Under certain conditions dust explosions occur in the alimentary industry. Following ATEX and other guidelines have not eliminated accidents. Therefore, more knowledge is needed. The current work delivers experimental results describing phase transitions and decomposition of dusts. Dusts from wheat flour, chili powder, corn starch, milk powder, cocoa powder, and by-product of grain are investigated. The temperature of pyrolisation has been identified using TGA to be in the range [250°C, 600°C] in air and [300°C, 450°C] in nitrogen. It was found that the compositions of the pyrolysis gases depend on temperature. Carbon monoxide, carbon dioxide, methane, and hydrogen were the main contributors to the pyrolysis gases. The distributions are described with a polynomial or Gaussian fit. The current paper proposes coefficients for Gaussian polynomials expressing the concentration for the four primary pyrolysis gases. 

This paper presents a recently developed method meant to act as a tool for objectively assessing and comparing the performance of automatic fire suppression systems. This methodology specifies requirements and procedures for evaluating the efficiency and performance of automatic fire suppression systems permanently installed in the engine compartments of buses and coaches. The testing is done according to SP method 4912 and carried out in a test enclosure where the fire performance of different suppression systems can be objectively assessed in a well-defined way. The test methodology includes a battery of fire tests simulating different engine loads, air flows and fire scenarios. Every tested system is rated according to its performance. The test method also includes testing of re-ignition due to hot surface ignition of liquid fuels.

Scheimpflug lidar is a compact alternative to traditional lidar setups. With Scheimpflug lidar it is possible to make continuous range-resolved measurements. In this study we investigate the feasibility of a Scheimpflug lidar instrument for remote sensing in pool flames, which are characterized by strong particle scattering, large temperature gradients, and substantial fluctuations in particle distribution due to turbulence. An extinction coefficient can be extracted using the information about the transmitted laser power and the spatial extent of the flame. The transmitted laser power is manifested by the intensity of the ‘echo’ from a hard-target termination of the beam located behind the flame, while the information of the spatial extent of the flame along the laser beam is provided by the range-resolved scattering signal. Measurements were performed in heptane and diesel flames, respectively. © 2023 The Author(s). 

The vibrational energy of water droplets has been investigated. Viscosity was neglected and only the lowest order symmetrical vibration, the quadrupole mode with m=0, was considered. An approximative solution was given by Rayleigh in 1879: w_vib=2a^2 ??r_0?^2 where ? is the relative vibration amplitude, ? is the surface tension, and r0 is the droplet radius at equilibrium, that is the radius of the spherical droplet. It was found that this solution agrees with the exact solution within a few percent for moderate values of the relative amplitude ?. The rationale of this study was to investigate whether dissipation of energy from a shock wave, e.g. from an explosion, into vibrational energy of droplets is a mechanism that needs to be considered on order to accurately model explosion mitigation using water mists. Traditionally droplet vibrations are not considered in such models whereas other mechanisms such as translational energy, heating, evaporation, and droplet breakup are considered. A useful parameter for quantifying the relative importance of vibrations as compared to linear acceleration of droplets is the ratio between vibrational and translational kinetic energy. This ratio is given by 3a^2 ?/(?p?r_0 v?_transl^2 ) where vtransl is the translational velocity to which the droplet has been accelerated by the shock front. This ratio is negligible for a particular severe explosion scenario where information on vtransl was available in the literature. For other cases vibrations might be of some significance but detailed information about the specific scenarios is needed to obtain detailed results. More work is needed in order to understand the effect of viscosity and higher order vibrations. Furthermore a model for the excitation of droplet vibrations by shock waves is required for modelling. Finally there is a lack of experimental knowledge on droplet size distribution for water mist interacting with a shock wave.

The Cutting Extinguisher is a Swedish invention that is used to fight fires both on land and at sea. The main application is to fight the fire from a safe area. The extinguisher can cut through building materials using an abrasive additive. Experimental measurements show that the spray is characterized by small droplets. The following characteristic diameters were measured at 10 m distance from the nozzle using 260 bar injection pressure: arithmetic mean diameter d10 ≈ 60 μm and the Sauter mean diameter d32 ≈ 170 μm. The velocity at this distance from the nozzle was approximately 7 ms-1 in the spray core. Droplet diameters decreased significantly when A-foam or X-Fog were mixed into the water, d10 decreased to 30-40 μm and d32 to 110-150 μm. These measurements support previous explanations of the efficiency of the Cutting Extinguisher and also lead to a more detailed understanding of the extinguishing process. © 2014: The Royal Institution of Naval Architects.

A method for measuring apparent soot particle size and concentration in turbulent combusting diesel jets with elevated and inhomogeneous optical density is presented and discussed. The method is based on the combination of quasi-simultaneous Laser Induced Incandescence (LII), Elastic Scattering (ELS) and Light Extinction (LE) measurements exhibiting a high potential for spatially resolved measurements of carbonaceous particles in flames and residual gases at a given instant. The method evaluates the LII signal by calculating the laser fluence across the flame and compensating for signal trapping, allowing measurements where laser extinction between the flame borders reaches values up to 90 %. The method was implemented by measuring particle size and concentration in the middle sagittal axis of optically dense, combusting diesel jets at a certain time after the start of combustion. Experiments were carried out in the Chalmers High Pressure, High Temperature spray rig under conditions similar to those prevailing in direct injected compression ignition engines. Measurements of apparent particle size and concentration together with volume fraction conferring an instantaneous single-shot case and an average measurement from several consecutive jets are presented and discussed.

A method for measuring apparent soot particle size and concentration in turbulent combusting diesel jets with elevated and inhomogeneous optical density is presented and discussed. The method is based on the combination of quasi-simultaneous Laser Induced Incandescence (LII), Elastic Scattering (ELS) and Light Extinction (LE) measurements exhibiting a high potential for spatially resolved measurements of carbonaceous particles in flames and residual gases at a given instant. The method evaluates the LII signal by calculating the laser fluence across the flame and compensating for signal trapping, allowing measurements where laser extinction between the flame borders reaches values up to 90%. The method was implemented by measuring particle size and concentration in the middle sagittal axis of optically dense, combusting diesel jets at a certain time after the start of combustion. Experiments were carried out in the Chalmers High Pressure, High Temperature spray rig under conditions similar to those prevailing in direct injected compression ignition engines. Measurements of apparent particle size and concentration together with volume fraction conferring an instantaneous single-shot case and an average measurement from several consecutive jets are presented and discussed.

This work presents measurements meant to study the influence of the spark energy on the time to ignition of a given material in the cone calorimeter. For this purpose, square slabs of particle board were tested under two radiation intensities until ignition occurred using two spark energies for each intensity level. Results show that increasing the spark energy leads to a reduction inthe ignition time regardless of the radiation intensity. However, the influence of the spark energy on the time to ignition is, in absolute numbers, larger for the low radiation intensity case than for the high radiation intensity case. Nonetheless, the proportional difference is nearly 10% for both levels of heat radiation. Results from this work confirm that there is an influence of the spark energyon the time to ignition of a given material suggesting that a narrower and more specific definition of the ignition circuits allowed in the cone calorimeter would be highly beneficial for ensuring repeatable results among laboratories.

The effect of thermochromic coatings of vanadium dioxide (VO₂) on the fire performance of windows was experimentally tested. Prototypes were subjected to radiant heat and the radiation transmitted through the specimens was measured as a function of time. The results indicate that windows coated with VO₂ can reduce radiative heat transfer from fires and thereby also reduce or prevent fire spread. The results clearly show that VO₂coatings on BK7 substrates hinder approximately 30% of the transmission of radiation from fire sources when compared with the performance of uncoated windows. It is expected that VO₂ will not be solely implemented for the purpose of increasing fire performance of windows, but it will rather provide a secondary positive effect if such windows are realized for energy‐saving purposes.

This paper presents a method intended for detecting the initiation of combustion and the presence of smoke in confined or open spaces by continuously applying an intermittent high-voltage pulse between the electrodes. The method is based on an electrical circuit which generates an electrical discharge measuring simultaneously the breakdown voltage between the electrodes. It has been successfully used for the detection of particle-laden aerosols and flames. However, measurements in this study showed that detecting pyrolysis products with this methodology is challenging and arduous. The method presented here is robust and exploits the necessity of having an ignition system which at the same time can automatically discern between clean air, flames or particle-laden aerosols and can be easily implemented in the existing cone calorimeter with very minor modifications.

Fires in the engine compartments of surface and underground non-rail heavy duty vehicles are still highly frequent. Statistics show that most of the reported fires commenced in the engine compartment and that these were not promptly detected by the drivers. Fires which were not detected rapidly, spread oftentimes beyond the firewall of the engine compartment having notorious economical and environmental repercussions; furthermore, endangering the safety of the occupants. Detecting fires in the engine compartments of heavy duty (HD) vehicles with inexpensive and simple automatic detection systems is in general challenging. High air flows and large amounts of suspended pollutants, together with the complicated geometry and wide range of surface temperatures typically occurring during the normal operation of the vehicle, complicate the reliable operation of almost all types of detectors. This work presents a theoretical study assessing the effectiveness of different detection systems in a simulated fire scenario. Results from calculations and Computational Fluid Dynamics (CFD) simulations of a well defined fire in a standardised engine compartment are used to determine the gas temperature and smoke concentration across the compartment and how these are affected by different engine configurations and driving conditions. The effectiveness of different detection systems is studied by means of simulating a fire and analysing predictions measurements of temperatures and smoke concentrations resolved in time and space in the virtual compartment.

A continuous current with a potential ranging between 10 and 30 kV was applied to a single-hole nozzle for modifying the properties of the generated water spray. The nozzle produced a full-cone spray by injecting water into quiescent air at atmospheric conditions varying the injection pressure between 0.2 and 0.6 MPa. Back-illuminated photography and laser-based holography were used for recording the effect of the electrical current on spray properties such as cone angle and droplet sizes. Results from this study indicate that applying a potential above 20 kV yields wider cone angles, more homogenously distributed spray patterns, and reduced droplet sizes than non-assisted sprays.Key words: electrosprays, water mist

Soot particle size, particle concentration and volume fraction were measured by laser based methods in optically dense, highly turbulent combusting diesel sprays under engine-like conditions. Experiments were done in the Chalmers High Pressure, High Temperature spray rig under isobaric conditions and combusting commercial diesel fuel. Laser Induced Incandescence (LII), Elastic Scattering and Light Extinction were combined quasi-simultaneously to quantify particle characteristics spatially resolved in the middle plane of a combusting spray at two instants after the start of combustion. The influence that fuel injection pressure, gas temperature and gas pressure exert on particle size, particle concentration and volume fraction were studied. Probability density functions of particle size and two-dimensional images of particle diameter, particle concentration and volume fraction concerning instantaneous single-shot cases and average measurements are presented. High injection pressure led to a reduction in the mean particle size, total number of particles and total amount of soot compared to a low injection pressure. Higher gas pressure resulted in larger amount of soot and larger soot particle size, with higher gas temperature having similar effects. 

Sprays produced by injecting water into quiescent air by three different types of nozzles were characterised by optical methods. The droplet velocities and droplet size distributions were assessed by the use of high speed shadowgraphs.

Heavy vehicles rolling on wet roads produce splash and spray clouds. These aerosols reduce the visibility of other drivers, contribute to a small, but quantifiable proportion of road traffic accidents and affect the operational capabilities of autonomous vehicles travelling near them. Even though knowing the physical properties of these aerosols is essential for testing and validating sensors for environment perception and recognition of autonomous vehicles, there is little information about them. In this work the physical characteristics of spray clouds produced by heavy vehicles rolling on wet asphalt were measured by optical methods. Time resolved droplet size, mass concentration, number density, light extinction and contrast attenuation parallel and perpendicular to the travelling direction of the vehicle were measured. Vehicle velocity, vehicle configuration and water depth were varied during the tests. Results show that the average droplet diameter ranges between 100 and 400 μm with maximum diameters of almost 4 mm. Mass concentration gamuts between 0,2 and 0,7 kg/m3 with peaks surpassing 1 kg/m3 while number density spans between 20 and 40 cm−3 and occasionally exceeds 100 cm−3. Light extinction can reach levels as high as 0,2 m−1 and contrast, evaluated from images, can reach values under 0,1. 

The ignition of natural fuels by sparks from strikes between metals and hard rock is far from understood and the ignition potential of sparks from rock strikes during heavy machinery operations is disputed in the scientific literature. This study utilises a spectrally resolved technique to study the temperature evolution of metal sparks from rock strikes. The study shows that initial temperature after collision can easily reach 1500 °C and this temperature can increase additionally by several hundred degrees as rapid oxidation processes are initiated, often leading to further disintegration of the fragment. The average temperature of fragments from such collisions is here measured to 1400 – 2000 °C and the combination of temperature, size and exothermic processes makes them viable for forest litter igniting. However, ignition on forest lands is always an unlikely, although possible outcome of heavy machinery operations and should be considered in risk assessment of the activity.

Developing tactics for extinguishing fires located in civil structures is needed. Nowadays, the most commonly procedure employed by most fire brigades when extinguishing fires located in the interior of buildings, consists in sending a unit of firefighters inside the structure spraying water on the surface of the burning fuels. This procedure has enormous caveats since it leads to the unavoidable necessity of exposing personal to situations where risks to their personal safety are major. An alternative to these tactics consists on using the Cutting extinguisher which in principle allows combating a fire by injecting water mist into the burning building without the necessity of entering it. This work studies the capabilities and limitations of the Cutting extinguisher when used for fire-fighting activities in conventional and idealised civil structures by the aid of computerised simulations and experimental data. The simulations were done using Fire Dynamics Simulator (FDS) which is an open-source code for modelling well-ventilated fires while experimental data was obtained from idealised and controlled fires and experiments. Findings of this study suggest that the Cutting extinguisher is effective for combating fires of moderated size in confinements using less water than traditional methods by reducing the relative concentration of oxygen in the room instead of by cooling the fuels as traditional methods do. The high velocity of the jet induces mixing in the confinement, enhancing the interaction of droplets with hot combustion products and promoting the vaporisation of the injected water. Furthermore, the induced momentum to the gases in the room together with the vaporisation of the injected water reduces the overall gas temperature inside the structure.

In-line holography, where the reference beam coincides with the beam that is scattered against the droplets, has been found to be a versatile and simple experimental method for spray diagnostics using holography. Such an experiment was setup and a water spray was studied and holograms of high quality was obtained using a CCD-camera.

The holograms were analysed with Wavelet analysis, implemented as a Matlab program. It was found that the droplets’s size and position could be reconstructed with reasonable accuracy. Future work will focus on a dynamic analysis program that dynamically adapts the wavelet analysis parameters to each detected droplet.

Key words: spray diagnostics, laser diagnostics, holography, image processing, wavelet analysis