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markwsf
Free Member@mrmonkfinger – thanks, I hope these replied are interesting / useful and not coming across as a bit lecture / I know better ish.
I'm certainly enjoying them. Will have to move on to YouTube to see some of films of pushrods in action soon, though 🙂
H2 has about 2.6 times the energy per kg of diesel, but even in liquid form it’s 11 times less dense
It also burns at very high temperature, so that causes NOx pollution. To lower the combustion temperature, the engine has to run very lean, so you get much less power for the same capacity engine.
I think fuel cell vehicles are much more efficient than hydrogen ICEs. Fuel cells might have a future, I doubt that hydrogen ICEs do except as a niche thing.
Hmm, re HCVs one would assume it's possible to use the same tech as a BEV and just stick a h2 tank instead of a battery. It'd be packaged differently of course but we've already shown it's possible with things like the Hyundai Kona. You'd have the front end of the BEV version and the body and back end of the petrol version with a different fuel tank.
Because drivers’ earnings depend on fares, Goldstone said, “if they have to spend 40, 50 minutes, an hour, two hours plugging a car in in in the middle of the working day, that for them is just not acceptable.”
Good job it doesn't take that long then.
Nah I totally disagree. We’ve already got the BEV cars, now we just need them to be cheaper,
And what about sustainable? How can anything that relies on digging rare crap out of the ground and putting it through complex, energy hungry and polluting processing before it can be used? Sounds familiar by any chance??
Batteries are not sustainable and no amount of technology into re-processing will change that. It is not scalable for demand. Hydrogen is the most abundant element in the universe...75% of the universe is Hydrogen and we can create as much as we want easily and cleanly and the byproducts of its use are just water.
The future will be a mix of all kinds of technologies...including conventional ICE engines burning sustainable synthetic fuels.
H2 has about 2.6 times the energy per kg of diesel,
Damn sight better energy density than batteries. Nothing can beat diesel and petrol...whatever the solution compromises will have to be made. The specific application will determine which compromises will be made. Domestic cars BEV might very well dominate...commercial applications then synthetic fuel burning ICE hybrid or hydrogen fuel cell might win out, big lorries and other industrial vehicles then hydrogen is by far the most sensible solution. It'll be Horses for courses.
I wouldn't be at all surprised if diesel and petrol engines will ever be fully retired. There will be a few very niche uses where only petrol or diesel will do.
also burns at very high temperature, so that causes NOx pollution. To lower the combustion temperature, the engine has to run very lean, so you get much less power for the same capacity engine.
True.
Modern natural gas engines (methane, similar to hydrogen) run very lean indeed, and this is linked directly to NOx. Airflow becomes important, hence high pressure ratio turbocharging, high energy ignition systems and significantly worse transient performance compared to Diesel. The resultant engine out emissions are very good though, so whilst diesels need aftertreatment lean burn NG often does not. That'd be a challenge if it was a direct replacement in a vehicle so would need to part of a hydbrid type system (likely IC engine driving a generator then the vehicle is electric drive which is quite a common arrangement already)
would need to part of a hydbrid type system (likely IC engine driving a generator then the vehicle is electric drive which is quite a common arrangement already)
I'm pretty sure a fuel cell EV would be more efficient.
And what about sustainable? How can anything that relies on digging rare crap out of the ground and putting it through complex, energy hungry and polluting processing before it can be used? Sounds familiar by any chance??
It does sound familiar, and that's the point. I'm not saying BEVs are necessarily the best choice, I'm saying that's what we'll get. And in the future, because BEVs will be well established, they'll come up with new battery tech that won't be as problematic. If you are a FB user find phys.org and like the page - you'll get a few stories a week about developments that are solving these issues. Because now, there'll be a shit-ton of money behind it. Companies are paying techies to tinker in labs, this is really really cheap. For widespread H2 adoption we'll have to invest massively in infrastructure and simply hope that it'll take off. That's a harder sell to investors.
Batteries are not sustainable and no amount of technology into re-processing will change that.
Odd thing to say - there is clearly SOME amount of technological development that will change it - what's not clear is if that's possible or not. There are lots of ways to make batteries, I think sodium ion batteries are a front runner.
Damn sight better energy density than batteries.
But as we've said, BEVs work. If you view H2 and BEV as competing technologies, I can't see that H2 will win out for a long time, given the political and economic climate even if the storage problems can be overcome.
would need to part of a hydbrid type system (likely IC engine driving a generator then the vehicle is electric drive which is quite a common arrangement already)
I’m pretty sure a fuel cell EV would be more efficient.
I agree. If the IC engine approach is used I would only imagine this being an interim as fuel cells develop. I'm not up to speed on fuel cell capabilities or developments so don't know how likely this would be.
The later part of this thread reminds me it's time to start getting a bit more knowledgeable around the new techs to avoid getting stuck in the past !
I wonder how they'd stop water condensing everywhere on a cold start with an H2 ICE engine? I mean they have made it work so presumably they've decided it's not an issue. Maybe you'd need a bleed valve on the exhaust like you have on brass instruments!
But as we’ve said, BEVs work. If you view H2 and BEV as competing technologies, I can’t see that H2 will win out for a long time, given the political and economic climate even if the storage problems can be overcome.
Well BEV's don't really work do they? I guess it depends on what you define as work. They move, but they're nowhere near as convenient as a petrol or diesel engine interns of range and time to charge vs. filling up a tank of fuel.
But H2 engines also work by the same comparison...its established technology both in fuel cell form and ICE form. Yes there is a challenge with distribution but you can generate hydrogen anywhere by renewable electricity generation so less of an issue even compared to oil and petrol where it has to be moved all over the country. Hydrogen can be generated locally. Yo. might not get as much range out of a tank of H2 but if it only takes a minute to fill up compared to 30 mins or so for a BEV then its not a huge problem.
Odd thing to say – there is clearly SOME amount of technological development that will change it
Well improve it but not transform it. The best Elon Musk has come up with for spent car batteries is to repurpose them in his power walls which is just kicking the can down the road...what then once the battery performance degrades beyond being useful for that? You're into heavy, energy hungry, expensive and polluting reprocessing of precious earth elements.
But anyway, my point was that these technologies and solutions in the future world wont be competing. There wont be a one single solution for everything. There will be a number of different solutions for different applications. We're never ever going to see battery powered aircraft for example. Well airliners at least.
There will be a number of different solutions for different applications.
This.
It will be dynamic and change over time as technologies and markets develop.
There isn't and doesn't need to be a one-size fits all solution.
There might even be the odd pushrod diesel engine in the mix 😉
I wonder how they’d stop water condensing everywhere on a cold start with an H2 ICE engine?
It's not a problem as far as the engine operation goes. The same thing happens with petrol or natural gas engines. Hydrocarbon fuels are compounds of hydrogen and carbon. When that is oxidized, the hydrogen combines with oxygen to form water, the carbon combines with oxygen to form CO2. If you only do a short run in a petrol car, the exhaust system doesn't get hot and the water vapour in the exhaust condenses. Combined with CO2 and NOx, this forms carbonic acid and nitric acid, you basically get acid rain in the exhaust. If you only do very short runs in a car, the exhaust system will rot out because it never gets hot enough to evapourate the water.
The same thing happens with petrol or natural gas engines.
I'd have expected much more with a H engine.
Well not sure of the chemistry of it, but hydrogen engines can run a hell of a lot leaner than petrol or diesel engines. Like upto ten times leaner, one of the many benefits of H2 over petrol and diesel, so you don't need to add so much fuel to start when the engine is cold, so less fuel in the mix means less H2O production. Not sure wether H2 produces more or less H2O relative to petrol or diesel but can't see how it is a problem or a blocker. There are more tricky problems to sort out to productionise H2 engines rather than concerns around water condensing in the exhaust.
Of course using H2 as a fuel for aircraft means production of more contrails which have a global cooling effect due to reflecting solar energy back into space so a potential proactive way to combat climate change. Over the 24hrs following the global grounding of aircraft immediately after 9/11 there was a definite step increase in global temperatures measured as a result of an instant removal of contrails reflecting solar energy.
so less fuel in the mix means less H2O production.
It also means less power. To make the same power, you need to burn the same amount of fuel, provided that's done with the same thermal efficiency. Therefore you need a larger capacity engine to get the same performance out of a hydrogen ICE. You're burning the same amount of hydrogen, so you'll produce the same amount of water. The lean burn engine will produce much less NOx though because the combustion temperature is lower.
I’d have expected much more with a H engine.
A typical petrol molecule is C8H18 (octane). That will produce eight molecules of CO2 and 9 molecules of H2O. Hydrogen has an atomic mass of 1, carbon 12, and oxygen 16. If my arithmetic is correct, one mole of octane has a mass of 114 grams and will produce 372 grams of CO2 and 162 grams of water when burnt. As a ballpark figure, a litre of petrol will produce roughly a litre of water when burnt.
A kg of hydrogen will produce 18 kg of water. So yes, a hydrogen vehicle will produce more water, but petrol vehicles also produce a surprising amount of water and it's not a problem as long as the vehicle is run long enough to get the exhaust system hot.
hydrogen engines can run a hell of a lot leaner than petrol or diesel engines
How come? (serious question)
hydrogen engines can run a hell of a lot leaner than petrol or diesel engines
How come? (serious question)
That statement isn't really correct. Petrol engines generally run close to a stoichiometric fuel-air mixture, which means that there is exactly enough oxygen to burn every bit of fuel. For maximum power under acceleration, it might be slightly rich, this extra fuel helps to cool the charge. For maximum economy while cruising, it might be slightly lean. With carburetors and port fuel injection, this was necessary to get the charge to burn properly. If the mixture is too lean, you'll get combustion problems. Also, you need to keep the combustion temperature low enough to meet NOx emission standards. After emissions rules were introduced in the 1970s, compression ratios had to be reduced to lower the combustion temperatures, which caused huge drops in power output for performance cars. Direct injection engines can run leaner by injecting fuel so that there's a rich mixture around the spark plug and a leaner mixture elsewhere. Compression ratios on modern direct injection systems seem to be much higher too, obviously they have put a lot of work into understanding the combustion process and how to control combustion temperature. Any modern engine has an oxygen sensor in the exhaust and continually adjusts the fuel-air mixture according to the conditions.
Diesel engines use a completely different combustion process. They have a very high compression ratio and direct injection. The air charge is compressed so that it's hot enough that the fuel burns as soon as it's injected. They vary power by altering the amount of fuel injected, so the fuel-air ratio is much more variable than the fairly stable mixture in petrol engines. If you look at tractor pull competitions, they crank out incredible power from turbo/supercharged diesels by just turning up the boost and injecting massive amounts of fuel. Those things send a plume of black smoke up, the combustion efficiency doesn't matter, it's just a matter of pushing in as much air and fuel as the engine can withstand.
Hydrogen burns at quite a high temperature if there's a stoichiometric fuel-air ratio, so it causes NOx pollution. This can be reduced by using a leaner mixture, but you can't burn as much fuel with a very lean mixture so the power output is reduced. Basically, once you go leaner than a stochiometric ratio, the engine power starts dropping for the same volume of air. If you have to run lean under full throttle to meet emission standards, you have to build a larger capacity engine to produce the same maximum power output. That larger engine will be heavier and more expensive to produce. Running lean to meet emission standards is a drawback, not an advantage.
Nice description of the combustion processes above 🙂
Re Gas engines - (either Natural Gas or Hydrogen - same broadly applies) can run at stoichiometric or very lean. At stoichiometric there are emissions issues so you'd need aftertreatment. Lean can avoid this need, but at the expense of increased cost of turbocharging (to avoid dropping power you increase the density of the air, so get more mass of air into the engine), a more expensive ignition system and "transients" (ability to cope with rapid changes in power or speed) become worse as you're reliant on the turbocharger speed to drive enough air in to the engine to allow enough fuel without misfiring etc.
You can't just add more fuel to cope with transients like a Diesel can (within limits - usually imposed by black smoke creation) as a gas engine will "knock" which is a very bad thing.
I expect that due to the above a passenger engine will run "as lean as possible" which actually won't be that lean, so will still need aftertreatment.
Note Diesel and Petrol can both run vey lean as well, and as time has progressed run leaner and leaner as technology has progressed to remove the limitations to doing so. As will all these things it's a compromise between many factors. Emissions, power density, driveability, misfire etc.
Petrol engines can run upto 34:1 AF ratio, but hydrogen could go upto 180:1 AF ratio. Whether or not it makes sense to run them at those lean rates in the real world is another matter, but similarly though petrol CAN run at upto 34:1 AF ratio doesn't mean there are any production engines out there that do. The benefits of the higher AF ratio is that NOx can be addressed/reduced and they are easier to start...however downside is reduced power...but you don't meed max power all the time so no reason why you couldn't run super lean when cruising at low power levels bagging better economy and emissions, then as you demand more power the AF is changed to delver the greater power. Or even marrying an H2 ICE to electric in a hybrid so the engine needs to only ever run in a mode where it is minimising NOX and the electric motor boosts power.
Appreciate that H2 engines might be larger and heavier to achieve similar power levels to petrol/diesel...but so what....the weight of electric motors and batteries in BEV's is hardly the light weight solution. We're never going to beat petrol and diesel engines so lets accept that (well not in the next hundred years at least). Petrol/diesel is just too good and convenient a fuel. So again...H2 engines don't have to compete with petrol/diesel engines and power plants....they need to compete with BEV's and whatever other alternative power plants there are out there. Provided there was a decent Hydrogen network out there then moving to hydrogen fuel cell or hydrogen ICE would be a much more familiar and convenient step to emissions free motoring for most people used to fossil fuelled cars. Future generations might develop different behaviours and drive different solutions - maybe even car free solutions...but thats decades in the future.
As an end result of all the above I'd expect a production hydrogen engine to be broadly comparable to a comparable petrol engine in terms of power density, in terms of power density and need for aftertreatment.
* Disclaimer - this topic is outside of my professional experience and so is now into just "my opinions".
There are some interesting papers on this from a quick google search.
One interesting conclusion - port injection hydrogen about 83% of the power density of gasoline, using more advanced techs potentially around 115%. So broadly comparable.
MDPI Applied Sciences paper
Another paper
Another thing to consider is the direction that F1 engines have gone in. They drastically reduced the maximum fuel and fuel flow to encourage economy. The engines are turbocharged, with the turbo also able to drive an electric generator (so basically a petrol-electric turbo-compound). To some degree, the ICE functions as a gas generator for the turbo-electric generator. It's hard to know how much of the public statements are just bullshitting to throw rivals off, but the Merc people said that they incorporated ideas from diesel combustion to improve combustion efficiency. Those engines are getting better than 50% thermal efficiency, which is impressive.
Thing is, using the ICE as a gas generator means that you need to find the optimum level of energy going out the exhaust (i.e. is it better to extract the energy through the ICE or the turbo-generator?) Just bolting a turbo-generator unit onto an existing engine would not be optimal, you'd need to rethink the entire engine and combustion process.
Those engines are fantastically expensive, but the basic concept might be applicable to things like HGVs which burn a lot of fuel and do massive annual mileages. Fueling them with a biodiesel/hydrogen mix might give better energy density than BEV tech and help with the NOx emission problem. Having them idle for 30 minutes while they stop to recharge batteries would be expensive down-time, so chemical fuels would avoid that. Not saying that's what'll happen, just that that's probably the types of things that engineers will be looking at.
Hydrogen burns at quite a high temperature if there’s a stoichiometric fuel-air ratio, so it causes NOx pollution.
At stoichiometric there are emissions issues so you’d need aftertreatment. Lean can avoid this need
Hang on. NOx emissions happen because there is 'spare' oxygen in the cylinder that hasn't got fuel to react with so it reacts with nitrogen at high enough temps. So that seems to me that running lean would create more NOx and running a stoichiometric mixture wouldn't have this problem. That's why diesels create much more NOx, because there's always hot air in there at some point and at light loads there's a lot. That's what EGR is for. Where am I wrong?
To some degree, the ICE functions as a gas generator for the turbo-electric generator.
This is what Toyota did with their first hybrid car. It's both a series and a parallel hybrid in varying amounts depending on load and road speed. Very clever bit of kit. I don't know if trucks use Toyota's hybrid system or if they could, however.
So that seems to me that running lean would create more NOx and running a stoichiometric mixture wouldn’t have this problem.
The combustion isn't instantaneous (i.e. detonation, which destroys engines). In a petrol engine, the spark plug ignites the mixture in one place. The flame front spreads out and burns through the charge. Controlling the timing and geometry of this is a big part of combustion chamber design. Remember that the mixture is ignited before the piston reaches top dead center, so the combustion chamber is still getting smaller, then it expands as the piston starts on the power stroke. If the ignition timing is too advanced, you'll get detonation. If it's too retarded, you'll lose power. At high revs, it needs to be advanced, at low revs, it needs less advance. Because the combustion isn't instantaneous, you have nitrogen and oxygen mixed at high temperatures and pressures. If the combustion is too hot, some oxygen will combine with nitrogen instead of fuel and produce NOx.
Because the combustion isn’t instantaneous, you have nitrogen and oxygen mixed at high temperatures and pressures.
Only if the mixture is poorly mixed, surely, as in the case of a direct injection engine (on purpose)? Otherwise the oxygen molecules will react with the petrol not the nitrogen?
Surely more air in the cylinder means more NOx not less?
Surely more air in the cylinder means more NOx not less?
NOx forms at very high temperatures. If you keep the combustion temperature low enough, it's not a problem. There are roughly 4 nitrogen molecules per oxygen molecule in air. There are roughly 17 oxygen molecules per octane molecule in a stoichiometric mixture. There is much, much more nitrogen in there than anything else. If it gets hot enough, some of that nitrogen will form NOx before the oxygen atoms encounter a fuel particle to react with.
+1 for @thols explanation of NOx formation.
Lower temperatures drive NOx down. Excess air helps to do that.
That's effectively what EGR does as well by the way - it reduces the peak temperatures.
NOx also only forms very locally - specifically around the flame front (not sure if it's been covered above but the flame "progresses" through the mixture rather like watching a forest fire spread but a wee but quicker. Conditions at the flame front dominate emissions. So controlling charge motion and mixture formation helps too.
Conditions at the flame front dominate emissions. So controlling charge motion and mixture formation helps too.
How do you measure / visualise this? Or is it all CFD (etc) modelling?
Just to answer the OPs question. I have 8 diesel engines on the farm. 7 of them are pushrod OHV ones 😉
Conditions at the flame front dominate emissions.
Considering this how does the speed of the flame front affect this? Another benefit to H2 is the is has a significantly faster flame velocity than petrol which benefits efficiency and power and enables higher RPM's, but what conditions at the flame front determine emissions? Is it just purely temperature or time or a combination of the two?
How do you measure / visualise this? Or is it all CFD (etc) modelling?
It's a combination of:
CFD and other simulations
Theoretical hypothesising
Experimentation - both on single cylinder enginess and multi (single cylinders both cheaper and you don't get the "averaging" effects to deal with)
Optical measurements - e.g. lasers embedded into cylinder heads etc
Occasional optical engines where cylinder walls, pistons, windows into the head can be made transparent.
There is a very cool youtube video from my old company from a project I was involved with that created a quartz (i.e. transparent) cylinder and piston with lens in the middle for optical visualisation of direct injection behaviour. Public domain so I can mention it.
Note all the the CFD needs correlating, hence the experimentation.
Oh - and reading this. It's a standard textbook for any engine related degree course. Pretty much the bible.
Very mathematical, technical and all around combustion rather than the oily bits.
how does the speed of the flame front affect this?
It basically determines the optimal piston speed. This is one of the main factors why Diesels "run out of power" at higher RPMs.
Flame speed is a function of many things - charge motion (motion of the air in the cylinder) being a major one. By designing the ports, cylinder head and piston appropriately plus manipulating the valve events you can influence this considerably.
Np sign of the video but there's a public domain marketing release here - apologies for the rubbish reader site.
Ricardo marketing publication - optical engine and analaysis
Brighton university marketing page talking about the optical engine
Flame speed is a function of many things – charge motion (motion of the air in the cylinder) being a major one. By designing the ports, cylinder head and piston appropriately plus manipulating the valve events you can influence this considerably.
This is what impresses me about modern engines. I was a petrolhead back in my youth, when you could pick up an old Escort or Datsun, take to the ports and combustion chamber with a dremel, throw in a cam, put on some sidedraft Webbers and a decent exhaust, and probably get double the stock horsepower. Problem is, they only ran well at a narrow rev band, so the stock engines ran well at low revs and the hot engines ran well at high revs. Carburetors didn't help, they can get excellent peak power, but can really only be optimized for a narrow range of airflow.
I think the last time I had an engine apart was 1993 or 94, it was making a horrendous knocking noise. The noise was because the pistons were bouncing off the cylinder head. The driver was used to seeing the oil pressure warning constantly flickering due to oil surge, so just kept driving with no oil assuming that no oil pressure was normal. Opening the sump plug and nothing coming out was an early warning that something was amiss. I took that one apart, but there wasn't anything to reassemble, it was utterly trashed. Very unsatisfying to have the final job being pulling an engine apart and throwing it in the bin instead of putting an engine together and seeing it fire up.
As much as I miss messing with engines, there's more money in desk work than getting dirty fingernails, but modern engines amaze me. I drive a basic 1500 cc Toyota Yaris, which gets amazing fuel economy. It puts out more power than the old twin cam Lotus Escorts without all the temperamental nonsense of old engines. Engine designers today obviously understand much more about how combustion works and how to optimize it across different engine speeds. I'm betting you have bugger all chance of improving a modern engine with a dremel to the cylinder head and a cam grind.
I’m betting you have bugger all chance of improving a modern engine with a dremel to the cylinder head and a cam grind.
You might make some improvements on an NA engine with your dremel - smoothing the port and intake manifold walls out, as they'll likely just be as-cast surfaces but not with the cams.
The exception to that is where tuners can ignore some of the restrictions that the original manufacturer had - cost and most commonly emissions, life and drivability compromises.
(Or just stick a turbo on it.... 😉 )
Or just stick a turbo on it….
Yeah, I worked with a guy who built truck racing engines. The biggest problem they had was keeping the intake system from bursting. They'd just keep cranking up the boost, but the manifolding and gaskets couldn't handle the boost pressure so it was like the Dutch boy fingering the dykes.
Edit: I gather from watching YouTube videos that they've solved the intake bursting problem and now they're dealing with the exploding crankcase problem. Ain't gonna solve that one by doubling up on hose clips.
One more.
modern engines amaze me
And yet people still complain about them and wish for the 'good old days'.
Now that Le Mans is running right now, I just remembered that Chevy pushrod engines have won a bunch of class victories in sportscar racing. For example, 2015 Le Mans 24 Hours, first in class ahead of a bunch of Ferraris and Porches. Not to mention the ALMS series. That big Chevy engine doesn't seem to do so bad for an old pushrod design.