Originally Posted by GXP Venom
I really don't understand the reasoning of doing this except for a single piston engine application where there aren't other pistons providing the inertia to allow the engine to utilize all the compression possible. And then you have to use a supercharger for it to work? Well then if you have to boost, wouldn't you want to make the most of it? The whole thing smacks of being different for no other reason to be different. Maybe Mazda should have sold the idea to Volvo. They like to do stuff just because.
It doesn't really make sense till you can understand it mapped out on a P-v diagram with the area being work. Same with the diesel cycle.
The key here is pumping loss. It takes energy to compress the air. This alleviates some of this energy input and results in a boost in efficiency. Remember that efficiency doesn't equal power when it comes to mpgs.. at the cost of power, you get mpgs basically.
The compression ratio in a miller cycle engine is not the same as a typical engine. The 2.3l mazda engine is constructed as a 3.0 That .7l loss is a result of the swept volume that isn't compressed. (from intake valve open longer) A high static CR is limited to the intake valve opening timing and IMO much boost is better since you're loosing a third of your dynamic compression ratio to start with. Boost and direct injection is the way to go.
The concept is very sound, works, and used more often than you think. Hybrids use a similar cycle to boost mpgs. They just don't use forced induction.