Idle throttle and Carb Ice !?
Thread Starter
Join Date: May 2001
Location: London
Posts: 51
Likes: 0
Received 0 Likes
on
0 Posts
Idle throttle and Carb Ice !?
Sorry if this is one of the less interesting questions 
but why is the carburettor more susceptible to icing when closed ?!? I hope it's not too obvious, or a silly question (I'm new to this game!), but it's been puzzling me. I thought the major contibutor to icing was due to the venturii effect - so how is this related (if it is) a closed throttle and ice !? Or is it simply due to a cooler engine at low RPM. Many books state this without explaining !
Cheers,
NB.
but why is the carburettor more susceptible to icing when closed ?!? I hope it's not too obvious, or a silly question (I'm new to this game!), but it's been puzzling me. I thought the major contibutor to icing was due to the venturii effect - so how is this related (if it is) a closed throttle and ice !? Or is it simply due to a cooler engine at low RPM. Many books state this without explaining !Cheers,
NB.
Join Date: Aug 2001
Location: Norwich, UK
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
When the throttle is nearly closed at idle or descent power, the air intake is more restricted than at fuller throttle settings. Air passing through the intake therefore suffers a greater temperature drop.
Also, downstream of the restriction caused by the throat and the butterfly valve the liquid fuel is introduced, where it will vaporise; when it vaporises it removes heat from the air (latent heat of vaporisation) and cools the air even more.
The temp drop can be greater than 30 degrees C - meaning warm, or even hot days of quite normal levels of relative humidity can be expected to produce carb icing at idle/descent power.
Also, downstream of the restriction caused by the throat and the butterfly valve the liquid fuel is introduced, where it will vaporise; when it vaporises it removes heat from the air (latent heat of vaporisation) and cools the air even more.
The temp drop can be greater than 30 degrees C - meaning warm, or even hot days of quite normal levels of relative humidity can be expected to produce carb icing at idle/descent power.
