Talk:Brake-specific fuel consumption

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Untitled

I find having numbers smaller then 1 confusing if they aren't preceded by a zero. i.e. .0123 I'd prefer 0.0123 Any thoughts? --Stripy42 14:18, 17 April 2007 (UTC) Also what is 9549.27 about?[reply]

Poor article

" A reciprocating engine achieves maximum efficiency when the intake air is unthrottled and the engine is running at its torque peak"

is demonstrably untrue, if you look at the bsfc map of a petrol engine. Also the article is self contradictory, the quoted best efficiency for a gasoline engine is refuted by the table in the article (and by the Prius' engine). Greg Locock (talk) 04:51, 20 May 2008 (UTC)[reply]

Wait a minute....Your comment shows you have no true understanding or explanation of why that issue exists.

What was said, is most certainly true, if you stay at optimal spark advance. The demonstrably untrue, graph uses spark advance to waste fuel and get more torque, is an entirely new topic. I was providing "basic" intuitive understanding of why BSFC has a sweet spot, and why it is where it is, not how spark advance works. The idea of complaining about something but not having enough knowledge to fix it, is poor style. So I will leave it to you Greglocock to fix it, or rather expand it into an advance topic about spark advance without confusing everybody in the process. I wrote this article to do my part because it did not previously exist and hoped someday this article (all articles) will grow in such a way that they will cover the basics and also dip into the advanced topics like the one you pointed out.(talk) —Preceding undated comment added 23:45, 30 July 2017 (UTC)[reply]

You are incoherent. The bsfc map shown has an optimum efficiency below the max torque line. I'm surprised you don't understand why adding more fuel beyond that point increases the torque (albeit inefficiently). Not too sure why we'd want clueless editors who can't make themselves understood working on articles, but I guess that is the wiki way. Incidentally you are responding to a 9 year old criticism of a much older version of the article. In its current state it defines the graph (its a diesel, hence no spark advance) and the wording about max torque has been corrected. Bizarre. Greglocock (talk) 00:36, 31 July 2017 (UTC)[reply]

The graph is not explained - the y-axis has unit of P_e / bar - but what that means is nowhere stated. — Preceding unsigned comment added by 87.3.126.198 (talk) 19:51, 15 May 2012 (UTC)[reply]

Jet engine figures for GE-CF6

I think I've got the calculation right. Basically power is energy per unit time, but energy is force times distance. Distance is speed per second. Hence if you multiply the N produced by the speed, you get power. Once you have power you divide by 3600,000 to get kWh. Stuff like that.- (User) WolfKeeper (Talk) 05:48, 20 May 2008 (UTC)[reply]

combined cycle efficiency

Sorry, this does not belong in this article. Brake power refers to shaft power. Combined cycle systems use the heat output as part of their claimed useful output. Compound cycles and such like are ok, as electric power is effectively shaft power. What do you think? Greg Locock (talk) 12:39, 20 May 2008 (UTC)[reply]

Posting of the Prius THS II BSFC figures

Greglocock posted the Prius THS II figures in the table on engine BSFC. Even though the figures are interesting, I thought the inclusion of the Toyota used engine being the 1NZ-FXE engine which has a BSFC of 245g/(kW-h) by itself, should also be posted. The table posted is of engines only and not of engines and electric motors combined (hybrids). All other engines in the table would show higher efficiency used with hybrid type setups. A reference to the BSFC figure of the Toyota engine is: http://www.electrifyingtimes.com/priustechspecs.html

The BSFC is for the engine alone. The reference for it is an SAE paper, for heaven's sake, not some blog. Greg Locock (talk) 07:11, 29 May 2008 (UTC)[reply]

What does anyone think on this matter? --Revetec (talk) 03:22, 29 May 2008 (UTC)[reply]

You reveal a disturbing lack of familiarity with the engineering literature. Greg Locock (talk) 07:11, 29 May 2008 (UTC)[reply]

Use of LHV to give energy efficiency

The gravimetric energy content of a fuel is the amount of heat energy released in combustion, per unit of mass. This is also referred to as the "higher heating value" or "HHV". "Lower Heating Value" or "LHV" is similar, except that the numerator is equal to the energy content minus the heat that the combustion products give up in cooling from an arbitrary temperature (which is agreed by convention) back to the original standard temperature.

LHV was developed for use in comparing the efficiencies of "non-condensing" equipment, hence the seemingly arbitrary decision to ignore a small but non-trivial portion of the actual energy in the fuel. (The temperature chosen is always ABOVE the condensation temperature of water, and much of the ignored energy is the latent heat of water.)

The efficiency of an engine is defined as the ratio of fuel energy consumed to used to energy produced. Thus, HHV must be used to give an accurate value, since it is the energy actually provided by combustion of the fuel, with none of it arbitrarily "forgotten". Because LHV was such a familiar term, one sometimes sees it used in giving the efficiency of engines, but it is technically an error.

I suggest that the article make reference to HHV. Mark.camp (talk) 02:08, 4 June 2008 (UTC)[reply]

I sort of agree, but logically the only valid rejection temperature to use would be absolute zero. Which would make the comparison practically useless. Since hardly anyone quotes LHV figures it will be harder to source refs. Greg Locock (talk) 02:20, 4 June 2008 (UTC)[reply]

The standard technique for measuring heats of reaction (including HHV) requires that the reactants start at standard temperature and pressure, are combusted in a bomb calorimeter (which ensures that no net work is done on or by the environment), and are returned to STP, which ensures that all of the energy released is measured, and that no energy added from the environment is measured.

So, with HHV, no arbitrary assumptions are needed concerning the rejection temperature. Does this address your concern that HHV may not measure the "true" energy of the combustion? Mark.camp (talk) 20:54, 4 June 2008 (UTC)[reply]

Actually I can't really see much of an advantage. The order would not change, the absolute numbers would, but you wouldn't be able to do comparisons with numbers from the literature, so people would pile in with 'better' efficiency figures that are measured on the usual basis. So overall, yes you are probably right, but changing it will create more problems than it solves. You could add another column to the table I suppose. Greg Locock (talk) 05:44, 4 June 2008 (UTC)[reply]

Thanks, Greg, I'll noodle on it.

Re comparisons between engines: You are right that the order would not change for two engines both using the same fuel. However, for shaft engines using other fuels such as hydrogen, the error introduced by using LHV is significantly greater than the error for gasoline. Fossil fuels create a lot of carbon dioxide, which remains a gas at STP, so LHV doesn't "forget" its "latent energy" or heat of condensation. Hydrogen burns to pure water, so 100% of the hydrogen energy that remains as combustion products' latent heat in the LHV methodology is arbitrarily considered to be non-existent--bad science. Actually, the fact that LHV introduces false comparative efficiency values for engines with different fuels is one of the arguments presented in the literature for eliminating LHV.

To your second point, I like the idea of giving both HHV and LHV. Then, comparisons with the widest variety of literature could be done. (I see a mixture of HHV and LLV used in the literature, and much of the literature gives both HHV and LHV.) Mark.camp (talk) 20:54, 4 June 2008 (UTC)[reply]

Thanks for the explanation. I entirely agree. Cheers Greg Locock (talk) 02:31, 5 June 2008 (UTC)[reply]

Prius efficiency

The prius does not produce it acclaimed efficiency of 236 g/(kW•h). The reference given is to do with compression ignition engines i.e. diesel engines, and has absolutely nothing to do with the prius.

According to this site it is only capable of a maximum efficiency of 245 g/(kW•h).

http://www.electrifyingtimes.com/priustechspecs.html —Preceding unsigned comment added by Siripswich (talk • contribs) 21:06, 17 December 2008 (UTC)[reply]

You've probably been misled by the mismatch between ref nos and footnote numbers the actual ref is to SAE paper SAE 2004-01-0064 . There was a difference between the first and second geenration prius motor. Greglocock (talk) 02:03, 18 December 2008 (UTC)[reply]

Sorted, the sae paper says 225 Greglocock (talk) 02:22, 18 December 2008 (UTC)[reply]

What does "engine only" mean? Are we talking about the Atkinson-cycle engine only or the combined gasoline-electric system? Aldo L (talk) 17:49, 18 March 2010 (UTC)[reply]

Article needs more links to lambda, swirl, Miller cycle, turbo

In a SI engine: why does a reduction of throttle losses increase the brake specific fuel consumption? One of the links in the headline probably offers the answer, but I am confused. Arnero (talk) 14:39, 7 March 2009 (UTC)[reply]

Does it? Greglocock (talk) 23:54, 7 March 2009 (UTC)[reply]

Why isn't it fuel consumption divided by ENERGY?

The first paragraph of this Wikipedia entry reads: "Brake specific fuel consumption (BSFC) is a measure of fuel efficiency within a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced. BSFC allows the fuel efficiency of different reciprocating engines to be directly compared."

I'm no engineer, but this makes no sense to me. If it were so, then let's say I put a teaspoon of fuel in my Bugatti Veyron and a teaspoon of fuel in my Prius. The Bugatti puts out 1000 hp for, say 10 seconds, while the Prius puts out, I dunno, say 50 hp for a few minutes. Yet if BSFC is in fact a measure of fuel per unit POWER, isn't the Bugatti getting a lower number, thus indicating it's more efficient?

I don't understand this definition, although I see it other places. BSFC's units are kg/kWh, and kWh, unless I am completely high, is a measure of ENERGY, not power. So says Wikipedia; so says common sense. What am I missing?Pschwiesow (talk) 23:06, 4 March 2010 (UTC)[reply]

You're almost/mostly right; but the article isn't wrong. BSFC is the RATE of fuel consumption divided by the power. Rate of fuel consumption is fuel consumption divided by time, and power is energy consumption divided by time. The time's cancel, which give you fuel consumption per energy which is what you say.- Wolfkeeper 23:46, 4 March 2010 (UTC)[reply]

They use rates though because a rate is an instantaneous thing, whereas fuel consumption and energy would have to be an average or total; but the BSFC is really the max, which is not an average, it's the peak.- Wolfkeeper 23:46, 4 March 2010 (UTC)[reply]

Is it correct to say that BSFC does not apply to turbines and other non-reciprocating engines?

The subject line expresses the idea. — Preceding unsigned comment added by Mark.camp (talk • contribs) 23:57, 13 March 2014 (UTC)[reply]

No. It is not often quoted, but the idea is still valid. The reason people wouldn't use it is that it assumes a calorific value, and turbines and many other engines are less fussy about fuels. If you are being finicky it is somewhat difficult to work from a nice easy number like the bsfc of a diesel to a thermal efficiency, and then comparing that thermal efficiency with a turbine, but it can be done. If you just want a rough comparator then higher calorific value*bsfc*some constants is a rough equivalent to efficiency for the IC engine.Greglocock (talk) 01:53, 14 March 2014 (UTC)[reply]

In that case, should the reference to "reciprocating" be removed? Mark.camp (talk) 15:46, 14 March 2014 (UTC)[reply]

Is the Volkswagen entry still correct?

Is the engine listing affected by the Volkswagen emissions scandal?

Assessment comment

The comment(s) below were originally left at Talk:Brake-specific fuel consumption/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Thus a diesel engine's efficiency = 1/(BSFC*.0119531)

and a gasoline engine's efficiency = 1/(BSFC*.0122225)

This is not true. Engine efficiency relates the power out to the power in. The calculations above use the lower heating value of the fuel and thus overestimate efficiency by assuming there is less energy in the fuel than there really is.

=

It would be clearer if the first calculations used SI units rather than kW-hrs etc, as that complicates explanation of a simple concept.

=

Some examples of real engine efficiencies would be good.

Last edited at 16:38, 18 January 2007 (UTC). Substituted at 10:11, 29 April 2016 (UTC)

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Honda Insight unbelievable

Sorry, I do not believe 200 g/kWh for the Insight engine, and if it is correct then the % efficiency is wrong. if you don't understand why then you should not be editing the numbers in this article. Greglocock (talk) 01:19, 15 August 2017 (UTC)[reply]

Ecomodder notes that the 200 figure was obtained with electric assist, without it was 215, still a very good figure. http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps#1st_Gen_Honda_Insight_1.0L. Greglocock (talk) 01:36, 15 August 2017 (UTC)[reply]

I did find the ref : R. Trigui; et al. (2003). "Hybrid light duty vehicles evaluation program" (PDF). International Journal of Automotive Technology. Vol. 4, no. 2. Korean Society of Automotive Engineers. p. 65-75. Archived from the original on 2004-09-11. {{cite news}}: Explicit use of et al. in: |author= (help) Testing methodology is inconsistent, as noted, with the whole car on a dyno (with the hybrid drivetrain), not the engine by itself : tests found 195g/kW/h for the prius, claimed for 225g/kW by Toyota. I removed the claim as unreliable.--Marc Lacoste (talk) 09:18, 15 August 2017 (UTC)[reply]

even 215g/kW/h is dubious and no serious ref is given by Ecomodder--Marc Lacoste (talk) 09:22, 15 August 2017 (UTC)[reply]

Figure 4 in SAE 2009-24-0065 https://deepblue.lib.umich.edu/bitstream/handle/2027.42/89873/SAE%202009-24-0065.pdf;sequence=3 suggests that 230 is more like it. Greglocock (talk) 22:35, 15 August 2017 (UTC)[reply]

It looks like from a simulation (fig.2), but at least it's coherent with the 30g/kW/h difference of R. Trigui et al.--Marc Lacoste (talk) 17:16, 16 August 2017 (UTC)[reply]

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Units

There is no column for BSFC in SI-units. Even though there is a column for g/(kW*h), neither g, kW or h are SI-units. I think there ought to be one in kg/(W*s)...--Petkr (talk) 12:56, 12 April 2022 (UTC)[reply]

g/KWh is usual in metric units. It gives the engineer an easy way to compute (even mentally) the total fuel consumption. kg/W/s figures would be smaller by 1000 * 3600=3.6M ! Illegible. MJ/kg would be the SI unit, and is often used for fuel energy content. I'm not sure there is a requirement in Wikipedia to use SI units, but to use widespread WP:units. --Marc Lacoste (talk) 13:18, 12 April 2022 (UTC)[reply]

Requesting to add data for 2 engines

... but as I'm unfamiliar with the table code syntax, I would prefer not to break anything. Please add. http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Packard_Merlin.pdf Packard V-1650-1 V12: SFC: 205 g/hp/hr, 0.452 lb/hp/h, 275 g/kW/h http://www.wwiiaircraftperformance.org/p-47/P-47B_41-5902_PHQ-M-19-1417-A.pdf Pratt & Whitney R2800-21 Radial: SFC: 0.78 lb/hp/hr

Mrdarrett (talk) 15:25, 19 October 2023 (UTC)[reply]