Talk:Thermal efficiency

message: What in blazes is going on in the thermal efficiency section?
E_hp - E_r = 1 ?!?! 
So E_hp was greater than one to begin with?! Something needs explanation or changing here!  —The preceding unsigned comment was added by 165.124.116.206 (talk) 23:06, August 22, 2007 (UTC) 
Internal combustion engines are not "thermal devices" like furnaces or steam engines.  Heat is a byproduct of burning fuel to generate pressure.  Heat is actually unwanted, thus radiators and so on.  External combustion engines are "thermal devices" because they specifically use heat, to generate pressure.  —Preceding unsigned comment added by Arantius (talk • contribs) 16:44, 3 January 2008 (UTC)

message: I undid your revision of the thermal efficiency article due to grammer and the material added being confused and out of place. I'm not sure the Carnot limit applies to Solar cells like you state (do you have any references?) and the bit about detonations just seemed odd to me. I don't think higher temperatures around shockwaves do allow higher efficiencies and while there are large temperature gradients within engines it doesn't seem relavent to the article to me. Andrew.Ainsworth (talk) 13:27, 13 January 2008 (UTC)
replies: text: And of course there are losses on the internal combustion side that have not been mentioned: the additional energy required to refine petroleum into gasoline as opposed to higher molecular weight fuel oil, the energy cost and evaporative fuel loss of transporting gasoline through the supply chain to gas stations, the energy cost of building, heating, lighting, manning, and maintaining an infrastructure of gas stations that would not be needed with electric cars, the energy cost of building, repairing and maintaining IC engines which are many times more complicated than electric engines, and particularly the energy saved through regenerative braking.  But you have a point.  I removed the adjective "much", and I will look for sources.  --ChetvornoTALK 07:05, 31 May 2010 (UTC)
thread_title: Applications

message: http://en.wikipedia.org/wiki/Internal_combustion_engine#Engine_Efficiency
Arnero (talk) 18:07, 16 January 2008 (UTC)
thread_title: Internal combustion engine

message: Unreferenced statement at the bottom concerning electric vehicle system efficiency("much greater") compared to I/C is incorrect because the analysis is very incomplete.  Author completely ignores losses in battery storage cycle, electric motor efficiency, weight of vehicle difference, transmission losses from power plant to battery charger, etc. Full analysis would also extend to difference in efficiencies all the way back to coal extraction and oil extraction, transportation, conversion to useful fuel, energy expense of waste disposal(including transportation, cleanup, etc). I agree it should be more efficient, but not much greater.  That yields unrealistic expectations.
:And of course there are losses on the internal combustion side that have not been mentioned: the additional energy required to refine petroleum into gasoline as opposed to higher molecular weight fuel oil, the energy cost and evaporative fuel loss of transporting gasoline through the supply chain to gas stations, the energy cost of building, heating, lighting, manning, and maintaining an infrastructure of gas stations that would not be needed with electric cars, the energy cost of building, repairing and maintaining IC engines which are many times more complicated than electric engines, and particularly the energy saved through regenerative braking.  But you have a point.  I removed the adjective "much", and I will look for sources.  --ChetvornoTALK 07:05, 31 May 2010 (UTC)
thread_title: Other inefficiencies

message: This article is riddled with conceptual flaws that will lead the reader to false conclusions.
example: electric heat pumps may have a thermal efficiency of >100% because they move much more heat than the electric energy consumed. The definition must be extremely concise about what parts of the system are included and excluded in the calculation, and where gains or losses from outside arise. -- 99.233.186.4 (talk) 16:52, 13 November 2009 (UTC)
replies: text: The point you made about heat pumps is actually included in the article:   " [COP]...can often be greater than 100%. Since these devices are moving heat, not creating it, the amount of heat they move can be greater than the input work."  However the article may not be as concise as it could be, as you say.  I added the energy balance (1st Law of thermodynamics) equations for heat engines and heat pumps to the article. --ChetvornoTALK 20:24, 13 November 2009 (UTC)
thread_title: conceptual flaws

message: Electric resistance room heaters are 100% efficient - all the energy is ultimately dissipated as heat into the room. Where else does it go?
:Electric heaters also produce significant amount of photons which might not be absorbed, which creates significant amount of loss.212.156.122.30 (talk) 09:09, 18 March 2011 (UTC)
replies: text: The tiny fraction of energy radiated as light photons is absorbed by surfaces and converted to heat.  Electric heaters are considered 100% efficient. --ChetvornoTALK 10:53, 18 March 2011 (UTC)
thread_title: 100% efficient

message: In the 'Engine cycles' section, there is this remarkable sentence:
< The higher the compression ratio, the higher the temperature in the cylinder as the fuel burns and so the higher the efficiency. >
but that is exactly what the equation immediately above does NOT say. What it says is that the efficiency depends ONLY on the compression ratio. The 'temperature in the cylinder as the fuel burns' is not relevant. (The same applies to the Brayton cycle).
86.3.108.41 (talk) 23:39, 29 September 2011 (UTC)
replies: text: I made an edit to fix this 86.176.165.110 (talk) 12:32, 18 October 2011 (UTC)
thread_title:  Wrong! (Completely and utterly) 

message: The statement under the section "Carnot efficiency": 
:"Carnot's theorem only applies to heat engines, where fuel is burned. Devices that convert the fuel's energy directly into work without burning it, such as fuel cells, can exceed the Carnot efficiency." 
is dubious. You can't convert fuel into energy without burning it unless you want to very narrowly define burning as only that which produces fire. As long as something is being oxidized it is being burned, just like our body "burns" calories without fire. TimL • talk 22:15, 19 September 2013 (UTC)
replies: text: The distinction is that in a fuel cell the chemical energy is not converted into heat first.  A fuel cell operates like a battery, the chemical energy is converted directly into electricity.  Carnot's theorem applies only to converting heat to other forms of energy. --ChetvornoTALK 01:03, 20 September 2013 (UTC)

text: Carnot's theorem applies beyond cases where fuel is burned (such as electric heat pumps and refrigerators). But the statement is otherwise correct; if your initial energy source has low entropy, you can convert the energy into work more efficiently than you can with an equal amount of high-entropy thermal energy. If you burned hydrogen fuel to drive a heat engine to run a generator system, you would likely recover much less electrical energy than with a fuel cell. One way of thinking about it is that minimizing losses is equivalent to minimizing entropy generation during the energy conversion process, so any step that creates excess entropy is wasteful. Any irreversible step generates entropy. Burning fuel is an irreversible, entropy-generating step; discharging a fuel cell or a rechargeable battery may be a reversible process, depending on the chemistry. That almost guarantees that it will be more efficient.JB Gnome (talk) 06:49, 21 August 2014 (UTC)
thread_title:  Carnot Efficiency and burning