Dilution of Aircraft Exhaust Plumes at Cruise Altitudes

Abstract

The dilution of jet engine exhaust in the plume behind cruising aircraft is determined from measured plume properties. The data set includes in situ measurements of CO₂, NO, NO_y, SO₂, H₂O, temperature, and contrail diameters behind subsonic and supersonic aircraft in the upper troposphere and lower stratosphere, for plume ages of seconds to hours. The set of data is extended into the range of milliseconds based on computations and measured temperature values. The bulk plume dilution is expressed in terms of the dilution ratio N which is the mass of air with which the exhaust from a unit mass of burned fuel mixes. For: 0.006 s ‹ t ‹ 10⁴ s, the bulk dilution ratio measured in more than 70 plume encounters follows approximately N=7000 (t/t₀)^0.8, t₀=1 s.