A step in the right direction but I can’t see how hydrogen burning with natural gas can only produce water as an emission. Surely it is burning with air and not pure oxygen and so nitrous oxides etc will be produced. It’s different if used in a fuel cell.
Yes, hydrogen will produce nitrous oxides when burnt in air, just as natural gas does. But the combustion is at atmospheric pressure, so oxides of nitrogen are formed at much lower levels than when burnt under pressure. One of the reasons that diesel engines produce so much NOx is that the compression ratio is high,
