Prevent yocto from removing bzImage output files

Question

I use 'bitbake' command 3 times, for 3 different layers, one after one. In the folder /build/tmp/deploy/images/{machine_name}/, there is only one kernel output file(bzImage). But, for example, file system output files, I have 3 output files for each bitbake I did. I would like to know what should I do to make 3 different kernel output files for each bitbake without the previous bitbake will override the next one. I tried already to use the yocto project docs, without success. Thank you.