There are no rules against submitting your own blog posts. As we know, it's quite common on HN. Though I have noticed personally that my blog posts get more activity here when submitted by others.

There are also no rules against plugging a product in a post. Again, it's extremely common on HN.

OP's user account was created 1339 days ago. I don't think his intention is suddenly to spam at all nor do I believe the post is "just a spam piece to advertise his app".