Autoignition of fuel sprays is of special relevance to compression-ignition engines. The high air temperature in diesel engines leads to heating, vaporization and autoignition of the injected fuel spray; typically part of the liquid fuel vaporizes before ignition occurs so that by the time the mixture autoignites, the hot air is partially premixed with fuel vapor. The present investigation concerns these processes in dilute fuel sprays with emphasis on including detailed reaction mechanisms for the gas phase. Reference fuels are methanol, n-heptane and n-octane. Both monodisperse and bidisperse sprays are considered, droplets are in the radius size range 10 μm to 50 μm. The study presents parametric dependencies of spray life-time and ignition delay time in dependence of initial droplet size, equivalence ratio, degree of premixedness, hot air temperature and pressure. For small droplets fuel vapor accumulation around the droplets causes a two-stage heating of the droplets. For bidisperse sprays it appears that a monodisperse spray with Sauter mean diameter represents the ignition characteristics of a bidisperse spray. It is also shown that fuel properties clearly affect ignition characteristics.