I'm assuming the purpose of developing a more efficient engine is to reduce emissions and thus "saving the planet"? That may seem commendable, but from what I have read it is actually a wasted effort, unless you can make it 99%+ more efficient (which you cannot). So, even if this engine is all that it claims (which most other comments here seems to question), it still uses oil and therefore is part of the problem and not the solution. (Wrote abit about this a while back with more references: http://torkeldanielsson.se/reducing-emissions-is-not-enough)
Edited comment: Man, I don't get hacker news... Why do you downvote this? I thought I was adding a valid and important point - that an increase in efficiency is fighting the wrong battle. I even added references via link. I would be super happy if I could be informed of what in this post is offending or off topic!
I downvoted you because your comment doesn't contribute anything useful to the discussion. Barring some kind of technological silver bullet, "saving the planet" is ultimately a problem of politics and economics.
The next problem, of how we can maintain our lifestyle without breaking the emission limits that we set, is what inventions like this one help with. I expect that piston engines will continue to have some applications for as long as I'm alive, so improving them is a good thing.
GP is correct and more relevant than you think, because fuel efficiency is immediately linked with the hope of avoiding global warming. Unfortunately people believe too much that "we can maintain our lifestyle without breaking the emission limits that we set", and the truth has to be reminded: We can't.
We need to reduce our lifestyle. Live closer to workplaces so we don't need the car at all, which requires a complete rearchitecture of the cities where jobs are knit with housing and public transport, like Sydney or many places in Europe. US people have a difficulty understanding this, because petrol have been so cheap and untaxed for so long that they've built their cities around "1 car, 1 person" - and now they secretely hope for fuel efficiency improvements "to maintain their lifestyle". No, sorry, they're just killing the planet.
"What about China, who pollutes much more?" Yes, they should be allowed to reach their economic development, because US should pollute much less per inhabitant. An American emits 6x what it should, a Chinese person 1/6th.
This is why GP wrote this warning. And it's important because some people still don't believe it.
Similarly, cigarette packets still have to remind "Smoking kills", because a lot of smokers aren't persuaded yet.
No offense but this fairy tale ideal that the city centric bunch always comes up with completely ignores that so many items people want or use in everyday life won't be made in their own city let alone one near by. Throw in the higher costs of living in the city both financial, mentally, and physical, and I still have a hard time justifying it.
Improving efficiency helps everyone because there is not going to be any overnight and likely within one generation shift to another lifestyle. You will never have all the jobs needed within a city to support all the people who live there. As in, your electronics, your food, and many other items, will be produced elsewhere and have to be sent there. The only things cities can self support usually are services.
Cars became popular not because fuel is cheap, they became popular because they represent the freedom to go where you want when you want. You are not restricted to some bus or train line whose routes and times are determined by a government agency.
So efficiency of the internal combustion engines is a needed move simply for the reason that not everyone can be put on the same schedule to change to the next means of individual travel.
OK, nice talking and all, but we need solutions applicable in real world, not something looking nice on paper (we ALL know this is best, and I hope most see it's unrealistic to expect mankind to behave like this... we never did and never will).
So I could say OP is more off than you think, and he could say... whatever. The worse the situation will get, the more people will be willing to sacrifice their well-being, invest in groundbreaking expensive new tech etc. We are not there yet, not the nations holding most of cash in their pockets.
Oh, and don't get fooled - you can put any cancerous lung photos on cigarette packages, I don't know a single smoker that would change their habit based on this. They ALL know it's bad and can kill you and go on nevertheless, don't treat people like stupid children.
"Unfortunately people believe too much that "we can maintain our lifestyle without breaking the emission limits that we set", and the truth has to be reminded: We can't."
Sure we can. It's called nuclear power. Too bad we're not allowed to use it.
"US people have a difficulty understanding this, "
Europeans have difficulty understanding the size of the United States. Oregon, a medium-sized state, is larger than the UK. Texas is larger than France. Alaska is larger than all of Western Europe.
Canadians use even more fossil fuels than Americans, and for the same reason. It's a really, really big country.
It has nothing to do with "cities". Our cities are reasonably high in density already, and the high density cities do have public transportation.
We just have a lot of people who don't live in cities, and we like it that way just fine.
Except that if we were able to replace oil from fossil fuels with oil from biodiesel or bio-engineered sources, without using something like corn/sugar ethanol, then this would also help solve the AGW problem. And an engine that is efficient enough that we could use less fossil petroleum and replace it with these sources is another tool we could use.
The CO2 emissions themselves are not the whole problem. It's the fact that they are coming from a source that is introducing new carbon into the cycle. It's not the engine, it's the way it is produced and the fuel we use.
Public transportation, except for perhaps NY, is actually less efficient than driving because no one uses it. It'd be cheaper to just buy everyone a Prius than most of these light rail or streetcar projects and it'd be better for the environment.
I would add technology to your list of things we need to save this planet. And I'd say it's useful to know that making things that burn fossil fuel more efficient is not a viable solution to the problem of global warming.
We are now beginning to have good products on the market that are sustainable: electric and solar. Making internal combustion engines more efficient seems a dead end. Or worse - making them more efficient may delay the move to what is actually sustainable.
Side note: I regret adding my comment about downvotes. But I will leave it to preserve sense of thread and to remind me not to go there again.
I didn't have time to elaborate, but I chose not to mention technology on purpose. Unless some inconceivable technological leap happens which makes energy cheaper than $15 oil or coal, technology won't be enough to save the planet.
Right now, if one country limits the amount of oil it uses, that just makes oil cheaper for another country which hasn't set limits. 50 years from now, Saudi Arabia could be still burning its last drops of oil to produce electricity, while the rest of the world has moved on to.
So yes, you're correct that improving internal combustions engines might not help at all, but that seems to be true of any other technology, too.
The only thing that will save out planet is our ability to organize ourselves globally to drastically cut emissions.
Side note: don't take the downvotes here personally. HN is a place where quality discussions happen, and a lot of folks would prefer to simply downvote something they don't agree with rather than clutter up the whole thread with responses. :)
The solar and wind stuff keeps getting better. We're already at an inflection point where the renewables are cheaper than the fossil fuels, in some areas. Oil is going to have continue to get cheaper if it wants to stay ahead. The longer Saudi keep their oil, the worse this gets. It's a vicious circle for them - they want to sell it all now, because the selling it in the future will be harder. This cycle ends in it being too expensive to get the oil out of the ground.
The Chinese don't like the fact that coal mining kills 1000s of their citizens each year, nor do they like the smog. They know growth in their economy has to come from an alternative fuel.
Making a better engine might slightly perturb the virtuous path we're on. If it does, it will slightly delay the trend away from fossil fuels. But mainly it is irrelevant.
Can you produce a car without oil? Especially one containing a large battery pack?
Last guess I read put it around 350 barrels for a family sedan. I don't know how much of that is plastics, smelting, and other materials and how much is energy requirements though (and to be fair, I have no idea how close or not that number actually is to the true cost).
But given that it takes some amount of oil at least, doesn't that invalidate the argument against increasing efficiency? Because you could call building any sort of car, even a Model S, a loosing battle then.
Another thing to think of: if you don't have access to a wall plug, and want to provide an air conditioned environment in a vehicle, there's no alternative to oil AFAIK for anything smaller than an aircraft carrier. Diesel Generators are the only option for air conditioning on Sailing Yachts for example. Nothing else has enough energy density and you can't fit enough renewable (solar, wind, hydro) power to keep up with the amps air conditioning will pull out of it.
I know that particular example is very niche. It's just an interest of mine and I'm hopeful we'll see some sort of game changer in the next decade or two.
It is possible to use very little oil for the energy of manufacturing. Most manufacturing processes require electricity, and it's possible to general electricity without oil.
In fact, in the U.S. most electricity is generated from sources other than oil. Unfortunately, a lot of it comes from coal, which is worse than oil in almost every environmental aspect. But theoretically the electricity could all come from solar, wind, hydro, and nuclear.
Cars have of lot of plastic in them, and oil is the main feedstock for the manufacture of plastic. But that's not really bad in terms of global warming, as a lot of the carbon remains locked up in the plastic (as opposed to burning oil).
The final piece of the puzzle is transportation--cars are not built all in one place, the subassemblies might be manufactured all over, and then come together for final assembly via rail, boat, truck, even airplane. Each of those burns oil, so that's a big part of the oil footprint.
Specifically on electric cars and hybrids, mining, refining, and processing the elements in the batteries is pretty nasty business, as is the recycling / disposal of them once they're flat. There are tons of EVs and hybrids out there, and I see this becoming a huge e-waste problem in the near future. Note that Tesla is/was doing something to make the part after they're discarded less bad: https://www.teslamotors.com/blog/mythbusters-part-3-recyclin...
Your last point is the tough part. True, actual manufacturing doesn't have to use lots of oil, but there's still a hefty supply chain network that does. Years ago I read an article showing how various car parts for an "American" car came from nearly two dozen countries, in almost every continent. Even if it's a container ship with 10,000,000 car parts (which is about as efficient as transportation can get) that's still an oil footprint being left behind. Even if they're Tesla parts.
Right, so transportation is the big issue. Last I checked it was the big tankers involved in large volumes of international logistics that generate the most green house gasses.
I am unaware of any technology, so-called "clean burning" oils, electric, or whatever, that solves this problem.
In fact this is probably unsolvable if I think about it free trade is going to keep these boats polluting our air until we die. I'm starting to really believe that sometimes when I'm really drunk
I think the argument (not sure how true it is because I don't know the facts) is that we can do more to (in the future) reduce carbon emissions from power plants and that we will get benefits of scale when we move burning fossil fuels to bigger plants as opposed to doing so in every car.
That's a horrible talking point that gets repeated by the people who have never done the math. Burning that same fuel in a modern efficient (80%+) turbine and then using the resulting electricity in an electric motor (also 88%+ efficient) is way way better than burning the fuel in a combustion engine, which is like 20-30% efficient at best.
They did the whole math in "Sustainable energy without the hot air", and over all, even burning coal and using an electric car is better than burning petrol in a comparitively small engine.
Funny enough, a similar analysis applies for heating: burning natural gas to make electricity to drive a modern heat pump is more efficient than burning the gas directly for heat at the premises.
From a physical point of view, that's possible because you only need low grade heat for your home, but burning gas produces high grade heat.
The trouble is that you're comparing apples and oranges, or rather efficiency of electricity generation with efficiency of heat generation. Remember that thanks to heat pumps, electric heating can often have greater than 100% efficiency, so waste heat is less useful than the same amount of electrical energy even for heating.
I think you don't understand what co-generating heat is. It's a part of generating electricity. You use that heat to heat up the next batch of water, so you end up spending less fuel turning it into steam.
On the downvotes, I assume it's because your point is not at all relevant to the article itself or the technology it discuesses. It could easily be copy-pasted to most any article about combustion engines. Technological improvement can be useful enough even if it doesn't "save the planet".
Hacker News comments are for discussion of the article content, rather than being a soapbox for your views and blogposts.
You been downvoted because you've said nothing on topic or substance and moved the conservation to a whole new pet political topic you seem to have. Nothing in the article talks about the environment
> the purpose of developing a more efficient engine is to reduce emission
Generally saving money is why.
And as hackers we love making things more efficient.
Plus as scientist we love new discoveries, cause who knows where they'll go. Why couldn't this work on a hydrogen or future engine X? Perhaps it won't but scientists discover cause we can.
Most people seem uninformed about this, but there are methods to produce clean oil (short-term carbon-neutral), such as green crude production from algae. Although large-scale production is not there. From that perspective, there is nothing inherently polluting about a combustion engine, in fact gasoline is an excellent chemical store of energy, and in that context possibly cleaner than current batteries. Either way this is great news.
I'd had a comment downvoted and flagged recently, perhaps understanably, though the follow-on discussion made pretty clear that I'd identified a pretty salient point.
Upshot: HN is no less immune to voting what it wants to see over what's true or not. I may even be subject to that myself, though I prefer to see my votes as aiming for at the very least a deeper truth and validity.
>I downvoted you because your comment doesn't contribute anything useful to the discussion
Sorry to go off-topic, but how do you down-vote people? I've looked through the FAQs and everything and can't find anything about it. I only have the ability to up-vote.
Thank you for this comment! I think your advice is correct: better not talk about it, and move on. Btw I am now in a weird situation - should I remove my edited comment or not. But I'll let it sit there, this thread makes no sense without it :)
I think it's always more honest to either append, or modify and summarize the changes if shortly after comment creation. If it's immediately after and it's just typo/grammar fixes sometimes I'll just modify without a note.
My thinking is that you can't have an honest discussion if people can't count on their replies applying to the parent after the fact, and if I've screwed up enough that I want something off the record, I really should have thought more before writing it, so leaving it and the sting of it's continual viewing is a good reminder for the future.
> When I first heard this I was surprised. Can’t we just aim to cut carbon emissions in half? I asked many scientists. But they all agreed that wouldn’t be enough. The problem is that CO2 lingers in the atmosphere for decades. Even if we halted carbon emissions tomorrow, the temperature would still rise because of the carbon that’s already been released. No, we need to get all the way down to zero.
So if we can only reduce them by 99%, we shouldn't even bother?
It seems to me that the closer we get to zero, the more expensive the next 1% will be. At some point, it's not worth the cost to keep going, and we'd be better off looking for ways to remove some of the CO2 that's in the atmosphere instead of just reducing how much we're pumping in. His equation notably omits that possibility.
I think they're really talking about opportunity costs. Dollars spent on making oil-burning engines more efficient are dollars not spent on developing technologies to replace oil-burning engines, and replace is really what we need.
but it is just ignorant that efficiency gains aren't paying off. The number of miles driven versus the fuel cost to do so quickly and absolutely justifies the efficiency gains of the past three decades. There is no reason to not think this won't carry forward.
Yes there are many opportunities in replacement but none have won out and more are on their way. None are at a price point where those least capable of the costs are going to be able to take advantage of them. So in that meantime we keep pushing the cost of burning fossil fuels down.
There is likely an efficient (in the economic sense of the word) level of CO2 emissions, but I doubt that anyone knows what it is. It's very difficult to price. However, I do agree with you that it's probably not zero.
The good news is that we have a proven carbon capture technology. Grow new forests.
Forests aren't sustainable unless you're also logging them and storing the wood permanently somewhere. They also consume valuable fertile land so it's not necessarily a worthwhile method. Perhaps in some post-oil economy they would become economical.
There are biofuels that (for a while at least) have better energy density than batteries.
There are applications for internal combustion engines where practical alternatives are not even on the horizon, big ocean freighters for example.
It's very narrow minded to dismiss this as "wasted effort", just because it's not part of the endgame vision where no fuel is burned for any reason ever. There are many steps between the status quo and that idealized scenario, and any improvement in efficiency is always a good thing.
There are advantages and disadvantages to internal combustion engines.
Compared to external combustion engines (steam engines), ICEs have much quicker start-up and response times. Steam engines require building up a head of steam, and actually exhaust the working fluid (water) over time, which is why steam railroads had water towers every so often.
ICEs have been improved over more than 130 years, and scale from a few CCs of displacement to many cubic meters -- the smallest ICEs could fit in the palm of your hand, you could stand in the largest and not reach the sides or top of the cylinder.
Liquid hydrocarbon fuels are exceptionally energy dense by both weight and volume. This makes certain classes of use very difficult to substitute for: commercial passenger and freight aircraft, overland truck transport, and powered marine shipping really have few tractable alternatives. Aircraft would all but disappear without liquid hydrocarbons (gasoline for piston engines, kerosene for gas turbines), trucks would probably be replaced with electrified rail, and shipping would return to wind power. Optimists might suggest nuclear marine powerplants, but I find that unlikely; ships are lost at far higher rates than is commonly realised: about 200 every decade, and existing trials of both military and nonmilitary nuclear marine power have proven it expensive and nonviable for all but the most demanding instances -- aircraft carriers and submarines.
They're also quite stable in storage (proved over hundreds of millions of years), relatively safe to handle (no respiration or exceptional contact protection required), and their combustion products are mostly benign: CO2 (I'll get to this) and H20 with scant quantities of carbon monoxide, sulfer and nitrogen oxides, and other contaminants or partial combustion products, all of which can be greatly mitigated with combustion and exhaust controls and treatment.
The CO2 exhausted isn't a problem in itself but for the, um, slight problem that in the past 200 or so years humans have returned to the biosphere carbon sequestered over several hundreds of millions of years. Which turns out to be a rather considerable problem.
But it's only a problem where what you're burning are fossil fuels. There exist several options, though all much more expensive and/or constrained than present fossil fuels, for creating synthetic hydrocarbon-based liquid fuels. These also have challenges. Biofuels are intractable at scale given natural limits on plant production: what's called "HANNP" -- the human appropriation of net primary production -- or the photosynthetic ceiling. There's only so much plant growth which occurs and humans already consume much of it (40%, biofuel replacement of fossil fuels would consume another 20%, see Jeffrey S. Duke's "Burning Buried Sunshine" (2003), PDF available online, for more on this.
Another prospect: sequestering carbon from the biosphere, and combining it with hydrogen, electrolised from water. The US Navy and national energy labs (especially Brookhaven), as well as M.I.T., have researched this for the past 50 years. It's proven expensive and hasn't been scaled past very low production (a few litres), but does work. It raises costs of fuel from one unit of input energy per 20-40 units made available to two units per one provided -- that's a 40-80x increase in the real cost of fuel.
1. Run silently or near silently. They're generating electricity via redox reactions, not combusting.
2. Have effectively no moving parts. Again, no noise or vibration.
3. Product electricity directly. For powering electronics, this means no secondary generation required.
4. Utilise extremely expensive catalysts. The reason you don't see fuel-cell automobiles (excluding very small numbers of test vehicles) is that the engines cost, literally, on the order of $1 million, as opposed to a few hundred for a typical ICE. This price premium has proven difficult to overcome.
5. Operate better delivering fairly steady-state power, from what I understand. A tremendous benefit of ICEs is that they can scale output in a second or few seconds, with very little throttle lag. Yes, straight-up electric motors are even better at this, but straight-up batteries tend to not store much power.
A fuel cell is essentially a battery whose electrolytes you fill rather than recharge or replace. This offers the advantages of fuel-based systems (high energy capacity) and batteries (direct electrical output). Unfortunately, it introduces the disadvantages of fuel cells (cost, power delivery profile).
Yes, that's one option. I'm a little shakey on the specific function, characteristics, and reaction materials, but some form of redox and electron flow is what you're aiming for.
Whether you're looking at hydrogen or hydrocarbons, you need some chemical energy carrier mechanism. In the long run, either will have to be formulated, and yes, there's about a 50% efficiency hit straight off the top in elecrolysing hydrogen.
But if you're trading an abundant, variable energy source (say, peak solar which is otherwise wasted) for a scarce but valuable and useful store, that's a net win.
Note that whether you're formulating H2 or hydrocarbons, the energy cost is about the same (the carbon sequestration from seawater mentioned above is low energy cost), though it requires fairly substantial capital investments.
Hybrid cars remove most advantages to IC engines as start-up and response times can be made irrelevant. Further, cars generally only need a small fraction of engine max power hybrids also allow for heavy engines relative to HP as most cars can maintain highway speeds with less than 40HP.
PS: As to fuel vs. energy costs. The vast majority of gas's costs has nothing to do with direct energy costs. Oil is already vastly more expensive than competing fuels so even a 2>1 energy loss could end up less expensive than current production methods.
BBS is good. I'd been of the inclination that biofuels were viable prior to that, it pretty much single-handedly changed my mind. I really like that it gives a detailed breakdown of how fossil fuels come to be and their various and relative formation efficiencies.
Carbon sequestration from seawater is a rather different animal from most CCS discussions. Though, in the world of strange bedfellows, it turns out that various coal industry organisations follow this information pretty closely and have some of the more complete compilations of research. Just ... beware biases.
> A 500cc two stroke can easily make some 80 Nt*m (8 Kp*m) torque.
> At 6000 rpm this torque makes some 50 KW (70 PS).
> 50 KW from 20 Kp means 0.4 Kp per KW.
> And 0.4 Kp/KW with direct injection Diesel efficiency sounds interesting, especially for an engine with such a low cost."
So, as I understand it, it combines the compression ignition of diesels with opposing pistons. The opposing pistons go toward one another and compress the air/gas mixture and ignite it. The exhaust escapes when the pistons move back through ports machined in the sides (kind of like a wankel/rotary engine removes exhaust gasses).
Sounds like they're trading the spark system (a pretty easy to maintain system) for a second piston/crankshaft/etc. Essentially pulling out a cheap and perfected system for one that adds a bunch of high stress, expensive parts. Just from that sounds like a bad idea.
They say the extra efficiency comes from heat loss from the cylinder head, but I have a hard time believing they're capturing that much extra (double-digits) efficiency from heat loss alone, especially given the reduced efficiency of having more moving parts.
> Sounds like they're trading the spark system (a pretty easy to maintain system) for a second piston/crankshaft/etc.
Opposing pistons and compression ignition are (mostly) orthogonal optimizations. From years of working on engines, I'd also be more willing to call the mechanical parts "perfected" and the ignition system "not perfected", at least for common consumer engines.
Sure, it's easy to maintain the ignition system, but it's also a system that needs maintenance: spark plugs, batteries, distributor caps, and alternators are all parts which wear out and need replacement during the normal course of vehicle operation. This is not true of pistons, crankshafts, and the like; it doesn't really matter that replacing them would be a difficult and expensive job, because they almost never break, and when they do you are generally better off just replacing the car and scrapping the old one. So, I think that an engine which had fewer of the former sort of components and more of the latter sort would, on balance, be a more reliable machine.
It seems to lack a defining characteristic of your typical 2-stroke though, that the fuel is initially drawn in below the head to lubricate the crankshaft (this require mixing oil in the gasoline, done automatically on modern mopeds).
"The new engine will meld the best characteristics of gasoline and compression ignition engines with an innovative piston architecture refined by Achates Power that sets two pistons moving in opposition in one cylinder."
That's what's puzzling. Opposed-piston Diesel engines have a long history. There are others now proposing them. Eco Motors [1] claimed they were going into production with one in 2014. Didn't happen. They might be a little better, but the claimed 50% improvement in fuel economy is a big jump.
These engines use valve ports, so piston motion produces the valve action. All the timing is set by the engine geometry. There are few variables adjustable at run time. This is also true of Wankel engines, which is why Wankels hit a wall - you can't tweak fuel injection timing or valve timing. In a Diesel, you can't even tweak the spark timing. Much of the improvement in IC engines has come from active control of fuel injection and spark, along with a few attempts at dynamically tweaking valve timing. These designs don't seem to be able to do that.
The Brits are just so much better at ship names than the US. We always name ours after places and politicians--boring! The Brits meanwhile have ships like Onslaught, Firedrake, Acheron, Invincible...
I agree completely. US Navy ship names are nothing short of horrible. They used to have some cool names back in WWII, like Wasp, Hornet, Enterprise, etc. They've kept Enterprise (there's a new Enterprise now planned to replace the now-decommissioned one). They had some cool submarine names way back too, like Nautilus, plus there used to be a bunch named after fish, which isn't too bad. But otherwise, over the last several decades, they just plain suck. The worst one ever is the carrier USS John C Stennis. WTF? They named a carrier after some dumb politician who was never even President, and all he did was get a lot of pork funding for military projects. He also got a Space Center named after him in Mississippi because he was good at this (and this was because he got the center placed there, even though there wasn't any really good logistical reason for it; they do NASA's rocket engine tests there. It's not anywhere near where the engines are actually launched from, it's just a pork project).
Not quite. The engine discussed in this article is almost the reverse of BMW's engine design. The crankshafts (where the rotational movement is transferred to the gear box) would be where the heads of the BMW engine are located. This means the explosion causing the rotational movement is at the centre of the engine, and keeps heat loss to a minimum. That's partly how they're going to get such high efficiency out of this design. The other way is the (I'm guessing) massive compression ratio they'll need to achieve for the auto-ignition of gasoline to occur.
What I think, and this is without being ICE engineer, is the same effect that helps Mazdas SkyActive engines achieve high efficiency, higher compression and longer exhaust cycle. That a two stroke achieves a high power output is not surprising, and is one of the main reason they're used, as the power to weight ratio is superior to 4 stoke.
To add to your comment, the SkyActiv engines are Atkinson-cycle engines, which improves efficiency by holding the intake valve during the beginning of the compression stroke, so that the exhaust compression ratio is greater than the intake compression ratio, extracting more work out of the exhaust gases. The disadvantage of this is that the engine has lower power density (it won't get the same HP/liter ratings that a similar Otto-cycle engine will). This can be made up for by adding an electric motor to make it a hybrid car, or by adding a supercharger (which makes it a Miller cycle engine).
2 strokes are terrible engines generally, because they have very high emissions, usually because they release unburned fuel in the exhaust.
This engine appears to burn gasoline rather than diesel fuel. I suspect the compression must be much higher to ignite gasoline than is required for diesel.
Compression required to "diesel" petrol (gasoline) is lower, which is why some autos have the problem of continuing to run ("diesel") after the ignition (and spark) are shut off. Most now incorporate other controls and limiters, such as controlled fuel injection, to eliminate this.
Gasoline is comprised of a shorter set of hydrocarbons (mostly 6, 8, and 10 chain) than diesel (about 12-16 chain length, though 8-21 carbon are listed at Wikipedia). Volatility (and ignitability) increase with shorter chains -- methane (C2H6) and butane (C4H10) -- that is, two and four chain hydrocarbons -- are both gaseous at or near room temperature.
Longer chains still get you heavy fuel oils, tars, etc.
actually it's the opposite, you could run a diesel car on gasoline if you wanted (not wise as diesel fuel is actually used as a lubricant in high pressure fuel pumps)
Efficiency aside, big two-stroke engines, particularly diesels, tend to have a very distinctive sound. I guess this one, being also two-stroke and compression ignition, would probably sound somewhat like this:
Modern car engines are already very silent, but many drivers love roaring sounds (probably due to false logic that more noise == more power). Car makers know that and fake engine sound using audio system(0) on many cars without anyone actually noticing, so I don't see why it can't be done in this case too.
Here's an opposed piston 2 stroke diesel. Basically the "Super Engine" that the article describes built in the 1930's, except it runs on diesel instead of gasoline.
I thought that gas based engines topped out at 30% due to the heat loss intrinsic with burning fuel(all that waste heat). Is this tackling that in some fundamental way or is it just an incremental improvement?
Carnot efficiency. 30% is pretty typical in land-based motive systems. Shipboard combustion engines and coal-fired power plants (of all things) are rated as high as 45% efficiency.
This is based on input and output temperatures, more than anything.
Good eye, though it's not immediately clear that that's strictly edging in on Carnot efficiencies or if other aspects (two-stroke power cycle, valveless port-based design, eliminating cylinder-head heat loss -- on which, doesn't that eventually reach equilibrium temp anyway?, etc.) are to credit.
I've seen a few other radical reciprocating energy designs, there are some interesting YouTube vids I should track down. I think "radial engine" might reveal something. New Zealand, possibly Australian engineering firm, IIRC.
Most IC engines are nowhere near the carnot limit, which is around 60%-70% in most cases. The majority of the efficiency losses come from excessive heat rejection in the engine block and also mass transfer in the exhaust. Most engine blocks are (in)conveniently made out of aluminum, which has a very high thermal conductivity, meaning more energy gets transferred to the cylinder walls and wasted during combustion.
As a mechanical engineer, this engine design seems much more promising, however:
http://liquidpiston.com/
Engine blocks used to be made of cast iron, but they've pretty much all moved to aluminum because of 1) weight, and 2) that higher thermal conductivity. IANAME, but IIRC the problem with iron's lower thermal conductivity is that it created hot spots which could cause pre-ignition, so you had to use lower compression ratios to avoid this. Aluminum has more uniform temperature so you can boost the compression ratio, which gets you more efficiency and power.
Carnot limit is over 60-70 percent in fixed load power plants. 70% is something only could be attained with very exotic materials(expensive and difficult to manage) that could handle high temperatures.
In a mobile system you could get 50% with a fixed load. The problem with the car is that is has to work in different regimes.
That is the reason hybrid engines are more efficient. They work at a fixed load and store the energy in a battery or super cap.
Opposed pistons is a way to have a very long stroke engine (high torque and smaller piston speeds = smoother), without the bigger radius that the crankshaft pin would have to rotate.
Large engines (in giant container ships) are supposed to be approaching the efficiency limit according to theoretical thermodynamics. Does this get small engines close to the limit?
That's a common pattern in new (combustion) engine designs; there's a lot of them being published every year, but almost none of them actually end up being mass-produced and they dwindle into silence or as just demonstration models. Why? I don't know; the media only seems to focus on the invention and potential, not the failure (or if I were to put on my tin foil hat, the disappearance under mysterious circumstances). The only nonstandard engine that (AFAIK) ever got some leverage was the rotary wankel engine, and even that was (iirc) in just one car model.
Mazda RX7 and RX8 had wankel engines. Nice cars, but higher maintenance than with normal engines.
I think the main reason for the pattern you observe is that what's optimal and what's cost effective in a car is highly non-intuitive. Take front-wheel drive, for instance. Mechanically more complex than RWD, but (apparently) worth it due to the space savings inside the car.
Or take water-methanol injection: well-understood tech that's been in use since WW2, can save fuel and reduce NOx emissions significantly, or give higher power output. But it requires changes to all the fuelling infrastructure, and that makes it essentially a non-starter outside of racing cars.
> The research is being conducted under a three-year project funded by a $9 million award from DOE's Advanced Research Projects Agency-Energy (ARPA-E) and an additional $4 million of cost share from the team members.
So, the total cost of designing this prototype was $13 million? What's the size of the R&D budget for a typical automaker?
To me this just shows that typically businesses are in the mindset of "business as usual" because it's what they are comfortable with rather than looking into radical, new, innovation.
The new engine will meld the best characteristics of gasoline and compression ignition engines with an innovative piston architecture refined by Achates Power that sets two pistons moving in opposition in one cylinder. As the crowns of the pistons slide toward each other, they compress a mixture of air and gasoline to such extreme pressures that the mixture auto-ignites without the need for spark plugs in a process known as compression ignition.
HCCI is difficult enough--high compression ratio requires strengthened materials. Plus there's the hydrocarbon issues that come up with low temps. Maybe the heat retained by not having a cylinder head would be able to compensate? High temp burn/lean burn can lead to high NOx which is pretty bad if you need a urea injector system.
Mazda, GM and others are known to be working on CI engines for gas targeting 2020, so this might be the next step in 10 years. Assuming we don't all switch to pure electric...
Claims of innovative internal combustion engine designs that will be significantly more efficient than current ones show up every few months. They never live up to the hype.
Government loans are supposed to be risky, or else they would simply be replacing private loans. The point is to put money towards projects that have large potential public benefit.
While not an earth-shattering amount, I'd rather see such grants/cost sharing go to tech that doesn't perpetuate dependence on fossil fuels. In the end, this tech only means we get to burn less, but not eliminate the emissions all together.
Combustion engines are so fundamental, they go far beyond fossil fuels. They are one of the best ways of converting chemical energy to work. Fossil fuels just happen to be very high in chemical energy. You can burn hydrogen, ethanol, bio-diesel, paraffin, methanol....
IMO the better combustion engines become, the more options for fuel we have. For example, ethanol compares poorly to gasoline in power & consumption, but with continued engine development, ethanol will be able to develop as much power & economy as gasoline does today.
Not familiar with burning paraffin, but of others only hydrogen produces relatively safe emissions (water vapor), the rest produce the undesirable by products.
It would be better for smaller applications to move to electric and produce energy by other means. This requires investment into better batteries/storage applications. I'd rather all the money go to that instead of combustion research.
Battery-powered 737's eh? While it's a nice dream, electric motors are way behind on power to weight ratio, thanks to batteries. We might get there someday, but we would need several stacking 10x improvements in battery tech, and who knows if they exist.
There are still a lot of places where very high power to weight ratio of combustion engines is extremely important.
Sure, jets burn fuel, so in that they count. However, the article is talking about a very specific application with opposing pistons and compression-based ignition. This is similar to how a traditional diesel works.
It's definitely useful to burn less fuel, but still.
I share this opinion with you and do the best that I can to do my share. I have a normal car with a combustion engine that I've converted to use E85/Flexfuel, which is becoming more available in the US and many other parts of the world.
Edited comment: Man, I don't get hacker news... Why do you downvote this? I thought I was adding a valid and important point - that an increase in efficiency is fighting the wrong battle. I even added references via link. I would be super happy if I could be informed of what in this post is offending or off topic!