Carburetor icing
As carburettor icing (engl. Carburetor icing ) is defined as the deposition of ice in the intake passage of the carburetor of a gasoline engine . Such a deposit significantly affects the function of the engine. The phenomenon is particularly important when operating aircraft engines .
Origin and conditions
In the carburettor , the air that is drawn in flows through a constriction ( venturi tube ); there it is accelerated, creating a negative pressure, which leads to a cooling of the air. In addition, the change in the physical state of the fuel from liquid to gaseous - the "gasification" (technically more of an evaporation or evaporation ) - heat energy that is extracted from the environment - that is, the air that has already cooled down, which cools it down further. Water vapor contained in the intake air can condense into liquid mist droplets as a result of this cooling, be subcooled to below freezing point and solidify to compact ice when the wall of the intake duct is touched.
This process typically takes place at outside air temperatures (OAT) of approx. −5 to +15 ° C and is promoted by high relative humidity . On the one hand, the fresh air must be cool enough to fall below the freezing point through the typical cooling temperature range - approx. 10-20 ° C, depending on the operating state of the engine - in order to be able to form ice at all; on the other hand, the formation of liquid droplets promotes caking. If the ambient temperature is well below freezing point, it contains - in absolute terms - very little water vapor, which moreover rather precipitates in solid form as small snow crystals, which are then carried away by the air flow rather than caking.
Risk of carburetor icing
If the carburetor is not warmed up when flying through layers of air with the appropriate conditions, the carburetor may freeze up. As a result, you first notice a drop in performance due to the mixture becoming richer, due to the narrowing of the intake duct. At this point at the latest, the carburetor preheating must be activated. However, the pilot is often warned by a carburetor thermometer installed in the aircraft , in which the temperature range with the highest risk of carburetor freezing is often marked. Some aircraft models have a selector switch that can be used to switch to an alternative engine air supply (e.g. Maule M7 260C ). If such measures are not taken in time, there is a high probability that the engine will fail.
Individual evidence
- ↑ a b Fischer, A .: Carburetor icing. SwissAviation.ch, May 7, 1999, accessed on July 23, 2015 .
literature
- Winfried Kassera: Compact powered flight; The basic knowledge of the private pilot license 3rd edition. Motorbuchverlag, 2010, ISBN 978-3-613-02758-9 , Motor, p. 70