zero emission
engine, motor, process, or other energy source, that emits no waste products that pollutes the environment or disrupts the climate
en-GB/ˈzɪəɹəʊ ɪˈmɪʃən/
en-US/ˈziɹoʊ ɪˈmɪʃən/
engine, motor, process, or other energy source, that emits no waste products that pollutes the environment or disrupts the climate