How to render with a custom render engine?

Question

My problem is as follows: I'm working on a script that renders all the scenes in a file (matching some criteria, in this case having a default Camera on Layer 0).

This works.

But I cannot make a Render option based on this.

The (bad) code is as follows

import bpy

class LoopRenderEngine(bpy.types.RenderEngine):
    bl_idname = 'loop_renderer'
    bl_label = 'Loop Renderer'

    def render(self, scene):
        #bpy.context.scene.render.engine = 'BLENDER_RENDER'
        bpy.ops.render.render()

bpy.utils.register_class(LoopRenderEngine)

Since this calls the render() function in when implementing the render() function, it's not a surprise that this doesn't work.

Switching back as mentioned above to the BLENER_RENDER engine didn't work.

Any idea how to render within the render function?

PS Here is the whole code to understand my intentions better.

import bpy
import time

class LoopRenderEngine(bpy.types.RenderEngine):
    bl_idname = 'loop_renderer'
    bl_label = 'Loop Render Test'
    bl_use_preview = True

    def render(self, scene):
        bpy.context.scene.render.engine='BLENDER_RENDER'
        bpy.ops.render.render()

bpy.utils.register_class(LoopRenderEngine)

This works (ie starts rendering), but crashes when rendering. The command line shows:

Error: EXCEPTION_ACCESS_VIOLATION