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Shortwave Sportfishing wrote:
On 1 Jul 2005 08:48:37 -0700, wrote: K. Smith wrote: zee-qi wrote: hi people. i would ask you something.Who can explain me how does work diesel engine.?and what kind of system it need to work normally. ..thx for your ansver... They use diesel fuel which has a very low auto ignition temp (about 200-210C) so if a "vapour" of diesel sees 200C it auto ignites without a spark. Petrol gasolene has a higher auto ignition temp (250-280C) so it needs an electric spark to ignite it. Are you sure you're explaining that correctly? I wondered the same thing - I just read what Karen wrote. It's my understanding that the auto-ignition point isn't relevant with gas engines because it doesn't rely on compression for ignition - it relies on a spark. Which, at least to my mind, would indicate gas would have a low flashpoint and a high auto ignition temperature. Conversely, a diesel has a high flash point and a low auto ignition temperature which is why the compression is high. Also, it's my understanding that the reason some gas engines have high compression ratios is more for power production. Or am I wrong? Hi Tom, It wasn't bait I promise, just as I promise you won't like this:-) Only a vapour will ignite; either because it's exceeded it's auto ignition temp or it's in contact with something well above it, say a "spark"?? All the spark does is be a point of heat above the particular vapour's auto ignition temp. Even petrol will not burn if it is in "liquid" form indeed if raw petrol gets on a spark plug (flooded) you can crank it till the cows come home & it won't go till the raw fuel evaporates into a form (vapour/gas) & then reaches an ignitable mixture. DIESEL The trick here is that diesel has a low auto ignition temp but also remains "liquid" at normal room type temps. So it's essentially not able to be ignited even if in contact with something well above it's auto ignition temp. You can throw a lit match in if you like but please don't!!!! just in case it's a hot day!!!:-) Also it takes either pre-heating or considerable mechanical pressure to vapourise it such that it will ignite & burn at all. So in a diesel the fuel isn't present at all till the moment the injection starts, save a small lag while the burn establishes itself (the characteristic diesel knock) the burn only continues so long as more fuel is injected, at low power or idle the injection stops almost immediately, at higher power it continues over a longer part of the cycle (giving better mechanical advantage because the most torque is generated when the crank is at 90 degs to TDC) PETROL Petrol can be a vapour at most normal temps unless in a sealed container &/or under pressure. So the combustion chamber must never have any even small surface that exceeds the petrol's autoignition temp or the vapour will auto ignite, even as the piston is still coming up on the compression stroke, it must all remain unignited till the correct timing when the plug "sparks". Once a vapourised fuel (either) is ignited in the presence of an oxidiser (air) in the right proportions (mixture), say because it's come in contact with something above it's auto ignition temp then the game is irreversibly on, the flamefront will advance in a predicatable manner (16m/s) till it consumes all the available vapour &/or oxygen. The ignitable mixture ranges varies with fuels but with most petrols it's usually around 11-1 to 17-1 by weight; so too much fuel & it's not a vapour (not enough oxidant can be present to supply the burn) below the min lean mixture & again the vapour becomes too dispersed to ignite at all &/or carry the flamefront. Some deluded engine makers claim they can get around these facts by creating what they oft call a "stratified" charge which is their way of admitting they know a lean mixture can't burn predictably but say by concentrating it around the spark they can cheat & get it to ignite (one totally discredited example was Ficht & now called E-Tec when not only did they claim "stratified" but it was so lean, they needed a continuous firing of the spark plug to even get ignition!!) The danger with over lean mixtures is that "if" you can get ignition at all then the trouble has just begun because as soon as the first so called "stratified" part of the mixture ignites the chamber pressure/temp (press & temp are one & the same) goes up (as intended after all that drives the piston back down) but any even small pockets of unstratified mixture (endgases) also immediately auto ignite. This uncontrolled auto ignition means the burn is totally erratic & unpredictable. You or your engines might get away with it forever or for a short time only, but whichever way you see it the risks are very high. Chrysler & Honda both very biggies in engines couldn't make it work, Ficht certainly couldn't the difference was Chrysler & Honda knew exactly what the problem was so stopped, but not Soros the convicted union lacky he persisted ****ing other peoples' money against the wall till an American icon Co went down the drain. So nothing new really all well known & pretty well understood since the 1930s over lean mixtures lead to chamber temp rises which leads to more detonation which leads to higher chamber temps which leads to more detonation which leads to .... well you already know the damage it can do??? it shook your electrics to bits, but hey don't feel bad it also blew injectors from heads, made the plumbing fall to bits such that the USCG had to make them have a safety recall, the gearcases (which being OMC were never much good anyway) really fell to pieces under the hammering repeated detonation can deliver to a direct drive train, then of course the biggest failure mode was just damaged & melted pistons, crack rings all the usual stuff expected of engines run at power in a lean condition. By the way Tom how are those new E-Tecs running have you got them all sorted yet?? or are you still being run around while Bomb try to decide how to back out of this latest consumer funded experiment??? K So as the lying idiot Krause has chosen to tell us below about his fantasy father lies here's some more for you to ponder as you enjoy asking why absolutely no verifiable fact can be found, after all in another of his father lies he claims he crossed the Atlantic in a 23ft outboard powered craft & got a fire tug welcome into NY!!! A sicker more dangerous simpleton there is not on this planet than our unionist organiser Krause. Nope. He was a successful boat dealer and marina operator for 30 years in New Haven County, Connecticut. He served several terms as president of the Marine Trade Association and also lobbied for boat dealers before the Connecticut legislature. Many of his best friends were competing boat dealers. They talked shop a lot. If someone with something strange showed up on his doorstep and he were interested in offering a trade-in on it, he'd call one of his buds to give him a price or drive on over for a look-see. The "usual list of suspects" he, of course, recognized because of his experience, and he had a pretty good idea of what a used rig might fetch on his sales lot. He never took a "price boat" in on trade, though. They always needed more work than they were worth. Many boat shoppers never were aware that most of the boat dealers in my dad's area were really close friends and shared information about potential customers all the time. If he didn't have what a customer wanted, he'd call "Dickie" or "Paul" or "Art," all competing dealers and see if they had something appropriate. "Dickie's" father owned the New Haven Arena, where boat shows were held, and was also chairman of the National Basketball Association. |
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