Scientific expert opinion based on combustion research plays an important part in justice to appropriately assume the cause or process of a fire. The roles of combustion research in the scientific expert opinion, vital points in giving the opinions, an actual example of the opinion, etc., are discussed with introduction of fire examination activities by fire authorities according to the Fire Service Law.

The expert knowledge concerning combustion phenomena is indispensable to forensic science, especially to investigate an incendiary fire. Forensic science is defined as the application of natural sciences and technological practices to the purposes of justice in the study and resolution of criminal, civil and regulation issues. However, the common sense about natural sciences in the judicial circles is sometimes far away from the scientific sense, of course without the exception of combustion science. In this paper, it is consider through the several matters of judgment related to combustion phenomena, how the scientific expert opinion should be, and how the combustion research should contribute to forensic science.

Fire appraisals presented for actual criminal actions insurance charge suits are reviewed to explore role of scientists in maintaining just judicial judgement on the responsibility of unwanted fires. The asymmetry in the forensic technical capability between the both sides at the court, general inferiority of indictees to investigators at a criminal action or that of common people to experienced enterprises at civil suits is suggested as the key background for the preservation of the asymmetry.

The rate processes involved in the soot and PAH formation from combustion are introduced and discussed. Firstly, the nucleation process of the carbon particle is discussed in comparison with the classical theory of homogeneous nucleation used for the atmospheric cloud condensation and the industrial fine particle production. The simple concept of the critical radius does not seem to be directly applicable for the soot nucleation. The potential improvement of the particle formation model is discussed based on the observed physical and chemical properties of the diesel soot. Secondly, the major reaction mechanisms of PAH formation and growth including the popular HACA mechanism are introduced with a special attention to the recombination reactions of resonantly stabilized hydrocarbon radicals, which is a class of reactions with potentially new and significant routes. The chemical and thermodynamic roles of the resonance stabilization of hydrocarbon radicals are introduced and discussed.

In this paper, an approach for measurement of PAH and soot is introduced. Previously, we measured PAH and soot concentrations of diffusion flames in a triple port burner. The co-annual burner consists of three concentric tubes, where air flows in both inner (central) and outer tubes, and fuel flows in the annulus between these air tubes. Two diffusion flames are formed in the boundary of fuel and air. To detect PAH and soot regions, laser-induced fluorescence (LIF) and laserinduced incandescence (LII) were used. GC/MS was also used to obtain quantitative PAH concentration. For comparison, measurement of diffusion flames in a co-axial burner (double port burner) was conducted at different fuel and air velocities. Additionally, its application for exhaust gas diagnostics is also shown, corresponding to the evaluation of diesel particulate filters (DPFs).

There always exists the possibility that acoustic combustion-instabilities take place in the combustion chamber of a solid-propellant rocket motor. This is a phenomenon that the energy-gain of a standing acoustic wave in the combustion chamber exceeds the energy-loss of that wave, the pressure amplitude of that wave increases because of the surplus energy, and this increase causes the unstable combustion of the propellant. The response function of a solid propellant indicates the inclination of the propellant to cause the acoustic combustion-instability. Therefore, those engaged in the engineering of the solid-propellant rocket must clearly understand the meaning of the response function and roughly know about the experimental methods for its measurements. This article gives them necessary knowledge. First, fundamentals of acoustics are described. Next, the expression of the coefficient of the exponential increase of the acoustic pressure amplitude caused by the interaction of oscillatory pressure with oscillatory velocity of gas particles at the propellant surface [Culick and Yang, Progress in Astronautics and Aeronautics, Vol. 143, pp. 719-747] is presented. Then, the relation between this coefficient and the response function is explained. Last, the experimental methods for the measurements of the response function are presented.

Water mist has been recognized as an alternative for halogenated hydrocarbon fire suppressants. In this study, the effect of water mist on the methane/air counterflow diffusion flame was investigated numerically. The numerical simulation was performed using OPPDIF code in CHEMKIN package, modified to include the evaporation process of water mist. When the water mist evaporates completely in the flame zone, the evaporation process itself scarcely affects the critical stretch rate at extinguishment. The flame temperature is slightly affected by thermal effect, and it decreases with increase of the amount of water mist added. The simulated stretch rates at extinguishment are in good agreement with previous experiments in the range of the mass fraction of water mist Y₀ < 0.060. The largest effect of water mist on stretch rate at extinguishment is attributed to sensible heat, followed by latent heat and chemical reaction. The chemical effect is rather small, but not negligible as compared to the dilution and thermal effects. The chemical effect is attributed to the decrease of radical species in chain branching reactions. The suppression effectiveness of water mist is better than IG-55, IG-541, N₂ and CO₂.