1. Center for Combustion Energy, Tsinghua University, 100084 Beijing, China
2. Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, 100084 Beijing, China
3. Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
4. Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain