Natural gas is a fuel that is expected to be supplied stably in the long term, and it is expected for the achievement of the low carbon society because of the least amount of carbon dioxide formation per unit calorific value in the hydrocarbon fuels. In this article, we introduce various burners and the latest trend of them that use gas fuels based on natural gas from the viewpoint of the combustion stability. Gas burners have some features. The degree of freedom of the flame shape is big, and gas burners have a wide variety. It is easy to obtain steady combustion and the automatic control of the ignition and the extinction. The blockage of the burner by the dirt and the wear-out rarely happen, and the emission of unburnt spieces and the soot is basically small, and the combustor efficiency is high with a little excessive air. Therefore, it is used for various fields such as industrial use, business uses, and the household uses. In the future, there will be a possibility that the zero emission will come true by achieving super-low NOx and CCS (CO₂ Capture and Storage) by using the oxygen burning.

Dry low emission (DLE) combustion technologies have contributed to reduce emissions of gas turbine systems. Recently, pressure and temperature conditions of gas turbine combustor rise to increase thermal efficiency and reduce emissions. Also, the gas turbine fuel is diversified to fuels such as syngas by gasification and by-product gases from various plants. Conventional DLE technologies do not necessarily meet these new demands, and new approaches are necessary. This article introduces present DLE combustion technologies, such as lean combustion and rich-quench-lean combustion, and their issues. It also introduces new approaches for the DLE combustion technology, such as lean direct injection and exhaust gas recirculation.

Fundamental studies have shown that tubular flame has potential for realizing many kinds of practical combustors, because the flammable range is very wide, the burner can burn various kinds of fuels with low NOx and SPM emissions, the burner is simple in structure and can be compact, and the tubular flame shape yields convenient ways to use. Based on these good points, recently developed tubular flame burners have been classified into four groups and briefly introduced in this paper; (1) wide flammable range, resulting in a torch burner which can burn blast furnace gas of low caloric heat, (2) fuel diversity, resulting in burners for by-product fuel gases, city gas, LPG, kerosene, banker A, banker C, and biomass powder, (3) simple and compactness, resulting in burners installed in the fuel processing system of PEFC, micro steam generator, and water heater, a burner for heating a hollow bolt, and a portable micro burner, and (4) tubular shape, resulting in a yellow flame generator for fireplace, a pilot flame for stabilizing main combustion in a high speed flow, an annular burner flame to assist PET powder combustion, and a Saturn-ring burner for heating a Stirling engine.

Stricter emissions legislation combined with the need to reduce greenhouse gas emissions drives fundamental research to produce cleaner, more efficient systems. Chemical kinetic mechanisms together with CFD codes are used to design more efficient and clean systems and optimize the operating behaviour of practical combustion devices such as internal combustion engines, gas turbines and other combustion devices.

However, in order to validate and produce accurate detailed chemical kinetic mechanisms, a wide range of data is needed, which is normally generated under well-controlled physical conditions of temperature, pressure, fuel/air ratio and dilution. These data include (i) ignition delay times recorded in shock tubes and in rapid compression machines, (ii) speciation data from flow reactors, jet-stirred reactors and flame experiments and (iii) flame measurements of laminar burning velocity. Typically, these mechanisms for hydrocarbon and oxygenated hydrocarbon systems are generated in a hierarchical way, starting first with the hydrogen/oxygen system, thereafter adding a carbon monoxide/carbon dioxide subset, followed by formaldehyde, methane and other larger C₁-C_n species.

This work will discuss the development of detailed chemical kinetic mechanisms in the context of hierarchy and range of validation. Some typical problems associated with these mechanisms will be discussed and some ideas on how they may be addressed will be explored. Application of detailed kinetic mechanisms of water addition to gas turbines to increase efficiency and reduce emissions will be explored in some more detail.

A survey of published papers was carried out to evaluate the technology applied to biodiesel fuel (BDF) in diesel engines. The paper describes the findings and the development of this research field. The analysis of 44 papers in Japanese and English established the following points as important with many related studies: (1) the differences in the combustion characteristics of BDF and ordinary diesel fuel, (2) relations among different feedstock for BDF (FAME composition), the fuel properties, and combustion characteristics, (3) studies of BDF made from waste edible oil, (4) the spray characteristics and the mechanisms of the spray combustion, (5) studies of oxidation deterioration of BDF, (6) improvements of low temperature fluidity for palm oil methyl esters, (7) applications to modern diesel engines, (8) improvements of combustion characteristics by mixing with volatile fuels or by water emulsification. For the future, the following research themes can be suggested: development of special engines fueled with BDF, and application of unused feedstock, especially for non edible oils.

The authors developed breath alcohol sensor with high accuracy, good durability, quick response, stability and linear output. Key technologies of sensor system are fine Ni coil and new catalysis of CoOx/CuO/Al₂O₃. Catalyst layers, which are coated by electrophoresis, are designed to form hollow cylindrical body on Ni coil. Large surface area of catalyst layer, large temperature dependence of Ni coil resistivity and high selectivity enable to detect level of 70~400ppm with high sensitivity.

Various factors that influence flame flashback of a laminar flame were studied. We focused on a stationary laminar flame base just before flame flashback to apply concepts of stationary conditions. In our experiments the flame stretch rate and the heat release rate in the vicinity of a lean methane/air premixed flame base were quantitatively measured using a single, rectangular port burner that controlled the surface temperature. The variations of the flame temperature and the mass flux were led from the analytical equations, that the previous study had shown, and our experimental results. In order to examine the mechanism of a flashback occurrence, it was explained that the equilibrium position between the fluid velocity and the burning velocity was located near the maximum position of the flame stretch rate along the flame. At this position, the local burning velocity estimated from the analytical equations increased in the maximum by 9% from the laminar burning velocity because the contribution of the flame curvature is the largest between factors that relate to the variations of the the local burning velocity. This result shows that the flame curvature according to the flame shape at the equilibrium position between the fluid velocity and the burning velocity becomes the main factor to occur the flashback.

In order to clarify the functions of the space heating rate (SHR) for a combustor of ultra-micro gas turbines (UMGT), the relation between the SHR, the residence time in the combustor (τ_b) and the heat loss ratio (HRL) were derived. It is deduced that τ_b depends only on the SHR without any relation to the scale of the combustor, and is inversely proportional to the SHR. This relation was confirmed for many gas turbine combustors of various sizes with a volume of 0.06x10^-6 - 0.146 m³ using H₂, C₃H₈, and Jet fuel. Experimental results of flat-flame type ultra-micro combustors indicated that the maximum value of the SHR corresponds to the chemical limitations on combustion rate for each type of fuel in the combustor, and the minimum permissible value of the SHR was limited by heat losses to the surroundings. The HLR is also deduced to decrease in approximately inverse proportion to the SHR, which was confirmed by heat loss measurements of flat-flame type ultra-micro combustors. The importance of the SHR in ultra-micro combustors is discussed.

The effect of gravity on flame spread over sub-flash liquids was investigated from scaling analysis and experiments. The role of three independent (surface-tension, gravity and viscosity) influences on the mechanism of pulsating flame spread was explored by scaling analyses based on sub-surface layer instability. These three influences form two independent pi-numbers, firstly the Marangoni (Ma) number and secondly Grashof (Gr) number, which include the characteristic length scale ratio (depth of sub-surface circulation)/ (horizontal length of preheated liquid surface). The Prandtl (Pr) number was introduced to compensate for the different thermal diffusivity and kinematic viscosity of different liquids. Also a non-dimensional flame spread rate, V/V_D (= Vδ/D, where δ is the quenching distance and D is the diffusivity of fuel vapor) was introduced. Using these non-dimensional parameters, the flame spread mechanism was divided into two separate regimes: for the shallow liquid pool the non-dimensional flame spread rate was correlated with {Gr^0.15 / (Ma·Pr)}^1.0, while for the deep liquid pool it was correlated with {Gr^0.15 / (Ma·Pr)}^1.5. Flame spread rate decrease with decreasing gravity. The effect of gravity on flame spread rate for deep liquid pool is greater than that for shallow liquid pool, so that the former is smaller than the latter under micro-gravity condition. Also scaling analysis shows that decreasing initial liquid temperature is similar effect of decreasing gravity on flame spread, i.e., flame spread at initial liquid temperature of 293K for n-butanol deep pool under micro-gravity condition seems to be same as that at 260K under normal gravity condition. The pulsation was not observed under micro-gravity at 293K, because this condition is thought to be same as psued-uniform flame spread which is observed at low initial liquid temperature under normal gravity.