If Combustion Engines Have A Future, What Is It?

hello everyone and welcome in this video we are talking about the future of combustion engines and you know clogs ticking so hopefully there's a good idea or two in here no in reality i think you know there's a lot of applications for better or worse that are going to continue to use combustion engines for a good while and so if we can make them better great we should make them better also i think it's just kind of interesting to look at future tech so we're going to be looking at what do we have you know what we've been using for the past 100 years or so and then where could we be what could exist this is kind of research that has come about in the past 30 years some of it much more recent than that so we're going to look at where could combustion engines be going so we need to understand what's wrong with what we have so let's start with our simplest example a four-stroke gasoline spark ignition engine s-i engine spark ignition so with this you of course have your four strokes intake you pull in air and fuel compression you compress that air and fuel you have a spark then ignite that air fuel that gives you your power stroke and then you push it all out the exhaust the good news with these spark ignition gasoline engines uh they tend to have good emissions if you're using a catalytic converter uh and they tend to you know not cost that much compared to like a diesel engine because they have lower pressures now if you get high turbocharged pressures within these spark ignition engines of course they can get more costly and the beautiful thing about spark ignition engines is that you directly control when that ignition starts because you control the timing of that spark plug so you have a lot of control that's a good thing well why don't we want to continue to use them well because they're not very efficient and there's two good reasons why they're not very efficient so first of all it part loads meaning when you're not flooring it you have this throttle that's mostly closed and so that acts as a restriction and so it's causing pumping losses for the engine the engine is trying to pull in air but this throttle is preventing it so it's having to work a lot to get in a little bit of air and it's not making power very efficiently the other part uh the other problem with the efficiency of spark ignition engines is that they have low compression ratios meaning when you take all that air and fuel and you squeeze it down you don't squeeze it down all that much and the more you squeeze it down the more efficient you are and the reason why you can't squeeze it down all that much is because that air and fuel will automatically ignite and you don't want that to happen at the wrong time you want to control when that happens so in order to prevent that from happening knock which can destroy your engine use this spark plug and use lower compression ratios unfortunately that means the engine isn't that efficient so how do we make an engine more efficient well we need to get rid of that throttle and we need to increase our compression ratio and so that's exactly what we do with a compression ignition engine ci so in this case you pull in that air same intake stroke you don't inject fuel yet you compress that air and then when you inject that diesel fuel it ignites because that air is super hot and compressed that it's being injected into so it automatically ignites as soon as that fuel starts getting injected in so you're controlling the timing when combustion starts by controlling when you inject that diesel fuel now the good news is as mentioned this is a very efficient strategy you're able to use higher compression ratios because the fuel is not floating around in there meaning you don't have to worry about knock it's not going to ignite on its own because there's no fuel there so you can use high compression ratios and then also you don't need a throttle with these in order to modulate how much power you're making you're simply modulating how much fuel you're injecting so you've got a more efficient engine which of course means less co2 emissions they're directly correlated uh that's the good news but they're still bad news with diesel engines so they're very good they're what we use today and a lot of you know applications where you want efficiency industrial applications but unfortunately there are there are some bad news here so soot particulate emissions that's one part of it and the reason you have these particulate emissions is because you have these rich areas so wherever there's a rich air fuel ratio meaning lots of fuel not enough air you can have this soot form and because you don't have a well mixed air and fuel ratio those rich areas where that fuel is being directly sprayed out that's going to form soot and then also that hot flame front is going to form nitrogen oxide emissions so nox emissions very bad not healthy you do not want to create these where you have that flame front both with spark ignition and with compression ignition where you have that hot local temperature around that flame front you're going to have nox emissions so that's not good okay so we know how to make an efficient engine but it still has bad emissions so how do we fix the emissions part of that problem and that brings us to low temperature combustion so these three technologies right here are all considered low temperature combustion and the whole idea is you don't have these hot localized spots where you have that flame front where you have very high local temperatures and these high local temperatures are what are helping to create nitrogen oxides so with a diesel engine you have that flame front with the spark ignited engine you of course have that flame front and that's helping to create nitrogen oxides which we're trying to eliminate by decreasing the temperatures that we see within the combustion chamber so one of the earlier developed methods of low temperature combustion is called hcci homogenous charge compression ignition and so the whole idea with hcci is you pull in a really well mixed air and fuel so it's all mixed together it's a homogeneous charge so all mixed really well together then you compress it down and as you squeeze it down it gets hot enough that it all ignites nearly simultaneously so you basically are having all of that air and fuel ignite at the same time very efficient to do you have all of that pressure that then pushes down the piston get the maximum amount of work out of it so it's very efficient and also because it's really well mixed you don't have soot formation so with this compression ignition with the diesel engine when you're spraying in that diesel fuel you have those pockets of really rich areas of fuel and those rich areas are what help create soot so by having a good mixture and lower localized temperatures since it's all combusting together rather than this hot flame that's traveling outward you don't have that knox formation and you don't have the soot formation so efficient and you don't have these bad emissions sounds great right the challenge is it's very difficult to control when all of that combusts so the timing of it you don't have a spark plug to say hey start now you don't have an injector to inject in and say hey start now you're relying on a temperature in order for that to happen and so you have to really modulate your intake temperature and make sure you have the temperature within the combustion chamber just right so that you have combustion occur at the exact moment you want it to if it happens too early then you're forcing pressure against the piston that's moving up you know best case you just lose some efficiency worst case you destroy your engine and then if it happens too late if it happens after the piston is already moving down well it's not going to be that efficient so timing is extremely difficult to control with hcci hence you don't really see it being done in production so that leads us to our next technology pcci premix charge compression ignition and so this is a bit of a middle ground between these two right here compression ignition and hcci so whereas uh direct injection compression ignition injects the fuel to start combustion and homogeneous in charge uh compression ignition injects that fuel really early so it has plenty of time to mix this is injecting somewhat in the middle ground between these two so not super early not super late and so the way that it works is you inject some fuel early to start that mixture going but not as early as you would with hcci and in order to control when combustion occurs you inject a bit more fuel later and that richer pocket of fuel as it compresses that richer pocket of fuel is what ultimately starts burning first and then that forces those leaner areas to then burn once that center area that's a bit richer starts burning so you do have a bit more controlled combustion phases starting you know more where that richer pocket is by your injector so you can kind of control the timing with the injector a bit more and then you have those uh you know lighter air fuel ratio regions then start to ignite and so the good news is slightly more control um better timing control versus hcci however it's still not perfect control of that combustion and you still do have hydrocarbon unburnt fuel and carbon monoxide emissions and part of the unburned fuel problem i mean you don't have as much time for that to mix really well so there will be different pockets that don't end up burning also they tend to have a smaller operational range so meaning you know when you're when you're flat out uh when you're you've got your gas pedal all the way to the floor these two engines right here don't really like that they don't operate really well at high loads they start to run into knock versus these you know of course the sparking night engine compression ignition engines they're happy at any range they'll work at any range consistently so the downside of these two technologies challenging to control when combustion starts and also challenging to have them operate at high loads well so is there a solution that allows everything to work out well that leads us to rcci reactivity controlled compression ignition and so this actually uses two different fuels one of them is port injected and this is your low reactivity fuel meaning it doesn't want to combust from compression and so that could be something like gasoline and then you have direct injection of a highly reactive fuel like diesel fuel which does want to combust from compression and so you have that port injection you've got a nice really well mixed air fuel ratio in there that's fairly lean and then you compress that and then you use a diesel injector to inject in fuel you create this rich little pocket and that diesel fuel does want to ignite from compression so you start the combustion in that center and then it kind of just travels outward from there the compression that has been created the pressure then ignites the rest of it and all just kind of burns out from there but it doesn't burn out in the same manner like you have here with this traveling flame front it's kind of just more in these phases where it all just kind of combusts so it's very rapid combustion but much more controlled because you're using that reactive fuel the diesel direct injector in order to kind of kick things off and so the good news is here you finally do have good ignition control you can control the timing of when this reaction starts to occur the other good news is you of course have the benefits of a low nitrogen oxide and low soot emissions and real world these engine styles are actually really efficient much more efficient um than real world they've seen you know testing done where they they beat actually all of these uh but definitely better than a diesel engine alone and finally uh it doesn't have to worry about quite uh as much of the the load range changes so if your partial throttle works great if you're at full throttle works great so it sounds all good right reactivity controlled compression ignition sounds great there are a couple issues still you still do have high hydrocarbon meaning unburnt fuel and high carbon monoxide emissions and the big downside you have to use two fuels so i think if you think about this from like a public scenario people aren't going to want to put two different fuels in their car just for them to work also that's you know complex you've got those two systems in the same car that's going to cost more so i think commercially you know there could be ways this could be implemented because if there's a way for a business to save money because this is so much more efficient then they're probably willing to do it uh you know using the the two different fuels and you know professionals are filling it up and that kind of thing but from a consumer base uh you know just the general public going out to their car and putting in two fuels every time seems like kind of a pain that people wouldn't really be interested in now i was curious what real world testing had been done on these different technologies to see if they're actually viable and so i found a study from 2018 and a study from 2020 where they took a single cylinder engine and they made it work with all these different operational modes and in doing so they could kind of compare them and see how they worked out and so there were some interesting things uh you know when they used the engine with these different modes and so using compression ignition um not surprised it had the worst nitrogen oxide emissions so no surprise there but one thing that is interesting is that the regular old diesel engine had the best carbon monoxide and the best hydrocarbon emissions moving on to hcci it was the absolute best for nitrogen oxides and for soot formation that's because of that really even mixture and those cooler localized temperatures because of that instant combustion but they weren't that efficient and that was surprising to see not actually that efficient and the reason being is if your timing is just slightly off you don't get to take advantage of that rapid combustion so again if it's a little early then you're working against yourself you're putting pressure against that piston that's coming up and if it's too late then you know you're not getting all of the work out of it so uh the the timing very difficult another interesting thing they saw in testing was that these uh they tried an engine with a 17.5 compression ratio and this could only operate at 20 percent load 20 of its potential load uh without knock so they lowered the compression ratio down to 15 to 1 and it could still only operate to 40 percent of its load before it ran into severe knock so pretty much useless uh if you think about it that you would never be able to get full load out of the engine then moving on to pcci similar results to hcci had that bad efficiency again timing is pretty challenging and also they could only get 20 load with a 17.5 compression ratio they were able to get up to 60 load once they switched to 15 to 1 compression ratio again but not ideal and then finally the rcci engine that was able to get the best efficiency out of all of them um so cool to see that there actually is you know possibility for getting better efficiencies and of course having the the most efficient engine means producing the least amount of co2 however all three of these were bad at producing carbon monoxide and producing hydrocarbons so you know there's a trade-off even though it seems like a superior technology in a lot of ways you still have those high carbon monoxide and hydrocarbon emissions now as far as a production example the closest thing to these technologies that exists in a production car would probably be mazda's skyactiv x engine which they use sp ccci which is a bit of a combination between spark ignition and hcci i've got videos describing how their engine works if you're curious to learn more about that as well as diving deeper into some of these topics if you'd like to learn more about them i've got links in the video description and one little fun note an electric car is about twice as efficient as rcci so even if you were to have a really really good rcci engine it's about half as efficient as an electric car so just throwing that you know stir the pot a little bit but anyways thank you all so much for watching if you have any questions or comments of course feel free to leave them below

Channel: Engineering Explained

Views: 411,368

Keywords: gasoline, diesel, rcci, how engines work, mazda spcci, spcci, hcci, hcci engine, skyactiv x engine, skyactiv x, reactivity, gas, petrol, petrol vs diesel, gas vs diesel, gasoline vs diesel, rcci engine, engine research, 60% efficient engine, super efficient, efficiency, engine efficiency, thermal efficiency, pcci, ltc, low temperature combustion, future engine, future combustion, future, engineering explained

Id: gwjbElCKkYs

Length: 15min 36sec (936 seconds)

Published: Wed Jan 20 2021