Talk:Engine efficiency

Gasoline (petrol) engines
"road legal cars are only about 20% to 35% when used to power a car"

This statement is an important fact and has no substatiation. It needs a reference. I can find nearly any number cited on the Internet that I wish, so it would be good to find a truly athoritative source, not a web equivalent to a magazine.

The statement is also poorly formed. It says "cars" are xxx efficient when used to power "a car". This should clearly state if the efficiency rating is for the engine, or for the car as a whole. Gnuarm (talk) 14:09, 3 April 2022 (UTC)

misc
"Gasoline engines also suffer efficiency losses at low speeds from the high turbulence and head loss when the incoming air must fight its way around the nearly-closed throttle; diesel engines do not suffer this loss because the incoming air is not throttled" - This HAS TO BE incorrect. Moving air is what takes energy. Not moving air (Maintaining the intake manifold vacuum) doesn't take energy. The inefficiencies of nearly closed throttle operation doesn't come from pumping losses but rather ineffeicient fuel/air combustion —Preceding unsigned comment added by Timmbacher (talk • contribs) 19:26, 30 September 2010 (UTC)

Just did a bit of spell checking (efficency->efficiency), apart from that this article has quite a few inaccuracy's. Don't have time to fix though.--Stripy42 14:01, 26 April 2007 (UTC)

I revised several factoids of the previous version. I based my input on mechanical-engineering textbooks in my possession but did not reference them. I hope that is not a problem.09:40, 4 October 2007 (UTC) —Preceding unsigned comment added by Raymondwinn (talk • contribs)

This article troubles me. In particular, the material below troubles me. It does not make any sense to me. I think it can lead to incorrect behavior. From where did this material come?

"Gasoline engines also suffer efficiency losses at low speeds from the high turbulence and head loss when the incoming air must fight its way around the nearly-closed throttle; diesel engines do not suffer this loss because the incoming air is not throttled. Engine efficiency improves considerably at open road speeds; it peaks in most applications at around 75% of rated engine power, which is also the range of greatest engine torque (e.g. in the 2007 Ford Focus, maximum torque of 133 foot-pounds is obtained at 4500 RPM, and maximum engine power of 136 brake horsepower is obtained at 6000 RPM)." —Preceding unsigned comment added by Ecarecar (talk • contribs) 17:26, 12 April 2008 (UTC)

"It should be noted that at lower power outputs, the effective compression ratio is less than when the engine is operating at full power, due to the simple fact that the incoming fuel-air mixture is being restricted."

What is an "effective compression ratio?" This needs a citation.

Compression ratio is defined as "the ratio of cylinder volume with the piston at crank-end dead center to the cylinder volume with the piston at head-end center." Van Wylen, "Thermodynamics," 1959 John Wiley & Sons, page 265.

The concept of "effective compression ratio" makes no sense. —Preceding unsigned comment added by 72.160.147.223 (talk) 17:45, 12 April 2008 (UTC)

Not very satisifying. I was looking for data on engine efficiency, and this article is long, rambling and random. Isn't there a table somewhere of engine efficiencies for a broad class of heat engines, from piston, to turbine to rocket motors? DonPMitchell (talk) 17:58, 29 June 2008 (UTC)

Confusing sentence about efficiency. " Engine efficiency peaks in most applications at around 75% of rated engine power, which is also the range of greatest engine torque (e.g. in the 2007 Ford Focus, maximum torque of 133 foot-pounds (180 Nm) is obtained at 4,500 RPM, and maximum engine power of 136 brake horsepower (101 kW) is obtained at 6,000 RPM). " This sentence is confusing. Is it saying that peak is at 75% of the RPM of the peak power point? Bradrh (talk) 15:48, 8 November 2013 (UTC)

Title change?
This really doesn't seem to be an article about engine efficiency in general. It's about the efficiency of engines in particular applications configured with other equipment. That is, the efficiency of engines being used to drive automobiles via a mechanical drive train (as opposed to, say, driving the generator of a serial hybrid) and without the benefit of ISG, etc.

I'd like to see another article that compares engine efficiency in a more general way. People are interested in energy efficiency of engines for other applications like running generators.

In the mean time it might help to break down some characteristics that are being lumped together. The efficiency of gasoline fueled piston engines are given after the losses to supporting equipment (which can vary). It would be helpful to know the efficiency of the engine both with and without that equipment.

Any other simple changes that would make the article a bit more general and useful would be appreciated.

Thanx, -ef  —Preceding unsigned comment added by 68.80.95.189 (talk) 23:51, 3 March 2009 (UTC)

Gasoline reciprocating engines are not 30% efficient. A good modern one such as in the Focus is about 18% efficient. I have updated the numbers. Mike163 (talk) 08:38, 16 September 2010 (UTC)

Engine eficiency table
A regular table is best also made (in a new article). I made a stub at appropedia: http://www.appropedia.org/Comparison_of_engines When finished, we can upload it here aswell KVDP (talk) 10:16, 8 June 2010 (UTC)

Stirling Engine Efficiency
http://www.bekkoame.ne.jp/~khirata/academic/kiriki/begin/general.html

The thermal efficiency of Stirling cycle that is used for Stirling engine is equal to that of Carnot cycle which is theoretical higiest efficiency. Expression of Carnot efficiency is follows.

1-Tc/Th

Where

Th : Higher temperature in the cycle Tc : Lower temperature in the cycle

This means as to be large for a temperature difference, theoretical heat efficiency are higher. Among Stirling engine developed, the engine to achieve a thermal efficiency 40 % exists.

From: Prof. Iwamoto, Department of Mechanical Engineering, Faculty of Engineering, Saitama University

Andy from Workshopshed  —Preceding unsigned comment added by 212.125.73.242 (talk) 15:28, 18 January 2011 (UTC)

Source for Gasoline Engine section improvement
If someone wants to edit the section on gasoline engine efficiency, the following .gov website would be great: http://www.fueleconomy.gov/feg/atv.shtml. It cites three sources that could be used to re-write some of the more technical components of the section that are currently completely uncited. 128.12.48.61 (talk) 22:28, 30 November 2011 (UTC)

Planned update of steam engine efficiency
I've just finished reading Hunter's Steam power and have some interesting material to add here. It is a bit too technical for the Steam engine article. Lots of interesting figures on actual operating parameters of different types of piston steam engines. It's going to take me a while to get it organized and figure out how to best present it. Perhaps I will have it ready in 10 days or so.Phmoreno (talk) 03:28, 5 June 2012 (UTC)

Diesel engine efficiency
I just watched a BBC TV documentary ('The Engine That Powers The World') which repeatedly claimed that diesel engines are far more efficient than petrol engines, as shown for example by the much longer range of diesel-powered submarines, but never (unless I nodded off and missed it) explained why this was the case. The different method of fuel ignition (compression versus spark) hardly seems sufficient to explain it. One would expect that in an engine based on the same fundamental physics (expansion of a hot gas within a cylinder driving a piston) there would not be a huge difference in efficiency. The article here does not suggest that there is such a huge difference. ( I wonder if the longer range of diesel submarines is due to lower oxygen consumption?) Anyway, someone sometime might want to give a fuller analysis.86.155.131.113 (talk) 21:49, 26 September 2015 (UTC)


 * The efficiency of internal combustion engines increases with the compression ratio. Diesel engines have higher compression ratios than gasoline/petrol engines because the latter suffer from pre-ignition at high compression ratios.  Part of the explanation of the higher efficiency at higher compression ratios is that a lower percentage of heat and pressure is lost in the exhaust cycle of diesel.  The Atkinson cycle, with it's longer stroke, is a way to improve efficiency of gasoline/petrol engines.  Atkinson cycle engines are being used in several vehicle models today, especially hybrids.Phmoreno (talk) 22:07, 26 September 2015 (UTC)


 * Thanks (for replying to my query). I checked what was said in the BBC documentary (at around 15 minutes in), and it claimed that in WWI diesel-powered German submarines had a fuel efficiency of 30%, while in British petrol-powered subs it was only 12% - a big difference.  It then said that by the end of WWI German subs had a range of 11,000 miles, whereas the first British subs had a range of only 280 miles.  This huge difference can't have been just a matter of diesel versus petrol, but in the context of the programme that was the impression given.  Even the smaller difference of 30% versus 12% seems too big to be explained by inherent advantages of diesel, as modern diesel vehicles typically have a fuel economy advantage of less than 50%.81.158.127.7 (talk) 14:36, 28 September 2015 (UTC)
 * Petrol had much greatest hazards than diesel: fire and explosion - especially with electrical switchgear arcing nearby. So the petrol submarines were only the very earliest and these were soon replaced by diesel engines. Although Germany was the leader in diesels at this time (arguably into the 1950s) UK shipyards like Vickers and Armstrongs had already licensed German diesel designs (Also see Doxford, for a highly efficient British ship cathedral engine). The main UK submarine classes of WWI (See the E-class) were diesel.
 * The range of a submarine depends on its size and its design. Small submarines designed to be small will not have the same range as something deliberately designed for long range. The British considered that the RN controlled all seas West of the Skagerrak and so had little need for a long-ranged submarine. There was no British need for a Deutschland as a blockade runner to the US or as a commerce raider on the Atlantic seaboard, and so they weren't built. Even the large M-class weren't built to have such range.
 * A similar thing happened in WWII with the E-boats and their hugely powerful diesels. There was nothing the Allies had that was comparable, and even the large Fairmile boats were slower, lighter and shorter-ranged. Andy Dingley (talk) 15:02, 28 September 2015 (UTC)

Compression or Expansion Ratio?
In the section entitled "Compression ratio" the first thing it mentions is expansion. Someone may wish to edit this to actually make some sense. If expansion is the most important, that it should be entitled as such. - KitchM (talk) 22:43, 20 January 2017 (UTC)

Grammar Problems
"Engines using the Diesel cycle are usually more efficient, although the Diesel cycle itself is less efficient at equal compression ratios." More efficient that what?

What does this sentence mean "Since diesel engines use much higher compression ratios (the heat of compression is used to ignite the slow-burning diesel fuel), that higher ratio more to air pumping losses within the engine."?

"Modern turbo-diesel engines use electronically controlled common-rail fuel injection to increase efficiency. With the help of geometrically variable turbo-charging system this also increases the engines' torque at low engine speeds (1200-1800RPM)." But isn't a diesel engine a low speed engine which produces its power at low speed to begin with?

"The gas turbine is most efficient at maximum power output in the same way reciprocating engines are most efficient at maximum load." Are you sure?

"The difference is that at lower rotational speed the pressure of the compressed air drops and thus thermal and fuel efficiency drop dramatically." That is no comparison because they are different cycles and rotational speed versus air pressure do not coincide.

"...is under 10% load or not having any useful output on the driveshaft." What?

Maybe this can be made a little easier to understand. - KitchM (talk) 23:07, 20 January 2017 (UTC)

Gasoline Section & 2nd Law of Thermodynamics
This particular statement in the gasoline section needs to be disputed: "However, modern tweaks like exhaust gas recirculation and fuel injection can slightly improve efficiencies upwards of what is predicted by the carnot theoretical construct. It’s possible to add exhaust gas heat energy back to the engine, slightly increasing its thermal efficiency, which isn’t part of the carnot cycle’s predicted best case scenario." Carnot engines are the most efficient ideal engines. The sentence suggests that "modern tweaks" can somehow violate the 2nd law of thermodynamics. 2601:1C2:4D01:6750:88B6:1178:1264:D792 (talk) 15:50, 17 May 2023 (UTC)