I’d love to get some citronella oil floating around the house, but I don’t want to burn candles indoors while we sleep. I looked in the air freshener aisle thinking it would be perfect for glade or renuzit to put it in one of their electric wall air fresheners but surprisingly it doesn’t exist. Is there a reason that citronella needs the heat of a candle or lantern and won’t work with a wall freshener?
I don’t think so. My sister makes and sells soap and one of the most popular bars they sell in the summer has citronella in it. They buy it as an oil which they add while making the soap. I think you can grow citronella plants to keep bugs away as well.
They suggest burning citronella candles for outdoor use only. Apparently sometimes it occ causes dermatitis, thus the thought that concentrated burning citronella is not a good thing to breath in a indoor environment.
It’s actually pretty safe, it gets the GRAS label in the USA- when used as directed. You can buy it as an oil to apply topically, in the insect repellent aisle.
http://www.burtsbees.com/natural-products/sun-outdoor-protection/herbal-insect-repellent.html
You must be the only person who actually likes the odor, incidentally. 
You just need to volatilise the oil. This can be done through heat or increasing the surface area by creating an aerosol.
Citronella probably isn’t a popular smell for indoors. People tend to associate it with the outdoor torches and insect repellent. When it comes to odours, it is all about association. BTW, citronella is not effective as an insect repellent.
Why not get an aluminium spray bottle and make a solution of water/alcohol/citronella (maybe with a drop of surfactant) to create a citronella spray. Experiment with the proportions to make sure it is not flammable or to ‘wet’. You do not need much of the oil.