Aircraft Cabin Air and Engine Oil - An Engineering View
Author: Dieter Scholz
Almost all passenger jet aircraft today use potentially contaminated bleed air for cabin ventilation.
A detailed look at the design of engine bearings, their lubrication and sealing reveals that jet
engines leak small amounts of oil by design and not only in failure cases. An equation is derived to
calculate the concentration of a possible cabin air contamination. The seal leak ratio is defined as
the percentage of oil leaving engine seals versus total engine oil consumption. If the seal leak ratio
is set to 2%, results show good agreement with measured concentrations of hydrocarbons in aircraft
cabins under normal conditions. The solution to the problem of cabin air contamination is a bleed
free design. Other partial remedies are briefly discussed.