Temperature is one of the most important information for flame researchers among many characteristics of the flame so that many methods to measure it have been studied and developed. Originally, those were static and point measurement but nowadays, they are time-dependent and three dimensional. Even the methods have been drastically developed, the accuracy of the obtained temperature should be ascertained. This report will look back on the most reliable calibration method, though it is very old and looks unrefined.
A new two-line OH-PLIF has been developed for flame temperature measurement using a single LIF setup. The longitudinal flame temperature distribution of manipulated coaxial premixed jet flame is obtained with the conditionallyaveraged OH fluorescence intensities at the OH front taken with two different excitation lines. CO emission characteristics of the controlled flame are discussed on the basis of the local fuel and the flame temperature. Flame temperature in a quartz microchannel is also measured by the phase-locked OH 2-line method, where the trigger signal is obtained with CH* chmiluminescence. It is found that the flame temperature increases after the ignition and gradually decreases during upstream propagation, leading to thermal quenching.
To improve internal combustion engines, it is critical to measure the temperature distribution of their walls. Authors quantitatively visualized the instantaneous temperature distribution of a wall exposed to flames. Lifetime-based temperature imaging was performed using a simple measurement system consisting of a non-intensified high-speed CMOS camera, a pulsed UV laser, and a phosphor coated quartz glass covered with a thin metal film. The uncertainty in the temperature measurement was ±2.0°C for measurements of uniform temperature fields in the range 40-250°C. Singleshot wall temperature measurements were demonstrated for combustion by flames in an engine cylinder. This enabled inhomogeneous temperature distributions in the engine with or without flames to be visualized. Even under motoring conditions, there was a large temperature gradient across the side window at the highest position of the piston. The engine speed and the coolant temperature increased the magnitude of temperature but they did not affect the overall temperature distribution, i.e. the spatial distribution and the spatial gradient of the temperature. The instantaneous temperature of the top of the piston was visualized in the transient process after firing had commenced. The measured temperature gradually increased.
2D temperature and concentration distribution plays an important role for the combustion structure and the combustor efficiency in engines, burners, gas turbines and so on. Recently, as a measurement technique with high sensitivity and high response, laser diagnostics has been developed and applied to the actual engine combustions. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions. In this study, the theoretical and experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a computed tomography(CT) technique using absorption spectra of water vapor at 1388nm. The CT tunable diode laser absorption spectroscopy method was applied to a burner and engine exhausts to measure 2D temperature distributions using 8-path, 12-path, and 16-path CT cells and the accuracy and the special resolution of this method was discussed compared with the measurement results of a thermocouple. Since CT tunable diode laser absorption spectroscopy has a potential of the kHz response time, this method enables the real-time 2D temperature measurements to be applicable in various industrial processes including engine applications.
Japan Aerospace Exploration Agency (JAXA) has conducted research and development of combustion technologies for aircraft engine to reduce nitrogen oxides (NOx) emissions drastically from the standard which is being stringent by International Civil Aviation Organization (ICAO). JAXA also has technical cooperation and collaborative researches about gas turbine combustors with manufacturers and collaborations about high temperature heat-resistant materials with government ministries and agencies. JAXA developed high pressure combustion test facilities to support research and development of manufacturers.
High-Temperature and High-Pressure Combustion Test Facility was improved in 2005. Its combustor inlet pressure is up to 5 MPa, temperature is up to 1,000 K, air flow rate is up to 4 kg/s and exit gas temperature is up to 2,000 K. Full Annular Combustor Test Facility was improved in 2007. Its inlet air pressure is up to 2 MPa, temperature is 753 K, air flow rate is 20.5 kg/s and exit gas temperature is up to 2,000 K.
By using improved facilities, JAXA carried out tests of multi-sector combustor models and annular combustors for selection of ECO engine combustor to assist “Research and Development for an Environment-friendly Small Aircraft Engine (so-called ECO engine project)” which is a project of the Ministry of Economy, Trade and Industry/New Energy and Industrial Technology Development Organization and started in 2004. And a verification test of an ultra-low NOx combustor for “the Research on Environmentally Friendly Clean Engine Technology (so-called TechCLEAN project)” was carried out.
This paper presents new application of microcombustion technologies to fuel reactivity measurement and research tool for combustion chemical kinetics. In prior works using a heated micro channel so called “micro flow reactor with a controlled temperature profile”, three kinds of flame dynamics were observed for a methane/air mixture: normal flames in the high flow velocity regime; flames with repetitive extinction and ignition in the moderate velocity regime; and weak flames in the low flow velocity regime. We focused on weak flames and theoretical background on the relation between weak flames and ignition is examined. Subsequently, experimental and computational results on weak flames of dimethyl ether/air and n-heptane/air mixture are examined. Three-stage reaction zones were observed in both experiment and computation. Investigating species profiles of the weak flames, it was found that transient, three-stage ignition (oxidation) process was realized as stable, three-stage reaction zones by the micro flow reactor. This micro flow reactor methodology was further applied to various fuels and effects of gasoline primary reference fuels on weak flames are introduced. Experiments and computations at elevated pressures (up to 5 atm) were conducted and pressure dependence of weak flames was investigated. Pressure dependence of weak flames for an ethanol/air mixture was computed using two different chemical kinetics and computed pressure dependence was different each other although the two chemical kinetics predict the same pressure dependence of mass burning velocity and ignition delay time. Finally, recent works using the micro flow reactor are introduced.
Micro- and meso-scale combustion as a component of micro-power generator has been investigated intensively, mainly for gaseous fuels. It is desirable to develop a microcombustor with liquid hydrocarbon fuels, which have relatively high energy densities, about two orders higher specific energy (energy per unit mass) than that of a lithium ion battery and about one order higher volumetric energy density than that of gaseous fuels. Several studies have been conducted on mesoscale combustors with liquid hydrocarbon fuel. It is difficult to keep stable flame inside a narrow space, due to limitation by inadequate residence time for complete vaporization and high heat loss rate associated with the increase in surface to volume ratio. Electrospray technique is often employed to produce a fine and controllable spray to solve the former issue. The latter issue is solved using catalyst or heat recirculation. This paper reports recent progress in liquid fuel combustion in a mesoscale tube using electrospray technique without catalyst.
The removal of hydrogen in the off-gas from fuel cells in a safe manner is desirable. Hydrogen oxidation by an atmospheric non-equilibrium plasma is a promising technique for the off-gas treatment. In the present research, characteristics of NOx formation in hydrogen oxidation by the pulsed plasma were investigated to determine an optimum oxidation condition in H2/O2/N2 gas mixture. The applied voltage, repetition rate, gas flow rate, and equivalence ratio were varied. NOx concentrations generally increased with an increase in the energy density and with a decrease in the equivalence ratio. To understand the reaction mechanism of NOx formation in hydrogen oxidation, a reaction kinetic study was carried out. The chemistry was resolved into separate contributions from radiolysis processes and gas phase reactions. N radical generated by electron impact reactions in the pulsed plasma and molecular oxygen play an important role for NOx formation (N + O2 → NO + O). At high equivalence ratios, NOx level was strongly reduced by gas phase reaction of N + NO → N2 + O. It was found that the equivalence ratio was the most dominant factor to control NOx concentration in hydrogen oxidation by the pulsed plasma. An energy efficiency of 0.26 g-H2/J and a NOx emission of 5 ppm was attained at an equivalence ratio of 2.0.
Flow and mixture formation of a methane jet with impingement on a cavity wall were calculated using a large eddy simulation (LES). The calculations were performed for varying wall shapes and the nozzle-to-wall distance. In addition, the spark ignitability is discussed based on the distributions of flow and fuel concentration. The result shows that flow and shear stress are suppressed and fuel concentration increases in the cavity and the flammable mixture is widely distributed. Furthermore, a distribution of the turbulent Karlovitz number Ka is estimated based on the velocity and equivalence ratio. When the mixture is spark-ignited at the point of Ka<50, a stable combustion is achieved.
This paper discusses the flame spread and its limitation along a thermally thin combustible solid (a sheet of filter paper) in a high-temperature / low-oxygen concentration opposed-gas flow, based on experimental investigations. The leading flame length along a solid surface for both horizontal flame spread and vertically downward flame spread decreases with decreasing oxygen concentration. Especially the flame becomes to be round shape in high-temperature/low-oxygen concentration gas flow, which is similar to the flame shape in microgravity condition. The flame leading edge retreats and extinction occurs at some oxygen concentration. We defined this oxygen concentration LOC (Low Oxygen Concentration) , as the flame spread limitation. The flame spread rate near the LOC is close to that in microgravity with normal air condition. To clarify the effect of buoyant force on flame spread, the Rayleigh number for spreading flame was examined. The Rayleigh number decreases with decreasing oxygen concentration, and it is less than the critical Rayleigh number near the LOC. The relation between the non-dimensional flame spread rate, V, and the Damköhler number, Da was also examined. The V both of normal gravity and microgravity decreases with decreasing the Da, and reaches to the flame spread limitation at some Da. This paper suggests that it may be possible to simulate the flame spread under microgravity environment by using high-temperature / low-oxygen gas flow under normal gravity.