Carb icing.

[matelot]

Academic interest only, guys. Nothing turned up on a search.

I understand the principles surrounding carb icing in aero engines, but what stops it happening in cars?

Is it the physical design of the carb, or atmospheric phenomena under the bonnet?

Cheers. :)

------------------
Me, sweat? I'm that cool, it's condensation.

[Cough]

Doesn't stop.....They have to get around it!
A large motorcycle manufacturer had to recall a number of bikes for modification due to this effect.

As for cars - Most are fuel injected these days which gets around the problem.

C......ough

[matelot]

Thanks, Coffee! :)

PS - which manufacturer? I'm a biker.

------------------
Me, sweat? I'm that cool, it's condensation.

Edited for carb ice!

[This message has been edited by matelot (edited 09 March 2001).]

[Pdub]

There are a couple of theories on why the engine in engine in the Mini is positioned like it is. One of them is that the Carb suffered ising when it was sat out the front just behind the grille.

This let to the classic mini "whine" the engine was turned round at a late stage of design, and so an idler gear was inserted to that you didn't have 4 reverse gears and 1 forward.

[Cough]

Fink it was Kwakazakkki, about 5 years ago? Cant remeber the exact model, but I believe it to be a big sports tourer..They sorted it though as I remember......However, my memory is faint......

C.....ough

[Genghis the Engineer]

I gave a talk a year or two ago to a branch of the IIE (Institute of Incorporated Engineers) where I mentioned carb icing. The question and answer session turned into a rather interesting talk about the subject. Several Engineers there claimed to have come across the problem on both car and motorcycle engines.

G

[OLD_EGG_BOUND]

IF I REMEMBER RIGHTLY, MY RENAULTS OF MID 80`S VINTAGE HAD THE COOLING SYSTEM ROUTED THROUGH THE CARB TO PREVENT ICING.

[ShyTorque]

Matelot,

Some years ago I brought my Mitsubishi back from the far East when I came back home. It had no hot air device for the air filter box as was apparently normal for that market. It used to suffer from carb icing in cold humid conditions and would run rough or cut out, even at cruising speed but more usually in town where small throttle openings were more likely. At such times, if you took the top off the air filter there was quite a lot of ice inside the venturi. Waiting for a couple of minutes for engine heat to reach the carb would melt the ice and all would be well.

[matelot]

Thanks for the replies, peeps - still surprising though that on some newer trainer types we still need to faff around with carb heat, when the auto industry appears to mostly have it solved.

Still, half the fun is levers, switches and knobs. It's the control, you know! Man over machine. :)

------------------
Me, sweat? I'm that cool, it's condensation.

[G SXTY]

Motor vehicle carbs can be very much affected by icing. Still have fond memories of having to keep stopping and thawing out my ancient VW Jetta on motorway runs whenever the ambient dropped below about 5 degrees.

VW's solution was to have 2 air intakes, one at the front of the car, one around the exhaust manifold. Selection was controlled automatically by a flap / temperature sensor in the intake system. If this failed in winter, you very quickly knew about it.

No worries these days, my intake air comes via a luverly big supercharger & engine management system - it'd be just the job for all those flying school 152s. ;)


------------------
Looks like I picked the wrong week to quit pruning.

[Genghis the Engineer]

Interestingly, the certified engine world seems a bit behind the uncertified engine world.

I flew a SkyArrow last year with a certified Rotax 912 engine - the carb heat was little different to, say, a C150.

On the other hand, look at the engine on a Pegasus Quantum 912 - same engine on a top of the range flexwing, and although carb heating is there, it doesn't involve the pilot at-all. A heating element using coolant is wrapped around the air intake - no carb icing and no loss of power.

G

[ShyTorque]

Genghis,

There is usually some slight loss of power with a heated intake of any sort, due to reduced charge density. On the other hand, a heated manifold may give better economy due to better fuel vapourisation.

Just nit-picking! :)

One other thing to remember about many light aircraft carb heat systems is that the filter is bypassed when it is operated.

[Code Blue]

<font face="Verdana, Arial, Helvetica" size="2">One other thing to remember about many light aircraft carb heat systems is that the filter is bypassed when it is operated</font>

That fact proved very helpful once after a bloody pigeon got stuck in my air filter http://www.pprune.org/ubb/NonCGI/eek.gif

------------------
-.-- --.- -..-
[email protected]

[SeldomFixit]

I blame Bernoulli, myself. If he hadn't insisted on decreasing the temperature of expanding air we would never have gotten into this fine mess Stanley.......

[barbox]

Kawasaki with Carb Ice problems was the GTR1000/ZX10 (same engine).They got round the problem by warming the carb up with exhaust heat by a simple mod that also reduced the BHP by quite a bit, didn't understand why at the time (I had a GTR 1000)
but when I sold the bike to get my PPL all was revealed!.
By the way, as an LUFC fan, can anyone tell me if a UK 'airline' flies direct into La Coruna in Northern Spain?.
Dont fancy flying down to Biarritz and turning right to La Coruna at 110kts!(and I certainly wont be routing 'direct' over Biscay with one engine).
Always wondered where Deportivo La Coruna were based, now I know I wish I didnt!.

[This message has been edited by barbox (edited 16 March 2001).]

[Airbanda]

Further to pdubs point, which is quite correct and had the side effect of putting the distributor in the way of a lot of cold water. In spite of this icing was still a problem in Minis as late as the 70's . The solution was to adjust the air intake by loosening the filter case mounting nut and rotating it until the air intake tube was over the exhaust manifold.

Other cars of similar age, my personal memory is of a Peugeot 104ZS, (where are you now ANB 736T)had manual sliders to alter the mix of ambient and warmed by the exhaust air to the intake. In later versions automatic devices controlled by a wax capsule carried out the function.

Presumably fuel injection and electronic engine management put this in the same category as the starting handle.

Now drive a diesel :)

[This message has been edited by Airbanda (edited 16 March 2001).]

[Pdub]

Ah but the distributer at the front was an easy fix, pop down the doctors ask for a latex glove, cut the very tips of the fingers and thumb off, then place over distributer cap with wires poking throuh fingers. Ahhh modern technology.

Now drive an Impreza Turbo, 300bhp and no chance of carb ice :)

[Airbanda]

Latex glove? Luxury

In my day it were origami with a plastic sandwich bag and half a can of WD40. http://www.pprune.org/ubb/NonCGI/tongue.gif

[Lu Zuckerman]

Near the end of WW2 the US Navy was losing a lot of patrol aircraft that were powered by R2800 P&Ws. Some of the losses were attributed to loss of power at low altitudes and it was blamed on carb ice. The Holly Corporation came up with a new design that used a variable venturi much like the operating principle of an SU carburetor. They put them on the R2800s and the loss rate went up. It seems that these carburetors would make ice faster than your refrigerator freezer. These carbs went into the bin and were replaced by a newer design Bendix Stromberg PD type carb and the problem went away.

------------------
The Cat

[matelot]

Ah, barbox - another poor sop like me who had to sell his bike to pay for flying.

Why can't women leave us alone?! :)

Interesting replies so far guys, thanks.

------------------
Me, sweat? I'm that cool, it's condensation.

[smallfish]

Sold my Lotus 7 rep to pay for an ATPL course, gutting in many respects but worth it in the end. Had a 2.0 l Ford Pinto engine with twin Weber 45s. Anyhow, hot water from the head was routed through the inlet manifold on this particular type. I guess you don't see this on aero engines as they are mostly of the air cooled variety.

[barbox]

Hi Matelot,,,yes but once a biker always a biker,,,,,, even bought a DiBlasi to put in the planes 'boot', have a look at the bike on their web site, folding moped,,, great fun (after the Gilera carb has had a drill wacked through it).

No relplies to my request for info on 'La Coruna',,,went on line to IBERIA, £685 return from London,,,next nearest large airport is Santiago La Composta,,,nice name, even this is £675,sent an email to Iberia asking if they really meant Santiago Chile!.

Looks like paying full LUFC travel club fares
or flying down in the AA5A,,,,?.

Aint told the wife yet, 50 yrs of age and still as mad as ever!.

[Skycop]

Smallfish,

Interestingly enough your water heated manifold wasn't designed to prevent carb ice but to ensure better fuel droplet vapourisation in the inlet manifolds after it had left the carbs!

If ice is going to form it will do so where the depression is; in other words in the carb venturi. To prevent this, most older vehicles had a flap with a "winter" setting that caused the carb to draw air from around a shield around the exhaust manifold (just like aircraft). Some car engines produce noticeably less power when this is selected. I drove a 4wd in NZ that wouldn't pull the skin off a rice pudding with hot air selected in winter. Fortunately I never suffered carb ice with it at cold.

[100LL]

Think this is what Genghis was talking about
www.skydrive.co.uk/sd_ch.htm (http://www.skydrive.co.uk/sd_ch.htm)