Timeline for Are internal combustion engines more efficient on cold days?
Current License: CC BY-SA 4.0
18 events
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| Feb 9, 2023 at 7:25 | comment | added | Bill | Does the greater heat loss by the engine casing and via the water-radiator cooling system have any additional benefits? | |
| May 25, 2018 at 5:41 | history | edited | user12262 | CC BY-SA 4.0 |
(additional minor corrections)
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| S May 25, 2018 at 5:29 | history | edited | user12262 | CC BY-SA 4.0 |
Add on to expand on "negated or reversed by other factors". Several people continued to mention less mpg during winter as "proof" of engines operating less efficiently with lower cold side temps.
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| S May 25, 2018 at 5:29 | history | suggested | JasonDean | CC BY-SA 4.0 |
Add on to expand on "negated or reversed by other factors". Several people continued to mention less mpg during winter as "proof" of engines operating less efficiently with lower cold side temps.
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| May 25, 2018 at 3:40 | review | Suggested edits | |||
| S May 25, 2018 at 5:29 | |||||
| Apr 12, 2015 at 11:54 | vote | accept | richard | ||
| Jan 30, 2015 at 22:13 | comment | added | supercat | @steveverrill: Turbines do have some advantages, but I would think they would "prefer" a flow of fluid which is smoother than what an engine would normally put out; expansion cylinders would have a cyclic "demand" for fluid which coincides with the main cylinder's exhaust stroke. Further, the cool thing about the approach in the white paper I wish I could find was the ability to use the expansion-harvesting cylinders as combustion cylinders during times of higher demand. Could an engine with multiple turbines use "trumpet valves" or something similar to dynamically reconfigure them? | |
| Jan 30, 2015 at 22:04 | comment | added | Level River St |
@supercat It's nice to see people try different things, but for that last bit of expansion I think a turbine (as used in a turbocharger) is probably best. Turbines have an advantage over reciprocating expanders at low pressure differences, as they use the principle of the wheel to reduce friction: perimeter velocity is n times hub velocity, so friction of the bearings feels n times less at the perimeter. Turbines are also smaller. The principle works with steam, too: the Titanic and her sister ships had 2 reciprocating steam engines, with the exhaust feeding into a low pressure turbine.
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| Jan 30, 2015 at 13:26 | comment | added | supercat | I wish I could find that paper again; does it sound like a neat concept? | |
| Jan 30, 2015 at 13:25 | comment | added | supercat | That's the five-stroke behavior of the engine I described, but the paper described an engine which could switch between having four combustion cylinders (and no expansion) and having two combustion cylinders and two expansion cylinders. Engines with dedicated expansion cylinders go back decades, but from what I understand they're not usually worth the weight. What was cool about the approach in the paper was that the inner two cylinders could be used for a combustion cycle in times of high power demand, but could be used for an expansion cycle, increasing efficiency, in times of lower demand. | |
| Jan 30, 2015 at 5:48 | comment | added | Level River St | @supercat I assume you mean this, or a development of it: 5-stroke-engine.com See also en.wikipedia.org/wiki/Six-stroke_engine . The Crower six-stroke adds (after the normal 4 strokes) a water injection which cools the engine by generating steam, followed by a steam expansion stroke and steam exhaust stroke. It's a good idea, but means carrying water as well as fuel, and the water must be pure to avoid furring up the engine. My view is, it's probably best to leave the engine as it is and add heat recovery to the exhaust: either closed cycle steam generation or thermoelectric | |
| Jan 30, 2015 at 2:03 | comment | added | supercat | I once read a paper about a five-cycle modification to an inline four-cylinder engine so that the inner two cylinders could either operate normally (when significant power was required), or could operate in tandem as an "expansion cylinder" (during times of lower energy demand). I would think such an arrangement would effectively double the expansion ratio, though I'm not sure what effect that would have on efficiency. Have you ever heard of such a thing? | |
| Jan 29, 2015 at 21:18 | comment | added | DarioP | +1 in a car this effect is tiny, but if you play a bit with a microengine (3.5cc or so) you would experience this very clearly, both in the higher amount of fuel per cycle that requires in cold days, and in absolute performances. | |
| Jan 29, 2015 at 20:54 | comment | added | Level River St | @Floris thanks, but I'm a an industrial combustion equipment engineer (mainly furnaces, boilers, and heat recovery systems for gas turbine exhaust) so I understand combustion pretty well. In particular it's counterintuitive to many people that cold fuel/air contains more energy per unit volume than hot fuel/air. tpg2114's comment about drag on your answer is an excellent point that didnt occur to me, though I'm sure it would have done to many on aviation SE. | |
| Jan 29, 2015 at 15:13 | comment | added | Floris | This is a far better answer than my own. | |
| Jan 29, 2015 at 12:07 | comment | added | Level River St | @mattecapu the temperature rise depends only on the mixture composition. The heat released per kg for burning x% fuel in y% air is constant, and if we assume the heat capacity is independent of temperature (which is a reasonable assumption for the purpose of this answer) the temperature rise is constant. I have assumed 2000K rise, which gives different theroretical post-combustion temperatures of 2000+600=2600K and 2000+540=2540K in the two inlet temperature cases considered. | |
| Jan 29, 2015 at 10:25 | comment | added | seldon | Why does the combustion of fuel increase the temperature by a fixed amount? Isn't it dependent from the air intake? | |
| Jan 29, 2015 at 0:28 | history | answered | Level River St | CC BY-SA 3.0 |