i made a Mantaflow Fire+Smoke Simulation and have to problem, that the fire looks very blocky and large. The Smoke looks pretty good nonetheless. It´s a Fire + Smoke Emitter and the Domain Resolution is 800. Are there specific settings in blender to control the size and blockiness of the fire? All i found is the Fuel slider in the Emitter settings, but it mainly changes the amount of fire and not the size. Adaptive Domain and Noise is activated. I don´t really understand, why the smoke looks very high resolution and the fire very low altough it´s the same emitter and Domain. Thanks for every answer!
If you look at one of the bottom corners of your domain, you should see a little wireframe box:
That's the size of one voxel according to your domain's resolution. If that voxel is too big, then either reduce the domain size, or increase the resolution. As the domain's resolution is basically just a matter of slicing the domain into boxes according to the domain's bounding box largest side by the resolution value.
I.E in your case, a subdivision of 800 means your domain will be made out of up to 800 blocks per side.
See more on Domain Settings — Blender Manual
Now, if your simulation looks good in the viewport when in solid view, then the issue can come from the domain's material itself.
A good way to start on a decent material is to just plug a Principled Volume shader to the material's volume input and nothing else. Set the density to 5 and Blackbody intensity to 1. That's a good base to start with:
Of course you can then customize it to your needs.