sheet and Schlieren techniques were applied to visualize the liquid and the vapor phase of the spray. With increasing turbulence, there was increasing formation of droplet clusters and ligaments, which resulted in a reduced detection of droplet vapor along the whole penetration length of the spray. From considerations of the Stokes numbers fir the droplet-turbulence interaction, it is concluded that the microlength scales of the ambient turbulence were the probable source of this droplet clustering.

Proceedings of the Combustion Institute, 2005

A new technique is reported for measuring burning velocities at high pressures in the final stage... more A new technique is reported for measuring burning velocities at high pressures in the final stages of two inwardly propagating flame kernels in an explosion bomb. The flames were initiated at diametrically opposite spark electrodes, close to the wall, in quiescent mixtures. Measurements of pressure and flame kernel propagation speeds by high-speed photography showed the burning velocities to be elevated above the corresponding laminar burning velocities as a result of the developing flame instabilities. The enhancement increased with increase in pressure and decreased with increase in Markstein number. When the Markstein number was negative, instabilities could be appreciable, as could the enhancement. For the iso-octane-air mixtures investigated, where the mixtures had well-characterised Markstein numbers or critical Peclet numbers at the relevant pressures and temperatures, it was possible to explain the enhancement quantitatively by the spherical explosion flame instability theory of Bechtold and Matalon, provided the critical Peclet number was that observed experimentally, and allowance was made for the changing pressure. With this theoretical procedure, it was possible to derive values of laminar burning velocity from the measured values of burning velocity over a wide range of equivalence ratios, pressures, and temperatures. The values became less reliable at the higher temperatures and pressures as the data on Markstein and critical Peclet numbers became less certain. It was found that with iso-octane as the fuel the laminar burning velocity decreased during isentropic compression.

Proceedings of the Combustion Institute, 2005

Hydrogen offers an attractive alternative to conventional fuels for use in spark ignition engines... more Hydrogen offers an attractive alternative to conventional fuels for use in spark ignition engines. It can 11 be burned over a very wide range of equivalence ratios and with considerable exhaust gas recirculation. 12 These help to minimise pumping losses through throttleless operation and oxides of nitrogen (NO x ) pro-13 duction through reduced temperature. Full understanding of hydrogen-fuelled engine operation requires 14 data on the laminar burning rate of hydrogen-air residuals under a wide range of conditions. However, 15 such data are sparse. The present work addresses this need for experimental data. Spherically expanding 16 H 2 -air flames were measured at a range of temperatures, pressures, and equivalence ratios and with vary-17 ing concentrations of residuals of combustion. Unstretched burning velocities, u l , and Markstein lengths, 18 L b , were determined from stable flames. At the higher pressures, hydrodynamic and diffusional-thermal 19 instabilities caused the flames to be cellular from inception and prohibited the derivation of values of u l 20 and L b . The effect of pressure on the burning rate was demonstrated to have opposing trends when com-21 paring stoichiometric and lean mixtures. The present measurements were compared with those available in 22 the literature, and discrepancies were attributed to neglect, in some works, the effects of stretch and insta-23 bilities. From the present measurements, the effects of pressure, temperature, and residual gas concentra-24 tion on burning velocity are quantified for use in a first step towards a general correlation. 25

Proceedings of the Combustion Institute, 2000

ABSTRACT A combined experimental and large eddy simulation (LES) study of flame kernel growth in ... more ABSTRACT A combined experimental and large eddy simulation (LES) study of flame kernel growth in isotropic, homogenous turbulence has been carried out. LES calculations using the combustion methodology of Weller were compared with experimental measurements from a fan-stirred bomb for iso-octane and propane air mixtures at various turbulence intensities and pressures. For the purpose of model validation, the mean radius evolution was compared with experimental measurements, obtained from Schlieren photographs. Initially, a small laminar flame kernel was produced that burned at an increasing rate as it grew and was wrinkled by the turbulent flow field. It was also observed that at atmospheric pressure propaneair flames demonstrated less variability between experimental realizations than did iso-octane air flames High-variability combustion events were associated with the convection of the flame kernel away from the spark plug during ignition. Good agreement between experiments and calculations was obtaiend for the full range of conditions investigated in this study, and the LES results were able to reproduce some of the observed variability between experimental realizations as a result of turbulent interactions with the small kernel during ignition. These results provided further validation of the combustion model, though the simple ignitiion treatment did not reproduce the full range of ignition variability due to strain sensitivity.

Proceedings of the Combustion Institute, 2011

A new technique is described for measuring turbulent burning velocities at higher pressures than ... more A new technique is described for measuring turbulent burning velocities at higher pressures than is usual in fan-stirred bomb explosions. Measurements are made during the final stage of inward propagation of two flames, initiated at diametrically opposite spark electrodes. Pressure records and schlieren high speed photography define the rate of burning and the smoothed area of the flame front. This implosion technique was validated at the lower pressures by the good agreement between the values of turbulent burning velocity it yielded and those obtained with the commonly employed central ignition. The new technique has the advantage of yielding values of turbulent burning velocity at pressures much closer to the safe working pressure of the explosion bomb. Subsequently, mixtures of ethanol–air and propane–air were investigated in the pressure range of 0.7–3.0MPa with a corresponding temperature range of 377–468K. For explosions with central ignition the maximum pressure was 1.2MPa.Findings over a wide range of conditions are generalised. Plots are presented of turbulent burning velocity normalised by the effective rms turbulent velocity, ut/u′k, against the Karlovitz stretch factor, K, for different strain rate Markstein numbers, a decrease in which, increases ut/u′k. At low values of K, ut/u′k is enhanced by flame instabilities, while at high values of K, it is gradually reduced due to increasing localised extinctions.

Proceedings of the Combustion Institute, 2007

Experimental and theoretical studies are reported of turbulent flame quenching, with premixed fla... more Experimental and theoretical studies are reported of turbulent flame quenching, with premixed flames of methane–air, iso-octane–air and hydrogen–air. Mixtures were exploded in a fan-stirred explosion bomb in which the rms turbulent velocity was varied by changes in fan speed. Influences of Markstein number, pressure up to 1.5MPa, and Karlovitz stretch factor, K, were studied. It was found that the ratio

Symposium (International) on Combustion, 1992

Accurate temperature measurement with the CARS technique is difficult when appreciable temperatur... more Accurate temperature measurement with the CARS technique is difficult when appreciable temperature gradients occur within the measurement volume. The problem is aggravated by the non-linearity of the spectral intensity with temperature. The paper reports on the results of steps taken ...

PLoS ONE, 2008

T-killer cells eliminate infected and cancerous cells with precision by positioning their centros... more T-killer cells eliminate infected and cancerous cells with precision by positioning their centrosome near the interface (immunological synapse) with the target cell. The mechanism of centrosome positioning has remained controversial, in particular the role of microtubule dynamics in it. We re-examined the issue in the experimental model of Jurkat cells presented with a T cell receptor-binding artificial substrate, which permits controlled stimulation and reproducible measurements. Neither 1-mM taxol nor 100-nM nocodazole inhibited the centrosome positioning at the``synapse'' with the biomimetic substrate. At the same time, in micromolar taxol but not in nanomolar nocodazole the centrosome adopted a distinct peripheral rather than the normally central position within the synapse. This effect was reproduced in a computational energy-minimization model that assumed no microtubule dynamics, but only a taxol-induced increase in the length of the microtubules. Together, the experimental and computational results indicate that microtubule dynamics are not essential for the centrosome positioning, but that the fit of the microtubule array in the deformed body of the conjugated T cell is a major factor. The possibility of modulating the T-cell centrosome position with well-studied drugs and of predicting their effects in silico appears attractive for designing anti-cancer and antiviral therapies. Citation: Baratt A, Arkhipov SN, Maly IV (2008) An Experimental and Computational Study of Effects of Microtubule Stabilization on T-Cell Polarity. PLoS ONE 3 (12): e3861.

Flow, Turbulence and Combustion, 2011

ABSTRACT

Combustion Science and Technology, 2012

ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependen... more ABSTRACT The development of spark ignited flame kernels in a turbulent field is strongly dependent upon the nature of the three dimensional (3-D) turbulence adjacent to the ignition source. The turbulence scales vary in 3-D from shot to shot, resulting in successive flame kernels developing differently and thereby causing cyclic variations in, for example, spark ignition engines. It is necessary to quantify the scales affecting the flame at any instant for the accurate measurement of burn rate of such flame kernels, which requires visualization of the flame surface in 3-D. The experiments reported here employ a multiple sheet mie-scattered light technique to successfully characterize a non-stabilized expanding turbulent flame kernel in 3-D. A novel algorithm was developed to construct the flame surface in 3-D which enabled accurate calculation of parameters such as flame surface density, reaction progress variables and turbulent flame thickness.