Wikipedia:Reference desk/Archives/Science/2015 December 13

= December 13 =

Leadership skills
Does volunteering with listening services such as befriended or Samaritans teach you leadership skills? — Preceding unsigned comment added by 2A02:C7D:B901:CC00:7CE7:1D53:9581:45DA (talk) 09:30, 13 December 2015 (UTC)
 * It can do, much depends on the role you undertake as a volunteer and how you use your time there. --TammyMoet (talk) 10:06, 13 December 2015 (UTC)
 * For those unfamiliar with the organizations, we have: Samaritans (charity) & Befrienders Worldwide. -- ToE 14:32, 13 December 2015 (UTC)

Why can ethanol be used as a rocket fuel but gasoline can't?
^Topic ScienceApe (talk) 16:51, 13 December 2015 (UTC)


 * Kerosene has been used as a rocket fuel. I imagine it was preferred over gasoline because it is safer to work with and used to be cheaper. Jc3s5h (talk) 16:56, 13 December 2015 (UTC)
 * Gasoline _can_ be used as a rocket fuel - Robert Goddard's first liquid-fuelled rocket, "Nell" (1926), ran on gasoline and liquid oxygen. See RP-1 for our article on hydrocarbon rocket fuels - apparently, OTRAG, a 1980's German hobbyist organization, built a rocket that ran on diesel. Tevildo (talk) 18:33, 13 December 2015 (UTC)
 * The article says the fuel is, "The fuel was intended to be kerosene with a 50/50 mixture of nitric acid and dinitrogen tetroxide as an oxidiser." ScienceApe (talk) 19:09, 13 December 2015 (UTC)
 * This article (New Scientist, May 1976) states that the prototypes, at least, were diesel-powered. This site has a list of (presumably theoretical) specifications, which include the use of diesel fuel. Tevildo (talk) 20:04, 13 December 2015 (UTC)
 * This is more of an educated guess than a factual one but based on the characteristics of gasoline. Firstly, consider starting. Have you noticed that just before a LOX kerosene engine starts, little pyrotechnics come on to shower the exhaust nozzle with sparks to ignite the fuel. Imagine using petrol – it is explosive. It could easily over pressure the combustion chamber and blow it apart – or in astronautical terms, cause it to under go rapid disassembly. Say all engines do successfully fire up – what then. Gasoline does not burn smoothly. Both kerosene and alcohol have a lower octane rating... they want to burn as soon as they get hot enough in the presence of an oxidizer. The fuel to air/oxidizer ratio is less important.  Petrol on the other hand may pause a moment and think about whether it wants to oxidise and having finally decided to  oxidize.... it-can-do-so-sudden. So such an engine running on petrol will not run smoothly. It with stutter and  cough. Should it burp in the process, the combustion chambers  could well scatter bit of themselves  all over the place. To run a petrol rocket engine one needs to run it very rich (i.e., much less fuel than the optimum amount of oxidizer and that lead to a lower SI). Even modern hydrogen/LOX  engine are run a little fuel rich. Better to waste a bit of fuel than waste a whole rocket.--Aspro (talk) 18:57, 13 December 2015 (UTC)
 * ? Nimur (talk) 19:08, 13 December 2015 (UTC)


 * Page five: One odd aspect of Goddard's early work with gasoline and oxygen is the very low oxidizer-to-fuel ratio that he employed. For every pound of gasoline he burned, he burned about 1.3 or 1.4 pounds of oxygen, when three pounds of oxygen would have been closer to the optimum. As a result, his motors performed very poorly, and seldom achieved a specific impulse of more than 170 seconds.


 * Page 20
 * Malina and company started experimental work with RFNA and gasoline as early as 1941—and immediately ran into trouble. This is an extraordinarily recalcitrant combination, beautifully designed to drive any experimenter out of his mind. In the first place, it's almost impossible to get it started. JPL was using a spark plug for ignition, and more often than not, getting an explosion rather than the smooth start that they were looking for. And when they did get it going, the motor would cough, chug, scream and hiccup —and then usually blow anyway.
 * Ref:
 * Yeah meant flame front propergation velocity not octane. Yeh got lean and rich mixed back to front too.--Aspro (talk) 22:51, 13 December 2015 (UTC)


 * Ethanol and especially methanol has a higher octane rating, not lower and less fuel would be lean not rich. Sagittarian Milky Way (talk) 19:40, 13 December 2015 (UTC)


 * It sounds as if your "just before a LOX kerosene engine starts, little pyrotechnics come on to shower the exhaust nozzle with sparks to ignite the fuel" is describing the Radial Outward Firing Initiators (ROFIs) used to burn off excess gaseous hydrogen during the start of LOX/LH2 engines, such as those used on the Space Shuttle, Delta IV, and SLS. Here is an NSF article discussing their operation.  See Rocket engine for a discussion of the ignition process.  ROFIs are not used for engine ignition, and having the engine lit from an external source like that would result in a hard start. -- ToE 13:59, 14 December 2015 (UTC)


 * I'm highly skeptical that NASA rocket scientists can't figure out how to keep a gasoline rocket from exploding. I mean, the Nazis could play with hydrazine and concentrated hydrogen peroxide, and they're supposed to be dumb, right?  I do note that kerosene has more energy per volume than gasoline  - 135 vs 125 kBTU/gal according to this.  Then again, several grades of fuel oil have even more, but maybe NASA scientists couldn't...  then again, there's also the matter of density... I'm seeing a figure of 0.71-0.77 for gasoline and 0.78-0.81 for kerosene ... thrills.  I have no idea how that comes out, too much fog in the numbers, but fuel oil is 0.99-1.01, so that probably is out?  Then again, the density also controls how big the rocket needs to be, which is also really important, so... well, at this point I admit I'm not a rocket scientist. Wnt (talk) 21:58, 13 December 2015 (UTC)
 * Aspro's reference is worth looking at. It's _possible_ to start a gasoline-fuelled rocket without it exploding - it's _much easier_ to start a kerosene-fuelled rocket.  It's even easier to start a rocket with hypergolic fuel, but the cost of the fuel would be prohibitive for an orbital booster stage (as opposed to a short-range atmospheric vehicle, like the Me-163).  I don't know how RP-1 compares in cost with a hypothetical rocket-rated gasoline blend, but I can't imagine it's significantly more expensive. Tevildo (talk) 23:15, 13 December 2015 (UTC)
 * Cost of fuel isn't the main thing against hypergolics (though they are more expensive), it's the poor isp. I assume you are aware that there are a number of hypergolic booster still flying (Proton, Long March), so cost isn't 'prohibitive'? That, and safety issues. Fgf10 (talk) 14:27, 14 December 2015 (UTC)
 * BTU's "per gallon" would be the wrong metric. "Per pound," though is a different story.  Kerosene is about 7 pounds per gallon while gasoline is 6 pounds per gallon so gasoline would be a better weight to energy tradeoff though not a volume to energy tradeoff.  I would think the problem would relate to compression with an oxidizer present.  Kerosene in turbine engines behaves nicely.  Gasoline engines have spark plugs because it does not behave well.  Higher compression engines need purer gasoline to retard the spark as do piston aircraft but they never rely on compression itself as the igniter (so called "knocking" is bad).  A rocket motor compressor would suffer the same problems I would think.  --DHeyward (talk) 05:50, 14 December 2015 (UTC)

How do waves and winds interact?
Is there a science dedicated to the interaction of winds and waves on oceans or another big mass of water?--Denidi (talk) 19:55, 13 December 2015 (UTC)


 * There is - see Wind wave. Tevildo (talk) 20:12, 13 December 2015 (UTC)


 * Also note that waves formed in other ways, like tidal bores, tsunamis, and boat bow waves and wakes, may be affected by wind after formation, especially at the peaks. StuRat (talk) 23:16, 13 December 2015 (UTC)


 * Hydrology - "the scientific study of the movement, distribution, and quality of water on Earth and other planets"; hydrometeorology - "a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere". Gandalf61 (talk) 12:03, 14 December 2015 (UTC)


 * If you google the definition of either of those they are not really specific to waves. Hydrology is to do with the movement of water through land to the atmosphere and hydrometeorology is to do with water in the atmosphere and its effects on the weather. Physical oceanography and fluid dynamics (see Boussinesq approximation (water waves)) are the branches of science that would deal with to the processes of wave formation. Richerman    (talk) 14:37, 14 December 2015 (UTC)