What is the best fire extinguisher to fit in my engine compartment?

Powder extinguishers use very fine dry powders. Most marine diesel engines have only a coarse air filter as they do not run in a particularly dust laden atmosphere, and these filters cannot filter out all the extinguisher powder. When drawn into a running engine the powder can build up into an incompressible bulk in the upper cylinder when mixed with fuel and cause a hydraulic lock. This can perforate a piston crown or bend a conrod.

https://jemascol.com/producto/exfoliante-corporal-chocolate Also some dry powder fire extinguishers contain ammonium phosphate powder which turns to phosphoric acid when exposed to moisture. This is highly corrosive and if drawn into a running engine can cause extensive damage. It is recommended that before tackling an engine room fire with a powder extinguisher, the engine is stopped. The only fire extinguishers suitable for use on running engines are FE-32 (halon replacement) which are class B (flammable liquids and live electrical circuits). These can be purchased from some chandlers, but many do not stock then as they are about three times the price of a powder extinguisher.