hey, it's me destin. welcome back to smarter every day (sed). so excited about this video in the last episode of sed i showed you my transparent potato gun, at 3,000 fps during the day.
priprism, 3, 2, 1 but this episode it's going to be the same transparent potato gun, meaning we can look directly into the science at night, at 20,000 fps.
google up! science is about to happen. what happens, if i start the ignition of the potato gun from the back? vs. what happens, if i start it from the middle? i always thought it would have worked better if you go from the middle, 'cause you get even expansion of those gases. but, let's record it in high-speed, and let's see what the difference is, between the two. we'll go from the back first!
we got some potato juices in there. (laughter) it's like 9 o'clock. alright, let's see it in high-speed. it's completely awesome. we saw that it started at one end and went all the way to the end. now, i'm gonna take this, it's a grill-ignitor, you can see the little zaps there. i've got electrodes, set up in the center of the potato gun
and we're going to zap it from the center and we should get a more even combustion, right? so, let me hook it up and then we'll give it a shot. literally. loading the potato gun again. it doesn't get old! was that cool, or what? ok, so check it out, so this is my combustion chamber, right? the first time i shot this thing, it was a flint-sparker on the end of this thing, right?
if i hold it, you can see a twist and i get the spark. what you saw on the second time - here are my electrodes that i told you about going to hit this button you can seedown in there. can you see what i'm sparking right there in the middle? that's how i fired that thing. when wefirst start the combustion from the end it's a wave you've got an oxygen/fuel mixture thatgoes all the way down to the combustion chamber; when we start right in themiddle,
we start to expand, we start using thatfuel and using that oxygen, but we run out of oxygen before we burn all thefuel. we're going to shoot this thing from the end, we're going to zoom in witha high-speed directly on the combustion chamber and we're gonna see if we cansee that flame front moving one mississippi two mississippi threemississippi four mississippi three two one ok, before i show you the next slow mo, iwant you to understand that it has enough information in it to provide forseveral phd's ,so i want you to be on the lookout for a couple of key things thati find interesting.
#1 when the explosion movestowards the closed off into the combustion chamber, unless the fuel/airmixture is just perfect, sometimes you'll run out of oxygen andhave unburned fuel this creates a compressed pocket of fuel,that stays unburned until it turns into a rarefaction and pulls more oxygen backin through the barrel, to burn it up #2 there's something thathappens in combustion chambers called "sidewall cooling" basically the pipeitself cools the gases down below the combustion point, so it can't burn right nextto the wall this leaves more unburned fuel andactually counts for most of the
pollution products caused by the enginein your car the slow-motion you're about to see isreal. i haven't ran the speed, to make it look more interesting, it's just pure awesome footage. straightout of a high-speed cameras. watch what happens, as the explosion overexpands, the system has to equalize so it pulls air back in through the barrel,into the combustion chamber, which causes that fresh oxygen in the air to meet upwith the remaining fuel and start the burning process all over again. it's a pretty inefficient way to burn afuel rich mixture;
so i think my original hypothesis mightbe wrong. i think it's cool that when the gassqueezes down into the barrel from the combustion chamber, it has to speed up sothat it can maintain the exact same flow rate one of the things i love about science,is the ability to look at a complex dynamic system like this and try tounderstand every physical phenomenon that's occurring, but equally important tome personally is the ability to look at footage like this and say "you know,that's pretty." to summarize, what we've learned tonight,think about this: when you have a
combustion chamber we've learned that it depends not onlyon the localized chemistry or the stoichiometry, the fuel/air mixture atany point inside that combustion chamber; it also depends on how its vented it'sreally fascinating the dynamics of venting a combustion chamber effectdirectly the ability to create localized pressures and rarefactions sometimes atthe end of the video when the add part comes up you kind of roll your eyes ,becauseyou're not excited about it. well, this time is different, you see,sed is supported by audible.com and they have supported me for areally long time and it's a really big deal
because it's kind of expensive to afford videos like this. so, what i'm going to do is i'm going tocreate an audible event so that you can remember to support sed ataudible.com/smarter. we're going to create the same flamefront that we did before, only we're not going to contain both sides of it we'regoing to vent one side i want you to listen to this hugeaudible vent and then we'll look at high speed ready? 3, 2, 1... it's on fire! if you want to support sed,feel free to go to audible.com/smarter. that's a very audible event, i hope youagree, anyway they have tons of free
audio books.if you get a free trial ataudible.com/smarter i'm super stoked that they have chosento support smarter every day for so long they've been a very valuable partner andi am very appreciative so if you want to support sed directly go toaudible.com/smarter get a free trial of audiobooks you're going to getsmarter and you're going to like it. so there you go, i hope you feel likethis video on your subscription if not that's it. i'm destin you're getting smarter everyday have a good one (inaudible) i ... going atwatermelons. yeah and i'm record in slow
motion you are?
yeah. is that cool? - that's what they all say... you don't do it at night too? is that all right? - it's your property, dowhat you want to do on it. you do anything you want to do over here! you ain't going to botherme i think it's time to go to bed