Trend of the recent combustor technology for civil aircraft engines are reviewed. NOx reduction is extremely difficult for aircraft engines, which have many strict requirements including light weight and compactness. However, the tightening of NOx regulations over the last 20 years has greatly advanced the technologies of aircraft engine combustors. In addition to NOx, in the near future PM and CO₂ emission regulations will become even stricter, but the required technologies are common to each other in that those are technologies that uniformly mix and react fuel and air in the smallest possible volume. Therefore, further development of RQL, Lean Burn, Spinning, etc. are expected. As computational resources expand, LES is becoming a standard tool which takes important role in the combustor development process. In order to precisely predict emissions such as NOx and PM, even more accurate atomization models and turbulent combustion models are considered necessary.

IHI has developed the domestic engines for the Ministry of Defense since the generation of the J3 in the 1960s as a coordinating manufacturer, and continued making an effort on the F3, XF5, and F7 engines, as well as the recent successful XF9-1 demonstrator engine for a next generation fighter. Our group has been responsible for the development of combustors for these various engines. Combustors for fighter engines, which necessitate high maneuverability, are required to have high combustion stability, while the need for better fuel consumption and lower environmental impact is increasing in response to the growing demand for commercial aircraft in recent years. In order to meet recent engines' needs, we have developed the innovative “cross jet swirler” type combustor, which can achieve both higher operational stability and environmental performance than the conventional RQL type combustor. By combining the swirler with various types of fuel nozzle the requirements of each engine system can be fulfilled. This paper describes the status of our development efforts for combustors for aircraft engines and the outlook for future research and development.

Numerical analysis technologies of the aircraft engine combustor are introduced mainly from the research of JAXA aviation technology directorate. In order to realize a practical numerical analysis for the design and development of aircraft engine combustors, it is necessary to generate a computational grid of complicated geometry at a practical cost. The applicability of high-performance computing systems is also important. HINOCA-AE, which is a CFD solver for aircraft engine combustor using the Cartesian grid with an immersed boundary method to satisfy these requirements, is introduced. Modeling of spray combustion processes, i.e. fuel atomization, spray dispersion, evaporation, chemical reaction, is also important. However, the modeling is insufficient because it is difficult to measure these processes in detail. Modeling researches of fuel atomization and droplet group evaporation using detailed numerical analysis are introduced.

In Japan and overseas, there is a rapid need to reduce the use of fossil fuels, and industrial gas turbines are being researched and developed to meet the needs of a wide variety of fuels. For hydrogen and ammonia in particular, the movement toward social implementation has been advanced to an unprecedented level. Although it takes time to build a fuel supply chain, it is based on multiple scenarios and is expected to be commercialized on a certain scale in 2030. In this paper, the correspondence of industrial gas turbine to carbon neutrality is introduced from the viewpoint of fuel conversion, and projects of ammonia direct combustion micro gas turbine and oxygen hydrogen combustion turbine which AIST is related to are also introduced.

Kawasaki Heavy Industries, LTD. (KHI) has been conducted research and development projects for a future hydrogen society. Within the development of the hydrogen gas turbine, key aspects are stable and low NOx combustion. KHI developed a Dry Low NOx (DLN) hydrogen combustor for a 2MW class industrial gas turbine with the micro-mix technology. Thereby, the ignition performance, the flame stability at engine start-up and loading conditions were investigated. NOx emission values were kept about half of the Air Pollution Control Law in Japan (70ppmv@16% O₂). In 2020, KHI started the engine demonstration operation by using an M1A-17 gas turbine with a co-generation system located in the hydrogen-fueled power generation plant in Kobe City, Japan. Finally, at a power output of 1800kW, the NOx emissions were 60 ppm (O2-16%, 60% RH). For the first time, a DLN hydrogen-fueled gas turbine successfully generated electricity and heat.

The role of GTCC systems in power grids as the means of absorbing the electric power fluctuations is growing in importance as the introduction of wind and solar power is being promoted. The development of large industrial gas turbines primarily focuses on raising the turbine inlet temperature (combustion temperature) for higher efficiencies. Various underlying technologies are employed to suppress the increase in NOx emissions and combustion oscillations due to higher temperatures. This special article introduces the combustion measurement technologies used for gas turbine combustor development, such as Planar Laser-Induced Fluorescence (PLIF), Computed Tomography (CT) of chemiluminescence, and Tunable Diode Laser Absorption Spectroscopy (TDLAS).

Tiny integrated giant-pulse laser induced breakdown ignitions promise to enhance the performance of internal combustion engine. It makes possible the ignition at the optimal spatial point apart from the cylinder “cold wall” with multi-points and multi-pulses. Giant-pulse lasers can fire leaner or high-pressure mixtures that are difficult to be ignited by a conventional spark plug and thus the fuel is used efficiently, while low CO₂ and harmful pollutant emissions are expected. Unfortunately, the giant-pulse laser ignition has been limited the basic researches until recently. In this paper, we'd like to review the brief history of laser ignition with regarding micro solid-state photonics. >50MW peak power and >20mJ pulse energy microchip laser is also discussed for the string ignition.

To improve the thermal efficiency of internal combustion engines, the achievement of volumetric ignition by discharge plasmas is one of the key issue. A very long gap discharge provides the ideal discharge ignition with small heat loss to electrodes, high energy coupling efficiency from power supply to discharge plasma, and suppression of re-strike discharge in flow environment. It is, however, difficult to realize the long discharge because the applicable voltage is practically restricted by the dielectric and/or surface breakdown of insulating material. New ignition method was proposed based on the possibility to reduce the discharge threshold voltage by supplying an initial charge between the electrodes with a laser. This paper outlines the new technology named Laser Breakdown Assisted Long-Discharge Ignition (LBALDI) used for ignition by forming a long-distance discharge assisted by laser breakdown plasma, expanding the lean and rich ignition limits, suppressing re-strike discharge in flow environment, and improved ignition performance under high pressure environment.

Biomass gasification processes are recently attracting attention to produce renewable gaseous fuels as alternatives of fossil fuels. However, raw woody biomass resources to be able to use for biomass gasification are limited because the biomass containing high moisture may lead to low heating values of the gaseous fuels produced, which are inappropriate for the use in gas engines. Then, the introduction of oxygen-enriched air into the gasification reactor has been proposed in this study, which can reduce heat loss during the gasification due to the sensible heat of nitrogen in the gasified gas and increase concentrations of combustible substances in the syngas. Additionally, high partial pressure of oxygen promotes the gasification reaction rates, improving the carbon conversion efficiency. A downdraft packed bed gasifier, which is known to be suitable for small-scale distributed utilization of biomass resources, was selected for woody biomass gasification experiments in this study. After switching the inlet gas from air to oxygen enriched air, the temperature at the top surface of biomass pellet bed rose sharply. The temperature through the packed bed was also kept high under the oxygen enriched air gasification, compared with the normal air gasification. Moreover, the syngas with more H₂ and CO significantly increased. The thermo-equilibrium calculations were conducted to confirm the gaseous compositions and their difference between the air and oxygen enriched air gasification. As a result, the calculation was almost consistent with the experimental results obtained.

Non-premixed lifted flames of hydrogen are investigated using direct numerical simulations. Initially, a laminar non-premixed flame of hydrogen and steam diluted oxygen is compared with a nitrogen diluted oxygen case to investigate the effect of steam dilution on the structure and stabilization mechanism of the lifted flames. Both cases result in a triple flame structure, typical of non-premixed lifted flames. The diffusion and lean premixed branches of these flames are observed to collide due to the high diffusivity of hydrogen. Even though the overall structure of both cases is similar, the cases showed some variations in their species distributions. Further analyses showed that these variations result from steam dilution, altering the rate of certain reactions. The stabilization mechanism of the flames is investigated using transport budget analyses. In the steam diluted case, the diffusion and reaction terms have the same order of magnitude, indicating flame propagation stabilization, whereas the reaction term is dominant for the nitrogen diluted case, indicating autoignition stabilization. The results suggest that even though the overall structure of the nitrogen diluted and steam diluted flames is the same, the effect of steam dilution on the rates of reactions may alter the stabilization mechanism. Then, the effect of pressure on the flame features of the steam diluted case is investigated at four different pressures varying from 2-20 atm. The results of the cases at higher pressures suggest that neither the overall structure nor the stabilization mechanism of the flames is affected by the pressure.