Time-resolved Temperature Measurements Research Articles

The dynamics of a non-premixed rotating detonation engine from time-resolved temperature measurements

The structure and dynamics of a hydrogen-air rotating detonation engine (RDE) are described based on 100-kHz laser absorption spectroscopy measurements of water temperature at four simultaneous locations within the detonation channel. The analysis focuses on the evolution of the flowfield over a 200 ms period for three separate air mass flow rate cases. Two-dimensional unwrapped visualizations of the temperatures show a flowfield structure containing regions with the detonation front, combustion products, oblique shock, and refilling reactants, qualitatively agreeing with previous simulations and experiments. A major conclusion is that water from the combustion products is measured throughout all space and time in the RDE, including near the injector, implying the presence of performance loss processes such as burning upstream of the detonation wave or the back recirculation of combustion products with fresh fuel–air. By analyzing the elevated temperatures of the reactants during the refill process, one estimation for the mass fraction of combustion products in the reactants is as high as 20–30% on average. This product mass fraction is found to be inversely proportional to the bulk air mass flow rate and decreases as time progresses. This indicates these non-ideal processes are more significant closer to RDE ignition for poorer performing operating conditions. For the largest air mass flow case, water temperatures near the nominally cold plenum conditions likely corroborate the presence of a recirculation region on the RDE inner body. Analysis of inter- and intra-cycle temperature dynamics further support non-ideal processes occurring behind the detonation wave and during the refill process. As a whole, the data indicates that the RDE performance is better as time progresses away from ignition or for higher air mass flow rates. These data are also important for comparison with numerical models.

Time-resolved, single-ended laser absorption thermometry and H2O, CO2, and CO speciation in a H2/C2H4-fueled rotating detonation engine

Rotating detonation engines (RDEs) require novel diagnostic tools to better understand complex detonation behavior and improve performance. To this end, a single-ended laser absorption sensor for in situ, time-resolved measurements of temperature, H2O, CO2, and CO concentrations has been developed and deployed within the annulus of a hydrogen/ethylene/air-fed RDE. With a measurement rate of 44 kS/s, the sensor delivers four co-aligned, mid-infrared laser beams into the annular detonation chamber and captures the back-reflected radiation through a single optical port. A ray-tracing optimization algorithm, designed to maximize signal-to-noise ratio and beam-perturbation tolerance, was used to determine the optimal sensor optical configuration. Wavelength-modulation spectroscopy (WMS) further compensated for interference sources in the harsh detonation environment. Time-resolved and time-averaged sensor measurements of gas temperature and species at equivalence ratios of 0.74, 0.87, and 1.03 are presented.

Surface Temperature Measurements of Burning Solid Propellants Using Phosphor Thermography

In recent years, phosphor thermography has received increased attention as an alternative to other common temperature measurement techniques (e.g., thermocouples, pyrometry). This technique has been successfully used for surface temperature measurements on coated surfaces (e.g., turbine blades, furnace walls) and, in some cases, mixed with a reacting material. However, this technique has yet to be used for measuring the surface temperature of burning energetic materials (e.g., propellants, explosives). Adapting this technique to the study of energetic materials would enable temporally and spatially resolved surface temperature measurements that also lack some of the shortcomings of conventional methods. This work investigates the feasibility of using phosphor thermography to measure the surface temperature of burning nitrocellulose, an energetic material used extensively in single-, double-, and triple-base propellant formulations. Using phosphor thermography, two-dimensional time-resolved surface temperature measurements were obtained across the surface of a burning nitrocellulose pellet. The average surface temperatures measured with this approach () were in good agreement with previously published measurements for nitrocellulose obtained with embedded thermocouples (). This work demonstrates the viability of using phosphor thermography for measuring the surface temperature of burning solid propellants as well as other types of energetic material compositions.

Temperature Measurement of Laser-Irradiated Metals Using Hyperspectral Imaging

Accurate noncontact surface-temperature measurements during laser-based materials processing remain challenging due to the difficulty of establishing reliable emissivity values as a function of temperature and wavelength. Direct measurement of emissivity is difficult, as the emissivity may be changing constantly in the laser-material interaction region, where the temperature gradients are extreme and surface displacement can complicate the measurement. Here, we present a hyperspectral imaging method using a multiwavelength camera to capture the spectral radiance in eight different bands and fit the wavelength-dependent radiance to Planck's law. Time-resolved temperature measurements during microsecond pulsed-laser irradiation of a metal plate made of the titanium alloy $\mathrm{Ti}$-6$\mathrm{Al}$-4$\mathrm{V}$ provide temperature information about the irradiated surface with an estimated accuracy of $\ifmmode\pm\else\textpm\fi{}10\mathrm{%}$. The extracted wavelength-dependent emissivity slope compares well with reported results for macroscale titanium melts obtained using IR spectroscopy, which measure temperature without any built-in assumptions about the emissivity. The results are directly applicable to temperature monitoring during welding, additive manufacturing, and semiconductor growth.

Time-resolved stagnation temperature measurements in hypersonic flows using surface junction thermocouples

Fast-response coaxial surface junction thermocouples have been used to measure time-resolved stagnation temperature of the Mach 6 flow produced by the University of Southern Queensland’s hypersonic wind tunnel, TUSQ. The piston compression and the nozzle expansion of the test gas were found to be approximately isentropic for the first 65 ms of flow. Thereafter, the stagnation temperature reduces from T0≈560K due to the heat lost to the cold barrel, and this process can be modelled based on the measured barrel pressure history to simulate the stagnation temperature in TUSQ to within 2% of the actual value for the first 150 ms of flow. By operating the thermocouples at the flow stagnation temperature, the fluctuations of the flow stagnation temperature were investigated. A 3–4 kHz narrowband stagnation temperature fluctuation appearing after t≈65ms was measured, and found to be correlated with the transition to turbulence of the flow in the barrel.

CO-concentration and temperature measurements in reacting CH4/O2 mixtures doped with diethyl ether behind reflected shock waves

The oxidation of CH4/diethyl ether mixtures was studied with laser absorption-based time-resolved temperature and CO concentration measurements behind reflected shock waves. Fuel-rich (equivalence ratio ϕ = 2.0) mixtures were studied because of their relevance for mechanism development for partial oxidation reactions in the context of polygeneration processes and measurements at ϕ = 0.5 and 1.0 were used to verify the mechanism performance in an extended range of equivalence ratios. Temperature and CO concentration were measured via absorption using two fundamental vibrations of CO (ν" = 0, P20 and ν" = 1, R21) with two mid-IR quantum-cascade lasers near 4.8546 and 4.5631 µm. Interference from broadband absorption of CO2 in the region near 4.56 µm was quantified based on measured temperature-dependent CO2 absorption cross-sections and mechanism-based prediction of CO2 concentrations. The measured temporal CO-concentration and temperature profiles were compared with simulations based on two mechanisms (Fikri et al., 2017; Yasunaga et al., 2010). For mixtures with ϕ = 0.5, the two mechanisms show similar results, and well reproduce the experimental data. At ϕ = 1.0 and 2.0, the Fikri et al. mechanism shows very good agreement with the experiments whereas the Yasunaga et al. mechanism predicts a too fast CO-concentration and temperature rise.

Hollow plasma structure during the breakdown phase of nanosecond pulsed pin–pin discharges generated with overvoltage

Atmospheric pressure nanosecond repetitive pulsed discharges are of interest for applications in combustion, material processing, plasma medicine and gas treatment. In this paper the observation of a hollow structure at the ignition stage of such discharge in a pin–pin geometry is reported. Plasma images show that the phenomenon occurs in a variety of gases (helium, humid helium, argon and air) suggesting that it is in first approximation non-species specific. The phenomenon is investigated in detail in pure helium discharges for peak applied voltages between 3 and 6 kV and 200 ns voltage pulse duration by performing time-resolved optical emission spectroscopy measurements of electron density, gas temperature and electric field. All the measurements were performed at the mid-gap during the early stages of the discharge, near the breakdown. The transition from a homogeneous filament to a hollow structure occurs between 4 and 5 kV in helium. Electron density measurements by Stark broadening of the He I line at 492.2 nm show no significant difference in electron densities for the applied voltage between 3 and 6 kV. In all cases, a maximum electron density of about 3.5 × 1021 m−3 was found. Electric field measurements performed by Stark polarization spectroscopy of the He I transition at 492.2 nm and of its forbidden counterpart show electric field strengths higher than the DC breakdown field of helium at atmospheric pressure consistent with the generation of the discharges with overvoltage. Moreover, a correlation between electric field values and the appearance of the hollow structure is observed and, remarkably, the phenomenon is not sensitive to the pre-ionization level (memory effect). Possible mechanisms for the phenomenon are discussed.

Time-resolved temperature-jump measurements and steady-state thermal imaging of nanoscale heat transfer of gold nanostructures on AlGaN:Er3+ thin films.

For a nanostructure sitting on top of an AlGaN:Er3+ thin film, a new thermal imaging technique is presented where dual cameras collect bandpass filtered videos from the H and S bands of Er3+ emission. We combine this thermal imaging technique with our newly developed time-resolved temperature measurement technique which relies on luminescence thermometry using Er3+ emission. This technique collects time-resolved traces from the H and S bands of Er3+ emission. The H and S signal traces are then used to reconstruct the time-resolved temperature transient when a nanostructure is illuminated with a pulsed 532 nm light. Two different types of samples are interrogated with these techniques (drop-casted gold nanosphere cluster and lithographically prepared gold nanodot) on the AlGaN:Er3+ film. Steady-state and time-resolved temperature data are collected when the samples are immersed in air and water. The results of time-resolved temperature-jump measurements from a cluster of gold nanospheres show extremely slow heat transfer when the cluster is immersed in water and nearly 200-fold increase when immersed in air. The low thermal diffusivity for the cluster in water suggests poor thermal contact between the cluster and the thermal bath. The lithographically prepared nanodot has much better adhesion to the AlGaN film, resulting in much higher thermal diffusivity in both air and water. This proof-of-concept demonstration opens a new way to measure the dynamics of the local heat generation and dissipation at the nanoparticle-media interface.

Characterization of the ECN spray A in different facilities. Part 1: boundary conditions characterization

The Engine Combustion Network (ECN) community has greatly contributed to improve the fundamental understanding of spray atomization and combustion at conditions relevant to internal combustion engines. In this context, standardized spray experiments have been defined to facilitate the comparison of experimental and simulation studies performed in different facilities and with different models. This operating mode promotes collaborations among research groups and accelerates the advancement of research on spray. In efforts to improve the comparability of the ECN spray A experiments, it is of high importance to review the boundary conditions of different devices used in the community. This work is issued from the collaboration in the ECN France project, where two new experimental facilities fromPPRIME(Poitiers) andPRISME(Orleans) institutes are validated to perform spray A experiments. The two facilities, based on Rapid Compression Machine (RCM) design, have been investigated to characterize their boundary conditions (e.g., flow velocity as well as fuel and gas temperatures). A set of standardized spray experiments were performed to compare their results with those obtained in other facilities, in particular the Constant Volume Pre-burn (CVP) vessel atIFPEN. It is noteworthy that it is the first time that RCM type facilities are used in such a way within the ECN. This paper (part 1) focuses on the facilities description and the fine characterization of their boundary conditions. A further paper (part 2) will present the results obtained with the same facilities performing ECN standard spray A characterizations. The reported review of thermocouple thermometry highlights that it is necessary to use thin-wires and bare-bead junction as small as possible. This would help to measure the temperature fluctuations with a minimal need for error corrections, which are highly dependent on the proper estimation of the velocity through the junction, and therefore it may introduce important uncertainties. Temperature heterogeneities are observed in all spray A devices. The standard deviation of the temperature distribution at the time of injection is approximately 5%. We report time-resolved temperature measurement fromPPRIMERCM, performed in the near nozzle area during the injection. In inert condition, colder gases from the boundary layer are entrained toward the mixing area of the spray causing a further deviation from the target temperature. This emphasizes the importance of the temperature in the boundary (wall) layer. In reacting condition, the temperature of these entrained gases increases by the effect of the increased pressure, as the RCM has a relatively small volume. Generally, the velocity and turbulence levels are an order of magnitude higher in RCM and constant pressure flow compared to CVP vessels. The boundary characterization presented here will be the base for discussing spray behavior in the part 2 of this paper.

Experimental investigation and 1D analytical approach on convective heat transfers in engine exhaust-type turbulent pulsating flows

The objective of the present work was to experimentally investigate flow field instantaneous characteristics and their associated heat transfer for pulsating flows representative of engine exhaust flow operating conditions. The experimental apparatus consists of a stationary turbulent hot air flow, with a variable Reynolds number, excited through a pulsating mechanism and exchanging thermal energy with a water cooled steel pipe. Pulsation frequency ranges from 10 to 95 Hz. Simultaneous time-resolved measurements of velocity and temperature were achieved by mean of coupled hot-wire anemometry and micro-unsheathed thermocouples measurements to investigate the impact of the pulsation frequency on heat transfers. Flow pulsation was found to enhance heat transfers in the entire range of frequencies. Significant improvements were observed when the flow was excited with a frequency equal to a resonant mode of the system. With the increase in velocity-amplitude ratio, an increase in the convective heat transfer was observed, with a maximum enhancement corresponding to a factor three and higher, with respect to the relative Nusselt number. Combining experimental results with an analytical formulation, derived from the 1D energy balance equation for a turbulent pulsating flow, the velocity amplitude ratio was identified as the characteristic term representative of the predominant heat-transfer enhancement mechanism.

Hypersonic shock-wave/boundary-layer interactions on a cone/flare

Time-resolved surface temperature measurements have been carried out on a 7° half-angle circular cone/flare model in the Air Force Research Laboratory’s Mach-6 Ludwieg Tube using infrared thermography. Measurements were performed at zero angle of attack on a total of 16 different nose bluntness/flare angle geometries at three different freestream unit Reynolds numbers. The boundary layer entering the interaction region was turbulent for the two sharper nosetips and laminar for the two blunter nosetips. Stanton-number contours and profiles were used to investigate the effect of nose bluntness, flare angle, and freestream unit Reynolds number on the length of boundary-layer separation and the peak heating achieved upon reattachment. The classical scaling analyses of Souverein et al.and Hung & Barnett for separation length and peak heating, respectively, have been extended for the use of axisymmetric cone/flare shock-wave/boundary-layer interactions. Scaling the peak heating with the density ratio across the separation shock wave, instead of the pressure ratio, significantly improves/simplifies the analysis.

Single-Ended Sensor for Thermometry and Speciation in Shock Tubes Using Native Surfaces

A single-ended laser absorption sensor for time-resolved measurements of temperature and H2O, CO2, and CO concentrations was designed and deployed on a cylindrical shock tube operating at combustion-relevant conditions. The sensor transmitted four monochromatic laser beams probing strong species-specific mid-infrared absorption transitions through a single optical port and measured the backscattered laser radiation from the native surface across the 13.97-cm-diameter shock tube. Despite the non-ideal concave reflective surface and the long optical path relative to the port diameter (1.37 cm), an optimal optical configuration that maximized signal-to-noise ratio and was free of physical blockage was found and implemented using a numerical ray-tracing optimization algorithm. Wavelength-modulation spectroscopy was employed to further compensate for interference sources in the shock tube environment. The four lasers were sinusoidally injection-current modulated at various frequencies near 100 kHz to yield a measurement rate of 44 kS/s. Demonstration measurements involving non-reacting mixtures of the target species and reacting mixtures of ethane and oxygen in a N2 bath were performed in a shock tube facility at temperatures between 1100 and 1800 K and pressures between 2 and 9 atm, with measured quantities demonstrating excellent agreement with the expected values. Despite experiencing strong vibrations induced by the dynamic shock tube environment, the sensor resolved sub-millisecond transients during ethane oxidation and detected H2O, CO2, and CO mole fractions as low as 0.025%, 0.012%, and 0.005%, respectively, representing highly sensitive detection limits suitable for single-port low-concentration multi-species sensing in shock tubes and other flow channels of comparable dimensions.

Detector calibration and measurement issues in multi-color time-resolved laser-induced incandescence

Time-resolved laser-induced incandescence is used to infer the size distribution of gas-borne nanoparticles from time-resolved pyrometric measurements of the particle temperature after pulsed laser heating. The method is highly sensitive to aspects of the measurement strategy that are often not considered by practitioners, which often lead to discrepancies between measurements carried out under nominally identical conditions. This paper therefore presents a well-documented calibration procedure for LII systems and quantifies the uncertainty in pyrometric temperatures introduced by this procedure. Calibration steps include corrections for: (1) signal baseline, (2) variable transmission through optical components, and (3) detector characteristics (i.e., gain and spectral sensitivity). Candidate light sources are assessed for their suitability as a calibration reference and the uncertainty in calculated calibration factors is determined. The error analysis is demonstrated using LII measurements made on a sooting laminar diffusion flame. We present results for temperature traces of laser-heated particles determined using two- and multi-color detection techniques and discuss the temperature differences for various combinations of spectral detection channels. We also summarize measurement artifacts that could bias the LII signal processing and present strategies for error identification and prevention.

Acousto-optically modulated quantum cascade laser for high-temperature reacting systems thermometry.

We demonstrate time-resolved temperature measurements in shock-heated mixtures of carbon monoxide over a temperature range of 1000-1800K for two pressure ranges, 2.0-2.9atm and 7.6-10.7atm, at rates up to 250kHz using a single acousto-optically modulated quantum cascade laser with mid-infrared output spanning from 1975 to 2260 cm-1. Measured temperatures were in excellent agreement with values determined by ideal shock relations, and the temperature profile after the passage of the reflected shock wave was found to be well-modeled by an isentropic compression assumption. Temperature measurements made with this setup are largely immune to effects of emissions and beam steering, making the diagnostic system well-suited for studying high-temperature gas-phase reactions of energetic materials such as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine and hexahydro-1,3,5-trinitro-1,3,5-triazine.

Characterization of high-current pulsed arcs ranging from 100–250 kA peak

In this paper, we present the laboratory study on three experimental setups that produce a free arc channel subjected to the transient phase of a lightning current waveform. This work extends the high-current pulsed arc characterization performed in previous studies for peak levels up to 100 kA. Eleven high-current waveforms with peak value ranging from 100–250 kA with different growth rates and action integrals are studied, allowing the comparison of different test benches. These waveforms correspond to standard lightning ones used in aircraft certification processes. Hydrodynamic properties such as arc channel evolution and shock-wave propagation are determined by high-speed video imaging and the background-oriented Schlieren method. The arc diameter reaches around 90 mm at 50 μs for a current of 250 kA peak. Space- and time-resolved measurements of temperature, electron density and pressure are assessed by optical emission spectroscopy associated with the radiative transfer equation. It is solved across the arc column and takes into account the assumption of non-optically thin plasma at local thermodynamic equilibrium. For a 250 kA waveform, temperatures up to 43 000 K are found, with pressures in the order of 50 bar. The influence of current waveform parameters on the arc properties are analyzed and discussed.

Time-Resolved Temperature-Jump Measurements and Theoretical Simulations of Nanoscale Heat Transfer Using NaYF4:Yb3+:Er3+ Upconverting Nanoparticles

We introduce for the first time a time-resolved temperature measurement technique which relies on temperature-jump luminescence thermometry using NaYF4:Yb3+:Er3+ upconverting nanocrystals. This new time-resolved technique is based on optical thermometry using upconverting nanoparticles (UCNPs) and does not have to infer temperature from changes in the optical properties of the heater or surrounding local environment. We have prepared gold-decorated UCNPs that function as a dual single-heater thermometer system. We measure the time-resolved temperature jump from nanocrystal clusters and compare our results to simulated thermal transfer data generated using finite element methods. The simulated data show that temperature dissipation follows a power law where the temperature change is inversely related to time. This result agrees with a thermal diffusion model where a semi-infinite medium is exposed to a sudden temperature change at its surface, but the simulated results do not agree that the heat transfer p...

Transport of Entropy Waves Within a High Pressure Turbine Stage

This paper presents the results of an experimental study on the transport of entropy waves within a research turbine stage, representative of the key aero-thermal phenomenon featuring the combustor-turbine interaction in aero-engines. The entropy waves are injected upstream of the turbine by a dedicated entropy wave generator (EWG) and are released in axial direction; they feature circular shape with peak amplitude in the center and exhibit sinusoidal-like temporal evolution over the whole wave area. The maximum over-temperature amounts to 7% of the undisturbed flow, while the frequency is 30 Hz. The entropy waves are released in four azimuthal positions upstream of the stage, so to simulate four different burner-to-stator blade clocking. Time-resolved temperature measurements were performed with fast microthermocouples (FTC); the flow and the pressure field upstream and downstream of the stator and the rotor was measured with five-hole pneumatic probes and fast-response aerodynamic pressure probes. The entropy waves are observed to undergo a relevant attenuation throughout their transport within the stator blade row, but they remain clearly visible at the stator exit and retain their dynamic characteristics. In particular, the total temperature distribution appears severely altered by burner-stator clocking position. At the stage exit, the entropy waves loose their coherence, appearing spread in the azimuthal direction to almost cover the entire pitch in the outer part of the channel, while being more localized below midspan. Despite the severe and unsteady interaction of the entropy waves within the rotor, they retain their original dynamic character. A comparison with measurements performed by injecting steady hot streaks is finally reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a succession of hot streaks of different amplitude.

Time-Resolved On-Axis Spectroscopic Stagnation Temperature Measurements in Shock Tunnel Flows

This paper demonstrates time-resolved stagnation temperature measurements in a shock tunnel at a frequency of 25 kHz using emission spectroscopy in air and nitrogen test conditions. The two most important parameters for determining the flow conditions generated in a shock tunnel experiment are the stagnation pressure and temperature of the flow just upstream of the supersonic nozzle. While the pressure can be measured using a wall-mounted transducer with relative ease, the measurement of the temperature requires a optical technique such as time resolved emission spectroscopy. Knowledge of the transient stagnation temperature behavior is critical to all subsequent expansion tube flow processes. The driver gas emission spectrum data at the post-shock condition shows continuum and atomic line radiation. The continuum radiation can be described by a black body radiator with the individual spectra showing sufficient continuum information for accurately fitting Planck functions. Atomic line radiation was excluded by skipping those data from the measured spectra. The fitting routine shows clear differences in determined temperatures including and neglecting atomic line radiation. These measurements allow for the exact determination of the shock tunnel flow conditions in combination with pressure transducer data. The flow condition used in the experiment corresponds to a nominal Mach-10 condition at an altitude of 65 km, however, the technique is not limited to this condition and can be used for a large range of flow conditions.

Time-resolved universal temperature measurements using NaYF4:Er3+,Yb3+ upconverting nanoparticles in an electrospray jet.

Hexagonal upconverting nanoparticles (UCNPs) of NaYF4:Er3+,Yb3+ (ca. 300 nm) have been widely used to measure the temperature at the nanoscale using luminescence ratio thermometry. However, several factors limit their applications. For example, changes in the peak shape, mainly is the S-band emission, hinders their ability to be used as a universal temperature sensor. Herein, we introduce a universal calibration protocol for NaYF4:Er3+,Yb3+ upconverting nanoparticles that is robust to environmental changes and gives a precise temperature measurement. We used this new procedure to calculate the temperature profile inside a Taylor cone generated with an electrospray jet. Inside the Taylor cone the fluid velocity increases toward the tip of the cone. A constant acquisition length leads to a decrease in excitation and acquisition time. This decrease in excitation time causes a peak shape change that corrupts the temperature measurement if the entire peak shape is integrated in the calibration. Our universal calibration circumvents this problem and can be used for time-resolved applications. The temperature at the end of the Taylor cone increases due to the creation of a whispering gallery mode cavity with 980 nm excitation. We use time-resolved energy balance equations to support our optical temperature measurements inside the Taylor cone. We believe that the findings of this paper provide a foundation for time-resolved temperature measurements using NaYF4:Er3+,Yb3+ upconverting nanoparticles and can be used to understand temperature-dependent reactions such as protein unfolding inside microjet/microdroplets and microfluidic systems.

Soot formation in shock-wave-induced pyrolysis of acetylene and benzene with H2, O2, and CH4 addition

Experiments on the pyrolysis of C2H2/Ar and C6H6/Ar mixtures with addition of H2, O2, and CH4 have been carried out behind reflected shock waves at temperatures ranging from 1400 to 2600 K. Soot formation was measured by laser extinction at 633 nm. Time-resolved temperature measurements were performed via two-color CO absorption on the P(8) and R(21) lines at 2111.54 and 2191.50 cm-1 using quantum-cascade lasers. For this purpose, 0.5–0.8% CO was added to the gas mixtures. The measured temperature dependence of soot formation in experiments with added O2, and CH4 was corrected for the temperature effect caused by the thermochemistry of either endothermic pyrolysis or exothermic oxidation or reactions that cause time-dependent deviation from the initial frozen-shock temperatures. In all mixtures, the addition of H2 resulted in a noticeable decrease of the soot yield. A considerable increase in the soot yield was found with addition of methane to acetylene mixtures. In contrast, in benzene mixtures, the addition of methane caused a decrease of the soot yield. The qualitative analysis of the kinetics of the gas-phase stage of the pyrolysis reactions elucidated the influence of all investigated additives on the change in the key routes of initial stages of PAH and soot formation. We observed that the addition of H2 to acetylene inhibits the initial stages of the pyrolysis reaction, while the addition of CH4 and O2 opens up new ways for the formation of benzene and phenyl and following growth of pyrene. In contrast to that, in benzene all the additives studied lead to the suppression of the kinetics pathways for the formation of pyrene and the subsequent growth of soot.