Engines 3

Fuel must have

Enough energy to vaporise, burn quickly and controllably, contain a high calorific value

Calorific value

The mount of heat obtained by a given mass of fuel

Vapour lock

Where fuel vaporises in the tube which restricts the flow of fuel

Which fuel is more likely to vapour lock

AVGAS

Detonation In cylinders

A fuel air mix that explodes rather than burns (where the flame rate is around 1000ft/sec, normal operation is 80ft/sec). Happens before piston is at TDC meaning the camdrive goes back on itself. It vibrates and gives a popping sound. Caused by weak mixture, wrong fuel used, excessive cylinder temperature or pressure. Lead additives (tetra-ethyl lead) help control detonation. You can hear a popping sound when it happens

Fuel rating

Usually rated with octave rating, you can use higher ratings but not lower

Pre-ignition

Before TDC, a hot spot occurs and combines with the spark, which forces the piston down and causes mechanical shock. Usually due to weak mixtures, usually worse at high RPM, and the engine wont turn off when it should. You can hear a popping sound when it happens

Engine air induction system

there’s an intake in the front of the aircraft which filters the air

Mixture ratio (stoichiometric ratio)

15:1 Air:fuel