Originally Posted by
harryn
That sounds like an interesting project.
I wonder what factors contributed to the loss of efficiency ? My guess is that it has to do with combustion temperature, because that was one of the big trade offs that the commercial engine makers to make to bring NOx levels down.
I don't remember the exact point, but somewhere around 2 000 C the NOx levels really start rising. If you don't mind pumping in more ammonia into the exhaust, this can be counteracted if this is a consideration.
If you can make the stroke as long as possible / low piston speeds, that can also make a big difference in fuel efficiency, although not necessarily to vehicle performance.
There is some interesting work in reviving the opposed piston type engine concepts, although these are not exactly small.