I understood what "combustion" means not until I was about to write this review. Now I am happy to know what the English term "internal combustion" stays for.
This puzzle is very interesting. It is one of my first of that type - fitting objects into another object or whatever the type is called (I am not that into the terms of puzzle types). The thing is that the four pieces inside the "box" or "frame" are only partially visible and one has to use their other senses to understand what the internal structure is. It is like cracking a safe or a combination lock. With the difference that the combination here is not that complex and you can find it with a few tries only.
I was surprised to find out that the intended solution was not what I have found. It appears that there could be different solutions to "Internal Combustion", depending on how the four pieces are put inside. Mine copy of the puzzle arrived with different initial setup than intended. And I think the solution I had at first was the most interesting and the most difficult. The intended one is fairy simple and discoverable. So far I have found only two different solutions, but who knows - there could be more as well.
With this feature (having different possible arrangements), I think "Internal Combustion" is an useful toy with time. Especially if you have forgotten the solutions which you have found so far. You will re-experience the joy of solving it.
Here are my ratings for "Internal Combustion":
This seems quite low, depending on how I really feel about this puzzle. But in time I might re-review it and change the ratings to higher.