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Hot petrol - andrew34ruby - 08-06-2020
Many of us seem bothered by petrol pipes, pump and carb getting too warm, and I can remember this being a problem nearly fifty years ago. This made me think - why do the vast majority of cars blow the air heated by the radiator straight onto the engine?
Cold air hits the radiator, then the warmed air is flowing over the carb, pump and petrol pipes. No wonder it vaporises in hot weather. And hot weather leads to more traffic, so stationary traffic has a lot of hot air heating up the petrol.
And to make things worse, the hot exhaust pipe is usually along the same side of the car as the petrol pipe!
Old minis and 1100s seemed rare, in directing the hot air away from the engine, exiting under a front wing. that makes more sense.
Your thoughts?
RE: Hot petrol - Tony Griffiths - 08-06-2020
(08-06-2020, 04:42 PM). Arranging for theandrew34ruby Wrote: Many of us seem bothered by petrol pipes, pump and carb getting too warm, and I can remember this being a problem nearly fifty years ago. This made me think - why do the vast majority of cars blow the air heated by the radiator straight onto the engine?A wise saying: "Inside a carburettor, it's always winter". In other words, in the UK colder weather is the norm and carb icing can be a real problem (even today some motorcycles have heating elements around the intake manifold to cure the problem). Remember those air cleaners of old with an intake pipe that could be swivelled around to collect hot air from above the exhaust manifold and then turned around for warmer conditions? However, why fuel pipes were not better protected on older cars is, indeed, a mystery.
Cold air hits the radiator, then the warmed air is flowing over the carb, pump and petrol pipes. No wonder it vaporises in hot weather. And hot weather leads to more traffic, so stationary traffic has a lot of hot air heating up the petrol.
And to make things worse, the hot exhaust pipe is usually along the same side of the car as the petrol pipe!
Old minis and 1100s seemed rare, in directing the hot air away from the engine, exiting under a front wing. that makes more sense.
Your thoughts?
I had a car once where the previous owner had taken some considerable trouble to shield the carb and fuel pipes from exhaust heat. Even so, in hot weather the car still stumbled badly; on checking the engine when this happened I discovered that the inlet manifold was covered in condensed water and freezing cold; arranging for the manifold to be heated solved the problem. Edit. Just remembered: I rigged up a temperature senor and drove the car. The outside of the manifold read between 1 and 2C when the outside temperarture was 17C.
RE: Hot petrol - A G Wood - 09-06-2020
BMC fwd cars are a special case I feel. I think I read somewhere that Issigonis' original design layout [which had to use the A-series non-crossflow engine] called for the manifold and carburettor to be at the front, but persistent carburettor icing issues experienced with that configuration meant it then had to be reversed with the carburettor at the back and the most moisture sensitive parts of the ignition system now at the front. I doubt there would have been room in most pre-Allegro BMC engine bays to put the traditional top to bottom flow radiator anywhere other than the side which then meant using a pusher type [engine driven] fan.
With the original 'heated air straight on the engine' issue I don't see how it can be avoided so long as the radiator is at the front, with a normal north-south engine fan or not that's where its going to go. Having said that I've never looked to see how veteran Renaults manage with the radiator at the back of the engine?
I have noticed on this forum that you chaps in the UK seem to report vapour lock quite a bit, I have rarely experienced it in this country back in the carburettor days , non event now with EFI of course. Perhaps it is down to the formulation of your summer grade fuel rather than fuel system design shortcomings eccentricities?
Carburettor icing I have encountered once only, [first starts of the day, inland North Island NZ Winter, prob 1-2 deg C] but that was down to the factory water passages in the intake manifold of the vehicle being blocked by gunge.
RE: Hot petrol - Robert Leigh - 09-06-2020
The Issigonis designed Mini and 1100 had an adjustable air intake, so that it could draw warm air from around the exhaust in cold weather, and unheated air in warmer weather. I doubt if most owners were aware of the feature. The sytem was also used by Fiat in the early fifties (and possibly earlier) on the Toppolino, which had the radiator behind the engine.
RE: Hot petrol - andrew34ruby - 09-06-2020
(09-06-2020, 10:33 AM)A G Wood Wrote: Carburettor icing I have encountered once only, [first starts of the day, inland North Island NZ Winter, prob 1-2 deg C] but that was down to the factory water passages in the intake manifold of the vehicle being blocked by gunge.
Carburettor icing is not at the first start of the day. The scenario is that it starts at first start of the day, then maybe 20 miles down the road the air flow through the carb is reduced to zero by the formation of a large chunk of ice. Of course by the time the AA man (me) arrives the ice has melted and the engine starts. I found it mainly occurred in damp foggy weather at just over freezing temperature.
RE: Hot petrol - Tony Griffiths - 09-06-2020
(09-06-2020, 09:07 PM)andrew34ruby Wrote:He's the griff on carb icing. As it shows, it's possible for it to occur even at relatively high temperatures when combined with high humidity. P.S. In a light aircraft when the engine starts misfiring and the carb ice-warning light comes on, you select "Hot Air". As the ice melts, the misfire will often worsen; unfortunately, a number of pilots have then concluded that the hot-air setting must be making the problem worse and switched back to cold - whereupon their engine stopped.....and would not restart.(09-06-2020, 10:33 AM)A G Wood Wrote: Carburettor icing I have encountered once only, [first starts of the day, inland North Island NZ Winter, prob 1-2 deg C] but that was down to the factory water passages in the intake manifold of the vehicle being blocked by gunge.
Carburettor icing is not at the first start of the day. The scenario is that it starts at first start of the day, then maybe 20 miles down the road the air flow through the carb is reduced to zero by the formation of a large chunk of ice. Of course by the time the AA man (me) arrives the ice has melted and the engine starts. I found it mainly occurred in damp foggy weather at just over freezing temperature.
RE: Hot petrol - A G Wood - 11-06-2020
Thank you Andrew34 ,Tony & Robert.
Andrew, your scenario fits exactly what happened, but I already had a post that was starting to look like a wall of text so I left some of the details out
. I could also have added that the same p.o.s. workshop van would also annoyingly and explosively overheat in Summer due to missing radiator core fins [the owner of the business & van was a renowned tightwad].Tony, I had forgotten about the carb heat function on piston engined aero engines, no AA man to get you out of that scenario...
Robert, also I remember seeing a 2-stroke SAAB which had a fully detachable [and easily lost ?!] L shaped piece of ducting to do the same job. Twisting air intake snouts from cold to hot and vice versa used to be an item on our Summer/Winter Service Checks list back in the day. Eventually we evolved to thermostatically controlled vacuum operated hot air intakes which theoretically removed the human element, but introduced issues of their own...
RE: Hot petrol - Steve Clare - 11-06-2020
It's interesting that a lot of 1920s American automobiles had a permanent tube, collecting warm air from the exhaust manifold, direct into the carb.
A 1923 Chevrolet I owned- and regret selling, had this feature, and ran like a wristwatch.
You might think this wouldn't work very well, especially when the exhaust got really hot, but it worked fine.
RE: Hot petrol - Tony Griffiths - 11-06-2020
(11-06-2020, 07:30 AM)Steve Clare Wrote: It's interesting that a lot of 1920s American automobiles had a permanent tube, collecting warm air from the exhaust manifold, direct into the carb.That sounds like a quick, dirty but satisfactory fix for an inlet system that didn't have an efficient hot spot - and far cheaper than tooling up for the production of a new inlet-exhaust manifold system!
A 1923 Chevrolet I owned- and regret selling, had this feature, and ran like a wristwatch.
You might think this wouldn't work very well, especially when the exhaust got really hot, but it worked fine.
RE: Hot petrol - A G Wood - 12-06-2020
There was evidently a change in the source/composition of the pump gasoline in the USA around that time [less volatile]. I have some automobile engineering text books published by the American Technical Society dated 1925 which mention the new 'heavy fuels' and discuss methods to overcome their disadvantages, whilst still taking advantage of their 'higher value of power units'. Heating the entire carburettor gets a mention, as does fuel injection; 'nevertheless, there are many engineers who adhere to the view that sooner or later fuel injection will supplant present systems of carburetion, and progress made recently with aviation motors of fuel injection types may seem in some measure to justify this view ' . There's an illustration of a Holley 'temperature regulator' , which apart from the driver adjustable dashboard control, worked like a 1950s/60s heated air intake. Holley was said to 'recommend a temperature regulator for use with its own and other carburettors', so it was also available as an after-market accessory.