That&#x27;s what&#x27;s puzzling.  Opposed-piston Diesel engines have a long history.  There are others now proposing them. Eco Motors [1] claimed they were going into production with one in 2014. Didn&#x27;t happen.  They might be a little better, but the claimed 50% improvement in fuel economy is a big jump.<p>These engines use valve ports, so piston motion produces the valve action.  All the timing is set by the engine geometry.   There are few variables adjustable at run time. This is also true of Wankel engines, which is why Wankels hit a wall - you can&#x27;t tweak fuel injection timing or valve timing.  In a Diesel, you can&#x27;t even tweak the spark timing.  Much of the improvement in IC engines has come from active control of fuel injection and spark, along with a few attempts at dynamically tweaking valve timing. These designs don&#x27;t seem to be able to do that.<p>[1] <a href="http:&#x2F;&#x2F;ecomotors.com&#x2F;video" rel="nofollow">http:&#x2F;&#x2F;ecomotors.com&#x2F;video</a>