The Difference Between Gasoline And Hydrogen Engines

hello everyone and welcome in this video we are talking about the differences between gasoline and hydrogen combustion engines now I'm sure plenty of you are familiar with how gasoline combustion engines work however hydrogen can also be used as a fuel source for combustion engines in fact you can use the same exact four-strokes intake compression power and exhaust and you can even use it with port injection you can use it with direct injection so a lot of similarities in using hydrogen as a fuel to a gasoline engine in this video we're going to be talking about eight key differences between gasoline and hydrogen when used in a combustion engine as you can see it took up all of the white board quite a bit of information but very cool stuff so let's go ahead and get started all right getting started let's look at the combustion process so what is the combustion process what is our fuel source what are our byproducts so we get started with two h2s hydrogen we add to that o two oxygen combustion occurs and then our by-product is 2 h2o so in other words water so water being our only by-product and that's a huge advantage of a hydrogen engine and that it's only emissions are going to be water perfect clean you still get the noise of combustion engines the fun of combustion engines without the negative side of those poor emissions but wait not so fast unfortunately with this combustion occurring and the heat resulting from that combustion your actual reaction is going to be something like h2 plus o2 plus n2 nitrogen leading to h2o and n o X so these NOx emissions unfortunately are going to be the harmful emissions created from a hydrogen combustion engine in theory you know you could have this perfect only h2o combustion occurring but unfortunately because the temperatures get hot enough the nitrogen and the oxygen will react and form nitrogen oxides so on the other hand gasoline combustion engines you start with a hydrocarbon so see number H number so you know for like octane it may be c8h18 you're gonna add to that oxygen and nitrogen and then your combustion byproducts are going to be co2 h2o and your nitrogen oxides so the benefit of the hydrogen engine here is that we are eliminating those carbon so we're not taking you know carbon from underneath the ground putting it into an engine and then dispersing it into the air there's no carbon introduced in this equation unfortunately you do still have those nitrogen oxide emissions next let's talk about air/fuel ratios because this is where hydrogen actually has a pretty big advantage because it has a very wide range of air/fuel ratios where combustion can still occur so its stoichiometric ratio meaning the ratio in which you burn all of the hydrogen in the cylinder and you burn all of the air in the cylinder all of the oxygen is 34 to 1 that is by mass for a gasoline engine it's about fourteen point seven to one and so the advantage here with hydrogen is that you can burn at an air-fuel ratio as high as a hundred and eighty to one so a very very lean air fuel ratio there versus in gasoline engines the leanest i've ever seen is actually in the Mazda's SKYACTIV ex engine and they're using some pockets of that gasoline mixture at about 37 to one and that's using compression ignition spark controlled compression ignition to do that so that's the highest in gasoline honestly you generally won't see much higher than about eighteen to one air fuel ratio and here with hydrogen you're seeing as high as a hundred eighty two one air fuel ratio so what are the advantages of this well one of them is that it's very easy to start the engine so if you think about a cold start with a gasoline engine you generally have to inject more fuel so you make sure that some of that fuel vaporizes enough that vaporizes in order to get combustion started with a hydrogen engine it's very easy to do because you don't need much hydrogen much gaseous hydrogen in that combustion chamber in order for combustion to start also running lean reduces fuel consumption generally speaking by running lean you're able to operate at a more efficient range that's why Mazda uses such a high air fuel ratio and that's Chi ActiveX engine that gets very good efficiency and some other advantages the by running lean with hydrogen you can actually get back one of its major drawbacks which is these nitrogen oxide emissions and so you're able to drop those NOx emissions when you are running lean but of course you can't get anything by for free and so by running with these very lean ratios and you know once you start getting into this range yes you reduce your NOx emissions but unfortunately you are reducing your power next let's get into ignition energy and this really isn't that big of an advantage for hydrogen so the ignition energy is the amount of energy required in order to start combustion and for hydrogen and for a hydrogen air fuel mixture it's about point zero to millijoules versus about 0.2 for millijoules for a gasoline engine so in order of magnitude different there between them meaning it's very easy to use a spark and ignite a hydrogen air mixture and so that's the advantage to it is that it's very easy to ignite that's also the disadvantage because if you have a hot spot in that engine it could lead to misfiring pre-ignition that kind of thing and because it can run it's such you know low air fuel ratios pretty much any random air fuel ratio in there if it's next to something hot it's going to be pretty easy for it to ignite the advantage is you can use different types of ignition sources if you wanted like a hot wire or a glow plug kind of like a diesel engine may use to get ignition started that's difficult for controlling timing so you would use something like a spark so that you could control the timing but if you perhaps did have a compression ignition hydrogen engine then perhaps you could use a hot wire or glow plug to get things started initially and then just run it off compression after that more common to use a spark in order to have combustion with a hydrogen engine next let's talk about flame velocity so this is a big advantage for hydrogen because it is significantly faster than gasoline and how quickly that flame travels and that's ideal the ideal engine would have instant combustion all of it burning at once and because hydrogen has that fast flame propagation that's more ideal because it means all of your pressure is created at the very top before the piston has moved down so you get the maximum amount of useful work out of it so just kind of comparing here with gasoline it's multiple times faster traveling versus gasoline through that air fuel mixture that flame traveling outward and so that means more power and that means greater efficiency it also means you could operate at higher engine speeds because that flame you wouldn't be limited by the flame speed itself now unfortunately there's another drawback so we want to run lean right because that's efficient and it means we won't have as many nitrogen oxide emissions but unfortunately by running lean you then start to reduce that flame velocity quite a bit so it does have a very high flame velocity when you're operating at that stoichiometric ratio of 34 to 1 about 34 to 1 but unfortunately once you start getting towards this leaner and combustion does take significantly longer next let's get into the auto ignition temperature and here hydrogen has an advantage over gasoline as well so you can think of the auto ignition temperature as the temperature at which if you had that perfect air fuel mixture if you bring that mixture to this temperature it will automatically combust you don't need a spark or anything like that just the heat alone will force it to combust and so by having a higher auto ignition temperature for hydrogen and air it's going to be about 500 degrees Celsius for guests lean and air it's gonna be about 230 to 280 degrees Celsius so quite a bit higher you can think of that as an octane number a hydrogen's fuels octane number is going to be over 120 verses in that you know 91 to 99 ish region for a gasoline fuel and so what this means is if you were to look at you know how much could you compress this air fuel mixture before it ignited you could compress that hydrogen and air mixture more than a gasoline engine and that means you can use a higher compression ratio so by using a higher compression ratio you make more power and you are more efficient it also means you can advance timing more you have more flexibility with timing with hydrogen fuels and it means it will be more resistant to knock because of that high octane number now remember this trait of it does mean it's less likely to have knock or pre-ignition occur but there are other traits about it that do mean that you know not could be a problem for example the ignition energy so you know a hot spot could cause a misfire because it only requires a very small amount of energy even though it has a low Auto ignition temperature so there are pros and cons here good on an auto ignition temperature side not necessarily great from an ending energy side because a very small hotspot could cause combustion to occur our next point is diffusivity so what this means is how quickly after you inject that fuel does it spread out and create a nice uniform mixture within that combustion chamber and this is a big advantage for hydrogen because it has a very high diffusivity and as a result that means you get a uniform mixture very quickly when you inject fuel that's great if you're using direct injection if you do have port injection you know it's gonna have enough time to make sure that mixture flows with gasoline or with hydrogen but for a direct injection application really cool that you can have that high diffusivity get the hydrogen to go all around that combustion chamber very quickly and have that nice even mixture and so by having that nice even mixture you're going to have complete combustion occur which is efficient and it's predictable it also allows you to have faster engine speeds because that fuel is spreading out very quickly combined with your high flame velocity and it also reduces the danger from leaks so let's say you did have a hydrogen leak somewhere on your fuel line well that that hydrogen as it's leaking out is going to start spreading out very quickly and so it's very quickly going to get outside of its air fuel ratio range in which combustion could occur so it'll spread out very quickly if you do have a leak somewhere in your fuel system the good news is it probably you know has a reduced likelihood of causing you know a thermal event of fire bad things to happen because it will spread out so fast our next point is quenching distance and the quenching distance is the distance between where you have that air fuel mixture igniting where that flame extinguishes relative to where your wall is so the distance from the wall at which your flame extinguishes for hydrogen this number is pretty low just 0.6 millimeters for gasoline it's a bit longer of a distance two millimeters and so with hydrogen you're going to have combustion occur all the way to that wall a little bit closer to the wall with gasoline it's not going to get quite as close so kind of the advantage there is that you're going to you know burn all of that air fuel mixture with the hydrogen the downside of it is it means you know that hydrogen combustion can work its way through some pretty small crevices and so for example if you were to have for some reason combustion occurring with that intake valve open perhaps due to valve timing overlap or something like that you could have backfire occur because it might be easier for that hydrogen combustion to pass through the distance between that valve and your combustion chamber where it's open so for the port you know let's say you just have a you know two millimeter gap well the gasoline is not going to travel through it but the hydrogen combustion could actually travel through it so a difference there in quenching distance a unique property of both fuels now our final point here is going to be talking about hydrogen's low density which is unfortunately a disadvantage it has and why gasoline does make sense for use in combustion engines so this is talking about density from a volume standpoint how much energy do you have relative to how much volume does that energy take up your fuel source so starting off let's talk about what's going on in the combustion chamber then apply it to the car as a whole so looking in the combustion chamber unfortunately if you were to have a naturally aspirated port injected hydrogen engine your air fuel ratio by volume is 2.4 to 1 so that means about 30 percent of the space within that combustion chamber is going to be taken up by hydrogen which only leaves about 70 percent of the space left over for oxygen for air now in a gasoline engine you're only going to take up about one to two percent of the space in that combustion chamber and about 98% of that space can be used as air which means you've got significantly more oxygen in there which means you can burn more fuel which means you can make more power so relative to the size you can make more power there assuming you're running a naturally aspirated port injected engine now you can of course use a high-pressure direct injection inject force more hydrogen into that scenario so you do use more air and thus make more power but just looking at it from a naturally aspirated standpoint you're generally going to be making less power combining that with port injection and that's as a result of having to take up so much space for hydrogen rather than air itself now hydrogen does have an advantage relative to its weight and so that's why it's used in rockets hydrogen as a fuel is one of the best as far as energy to weight it's not one the best as far as energy to volume so if you think about a rocket it can be gigantic if it doesn't weigh much like hydrogen fuel it's not all that heavy but it has a ton of energy in it then it's great for sending that rocket out into space obviously you want to minimize weight on a rocket in a car you kind of want to maximize available passenger space so if you're using a hydrogen tank and taking up all the trunk room taking up all the passenger room then the core becomes less practical so with gasoline you have this higher energy density so it doesn't take up as much space in the vehicle and as a result you have you know a better passenger compartment more cargo space that kind of thing so if you look you know at a car like the Toyota Mirai which uses hydrogen it doesn't use a combustion engine but it uses a fuel cell if you look at a vehicle like that it's got these massive hydrogen tanks that are required and so that's a bit of a disadvantage for a hydrogen engine is that you're going to have very large fuel tanks relative to how far that fuel can get you so thank you all so much for watching if you do have any questions or comments of course feel free to leave those below

Channel: Engineering Explained

Views: 911,380

Rating: 4.9172192 out of 5

Keywords: internal combustion engines, engine differences, gas vs hydrogen, gas vs diesel, gasoline, diesel fuel, petrol, hydrogen fuel, hydrogen engines, combustion, engineering, science, technology, innovation, STEM, engineering explained, flame propogation, diffusivity, mechanic, mechanical, mechanical engineering

Id: l6ECwRnJ0Sg

Length: 14min 19sec (859 seconds)

Published: Wed Dec 19 2018

Reddit Comments

[u/[deleted]]

[removed]

[u/PhilMcCracken2]

Would rather completely renewable alcohol fuels. Methanol and ethanol are actually more efficient than petroleum in combustion, and offer higher octanes as well, and helps the engine run cooler. F1 used to use methanol in the 50s to dramatically powerful effect before it was banned for health reasons. [far more poisonous than petrol]

[u/shigs21]

If they can get its efficiency up I could see it being an option.

[u/Vinura]

Been saying this since 2009. Better racing solution than boring full electrics.

[u/brewer522]

Hydrogen? Is it 2008 again?