Mitsubishi Heavy Industries, Ltd. (MHI) has proposed a rich-burn, quick-quench, lean-burn combustor for use as a simple, low NO_X-emission combustor for the ECO Engine (environmentally compatible small aero engine). MHI promoted the research and development of the ECO Engine from 2004 to 2006 as a national project with a subsidy from the New Energy and Industrial Technology Development Organization (NEDO). The performance evaluation tests, conducted at the combustion test facility of the Japan Aerospace Exploration Agency (JAXA) in 2006, indicated that many requirements were satisfied, such as emissions, combustor exit temperature distribution, and combustion efficiency. The NO_X emissions were less than 50% of the international regulations.