Wikipedia:Reference desk/Archives/Science/2012 August 22

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August 22

A New Life Beginning at Fertilization

Is the statement that a new life begins at fertilization (also known as conception) a "soft" scientific fact, rather than a "hard" scientific fact? The reason that I'm asking this question is because I have an intelligent (overall, not necessarily on this topic) friend who said that life beginning at fertilization is a soft scientific fact, since the definition of life is based on scientists' opinions rather than on any universal truth. This is in contrast to, say, the Earth orbiting the Sun, which is a hard scientific fact since there is absolutely no disputes about it and it is based on universal truths rather than on opinions. My question is--is my friend right or not, and if not, why not? Futurist110 (talk) 02:51, 22 August 2012 (UTC)

Life began at some unknown event a little less than 4 billion years ago or so. Everything else is continuation of that event. --Jayron32 02:57, 22 August 2012 (UTC)

I meant a new life. Sorry for the confusion. Futurist110 (talk) 03:02, 22 August 2012 (UTC)

Now you have to define "new". Someguy1221 (talk) 03:05, 22 August 2012 (UTC)

And you have to define "a". The problem is, there are lots of events, and lots of slow processes which lack a single event, along the path of life, where by an individual "organism" is said to be progressing towards its own independence. If it were that simple, we wouldn't have the controversy. The point is, the only reasonable event where one could say there was a definite start was the original moment of abiogenesis. After that, there are not any convenient single moments in time, nailed to the exact second, which differentiates you as an individual from that initial event. Conceptually, "birth" and "conception" mark the two most convient, for the simple minded, but only because they seem to be nice, simple events. But as moments, they aren't necessarily all that advantageous for defining a "start" since anything which would grant them that primacy seems trivial once you get into the processes. Why is birth special? A newborn infant would die if left unattended after birth, and a child delivered before natural birth (either by caesarean or induced labor) can be cared for and raised to an adult. So why birth? And why conception? There are similar problems with making that moment special. Any reasoned argument that attempts to nail down that "moment" can be presented with similarly reasoned and reasonable arguments to the contrary. The real answer is that the only answer is political: there is no agreed "scientific" definition which will satisfy the need to define when a human being becomes an individual being, and when it isn't. So, you're going to need to find your guidance elsewhere. --Jayron32 03:38, 22 August 2012 (UTC)

Note in particularly saying a new life begins at conception is problematic because monozygotic siblings come after conception, so your 'a new life' can become two or more new lifes. Ultimately as Jayron32 and BenRG said, this isn't a scientific question. Nil Einne (talk) 04:06, 22 August 2012 (UTC)

Conception is a good mark in the sense of defining as to when a new human development process begins, since human development generally goes from conception (or when a zygote is split into twins, etc.) to death. Futurist110 (talk) 04:23, 22 August 2012 (UTC)

But there is no conception without ejaculation. So why is conception more important than ejaculation. And there is no ejaculation without that person having being conceived, and then you get a recursive set of events back to the moment of creation. Conception is not an event without its own causes and precedents, so there isn't anything particularly "first" about it. --Jayron32 04:38, 22 August 2012 (UTC)

WP:EC (Assuming I understand the spirit of your question...) Whether or not a definition of life is a matter of opinion is, in itself, somewhat of a matter of opinion. See Life#Definitions, which says "It is a challenge for scientists and philosophers to define life in unequivocal terms.", and gives three references. A counter argument to "life begins at conception" could revolve around whether or not a zygote meets all the criteria for life. You do not specify human life per se, but often these sorts of questions come up in the context of human reproduction. A related, but much more difficult question is then, if a zygote is alive, is it a human? Harder yet: is it a person? By nature, these questions are not purely scientific in nature, and must perforce be answered in the context of some philosophical, political, and/or legal framework. Needless to say, the answers to these questions are the subject of much discussion and dispute. SemanticMantis (talk) 03:06, 22 August 2012 (UTC)

(ec) I don't believe many scientists argue that an embryo isn't alive. However, for setting abortion policy and such, other questions come up, like at what point the embryo becomes viable, outside the womb. There you will get a range of answers. StuRat (talk) 03:08, 22 August 2012 (UTC)

I am aware of the difference between life and personhood. The fetus becomes viable at about 21.5 weeks or so right now (with current technology), which is a hard fact. Futurist110 (talk) 04:23, 22 August 2012 (UTC)

Sperm are alive too. Conception means the death of a sperm. HiLo48 (talk) 03:19, 22 August 2012 (UTC)

Sperm are a part of your body. They have your DNA and are not a whole entity passing through any stage of human development, unlike a zygote. Futurist110 (talk) 04:23, 22 August 2012 (UTC)

Interesting perspective. The question didn't explicitly ask about human life. HiLo48 (talk) 07:45, 22 August 2012 (UTC)

Futurist110, apparently you slipped when you said that "the Sun orbiting the Earth" ... "is a hard scientific fact". [I need to use your username for clarity, because the previous comment is not indented.]

—Wavelength (talk) 03:25, 22 August 2012 (UTC)

(now indented)

If object A is orbiting object B, it also means that object B is orbiting object A. Ergo the Sun is indeed orbiting the Earth. A8875 (talk) 03:57, 22 August 2012 (UTC)

Also not true. The Earth does not orbit the Sun, nor does the Sun orbit the Earth. The two orbit a common barycenter. Insofar as barycenter of the earth-sun system is located within the sun itself, it is more correct to say the Earth orbits the Sun than the other way around, but the scrupulously correct answer is that they orbit their common barycenter. --Jayron32 04:15, 22 August 2012 (UTC)

Sorry. That was obviously a typo on my part. I obviously meant "the Earth (and the other seven planets) orbiting the Sun". Futurist110 (talk) 04:23, 22 August 2012 (UTC)

Even if the barycenter is outside both object A and object B people still use the word "orbit". In vernacular speech "orbit" pretty much applies to all circular and elliptical movements, regardless of where barycenter is. This usage is not scientifically correct as you pointed out, but it's what people uses. A8875 (talk) 04:29, 22 August 2012 (UTC)

Your real question is when a new human life begins. That isn't a scientific question at all, "hard" or "soft". It's a question of definition or, at best, of ethics. The only scientific answer is Jayron's. -- BenRG (talk) 03:42, 22 August 2012 (UTC)

Is there an impartial, objective (non-biased) definition to life, though? My friend says that even if all scientists agree on one definition, that this definition of life isn't objective and that there is no objective definition to life. Futurist110 (talk) 04:23, 22 August 2012 (UTC)

Scientific definitions of "life" are usually objective, in that they consist of a set of criteria that can be judged objectively; any system that meets the criteria is defined as being alive. There is no unified scientific definition of life (different groups use different definitions) and the definitions don't always correspond with common non-scientific definitions, but that doesn't make those definitions non-objective. --Carnildo (talk) 00:51, 23 August 2012 (UTC)

Like others mentioned above, the definition of when a life begins is mostly a philosophical and a political one. Since definitions are tautologies (by definition), they are not subject to the scientific process. Definitions cannot be "wrong", but they can be counter-productive. For example if the Sanctity of Life Act passes, it would mean that 27% to 37%[1] of new-born US residents die in the womb, bring the average life expectancy down to the low 50s, behind Kenya, Congo, and Niger. A8875 (talk) 04:17, 22 August 2012 (UTC)

Yes, but by the new standards of this law, all other countries' life expectancies would significantly decrease as well, while life expectancy since birth (the traditional measure) would still stay the same in the U.S. and everywhere else. Futurist110 (talk) 04:25, 22 August 2012 (UTC)

Precisely. It would necessitate the concurrent usage of two definitions, and two separate life expectancy rates in pretty much all birth related international documents and discussions. Hence "counter-productive". Thank God WP's country infobox doesn't have life expectancy on there.A8875 (talk) 04:34, 22 August 2012 (UTC)

It probably won't be that counterproductive considering that one would be able to calculate the new life expectancy very quickly. Futurist110 (talk) 04:38, 22 August 2012 (UTC)

It will still be a hassle though. Since each country publishes their own statistic based on their indigenous definitions, every time an American hears a birth or life expectancy related statistic from another country, they have to perform the mental calculations. This is by no means a new problem. Cuba has higher infant mortality rate than US[2] because the definition of "infant mortality" differs between the two countries. Many people interpret this statistic erroneously by concluding that Cuba's universal healthcare is responsible (admittedly it's a minor contributor). A8875 (talk) 05:36, 22 August 2012 (UTC)

• Speaking of "a" life is problematic at any time, even for adults. Consider split-brain experiments. Life is not really designed to be counted in this manner, as is particularly evident in some phyla such as siphonophores. In humans, every cell is potentially clonable, and thus potentially a life.

• Sperm and eggs are each arguably a haploid generation (gametophyte) and their union marks a diploid generation.

• The end of human life in the legalistic sense, as opposed to viable cells for culture, is defined in terms of brain death. The brain death criteria might also be applied to fetuses to define the beginning of life.

• As I recall, neurotransmitters start up around 6-7 weeks, forerunner neurons around 10, and others around 12 weeks. These time intervals are not dissimilar from comments about quickening by Aristotle and Saint Augustine (I think it was) at 40 to 80 days after conception, which presumably are based on a subjective sense of when an aborted fetus appears alive. (After all, they had abortions back then) However, authorities have long maintained that the "higher" ability to sense pain awaits the 8th month of gestation or so. (I'm not going to look up cites for all this stuff because it's not the question asked).

Bottom line: not a hard scientific fact. You might as well ask how many pieces of yellow there are in a lemon. Wnt (talk) 04:51, 22 August 2012 (UTC)

As others have said, the concept of "life" as it is being used here, is an ethical question more than it is a scientific one. At best science can inform some of those moral opinions. Conception gets thrown around as some sort of brightline quite a bit, but whether or not the science backs that up is questionable. An enormous number of fertilized eggs are lost without the woman ever knowing it. Historically there have been a wide variety of determinations about when "life" begins, including conception, quickening, birth, and even after that. In a very strict legal sense, personhood has been understood as birth in the U.S. for example. There are laws that make the death of a fetus criminal, whether it's abortion or something else, but that doesn't mean the fetus is considered a person. From a strict legal standpoint, birth is a clear brightline. Shadowjams (talk) 05:08, 22 August 2012 (UTC)

Just because a lot of fertilized eggs are lost naturally doesn't mean that they weren't alive. Those historical definitions were generally based on the knowledge back then, not on the knowledge now. For instance, in the pre-industrial era many people thought that life only began once the fetus began to move (quickening, as you say), whereas we now know that this is not the case. The legal sense isn't very practical when it comes to these matters, as the law can and often does change and since the law is currently inconsistent (if the woman wants the offspring, then the offspring is a person, if not, than the offspring is not a person). Futurist110 (talk) 05:14, 22 August 2012 (UTC)

My point in mentioning the number of lost fertilized eggs is simply to suggest that conception isn't a defacto brightline moment; you could choose others including implantation, quickening, third-trimester, sentience, birth, etc. Shadowjams (talk) 05:41, 22 August 2012 (UTC)

The question we're all skirting around here is "So what?" The usual goal of defining when life starts is to justify one's policy position in the abortion debate, as though the first should lead unambiguously to the last, but that isn't necessarily so. In no other policy decision is the "scientific definition of life and its start" used to provide a rationale for the taking of (or for the preservation of) life, whatever your working definition is. If we really want to get down to it, human societies since time immemorial have never really had any universal principles which preserved all human life in all cases. Every society has defined situations when the taking of a human life (either through self defense, war, capital punishment, or whatnot) is allowable. So even conceding that it may be possible to define the "start of life" (not admitting that one can, merely conceding to make the next point), it doesn't mean squat when trying to decide where one stands on the abortion debate. There is no universal principle, it is merely a weighing of competing interests, and reasonable people will value those interests differently. People who place values on one side of the scale end up as "pro-life" and others, with different values, end up as "pro-choice", but it doesn't mean that either position is based more than the other on "sound science". Neither is, fundementally. That's why the debate is intractable: it ultimately comes down to individual conscience, and in matters of conscience, it is possible for reasonable people to arrive at different conclusions. --Jayron32 05:23, 22 August 2012 (UTC)

For the record, I wasn't trying to say or imply that one acknowledging life beginning at conception as equivalent to saying that abortion is wrong and/or morally unjustifiable. The abortion debate has a lot of other factors at play other than when life begins. I was simply wanting to know the validity and accuracy of my friend's statement. Futurist110 (talk) 05:38, 22 August 2012 (UTC)

As Shadowjams says succinctly above, there isn't a magic moment, however. Conception is as good as any other moment, which is to say that it isn't better than them either. You're friend's statement isn't even wrong, as the saying goes. --Jayron32 05:46, 22 August 2012 (UTC)

As I said above, we do use brain death to make decisions, i.e. we evaluate the "scientific definition of life and its end" based on the belief that neural signalling is required for "life", even though obviously many other organs of the body remain alive after brain death. The zygote is one more type of cell that is not a neuron. Wnt (talk) 12:30, 22 August 2012 (UTC)

True, but we also use other events to decide when a person is worthy of death; i.e. when they are a soldier in the army of another country, or when they have committed certain crimes, or have certain diseases, or any of a number of other criteria, that have little to do with definitions of "life" and its milestones. No society has ever, as a culture, taken the step that all human life in all forms is to be preserved at all costs, and no society that has decided that some lifes aren't worth protecting (or that some lifes are worth ending) has ever based those decisions on such purely on such milestones. Thus, even conceding that there are some milestones in a life which are worth taking special note of, it doesn't directly follow that policy needs be based solely (or even primarily) on those milestones. It comes down to subjective value on individual lives, and on qualities relating to those lives, and reasonable people will disagree about subjective value. --Jayron32 12:41, 22 August 2012 (UTC)

Well, it sounds like you're saying that by allowing those who have suffered brain death to die completely, that we are making a decision to perform euthanasia. I suppose that is a position you can take, but I think that most people making that decision do so out of the genuine belief that those in that situation are not meaningfully alive, rather than out of a belief that their lives aren't worth protecting. Wnt (talk) 12:56, 22 August 2012 (UTC)

Well, that's because you define "meaningfully alive" to exclude a certain group of people. If we have differing definitions of what it means to be "meaningfully alive", then we have differing definitions over what value to place on what bits of living tissue. That's the crux of the problem. Human society has for millenia redifined humanity to make killing and other inhumane acts ethically tolerable. Without making any judgement (for the sake of this discussion) which definitions of "really human" and "meaningfully alive" and any of a number of other concepts, people generally agree that "really alive, really human people" are accorded certain rights, but if we don't all have the same definition of what those terms mean, then we have conflict. Again, I'm not saying whether or not your criteria for "brain death" is the correct one to choose when making decisions about what it means to be alive, rather I am saying that no particular choice is entirely incontrovertable: there is no single choice where every single person will reasonably agree with you. That doesn't mean you aren't right, it just means that you aren't going to be free from conflict or controversy, and that any particular choice about your criteria is going to be so self-evident as to be agreeable to all people. --Jayron32 14:29, 22 August 2012 (UTC)

Not to beat a dead horse here (oh wow that's a bad pun...) but Jayron's point is particularly acute given your example of brain death. It's only relatively recently (past few decades) that brain death rather than cardiac death has been the relevant standard in terms of law and medicine. The most obvious consequence being the wider (although still too small) availability of organ transplants. Shadowjams (talk) 17:07, 22 August 2012 (UTC)

Reference Needed for Multiplicity (psychology)

Does any psychologist recognize this and have good source for it? It is risking to be deleted. Thanks.Wikipedia:Articles_for_deletion/Multiplicity_(psychology)#Multiplicity_.28psychology.29 -- RexRowan  Talk  18:11, 22 August 2012 (UTC)

WP:CANVASS might be relevant to posting about an ongoing AFD. Edison (talk) 19:07, 22 August 2012 (UTC)

Thank you for pointing it out for me. I have looked for reference on the psychology project. -- RexRowan  Talk  19:12, 22 August 2012 (UTC)

srface charge density on a sphere

Let's say you know the potential at every point on the surface of a sphere. How then do you find the surface charge density? --150.203.114.14 (talk) 15:17, 22 August 2012 (UTC)

Does the article charge density help you figure that out? It looks like it involves some simple calculus to solve. --Jayron32 15:21, 22 August 2012 (UTC)

I see no equation relating charge density to potential. --150.203.114.14 (talk) 15:29, 22 August 2012 (UTC)

That equation would be Gauss's law... which can be stated as an integral, or formulated into an inversion-problem so that you can determine the charge distribution, given the potential. In nontrivial cases, the inverse problem may be underconstrained. In realistic physical situations, complicated potentials are unlikely, as a conducting sphere will relax to an equipotential surface after some period of time. So: to directly answer your question: given, potential as a field, to solve for charge distribution we invert Gauss's law, making suitable approximations that match our physical expectations. Depending on those assumptions, and the condition of the potential field, the mathematical methods could simply be direct solution of a simple algebraic formula, or may require very detailed machinations. Nimur (talk) 16:01, 22 August 2012 (UTC)

Double tolerance problem article ?

Do we have one ? Perhaps under another name ? (I suppose this is a special case of tolerance stack up.)

The problem, in short, is that two mating parts (lets say a jar and a lid) normally fit fine, but when the jar is at the wide end of it's tolerance and the lid at the narrow end of the tolerance, they don't fit. This could either be a result of the design tolerances being too generous, or the items exceeding those tolerances. (I suspect that manufacturers will accept a certain degree of this problem, as avoiding it by tightening up on tolerances can be more expensive than the occasional pair that don't fit together.)

The result is that most lids fit most jars, but occasionally a certain combo won't work. Tellingly, if either a different jar or lid is swapped in, then they usually fit again.

If we don't have an article, I'd like to create one, so would like any other names for this and examples you can think of.

There's some mention of it here. 203.27.72.5 (talk) 20:57, 22 August 2012 (UTC)

can't break speed of sound?

I've heard that in the 1920s, 30s, or 40s, scientists thought that an airplane could not break the speed of sound. I googled and couldn't find anything. Did scientists really think that? Did some think that? Is it an urban legend? Bubba73 ^{You talkin' to me?} 21:33, 22 August 2012 (UTC)

Early planes that approached the sound barrier when diving often crashed due to the (by their standards) extreme forces. At the time, these problems were believed to be insurmountable. See note 2. 203.27.72.5 (talk) 21:49, 22 August 2012 (UTC)

Supersonic airplanes do need quite a few differences in design, to fly properly, like swept back wings, a long, narrow fuselage, etc. So, when trying to fly a plane not designed for such speeds over the speed of sound, it may indeed crash. StuRat (talk) 22:01, 22 August 2012 (UTC)

A major breakthrough was the discovery that in the transonic phase an effect called Mach tuck occurs, in which shock waves build up on the lifting surfaces causing the nose to plunge downwards. This was discovered by the team working on the Miles M.52 project during WWII. They devised the "all-moving tail" or Stabilator to overcome this, which is now universal on all supersonic aircraft. Sadly, before the project was cancelled, the Bell Aircraft company was given access to the drawings and research on the M.52, but the U.S. reneged on the agreement and no data was forthcoming in return." The Bell X-1 took all the credit, complete with British designed tail. Alansplodge (talk) 22:16, 22 August 2012 (UTC)

I'm not sure that scientists thought there was a real barrier there, but tabloid media enjoyed playing up that word. A bit like the four minute mile. HiLo48 (talk) 08:45, 23 August 2012 (UTC)

I don't think that you are correct HiLo; there are a number of effects on an aircraft as it enters the supersonic stage - in the 1940s these caused the loss of control or destruction of aircraft not designed to cope with these. See the sorry tale of Britain's first supersonic jet, the de Havilland DH 108, which killed the company's owner / test pilot before the problems could be ironed out. The four minute mile was just a case of running a bit faster than anybody else had. Alansplodge (talk) 17:01, 23 August 2012 (UTC)

Ok, I take some of that back; I have just found This NASA article; "The myth of the sound barrier had its beginning in 1935, when the British aerodynamicist W. F. Hilton was explaining to a newsman about some of the high-speed experiments he was conducting at the National Physical Laboratory. Pointing to a plot of airfoil drag, Hilton said: "See how the resistance of a wing shoots up like a barrier against higher speed as we approach the speed of sound." The next morning, the leading British newspapers were misrepresenting Hilton's comment by referring to "the sound barrier." The idea of a physical barrier to flight —that airplanes could never fly faster than the speed of sound— became widespread among the public. Furthermore, even though most engineers knew differently, they still had uncertainty in just how much the drag would increase in the transonic regime, and given the low thrust levels of airplane powerplants at that time, the speed of sound certainly loomed as a tremendous mountain to climb." Alansplodge (talk) 17:36, 23 August 2012 (UTC)

Thank you very much for finding that! Bubba73 ^{You talkin' to me?} 18:46, 23 August 2012 (UTC)

Or, we could quote from what was actually written by scientists about the subject at that time, "For various reasons it is fairly certain that the maximum attainable speed under self-propelled conditions will be that of sound in air"[3]. 203.27.72.5 (talk) 22:52, 23 August 2012 (UTC)

Thanks for that too. Bubba73 ^{You talkin' to me?} 01:50, 24 August 2012 (UTC)

Using fuel to cool an internal combustion engine

Jet engines commonly use the fuel to cool the area around the engine. Could the same approach work on an internal combustion engine, in conjunction with air cooling, or is the amount of fuel burned just insufficient for this ? (In the case of a gasoline engine, the gasoline could boil in the engine block, to cool it, and the fumes would then be burnt inside the cylinders.) StuRat (talk) 22:36, 22 August 2012 (UTC)

The specific heat - based thermal capacity, and the latent heat of vaporistion, does have a cooling effect on any IC engine (you obviously mean a piston engine here - an aircraft "jet" engine is also an internal combustion engine), but the effect is not that strong, and how/where it does it, depending on the type of engine, is not so obvious perhaps to a lay person as it may be for a turbine ("jet"). In a turbine, the design specifically involves having relatively cool areas (including cooled by fuel) and relatively hot areas (the downstreem combustion area) for properties of materials reasons. In piston engines, cooling happen, but the design aims are different.

In a diesel egine, fuel is injected into the combustion chamber at ignition time, in liquid form at a temperature below the air temperature at that time. Therefore, the fuel provides a cooling effect from its thermal capacity, and by absorbing latent heat of vaporisation as it is vaporised in order for combustion to occur.

In a diesel engine, the cooling effect of the fuel is undesirable, as it lowers combustion temperature and thus lowers gas expansion and thermodynamic efficiency.

In a gasoline engine, the fuel still has a cooling effect, but how it does it is a little less obvious. In a carburettor engine, evaporation in the carburettor casues the intake charge to be cooled, so combustion has a lower temperature to start from.

It should be realised that in a typical aircraft "jet" engine, thermodynamic efficiency is not that high, and gas velocities are high. These two reasons mean that cooling of combustion chamber walls is important. In practical pistion engines, efficiency is high and gas velocities low, so cooling of combustion chamber walls is not critical - typically only about 6% of combustion heat is lost via the combustion chamber surfaces. Ratbone124.178.39.239 (talk) —Preceding undated comment added 23:21, 22 August 2012 (UTC)

(ec)It would be extremely dangerous. In the air, if you get a leak it has plenty of air to dilute the fuel air mixture. In your car, you don't have that dilution in your engine bay, and the battery and other components provide ample opportunity for a spark. The high pressures of boiling fuel is going to make a leak all the more likely. I can't find any information on any attempts to do this or even suggestions that it could be done. 203.27.72.5 (talk) 23:25, 22 August 2012 (UTC)

Would it be any more dangerous than a CNG vehicle ? StuRat (talk)

Yes, very much so. Has your radiatior ever leaked? Now imagine hot pressurized gasoline is squirting out into the engine bay instead of radiator fluid. At least the natural gas isn't that hot if you get a leak, and there's much less chance to get a leak compared to a pressurized jacket around the engine. Plus the way cars are engineered to crumple when in a crash, doesn't require the engine to be protected. For most front engine cars, if they had this system of cooling they'd just about be certain to explode in a head on collision. The gas tanks on the other hand are in the rear of the car and engineered to rupture outwards. 203.27.72.5 (talk) 02:16, 23 August 2012 (UTC)

Not correct - see below. Ratbone124.182.134.244 (talk) 02:41, 23 August 2012 (UTC)

Perhaps it could, but why would it? Both diesel and petrol engines are usually cooled with a water jacket, occasionally by air; air's available in large quantities for free and water's not that much more expensive (given the cost of introducing water channels into an engine, anti-freeze and so on), so what would the advantage be of using fuel to cool an engine? Tonywalton ^Talk 00:26, 23 August 2012 (UTC)

Poster 203.27.72.5 is misinformed about practical engines. Having fuel in the crankcase is not especially dangerous. In loop-induction 2-stroke engines (as is common in small engines e.g. lawnmowers, some motorbikes), the fuel passes through the crankcase before entering the cylinder - this is because such engines cannot have useful cylinder suction - carnkcase suction as the piston goes up draws the fuel and air mix in, and then as the piston goes down, forces the fuel/air mix into the cylinder. Secondly, in 4-stroke engines, some fuel does leak past the piston and rings and get into the crankcase, especially as the engine accumulates wear. This does pose an explosion risk, and in small engines is managed by suitable venting. In large engines, as in large diesel engines used in power stations and marine propulsion, special pressure relief valves (biccari valves) are provided to allow crankcase combustion gasses to vent safely to atmosphere. In the early days on IC engine marine propulsion, crankcase explosions and consequent ship loss did occur until the problem and solution was understood.

As I explained above, the fuel DOES provide some cooling, either directly when injected, or indirectly by cooling the charge air. As it cools the engine anyway, it is unnecessary to pass it thru the crankcase for that purpose. Passing it through the crankcase, cooling-wise, will not achieve anything - heat removed from teh crankcase would be returned to the cylinder.

Passing fuel through the crankcase would be undesirable in a 4-stroke engine as it would pick up lubricating oil, causing increased oil consumption, cylinder & exhaust glugging, and bad emissions. These problems do not arise in an aircraft "jet" engine.

Ratbone124.182.134.244 (talk) 02:15, 23 August 2012 (UTC)

Just to be clear, I'm not saying that small amounts of fuel in the engine bay are going to cause an explosion. I'm saying that hot gasoline could leak out in large quantities due to the pressure of boiling it (as suggested by StuRat) and the resulting fuel air mixture would be very explosive. Diesel wouldn't be such a worry due to it's much lower vapour pressure. My comments were about modern 4-stroke petrol engines used in cars. 203.27.72.5 (talk) 02:24, 23 August 2012 (UTC)

Ok, but consider these facts: Firstly, it takes no great pressure to boil/vaporise gasoline. In carburettor engines, it's done in the carburettor at atmospheric pressure. In fuel injected gasoline engines, its doen in the intake manifold, at less than atmospheric pressure. In loop induction 2-strokes, the fuel/air mix is first sucked into the crankcase, and then compressed, not as much as in the cylinder, but it is to 2 or so atmospheres. Thse engines are very common, and leakage is just not an issue. Lastly, somewhat off-track, explosion of diesel in crancases sunk ships until (100 years ago) they learnt to put in relief valves. It is a mistake to think diesel is safer in this regard. Ratbone124.182.134.244 (talk) 02:41, 23 August 2012 (UTC)

I don't think you see what I'm saying. It's not that a great pressure is required to boil gasoline, it's that boiling gasoline will greatly increase the pressure in a sealed jacket around the engine (i.e. constant volume). If that pressure is released because of a leak, that fuel will vapourize more or less instantly and fill the engine bay, causing an explosion hazard. 203.27.72.5 (talk) 02:47, 23 August 2012 (UTC)

It need not raise the pressure though. It does not in conventional carburettor and injected gasoline engines. One could arrange for fuel vaporisation in a crankcase or other chamber at a near constant pressure or a controlled pressure rise. It's just pointless, cooling-wise, to do, that's all. Ratbone124.182.134.244 (talk) 03:03, 23 August 2012 (UTC)

The understanding I have of StuRat's question is basically, could you have an engine that is cooled by pumping fuel into a jacket around it, and as it vapourizes from the heat given off by the engine, inject it into the cylinders? Maybe that's not really what he meant, but I assumed it is. Now, as you've pointed out, you would need more fuel to vapourize for cooling the engine than you would need as fuel to burn, so there's that problem with this idea. My comments were based on the assumption that to stop so much fuel from vapourising, you would have to allow the hot fuel to pressurise in the jacket. True enough, you could instead pump far more fuel as coolant around the jacket than what actually gets consumed and return it to the fuel tank. But that's not really any different to a conventional radiator system, so there's no savings in terms of efficiency there. 203.27.72.5 (talk) 03:21, 23 August 2012 (UTC)

Ah, now I see what you were getting at. You have it all pretty right, I think - expecially your last sentence. If you circulated fuel around, the tank would become the radiator - its radiant equivalent volume, and the air stream would have to be much the same as a normal radiator & fan system. However, the specific heat of fuel is a about 30 to 40% of that for typical water+glycol mixes, so the engine would require a bigger coolant jacket, and need to run a bigger coolant pump. That will increase weight quite significantly. In car engines, cylinders are oftem "siamesed". You might not be able to do that using fuel as coolant, so the block will need to be longer. Ratbone124.182.134.244 (talk) 03:44, 23 August 2012 (UTC)

Yes, you're right about the difference in specific heats, I didn't take that into account. Anyways, glad we got there in the end. I was already thinking of how I was going to draw a diagram using ASCII :D. 203.27.72.5 (talk) 04:25, 23 August 2012 (UTC)

The object would be to reduce vehicle weight by eliminating the radiator, coolant, auxiliary coolant tank, coolant hoses, etc. Drag could also be reduced since you wouldn't need air to ram the radiator to cool it. The result should be improved fuel efficiency. Since air-cooled engines do work, but only for small (low compression ?) engines, hopefully this would allow it be used in beefier engines. StuRat (talk) 01:57, 23 August 2012 (UTC)

Just for your interest, air-cooling is not limitted to small sizes. Until rendered obsolete by turbojets, air-cooled aircraft piston engines were made up to megawatt sizes - the Wright Cyclone (up to 2.76 MW) and the equivalent Pratt & Witney being the most famous. Aircooling does not limit compression ratio - in any case a higher compression ratio gives greater thermodynamic efficiency, reducing cooling requirements. Ratbone124.182.134.244 (talk) 03:58, 23 August 2012 (UTC)

Well, aircraft are a bit different, as air is available at higher velocities to use for cooling, except for when idling on the ground (I wonder if this makes them overheat). StuRat (talk) 04:42, 23 August 2012 (UTC)

True - then there is the flat-4 volkswagen engine - 1600 cc, very sizeable compared to a lawnmower, and can be hotted up to deliver as much power as any 1600 cc engine. They had a well known tendency to overheat in Australia, but that does not negate aircoooling. It was just a consequence of being designed in Germany, which has a much colder climate. Some owners here added extra outboard scoops that increased airflow - they cope with our climate just fine then. Ratbone124.182.179.59 (talk) 05:59, 23 August 2012 (UTC)

I wonder if using the gasoline to pre-cool the engine would be a viable alternative to those air scoops (which must increase drag and reduce fuel efficiency). StuRat (talk) 07:15, 23 August 2012 (UTC)

I doubt it. Give it away Stu. The scoops would increase drag, but it is a matter of proportion. Going purely on my memory (almost all flat-4 VW's are worn out now, you hardly ever see one) the scoops usually had a frontal area of about 150 x 300 mm, one on each side. That's very much larger than the factory standard air intakes but is only about 2% of the vehicle frontal area, so I doubt it would be possible to measure the increased drag. Gasoline cooling could only amount to roughly 2% of engine non-exhaust heat output, as explained elsewhere. A more important consideration is that the scoops violate current Australian design rules aimed at eliminating side projections (door handles/locks must be flush for example). If a VW factory standard passes an inattentive pedestrian within 100 mm at (say) 30 km/hr, the pedestrian will only get a fright, or perhaps severe bruising if he makes contact. A VW fitted with the scoops will take the pedestrian's head off, killing instantly. Ratbone124.182.179.59 (talk) 08:10, 23 August 2012 (UTC)

I bet the drag is more than an additional 2%. That's what you would get with a nice rounded lump. The turbulence created by a scoop is far worse. StuRat (talk) 08:37, 23 August 2012 (UTC)

It could well be. And could well be less. I've seen very professional looking rounded scoops, and also very rough square box types obviously home made. We should, for the purpose of this discussion assume a reasonably professional low turbulence design. I only meant to show you the rough scale of it. You'd need a much larger increase for it to be measurable, and very much larger for a typical owner to notice it in fuel consumption. Ratbone124.182.179.59 (talk) 09:02, 23 August 2012 (UTC)

80 H.P. Le Rhône 9C rotary engine - and yes the whole lot rotates

See Rotary engine for a solution to that: fix the crankshaft to the engine bulkhead and have the pistons and cylinders (and attached propeller) rotate around it! AndyTheGrump (talk) 04:57, 23 August 2012 (UTC)

That seems nuts. Doesn't the gyroscopic effect make it difficult to turn the plane ? StuRat (talk) 05:42, 23 August 2012 (UTC)

Such engines were the norm with World War 1 aircraft. They were popular due to certain simplifications enabling high power (for the day) with light weight. Yes, the gyroscopic effect does make it harder to turn in one direction, but easier to turn in the other direction. There are 2 factors that sort of mitigate it: Firstly, aircraft back then were biplanes with low wing loading, low speeds, and big control surfaces. Secondly, you get a lot of gyroscopic effect from the propellor anyway. The prop may not be as heavier, but its much larger in diameter, and the gyro effect is proportional to the square of the radius. Single propellor aircraft with any real power (i.e., not your user friendly but underpowered Cesna) are well known for handling vices due to propellor gyroing. Look up takeoff procedure for the British Spitfire, and US military evaluation of captured Japanese Zero fighters for clear examples. Ratbone124.182.179.59 (talk) 06:13, 23 August 2012 (UTC)

Cooling of aircooled radial engines on the ground doesn't seem to have been a problem. Even the non-cylinder rotating types get airflow from the prop. Typical operating instructions for WW2-vintage types werr to start and warm up the engine(s) with the cooling flaps (they are the flat projections you see just behind the cowl) closed, and open them for take-off, or opne them when the temperature gauge gets past x-many degrees. See http://www.zenoswarbirdvideos.com/main.html for a fascinating collection of old US military training films that show this. Ratbone124.182.179.59 (talk) 07:52, 23 August 2012 (UTC)

The cooling effect of fuel, in the quantities used for combustion, is far too small to enable any noticeable reduction in radiator size, etc. In a typical 4-stroke, say a 15 litre diesel truck engine al la Cat C15 producing 276 kW at 1500 RPM, cooling from injected fuel amounts to around 5 kW, whereas the total heat rejected to coolant is 202 kW. You may be confusing the total cooling requirement for a piston engine (of roughly the same order as its power output) with the relatively small part of the aircraft jet engine cooled by fuel. Ratbone124.182.134.244 (talk) 02:31, 23 August 2012 (UTC)

Yes, that sounds insufficient to cool such a big diesel engine, but how about a more modest gasoline engine, say a 3, 4, 5 or 6 cylinder ? StuRat (talk) 04:45, 23 August 2012 (UTC)

Stu, obviously, all the heats go up or down more or less in proportion to the engine power. I don't have data for any small three-cylinder engines, but taking the Daihatsu 3-cyl gasoline car engine as an example (800 cc or thereabouts, bore & stroke 69 x 70 mm, reasonable assumptions about bearing sizes, valve train, head configuration etc) a computer engine simulation tool I have predicts the following at 4000 RPM: Brake power output 28.2 kW, heat lost to exhaust 39.3 kW, heat rejected to coolant 27.1 kW, coolant effect of fuel ~~0.7 kW. The program is known to be within 2% for large diesel engines and is not optimised for small gasoline engines, but these figures will be reasonably close. The coolant effect of the fuel is substantially higher in this case than you would expect by scaling down from the C15 Caterpillar engine I quoted earlier, but this is only because the Daihatsu, as a gasoline engine, is a lot less efficient, so burns more fuel. The cooling effect of the fuel is never the less still too small to affect radiator sizing. I assumed a compression ratio of 9.5:1 as any higher resulted in the software predicting detonation, and it would take too much time to find out the actual detonation-affecting parameters. Ratbone124.182.179.59 (talk) 07:00, 23 August 2012 (UTC)

Thanks. How does air cooling fit into the equation ? Of course, cooling fins and such play a part, but there's also a surface area to volume ratio effect, where lawn mower engines are just fine with air cooling, but it's rather iffy for even small car engines. I'm hoping that the gasoline cooling might be just enough to make it a bit more practical to air cool a small gasoline engine. StuRat (talk) 07:12, 23 August 2012 (UTC)

Stu, you're not paying attention. Air-cooling car engines is completely viable - flat-4 VW's being just a not particularly well executed example. They were originally designed down to the cheapeast possible price on Hitler's instructions. A historically important reason for air-cooling not catching on is the noise. Cylinder cooling fins are effective at transfering mechanical noise to the air. Water cooling pretty much damps it out. Historically, air cooling made for higher engine wear, higher fuel consumption, and poor emissions, due to dificulty in maintaining a constant engine temperature. Water cooled engines incorporate a thermostatically controlled valve in the coolant circuit, and regulate their temperature quite precisely. With modern electronically controlled servo motors, it would be quite possible to regulate engine temperature almost as well with air cooling though (it can't be quite as good, as the heat has to get from the combustion chambers thru the fins and into the air. In a water cooled engine the heat has a short direct path into the water, which has a specific heat 1000 times better than air.) Have you not stood next to an idling air-cooled Volkswagen and heard the dreadful noise it makes? The radiator fan in a water cooled car engine absorbs power at low speeds, but it's not much, and a VW engine has a fan too.

Regardless of air cooling or "water" cooling, the amount of heat to be got rid of is the same, about one third of the combustion heat. So fuel cooling, as a "helper", is no more viable for air cooling than it is for water cooling. The fuel is ALREADY cooling the engine anyway, as explained, not withsatnding the consideration that some of the recovered heat will end up going out the exhaust. Engines of the lawnmower sort are less efficient than car engines - this means that more fuel cooling is available, but there's more heat to get rid off, and it doesn't change the viability. If you wish, I can calculate heats for a couple of small lawnmower-size engines I have comprehensive data for, thoough it won't be accurate. Ratbone124.182.179.59 (talk) 08:31, 23 August 2012 (UTC)

So you're saying a large air-cooled car engine is possible, but would just be too noisy ? How about using active noise control ? StuRat (talk) 08:41, 23 August 2012 (UTC)

You've GOT to be joking!!! Noise is of course in the ear of the beholder - witness Harley Davidson motorbikes. I did include the word "historically". I can think of ways of installing sound damping baffles, but they did not think of that back then. It would add cost and considerable volume to the car though. There may be other ways. Ratbone124.182.179.59 (talk) 08:49, 23 August 2012 (UTC)

Please humor me and explain why active noise control won't work here. StuRat (talk) 19:44, 23 August 2012 (UTC)

He's not saying it won't work. It's wholey impractical though. Most jurisdictions have noise pollution laws, so it's not just a matter of the driver wearing noice cancelling head phones. And on the point of air cooled car engines, here's another example; Porsche used air cooling in all of the 911 models up until 1998. 203.27.72.5 (talk) 20:33, 23 August 2012 (UTC)

So how did they handle the noise problem ? StuRat (talk) 02:33, 24 August 2012 (UTC)

Who would want to drive a Porsche that didn't make noise? I mean, besides the guys who made this thing. 203.27.72.5 (talk) 06:35, 24 August 2012 (UTC)

If you increase the noise level from an old VW beetle in proportion to the power increase in a Porsche 911, it would be too loud to be street legal, wouldn't it ? How do they prevent this ? StuRat (talk) 20:40, 24 August 2012 (UTC)

I don't know anything about Porsche 911's - they are a rare vehicle here in Australia. And I have no idea what the noise regulations are in Stu's USA. I do know that 911's are 6-cylinder whereas the VW is 4-cylinder. Just on this you would expect the 911 to be 50% louder arithmetically, i.e., an increase of 1.8 dB. As the human ear has a logarithic perception, this is pretty minor. The minimum discernable sound increase is 1 dB. For a perception of twice as loud, 10 dB, 10 times the sound power, is needed. VW's are cheap rubbish are built down to a minium price, but Porsche is an expensive brand - this may have allowed Porche to do some sound engineering (double meaning pun intended). At least in Australia, with regard to vehicle noise, the focus has been politically driven - politicians and police have reacted to young men hotting up their cars, and driving in an obnoxious manner. Hence the focus is not on a rational total noise level basis. The police never react to motorbikes ridden by older men, and some bikes, factory standard, are extremely noisy. But a teenager, driving an ordinary car, showing his friends what it can do by accelerating flat out in first gear gets pulled over and charged for excessive noise every time, regadless of how quite or noisy the car actually is. Is it the same in the USA? Ratbone58.170.164.33 (talk) 01:28, 25 August 2012 (UTC)

Yes, although they tend to pick on anyone who "doesn't fit in" rather than just the young. If you are to wrong race, or poor in a rich area, you will be pulled over for the most minor of offenses. I was the victim once. While in college, on a tight budget, I drove a rusted out 1973 Mercury Marquis. I was once in a situation where some idiot was trying to make a left on a street with no left turn lane, and only one lane in each direction, in the middle of rush hour, creating grid lock. I, along with everyone else behind him, quite sensibly pulled around him on the shoulder. The cop ticketed me for driving on the shoulder, and let everyone in more respectable cars go. StuRat (talk) 02:06, 25 August 2012 (UTC)

While I wouldn't say that they are common, Porsche 911s aren't what you'd call rare over in Brisbane. I've seen the Porsche club line both sides of entire streets with them when they meet. Another Important thing to note is that the VW beetle was designed by Ferdinand Porsche who also designed the Porsche 356, which later evolved into the 911. All of these cars are German engineered, rear engined and air cooled, so they're more similar than a cursory glance might indicate. 203.27.72.5 (talk) 06:49, 25 August 2012 (UTC)

I think the bit about lining a street is a) not impressive, and b) perhaps misleading. Brisbane and Perth where I am are pretty similar. You only see a Porsche 911 on the roads maybe once every few months, but you see Fords, Holdens, & Toyotas literally every minute. I see carreras every second day or so - even that rate means it is pretty unusual. I have a friend who owns an MG TC. When their club meets, they fill streets with TA/TC/TD's too. Nobody would they they aren't rare. There's no doubt though that the VW "beetle" and the 911-style Porsche cars are at least superficially similar - but that doesn't stop the VW being junk. I'm not saying the Porsche is junk - I'm not in a position to know. I do know about beetles and Combis - a company I worked for for many years had a fleet of both of them. They were worse than Morris Mariners to drive, scary, and had the shortest engine life of anything - sometimes failing catastrophicly within 2 years or even less. It is well known that the beetle originated in a car designed to Hitler's requirements - which were essentially "make it as absolutely cheap and nasty as posible, so the peasants can buy them, while we Masters can ride around in our big chauffeur-driven Mercedes." It was the same concept as the 3-tube VolksRadio - another Hitler-era piece of junk just able to pick up the local Nazi station. At that time German electronic engineering was the best in the World, but that VolksRadio was just weird junk. Ratbone60.230.234.239 (talk) 11:07, 25 August 2012 (UTC)

I think you're being a bit harsh with the VW Beetle. Yes, it's a basic economy car, but any model that lasts some half century after it's introduction definitely had something going for it. Tall people liked them because of the domed roof, which meant they actually had headroom, versus other econoboxes. I seem to recall another quirk, that the windshield wiper fluid was squirted out by using pressure from the spare tire, as opposed to a little pump. As long as you remember to add air to the spare tire every time you gas up, this seems like a good way to reduce complexity. StuRat (talk) 19:39, 25 August 2012 (UTC)

The VW is in this regard like the British Morris Minor. Both were kept in production for years without much change, for as long it could be sold, and for as long as they still passed Govt safety requirements. The VW is an extreme example of this. It contrasts with the American manufacturer practice of a 3 year model cycle. It must be noted that while American-owned car manufacturers have seen to it that the cars look different every 3 years or so, mechanically they hardly ever changed. For example, 6 cylinder cars made in Australia by Holden (Holden is a local car maker owned by GM), they used the exact same Stronberg BV2 carby, and the same diff from 1948 to 1979, only two different engines (the "grey" and the "red"), only 2 different auto transmisions, etc etc. VW's were truely awful. Not only did the engines have a short life as I said, the controls were an ergonomic disaster (for instance the pedals hinged from below, unlike every other car since the 1920's). The procedure to change gear during acceleration in any manual car is as follows: We are in first, now its time to change up. Put in clutch quickly & take foot off go pedal, move stiff gear lever from "1" to "2", let out clutch smoothly while pressing go pedal. Procedure in flat-4 Volkswagen: We are in 1st, now it's time to change up. Put in clutch quickly & take foot off go pedal. Pull gear lever out of "1". Now, waggle the bendy gear lever around where "2" should be, until you feel a slight click. Gently let the clutch out a bit to find out what gear it is - shit, it's 4th. Press clutch back down, pull bendy lever out of 4th, waggle it round again until click. Seems like that's the same spot as before, oh well, let the clutch out a bit. Ah, good, it is "2" this time. Engine lugs because the vehicle speed has dropped too much. That's part of why VW's could last a fair while in private use, but in company fleets they were very failure prone. An indication of how bad the VW Combis were is this: Until 1977, the only low cost boxy side-door delivery vans available in Australia were the VW Combi, and the Commer (itself almost as bad in its own way). There has always been a considerable commerical need for such vans, and so the Combi enjoyed big sales. There were things like the Ford Transit, but they were a much bigger & heavier vehicle, for which there is not so much need. In 1977, Toyota introduced the first "Hi-Ace" van. Combi sales evaporated virtually overnight, and VW Australia withdrew it from sale. In a similar way the Ford Escort displaced the fleet market for VW beetles and Morris Minors. Ratbone124.178.177.224 (talk) 01:26, 26 August 2012 (UTC)

How can you insult a car that was exported from Aussie in one of your pop songs ? Although, come to think of it, it was a "fried out Kombi" and the song implied that people who drive them must be drunk, on drugs, or both... :-) StuRat (talk) 02:30, 26 August 2012 (UTC)

Well, as another, somewhat less subjective measure of the relative frequency of Porsche cars in Australia, have a look at carsguide.com.au. Currently, there are 458 Porsches for sale, compared to 73 M.G.s, 675 Land Rovers, 311 Daihatsus, 390 Daewoos, 24,616 Toyotas. I'm not suggesting that they're common, but you definitely encounter them on a pretty regular basis, especially if your route takes you through some of the nicer suburbs. 203.27.72.5 (talk) 20:35, 25 August 2012 (UTC)

You can't be serious! Assuming for the moment that the number for sale is proportional to the number registered for road use, and not significnatly affected by durability, owner satisfaction, etc, that's 0.019 Porches, of any sort, for every Toyota of any sort. Sounds like a rare car to me. Only a small part of those 458 Porches will be the 911's we were talking about - as I said you see Carreras quite often. You can see your data is dubious by the figure for Daewoos - they are certainly far more common than Porsche. You left out data for Fords, Holdens, & Nissans. It would be reasonable that compared to all four major brands of long standaing (Toyota, Ford, Holden, Nissan), you'd get Porsche 911 at less than 0.002 911's per car of any brand & type. Ratbone124.178.177.224 (talk) 01:26, 26 August 2012 (UTC)

It's not meant to be the be all and end all of measures. It's just meant to be better than "well I think I see them lots when I drive around". I'm not sure what you're talking about when you say "Carreras", which are almost all 911 Carreras (all Porsches were rear engined and air cooled prior to 1998 except for the unpopular 924s, 928s and 944s anyway). The reason I stuck in Daewoos (I just chose a sampling from the 50-100 brands listed) was to illustrate that it's approximately similar to the number of Porsches, so they have similar rarities. Given that Daewoos badged as such were only made between 1982 and 2011, and Porsche 911s have been made since 1963 and always badged as such (with the tiny exception of RUF), and their higher value and quality makes them worth maintaining for decades after production, it's not inconcievable that they'd number about the same as Daewoos. 203.27.72.5 (talk) 03:27, 26 August 2012 (UTC)

Can the OP give a particular reference as to where what components jet engines use fuel for cooling? Rockets are jet propulsion engines but normally they use the liquid O2 for cooling.. MW 50 (alcohol and water mixture) was used to boost the power of German bombers, and a similar system for US Tomahawks by cooling the intake air. Military gas-turbines similarly, often use just water injection to cool the intake air during compression in order to boost power but it reduces the life of the power plant -so is little used for normal operations.--Aspro (talk) 00:54, 23 August 2012 (UTC)

Maybe this isn't as common as I thought. Precooled jet engine mentions the concept of cooling the intake air using the fuel, but apparently this isn't in production yet. StuRat (talk) 01:52, 23 August 2012 (UTC)

It depends on how you define what you mean by useing fuel to cool the engine I guess. Precooling is about cooling the fuel before it enters the engine, a totally diffrent concept to using the thermal capacity (specific and latent) of the fuel to help manage temperatures in an engine. Ever since Wittle and others introduced jet engines for aircraft, jet engine design engineers have specifically calculated on the basis of using fuel thermal capacity to keep parts of an engine at temperatures low enough metallurgically. I had thought that that was what you were refering to. I hope you caught the basic points I made ealier - 1) fuel consumption is relavtively high in a jet, so the usable fuel cooling effect is larger, 2) it only cools part of a jet combustion system, and 3) combustion chamber wall cooling is more critical in a jet than in a piston engine. Ratbone124.182.134.244 (talk) 02:52, 23 August 2012 (UTC)

Actually, precooling in the article StuRat linked to above is about cooling the air going into the jet engine (using the fuel as the coolant), not cooling the fuel. 203.27.72.5 (talk) 03:00, 23 August 2012 (UTC)

Darn it! You are right. I should have read the article Stu linked, before posting, instead of going on my memory of what I read in a text book. Ratbone124.182.134.244 (talk) 03:09, 23 August 2012 (UTC)

Also, as far as it being a wash because the cooling of the engine block is made up by the heating of the fuel, wouldn't most of that heat end up going out the exhaust, after combustion, rather than going back into the engine block ? StuRat (talk) 04:50, 23 August 2012 (UTC)

In a modern gasoline engine, roughly speaking, of all the combustion heat, one third gets turned into mechanical effort on the piston, one third ends up via various paths heating the coolant, and one third is lost as waste heat in the exhaust gasses. So, roughly speaking, you could expect the recovered heat to also split equally the three ways. I should have thought of that, though for reasons discused by myself and 203.27.72.5, the amount of heat that can be recovered by combustion quantity fuel is necessarily too small to matter. Ratbone124.182.179.59 (talk) 06:34, 23 August 2012 (UTC)

Don't think anyone has so far mentioned our article on internal combustion engine cooling, have they ? Gandalf61 (talk) 08:43, 23 August 2012 (UTC)

Stu's smart enough to have already read that. As a long time committed Wiki man, I expect he already read it and didn't get what he wanted. He doesn't need us to tell him it's there. As a general rule, I assume that OP's asked their question because they did get what they needed from Wikipedia. In any case many articles are not exactly good quality. Ratbone124.182.179.59 (talk) 08:56, 23 August 2012 (UTC)

From his statement of the question he already seemed to understand how a radiator works, so I don't see what he would have gleaned from that article. 203.27.72.5 (talk) 20:39, 23 August 2012 (UTC)

There's another interesting aspect to this fuel cooling / pre-cooling /fuel efficiency business, that I should have thought of before. It was common up to the late 1970's for car engines to have a water-jacketted intake manifold or "hot box". The hot box heated the intake air, and the reason thay did it is that it improved fuel economy slightly (minor reason), and it hastened engine warmup (strong reason) as the water flowed in the manifold jacket even when the therostat blocked off radiator flow. It is thermodymamically the same as passing the charge thru the crankcase, and so in that sense StuRat's idea has been in use. It was dropped in the late 1970's when car manufacturers had to meet tight emission standards. After then, they heated the intake air by passing part of it through a cover on the exhaust header. A servo-controlled vacuum powered motor moves a baffle to vary the percentage of intake air moving over the exhaust, to regulate the intake air temperature faster and more accurately than is possible with a water jacketted manifold. Altough the prime purpose is to ensure precise combustion conditions and low emissions, it will improve fuel consumption. So, in a sense, StuRat's idea is still in use.

In modern diesel engines, turbo-charging is almost universally used, in order to stuff more air in and increase power output. It also significantly improves fuel ecomony as it recovers some exhaust heat and puts it to use. Because compressing air increases its temperature, which reduces density, a turbo on its own has limitted effectiveness. To fix that, and intercooler is used. The intercooler uses radiator coolant to cool the intake air, increasing its density and thereby increasing power output. Well, that's what it does when the engine is heavily loaded. At light loads, the turbo doesn't spin very fast, and doesn't heat the air. The intercooler becomes an interheater, improving part-throttle economy.

Still with me, Stu? Ratbone120.145.40.59 (talk) 23:14, 23 August 2012 (UTC)

Yes, the turbo lag is why superchargers are sometimes used. StuRat (talk) 02:33, 24 August 2012 (UTC)

Actually, Stu, superchargers have long since ceased to be used, except for special cases that have nothing to do with avoiding turbo lag. Superchargers are low tech - no special materials required. Turbos had to wait for development of high temperature materials. Reasons for supercharger decline in use: (1) a turbo, by utilising eshaust heat otherwise wasted, improves fuel efficiency, whereas a supercharger, by taking mechanical power from the crankshaft, while it can increase power output, reduces fuel efficiency. (2) A turbo is cheaper. (3) thermodynamically, except for taking power from the shaft, a supercharger is much the same as increasing the compression ratio & swept volume - it's simpler to just build an engine with increased swept volume and compression ratio.

Superchargers get used when: (a) a vintage car enthusiast want to hot up his relic and wants to do they way it would have been when the vehicle was current. (b) a manufacturer is loosing sales because a competitor has introduced a bigger engine, and the afore mentioned firm need to do something quick and cheap; (c) the engine is a uniflow 2-stroke, which cannot itself suck air in. (although it is common with uniflow 2-strokes that the blower is driven electrically, and not from the crankshaft); (d) high altitude aircraft piston engines.

Turbo lag can, in most applications be made acceptably short by: (1) using two or more small turbos in parallel, insterad of one big one - this method is very common; (2) using a larger turbo in conjuction with a waste gate - this is reasonably common. Waste gating is simple, cheap, and can, if desired, completely eliminate turbo lag. (3) Using a camshaft that opens the exhaust valves early. This gives more exhaust energy and shortens the response time, and doesn't reduce efficiency very much, and you can get that back with just a bit more turbo boost. This method is not common, but is gaining ground. Ratbone120.145.168.86 (talk) 11:26, 24 August 2012 (UTC)

OK, thanks all. StuRat (talk) 08:36, 25 August 2012 (UTC)

Resolved