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My uncle used to joke that his car ran better in the mountains because the air was cleaner and thus had more oxygen. He was not serious, but in case of cold ai

My uncle used to joke that his car ran better in the mountains because the air was cleaner and thus had more oxygen. He was not serious, but in case of cold air there would be more oxygen per unit volume due to density so that might improve the combustion.

munk-a 6y ago
The air pressure is also higher at colder temperatures so if the fire is underground it'd have more forces working in its favor to cycle fresh air to it and the relative temperature difference between the freshly heated and exhausted air and the fresh air would be wider causing there to be more turbulence cycling the air around.
pletnes 6y ago
Hence the invention of the intercooler diesel engine.
- llampx 6y ago
  The turbocharger is what helps at high altitudes, not the intercooler which just cools the air. The turbo packs more air in to the engine, which helps at sea level but makes a big difference at high altitude. Superchargers do the same.
deleted 6y ago
[deleted]
klodolph 6y ago
Heat engines generate power from a difference in temperature. The larger the temperature difference, the more power. You can increase the temperature difference by making the heat source hotter or by making the heat sink colder.
mikestew 6y ago
Ignoring, of course, the fact that "in the mountains" means an increase in altitude and thus a decrease in air density. My carbureted vehicles that were jetted for sea level always ran like shit in the mountains. And fuel injected vehicles run fine (because they can adjust for the altitude on the fly), but with noticeably less power. Apologies for pedantically deconstructing what your uncle meant as a smart-assed joke.
- bigiain 6y ago
  Lower air density means old carburetted engines run leaner - which since most such engines are tuned to run slightly rich for reliability in favour of slightly lean, gives you more power up until the point they overheat and if they're a 2 stroke motor relying on the oil mixture in for lubrication the fuel, seize. One of the old traditional racetracks here in Australia is Mt Panorama at Bathurst. It's got about a 180m elevation change between the start/finish/pit straight and the top of the mountain. Back when they were allowed to race motorcycles there, old 2 stroke racebikes were notorious for seizing at the top of the hill if they'd been jetted down at the bottom and hadn't been set "rich enough" to allow for the altitude change. Many many riders crashed and said "It was running really strong, til it locked up on me and spat me down the road..." (No apologies at all for my off topic response to pedantry...)
  - mikestew 6y ago
    Mmm, pretty sure sea level carbs run rich at altitude. Less air means a need for less fuel for the same ratio. But the fuel side didn’t change because we didn’t rejet, so now too much gets pumped in. If I’m guessing the bikes might have seized at the bottom of the hill instead? Or it just took until the top before the damage was done.
    - bigiain 6y ago
      Ahhh, yeah - you're right. I've got it back to front there. In my defence it's been a long time singe they've been allowed to race motorcycles there. At least 20 years. And now you mention it I do recall bikes seizing at the end of pit straight, right down the bottom of the hill.
      - mikestew 6y ago
        In my defence.. In your defense, anyone old enough to remember carbs how work, even if only slightly, is forgiven the occasional lapse of memory. ;-)

munk-a 6y ago

The air pressure is also higher at colder temperatures so if the fire is underground it'd have more forces working in its favor to cycle fresh air to it and the relative temperature difference between the freshly heated and exhausted air and the fresh air would be wider causing there to be more turbulence cycling the air around.

pletnes 6y ago

Hence the invention of the intercooler diesel engine.

llampx 6y ago
The turbocharger is what helps at high altitudes, not the intercooler which just cools the air. The turbo packs more air in to the engine, which helps at sea level but makes a big difference at high altitude. Superchargers do the same.

deleted 6y ago

[deleted]

klodolph 6y ago

Heat engines generate power from a difference in temperature. The larger the temperature difference, the more power. You can increase the temperature difference by making the heat source hotter or by making the heat sink colder.

mikestew 6y ago

Ignoring, of course, the fact that "in the mountains" means an increase in altitude and thus a decrease in air density. My carbureted vehicles that were jetted for sea level always ran like shit in the mountains. And fuel injected vehicles run fine (because they can adjust for the altitude on the fly), but with noticeably less power. Apologies for pedantically deconstructing what your uncle meant as a smart-assed joke.

bigiain 6y ago
Lower air density means old carburetted engines run leaner - which since most such engines are tuned to run slightly rich for reliability in favour of slightly lean, gives you more power up until the point they overheat and if they're a 2 stroke motor relying on the oil mixture in for lubrication the fuel, seize. One of the old traditional racetracks here in Australia is Mt Panorama at Bathurst. It's got about a 180m elevation change between the start/finish/pit straight and the top of the mountain. Back when they were allowed to race motorcycles there, old 2 stroke racebikes were notorious for seizing at the top of the hill if they'd been jetted down at the bottom and hadn't been set "rich enough" to allow for the altitude change. Many many riders crashed and said "It was running really strong, til it locked up on me and spat me down the road..." (No apologies at all for my off topic response to pedantry...)
- mikestew 6y ago
  Mmm, pretty sure sea level carbs run rich at altitude. Less air means a need for less fuel for the same ratio. But the fuel side didn’t change because we didn’t rejet, so now too much gets pumped in. If I’m guessing the bikes might have seized at the bottom of the hill instead? Or it just took until the top before the damage was done.
  - bigiain 6y ago
    Ahhh, yeah - you're right. I've got it back to front there. In my defence it's been a long time singe they've been allowed to race motorcycles there. At least 20 years. And now you mention it I do recall bikes seizing at the end of pit straight, right down the bottom of the hill.
    - mikestew 6y ago
      In my defence.. In your defense, anyone old enough to remember carbs how work, even if only slightly, is forgiven the occasional lapse of memory. ;-)