air flow meter using thermistors
have a look at most modern car engine management systems
the under bonnet environment is one of the most hostile electronics will encounter other than military - very high temp Δ, high G, high alititude Δ, very high electrical noise.
most systems use hot wire or ultrasonic Air Flow Meters and are electrically very robust, accurate, and normally have signal conditioning for 8-16V supply and 0-5V output.
save yourself time and effort and get one from a scrap vehicle and adapt it for your flow rate
good ones to use are Hitachi, Ford (Hitachi Clone) or Bosch
Polymath