Such engines date back LONG before folk began worrying abiut NOx.
I grew up in an agricultural, rather than industrial, city, but can remember fogs so dense that you had to stand at the bottom of short lampost to see if the gas was alight! You couldn’t see across the road!
No wonder the London smogs killed people.
We need to preserve such machines from our past. There are still lessons to be learned by those too young to have seen them operating.
Already, the world has lost too much experience of those who have done it before.
Twice, i was sent on brainstorming sessions to cure problems that had been, to me, fairly recently solved.
Each time that i said that we had solved the problem on a legacy product, my fellow brainstormers did not know what had been made previously!
So they were hell bent on inventing a wheel to ease moving things!
Those who ignore history are condemned to repeat the mistakes.
Howard