Finnair are experimenting with using biofuel, made of grease and fat recycled from restaurant kitchens to power their planes. They have been using it since 2011.

Emitting less greenhouse gas than regular aviation fuel, it does not compete with food production or negatively impact biodiversity. The only drawback is that it costs twice what teh airline pays for aviation fuel. Finnair believes with increased demand  and the development of supply chains will see the cost fall.

(and no it is odourless, you wont smell French fries or hamburgers in the exhaust fumes).