[trevorjohnson32 (OP)]

Could one obtain the pressures required to ignite fusion with a string of engines in circuit? If not why? and another idea might be to use large amounts of non nuclear explosives to get the pressures required. Does anyone know if they already tried that?

[Kryptid]

As a gas becomes more compressed, it becomes increasingly difficult to compress it further. So while the first engine would get efficient compression, the second engine would be less efficient, and the third one even less so. You eventually reach a point where the engines aren't able to compress the gas any further. A second limitation is the strength of the container that is holding the compressed gas. I don't think there is a substance on Earth that can withstand those pressures. A third limitation is the temperature. When a gas is compressed, it becomes hotter. Taking a gas from standard pressure up to fusion pressures is going to melt any container known.

There is an inverse relationship between pressure and temperature when it comes to fusion. The higher the temperature, the less pressure needed to achieve fusion and vice-versa. Since we can't reach the pressures at the center of the Sun, we compensate by making the plasma hotter instead. Current fusion reactors use low-density, extremely hot plasma that is held away from the container walls with magnetic fields.

[Bored chemist]

Does anyone know if they already tried that?

No.
Science and research budgets are quite restricted so scientists don't waste them on ideas with no hope of success.