(From left in the rear row) Takeshi Yamamoto, Mitsumasa Makida, Takuo Sato, Kazuo Shimodaira, and Tsunetoshi Iwase (From left in the front row) Ryusuke Matsuyama and Hitoshi Fujiwara

  Clean Engine Team is conducting a research on a low NOx (nitrogen oxide) combustor for future aircraft. NOx is produced by the oxidation of nitrogen in the combustor, where a mixture of fuel and highly compressed air burns under a high temperature condition. The fuel consumption rate of an aero engine, equivalent to the amount of CO₂ exhausted, can be reduced by increasing the temperature of the combustor gas. This has a tradeoff, however, as the higher temperature of the combustor gas leads to the production of more NOx in the exhaust gas.

Succeeded in reducing NOx emission down to one fifth of the current regulation

  The combustors for aero engines being built nowadays are undergoing dramatic modifications to achieve both low fuel consumption and low NOx targets. The combustor is made up of a "fuel nozzle" which mixes fuel and air and a "liner" which covers the combustion area (Fig. 1). The conventional combustors adopt a so called “rich-lean” technology in which a small portion of the air enters through the fuel nozzle for rich combustion while most of the air enters halfway across the liner for lean combustion downstream. The NOx can be reduced even in this type of combustion when the nozzle and liner is properly designed. As an alternative, the recent “lean burn” technology attempts to drastically reduce the NOx exhaust by removing the rich combustion zone altogether. In a lean burn combustor, most of the air enters through the fuel nozzle, while only a small portion of air enters through the liner for cooling. These combustors inherently produce less NOx than the conventional combustors because the fuel tends to combust at a lower temperature.
  In current research, our team is developing a lean-burn combustor that reduces the NOx emission to only one-fifth of the limit under the current regulation. We are now planning future research, including demonstration tests at a large-scale facility outside of Japan, to develop a fuel nozzle for practical use in aero engines.

Fig.1 Combustor for aircraft engine

Contribution to global environment

  Besides, safety and reliability, engines for large aircraft nowadays must satisfy a host of ever-more severe standards on cost and measures of environmental performance such as noise and exhaust gas. Investment into development to satisfy these standards is huge. Aero engine manufacturers are trying to diversify the risks of the their investments by conducting an international joint venture for commercial aero engine development. Though Japanese engine manufacturers have a large share in this venture, their activity is mainly restricted to manufacturing. These manufacturers have thus faced difficulty in moving into the most advanced core technologies for the aero engine. The Clean Engine Team is eager to support Japanese engine manufacturers in their efforts to develop their own technologies for future aircraft engines. Part of this support has been extended through joint research with the engine manufacturers. Part has been expended through the provision of a large-scale test facility too extensive for a single company to maintain (Fig. 2). The current research for the low-NOx fuel nozzle is part of this activity (Fig. 3). The Clean Engine Team also believes that today’s research will help solve global environmental issues by providing a cleaner gas exhaust technology for future aircraft.

Fig.2 High temperature and high pressure combustion test facility

Fig.3 Fuel spray laser measurement (Left) and CFD (Right)
Left : The state of fuel spray from the nozzle is being observed by using a laser.
Right : Visualization of the simulation result of a flow inside of the fuel nozzle

(Hitoshi Fujiwara)