**The Engineering Behind Two-Stroke Engines**

Well, it's right in its name. The first piston draws in air and compresses it. That pressurized air moves through a valve into the mixing chamber where fuel is injected. Another valve opens and that compressed air-fuel mixture rushes into the combustion cylinder. And it does this because the combustion cylinder is at a lower pressure, and air naturally moves from areas of high pressure to low pressure.

But it's also very hot in that cylinder, that's because the exhaust valve is designed to close before all the hot gases from the last round of combustion are pushed out. Like in a diesel engine, it's the heat in the cylinder that starts the burn. Igniting the intake charge on entry to the cylinder hints at entry ignition. And because the pressure is higher in the mixing chamber, the flame only travels downward towards lower pressure in the piston.

Look at that, you guys now learned a new engine, cool. A Brayton cycle engine separates compression and expansion in different parts of the engine. That division of labor is exactly what's happening here. And because every step intake, compression, combustion, exhaust, or as I say, suck, squeeze, bang, blow, is happening with every rotation of the crank, like Brayton's original piston engine, this is a two-stroke engine. There's one power stroke for every 360 degrees of crank rotation.

So what are those other two cylinders out here? Well, those are sort of helpers that maximize the thermal efficiency of the engine. That's the amount of energy from the fuel that's actually converted into work and not lost as heat. So increasing thermal efficiency, not only improves miles per gallon, it also increases power per gallon.

The first cylinder gives the engine two-stage compression, almost like forced induction. The piston compresses air before sending it to the second cylinder, which compressed even further for combustion. And the reason those are two different sizes has to do with heat loss. A larger cylinder, a greater surface area creates a charge with lower temperature than the smaller second cylinder. That extra compression increases the amount of oxygen delivered to the combustion cylinder and more oxygen means more energy can be extracted from the fuel.

I can hack, yeah, men. You guys gotta get pumped about engineering, man. This (beep) is cool, man. This is why I went to engineering school. And this is why I do donuts now. So I can get you guys jacked up. Just (beep) pumped. Just (beep) psyched on new engine technology. This (beep) engineering is sick, dude, just like (beep) bashing, like best bro stuff.

Breathes deeply. Are we cool? Yeah, cool, cool, cool, cool.

**A Brief History of the Two-Stroke Engine**

Using a separate cylinder to pre-compress air was part of one of the very first two-stroke engines developed in 1880 by Scottish inventor Dougald Clerk. In fact, that design laid the foundation for most modern two-strokes. We sometimes describe those as using a modified Otto cycle, but really they're the Clerk cycle, the name just never caught on.

Dang! I just got you all jacked up about engineering, and now we find out that when you invent something, some time people don't use it, that hurts. It's like a stab to the engineer's heart. It's okay though, we'll give Clerk his due. History is written by the videos you put on YouTube.

**The EI Engine: A Major Breakthrough**

The final cylinder is there to extract energy from the exhaust that most other engines let go to waste. The gas force out of the cylinder during the exhaust stroke hasn't reached atmospheric pressure. It's still compressed. The sound of your car's exhaust is actually the sound of wasted energy. It's those gases expanding.

The EI engine harvests that normally wasted energy in a really large cylinder to make room for their expansion. The expanding exhaust gases push on that extra piston, and that means more power going to the wheels instead of out the tailpipe. That power also happens on the off stroke, the non-combustion non-power stroke.

Oh, dude, I'm telling you guys, this is sick. Those two extra cylinders help the EI engine extract more energy from burnt fuel, and the effect is a major increase in thermal efficiency. Ready to talk about something else?

WEBVTTKind: captionsLanguage: en- The gasoline, diesel, rotary,and even jet engines we havetoday have evolved from designsthat are over a hundred years old.With the push in EV tech oflate it's tending to thinkthe advancement of ourinternal combustion enginehas run its course.The thing about engineers isit never stopped engineering.And a brand new design calledthe entry-ignition-enginecould change the combustion game.And on top of that, it's a two-stroke.(motorbike roaring)But not the type of two-strokeyou might be thinking about.Could a two-strokeengine, save us from EVs?I don't know, maybe.Watch to find out.(upbeat music)- Thanks to Jackery forsponsoring today's video.Snowfall can be beautiful,but it can also be awinter disaster, blizzards,extreme cold power outages.It can feel like you're atthe whim of the weather.We'll take the power back with Jackery.(machine whirring)You'll be ready for everythingwinter has to throw at youwith the Explorer 1000.Jackery most popular modelwith the ability to supply1000 Watts from multipleports, like AC outlets,a DC car port, and USB charging port.But if you're trying tobring your power game upa few more notches, thesolar generator 1500has a massive 1800running wattage capacitypowering 99% of yourdevices and appliancesin the event of an epic snowstorm.Unlike most home generatorsthat burn dyno juice,Jackery solar generatorscan be used indoorsand are real quiet.And hook them up to Jackery solar panelsto create a power pack portable solution.So what are you waiting for?Power the warmth thiswinter by clicking the linkin the description below today,because not everybody livesin Southern California.(soft music)- The appearance of abrand new kind of engineis a rare and exciting event.That's exactly what happened in 2020when the entry-ignitionengine design debutedin the journal of Societyof Automotive Engineers.The way it works is a bitlike an ordinary four stroke,a bit like a diesel and alittle bit like two-strokesfrom over a hundred years ago.I'm frigging (indistinct) over here,just a little bit, alittle dash of four-stroke!(chemicals exploding)A little bit of two-stroke!(chemicals exploding)A little bit of diesel!(chemicals exploding)(liquid boiling)(chemicals exploding)Entry-ignition-engine.That was my hacky part.So don't understand the significanceof the entry-ignition-engine?Let's take a quick look ata typical two-stroke engineand why they haven't beenused very often in cars.And when most people think of two-strokes,they imagined lawnmowers, chainsawsor the good old dirt bike, yeah,the kind of low-tech engineswere premixed gas and oiland no valves, but theydo make decent powerand they go.Those are incredibly simple.And at their most basic atwo-stroke engine can haveas few as three moving parts, a crank,a piston and a connecting rod.That's simplicity makestwo-strokes lightweightand inexpensive perfectfor lawn care equipment.Of course we like lightweightand inexpensive cars as well.And over the years,there have been a handfulof two-stroke cars,cars like the Saab Sonic, Subaru 360,and models from Germanmanufacturers like Trabant,Wartburg and DKW whichlater became part of Audi.But these engines have somedrawbacks that make thema poor fit for most road cars.They're smoky, loud, inefficientand not really designed torun for long periods of timeor under the conditions thatordinary road cars face.Let's take engine breaking, for example,that's when you let off the acceleratorand use the drag from the car'sengine to slow the wheels,instead of the engines combustionkeeping the wheels turningit's actually the wheelskeeping the engine turning.That's a perfectly normal thing to dowhile descending a hillor slowing with traffic.But in a two-stroke usingpremixed gas and oil,there is no separate systemto provide engine lubrication.When you let off theaccelerator gas and oil,aren't going to the engine,but all the parts in theengine are still moving,wearing down their thin layer of oil.In an ordinary two-stroke,that oil makes its wayout the tailpipe andwith no throttle input,isn't being replaced with new oil.On a long up-hill thatcan lead to oil starvationcausing the engine tooverheat or become damagedfrom excess friction.Gotta have that oil in there.Well, you don't have oil,you have metal on metal,and metal on metal it's like.(metals cracking)You need to lube it up.Get lubed, bro.With these two-stroke problems,car makers either had tocome up with solutionsor face the fact people couldjust go buy something else.When your customers have choices,you have to respond or youend up out of business.Just remember Blockbustercould have bought Netflixfor 50 million bucks,but thought there wasno future in Netflix.So most automakers use newer technologyto make their two-strokes better.For oil starvation, somesimply add in an oil pumpto keep lubrication flowingeven when the throttleisn't being applied,the same technology has beenin many two-stroke motorcyclessince the 1970s, or youcould do what Saab didand add a freewheel.That's a mechanical devicethat disconnects drivefrom the wheels if thewheels are spinning fasterthan the drive source.Bicycles use a ratchet in freewheel,and that's why you hear a clicking noisewhen you're coasting.(bicycle clicking)Cars that use a freewillinstead of relyingon our centrifugal clutch freewheel.When the drive shaft is spinning,centrifugal force movesclutch pads outward,completing the connection with the wheels.But when the drive shaftsspin slower than the wheels,those pads release,allowing the engine andwheels to spin independently.But that does make enginebreaking ineffective,but it lets the engine idlenormally when there's no load.So it still receives asmall amount of fuel and oilpreventing that oil starvation.I'm so hungry for oil feed me.The point is, is that two-stroke motorsdon't have to be like theones found in lawnmowers.In our previous episode,we explained how designeda two-stroke enginethat solved all of the typicaltwo-stroke stroke problemsback in 1994.They implemented modern engine technology.They added an oil sump,which prevents starvation,and reduces smoke inemissions from burning oil.They added overhead valvesto stop unburned fuelescaping during the exhaust strokeand prevented exhaust gas from lingeringin the combustion chamber.They even added a superchargerfor a little extra punchto make up for that pressure boost lossby not routing air andfuel through the crankcase.It's not just Ferrarithat continued to try outtwo-stroke designs.In 1990 GM showed a prototypeMiata Fighter calledthe Micro.Hell, yeah, Micro machine.And in 2014, Renaultunveiled a superchargedtwo-stroke diesel that made107 foot pounds of torquewith just 0.7 liters of displacement.That's tiny dude.But here's the thing,none of these designshave made it into production.The reasons are similarto why we won't gettwo-stroke F1 cars.four-stroke engines are whateveryone has put decadesof development into.Nobody's going to adopt a drasticallydifferent engine design now,unless it has some huge benefit,like a massive increase in efficiency.Massive and efficient?Stop it.And a huge increase inefficiency is exactlywhat the inventor of theentry-ignition-engineclaims to have done.But unlike Ferrari,instead of just lookingto modern technologyto build a better two-stroke,they've also incorporatedtwo-stroke ideas from the past.(Burton clears nose)Sometimes you got to learnfrom your mistakes, am I right?See two-stroke andfour-strokes are general termsfor how often an engine makes power.In a two-stroke, everydownward movement of the pistonis a power stroke.In a four-stroke, everyother downward movementof the piston as a power stroke.But in another way, in a two-strokethere 1-power stroke for every 360 degreesof crank rotation, infour-stroke it's 720 degreesof crank rotation.That's if you're into degrees, heck yeah.Apart from that, the specificdetails of combustion,how that power stroke happens can vary.Most car engines use a sparkplug to start the burn.Those are called spark-ignition-engines,and that includes bothtwo and four-strokesusing the Otto cycle.That's O-T-T-O not A-U-T-O,and it's name from NicholasOtto, the German inventor,who first harnessed thatthermodynamic processto extract energy from fuel with an engineall the way back in 1876.That was a hundred yearsafter America was born.What do you think about that?Now instead of spark, dieselengines use heat producedby high pressure in thecylinders to start the burn.Those are compression-ignition-enginesand they use the diesel cycle,another thermodynamicprocess described by yet,another German inventor Rudolph Diesel.Compression ignitionengines also come in twoand four-stroke varieties.What makes theentry-ignition-engine unique,but not entirely new is thatit doesn't use a spark plugor pressure to start the burn.It actually uses the Brayton cycle,something more oftenassociated with jet turbines.That's yet another thermodynamic processnamed from George Brayton,an American inventor.Heck yeah, dude America isin the frigging chase, man.Yeah, we had two Germans,we got one America.Bryton's original design in 1872,used pistons, not turbines,and the entry-ignition-engineis a Brayton cycle engineoperating with the same principle.And here's how the EIentry-ignition-engine looks like.It's got four cylinders,all different sizes,that's pretty unique,but it isn't really afour cylinder engine.Only one of those cylindersthat is creating combustion,but two of them are producing power.To understand how all that works,we need to start right in the middle.Unlike most two and four-stroke designs,the EI design doesn't mixintake, compression, combustion,and exhaust in a single cylinder.Suck, squeeze bang, blow.A skinny cylinder handlesintake and compression,and the wide boy next toit handles the rough stuff,combustion and exhaust.The two pistons move together,so on the downstroke,skinny is doing intake,wide guys making combustion.On the upstroke skinnyis making compression,big boys pushing out exhaust.So if it's not spark or compression,so what starts the burn?How do we get this thinggoing from the jump?Well it's right in its name.The first piston drawsin air and compresses it.That pressurized air moves through a valveinto the nixing chamberwhere fuel is injected.Another valve opens and thatcompressed air fuel mixturerushes into the combustion cylinder.And it does this becausethe combustion cylinderis at a lower pressure,and air naturally movesfrom areas of highpressure to low pressure.But it's also very hot in that cylinder,that's because the exhaustvalve is designed to closebefore all the hot gases fromthe last round of combustionare pushed out.Like in a diesel engine,it's the heat in the cylinderthat starts the burn.Igniting the intake chargeon entry to the cylinderhints entry ignition.And because the pressure ishigher in the mixing chamber,the flame only travelsdownward towards lower pressurein the piston.Look at that, you guys nowlearned a new engine, cool.A Brayton cycle engineseparates compressionand expansion in differentparts of the engine.That division of labor isexactly what's happening here.And because every step intake,compression, combustionexhaust, or as I say,suck, squeeze, bang, blowis happening with everyrotation of the crank,like Brayton's original piston engine,this is a two-stroke engine.There's one power strokefor every 360 degreesof crank rotation.So what's what these othertwo cylinders out here.Well, those are sort ofhelpers that maximizethe thermal efficiency of the engine.That's the amount of energy from the fuelthat's actually converted intowork and not lost as heat.So increasing thermal efficiency,not only improves miles per gallon,it also increases power per gallon.Didn't think of power pergallon as a metric, did you?The first cylinder gives theengine two stage compression,almost like forced induction.The piston compressesair before sending itto the second cylinder,which compressed even furtherfor combustion.And the reason thoseare two different sizeshas to do with heat loss.A larger cylinder, a greater surface areacreates a charge with lower temperaturethan the smaller second cylinder.That extra compressionincreases the amount of oxygendelivered to the combustion cylinderand more oxygen means more energycan be extracted from the fuel.I can hack, yeah, men.You guys gotta get pumpedabout engineering, man.This (beep) is cool, man.This is why I went to engineering school.And this is why I do donut now.So I can get you guys jacked up.Just (beep) pumped.Just (beep) psyched,new engine technology.This (beep) engineering is sick, dudejust like (beep) bashing,like best bro stuff.(breathes deeply)Are we cool?Yeah, cool, cool, cool, cool.Using a separate cylinderto pre compress airwas part of one of the veryfirst two-stroke enginesdeveloped in 1880 by Scottishinventor Dougald Clerk.In fact that design laid the foundationfor most modern two-strokes.We sometimes describe those asusing a modified Otto cycle,but really they're the Clerk cycle,the name just never caught on.Dang!I just got you all jackedup about engineeringand now we find out thatwhen you invent something,sometime people don't use it, that hurts.It's like a stab to the engineer's heart.It's okay though, we'llgive Clerk his due.History is written by thevideos you put on YouTube.Now the final cylinder isthere to extract energyfrom the exhaust that mostother engines let go to waste.The gas force out of the cylinderduring the exhaust stroke,hasn't reached atmospheric pressure.It's still compressed.The sound of your car'sexhaust is actuallythe sound of wasted energy.It's those gases expanding.The EI engine harvest thatnormally wasted energyin a really large cylinder tomake room for their expansion.The expanding exhaust gases,push on that extra piston,and that means morepower going to the wheelsinstead of out the tailpipe.That power also happens on the off stroke,the non combustion non power stroke.So the EI engine is still making powereven when no combustion is happening.Oh, dude, I'm tellingyou guys, this is sick.Those two extra cylindershelp the EI engineextract more energy from burnt fuel,and the effect is a majorincrease in thermal efficiency.Ready to talk about, well, that's good.According to theinventor, Peter Cheeseman,the EI engine has atheoretical thermal efficiencyof 63% giving this Cheesmancycle two-stroke enginea 15% advantage in efficiencyand potentially powerover the usual auto cycle forstroke, the Cheesman cycle.Let's get this thing going!Let's go!(tools crashing)"So what's the catch Jerremiah?What, are you gonna tell meabout this cool sick technology,there's gotta be a littlestring associated with it."Well, the string is rightnow it only exists in theory,there's no workingprototype, just the idea.And theory, and fact, don't always line upand some pretty important factscould get in the way here.One potential problem withthe EI's division of laboris that it takes fourcylinders to do job of onein an ordinary engine.That makes the engine incredibly complex.To get the equivalent of a V8,you need an engine with32 separate cylinders.Not only would that be incredibly heavywith all those different sized pistons,that engine would be ahuge challenge to balance.Critics of the designhave already popped upin the scientific community as well.A follow-up analysis by ateam of automotive engineersclaimed that once morerealistic assumptions are added,much of the EI's theoreticalefficiency gains disappear.Those assumptions includethings like internal friction,high temperatures in varying engine loads.According to that follow-up analysis,these facts about how an engineoperates in the real worlddrop the EI's engineefficiency to the same levelsor even worse than thatof an ordinary engine.And while the emissionsdo improve, in one sense,the same analysis claims the EI designsimply trades a reductionin nitrous oxidesfor an increase in carbon monoxide.But what might be the nailin the coffin is one factwe never seem to get away from prayer.Friggin, money, money, money.A completely new enginedesign is already startingat a deficit.Current engines have over ahundred years of development,and getting an unproven design like the EIto get to the samelevel could take decadesand billions of dollars.Everyone, they're tryingto squeeze the last bitof efficiency out of cars.That's why companies are investing so muchof their R&D dollarsinto electric solution.A brand new unproveninternal combustion engine,even one with potential forefficiency and emissions gainsis unlikely to attract theinvestment it would needto become a viable alternative to the old,but well tested design.- Hey, you wanna get buff this year?Well, listen up pastaarms, Donut just releasedthe ultimate gym attire.And I'm here to show youhow to get it workout ready.So pay attention!- Step one!- Buy thisbeautifully designed shirtfor just 29.98.- That's way less than $30.- Step two.- Get some scissors 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the sickest dude.Just saying what's up?It's Cheese over there.Yo, Cheese, Cheese meansmoney too, he's money man.Cheeseman the money, man, come on!(Burton laughing)Thank you guys so much forwatching this episode of B2B.We love you, man.We appreciate you guyswatching these videos,that really helps usout, lets me keep my job.So if you could hit thatlike button if you like it,hit the not like buttonif you don't like it,that lets me know that,hey, I don't want to see this stuff.We wanna see otherengineering type videos.If you wanna see more of us here at Donut,follow us on Instagram at Donut Media.We got a whole team of,all team meme makers,and it's one guy named Brett.Follow me on Instagram atJeremiah Burton until next week.Bye for now.