A non-turbo diesel is an interesting choice of competitor. The big selling point of the Kohler motor is that it's almost silent - even the valve train is belt-driven to reduce noise.
Not sure a rotary engine screaming at 6500RPM is comparable here to a diesel with a peak torque at 2000 and peak power at 3600.
> LiquidPiston has been working on these X-engines for nearly 20 years now,
I'm guessing they will never actually release a commercially viable product. 20 years to design an ICE is...too much.
I think a lot of commenters in articles like this will only think about automotive as a use case for alternative engine designs.
I'm reminded of a linear piston engine (iirc two pistons that just go back and forth without their motion being translated into rotation; one where they were side-by-side moving alternately, the other one where they'd actually move towards each other and share a combustion chamber). The use case for that was to have the pistons move through coils, thus generating electricity. We used to have a flashlight that works with the same principle, shake it to generate electricity.
My first thought went to cargo ships. They require huge motors, so I imagine that if you can keep or gain performance while reducing size they would be very interested.
this is backwards. the reason cargo ship engines are big is because they don't care about size. they would rather have a 2x bigger engine that was 1% more efficient
> this is backwards. the reason cargo ship engines are big is because they don't care about size. they would rather have a 2x bigger engine that was 1% more efficient
Seems likely. Several years ago when working on a hybrid-powered UAV, I was checking out high power/weight engine platforms, and actual Wankels in development or available did better.
A 30sec DDG search turned up options that are definitely better, e.g., the AIE 80S, with 15BHP/11.2kW at 5kg or their 225CS, with 40BHP/30kW at 10kg [0]. In contrast, this weighs 19kg to produce 26HP/20kW. The net power - weight for these Wankels is 2.24kW/kg and 3.0 kW/kg vs Liquid Piston's 1.05kW/kg.
While IDK about availability from AIE (it just turned up at the top of the search), I know there are others on the market that are/were available. Meanwhile the LP prototype still isn't available 7+ years after I was first looking at them, and the were suppose to ship "real soon now".
rotary engines do not really scream at peak power... this is why Mazda has plans to use rotary at peak power to generate electricity for their hybrid EVs.
re 20 years to make a new engine point, compare investment $ in traditional ICE across the car industry vs investment $ into rotary or other alternative engines (the former is order of magnitudes more)
We will be driving an old RX7 in the '24 hours of Lemons' this year. Looking forward to pushing it in a nice casual race. Mechanically, we were not at a point where it was solid enough for 2022. I think the rotary engine was the only thing that was working. :)
I guess you already seen it, but for anyone who shouts at Wankel engine unreliability, small plug for Rob Dahm and his video about fixing that engine biggest problems: https://www.youtube.com/watch?v=BwM6JJYPzkM
Good luck with the seals! Between rotary and Stirling I find it hard to pick a favorite and both of them have similar problems despite the completely different geometry.
btw: I had a mazda rotary engine car, and the 7000rpm shown on the tach seemed exciting compared to a piston engine... except it wasn't really true. It really ran at 1/3 that speed.
There's only a grain of truth to what you're saying here.
The eccentric shaft does indeed spin at the indicated RPM, just as a crankshaft on a piston motor does.
It's just the rotors move at 1/3rd the eccentric shaft's rate, which is a design feature enabling substantially higher than 7000RPM with little effort.
I know this is targeted towards military/aviation applications (now, initially it was different), but, I honestly cannot understand why there is so little research on just making a hyper-efficient low-maintenance engine that runs at maybe 2 optimal rpms and powers a small battery bank plus electric motor (i.e.. typically series hybrid). None of these gas engines will come anywhere near the power-per-pound & torque output of a electric motor.
If traditional carmakers had done that research about 10 years ago they wouldn't be facing such crisis with EVs today. a high-efficiency multi-fuel range extender engine is all we need today but still I cant find many automakers jumping on it.
PS: it would have been nice to see a micro-turbine based generator with high thermodynamic efficiency but my understanding is that need a lot of maintenance so not suitable for consumer applications.
One of the reasons is government regulation. I'll talk about US regulation but similar situations exist in other countries.
1. US incentives and regulation result in car manufacturers having to shift production from hybrids to EVs.
2. In order to qualify as an EV a vehicle can't have a range extending ICE that provides more than a 50% range increase. There's also a very low limit to the size of the fuel tank.
These regulations have resulted in very few vehicles with ICE range extenders. Existing engines are easily capable of maxing out that regulation so there's no incentive to research other engines.
US incentives aside, Nothing was stopping them from doing this for more expensive vehicles even if they didn't care about environment. I mean wouldn't you want to have a pickup truck with acceleration & torque of an EV with 2+1 motors powered by series hybrid and also have fuel economy of a 40mpg in city?
I think its just institutional laziness & innovators dilemma. Even in last 5 years when it was clear Tesla is starting to rise they decided to sit on their hands and do nothing. Even till last year toyota has been singing BS about hydrogen cars and not enough lithium. they deserve whats coming to them.
Are you aware you are essentially describing the original Toyota Prius? the engine is optimised for constant low rpm/low torque/high efficiency, whilest relying on the battery/electric motor for torque and temporary extra power
yes I am well aware of Prius series configuration but it is still a regular engine shrunk down and fine tuned. What I am asking for is something very ground up redesigned for maximizing one thing only efficiency of energy conversion. couple of examples of this are Aquarius engines or [1]. basically you cut out all the unnecessary stuff and all the maintenance/repair plus cost with it. Current engines are complex because they are operating over a large range or rpms and optimizing for other factors like torque etc. the you have losses in mechanical power transfer at each stage. Cut that all out and make something thats super easy to manufacture & replace and you have added another 50 years to ICE.
The Prius utilizes the Atkinson cycle rather than the conventional Otto cycle, which is more common in traditional gasoline engines. The Atkinson cycle is designed for higher efficiency, sacrificing some power output for improved fuel economy.
The Atkinson cycle has a longer expansion stroke compared to the compression stroke, resulting in a more efficient conversion of heat to mechanical work. However, this cycle tends to have a narrower range of operation, with less torque and power available at lower RPMs compared to an Otto cycle engine.
Perhaps a more efficient cycle is possible by reducing the RPM/torque range even further, but I am under the impression that a lot has been left on the table efficiency wise.
I think you're greatly overestimating just how efficient a conventional ICE can be if designed and tuned for single-rpm, maximum-efficiency operation.
Basically, the Chevy Volt is exactly the car you're describing. It wasn't that great: it had a separate engine that only ran a generator, and would only come on when the battery was depleted. The problem is having a full EV powertrain, plus an ICE driving a generator, adds a lot of hardware, complexity, and cost to the vehicle, and the result was a car that people liked, but just wasn't cost-effective compared to the Prius, or to a BEV.
The Prius can get away with a much smaller battery because it's just a parallel hybrid and doesn't need to drive 50 miles on a charge like the Volt. Batteries are expensive and take up a lot of space. And a BEV can get away with not wasting space and weight on an ICE engine (plus fuel tank), and instead just have a big battery. The Volt basically had the worst of both worlds. Reportedly, the car worked well, but with all that stuff packed inside, it just cost too much, plus it didn't have a lot of cargo space.
Just FYI, the latest Prius Prime is functionally identical to the Chevy Volt. It just costs a lot less (starts at $33k). GM simply failed to design it properly.
Last I checked toyota's market cap was 220B+, they have been burning cash on Hydrogen fuel cell BS for a decade plus. that costs money too. BTW if a startup like Aquarious & some research center in UK can do it then so can they. all the rest of expenses come later when technology is promising & starts deploying. But thats when market also rewards you for innovation & not just maintaining you P/E ratios & EBITDA margins. That is essentially what tesla did. The sad thing is that hybrids now have existed for 2 decades+ but they chose not to scale up any hybrid production beyond compliance cars. Basically they are Kodak-ing their way out of existence if Stanford professor Tony Seba is to be believed.
> Last I checked toyota's market cap was 220B+, they have been burning cash on Hydrogen fuel cell BS for a decade plus. that costs money too. BTW if a startup like Aquarious & some research center in UK can do it then so can they. all the rest of expenses come later when technology is promising & starts deploying. But thats when market also rewards you for innovation & not just maintaining you P/E ratios & EBITDA margins. That is essentially what tesla did.
So this was your intended comment?
If so, I don't see how it's relevant. The money Toyota 'burnt' on hydrogen stuff has already been spent, it can't be recovered.
And the rollout your imagining would require at least 10x the money to do so worldwide.
Relying on a stock market boost to fund such a huge investment is silly because Toyota doesn't pay the vast majority of their suppliers or their staff in shares or options, but in cash.
>The money Toyota 'burnt' on hydrogen stuff has already been spent
Well was the decision to go all in on a entirely new tech (hydrogen fuel cells) was conscious choice by Toyota or not? So you agree that they have capacity to spend investment dollars, right? Now could they spend maybe an order of magnitude less money on improving ICE, Most definitely yes. Its definitely less costly trying to reinvent and entire new scientific field (fuel cells) than repurposing ice engine as demonstrated by companies I highlighted (& many more).
>And the rollout your imagining would require at least 10x the money to do so worldwide.
would this rollout be any less expensive for hydrogen cars, I'd argue orders of magnitude more expensive because no hydrogen infra exists. yet you chose to conveniently ignore it. Also, you are making a strawman here by indicating that I am saying need to fund it with stock-market (go back and read my comment). they dont Need that money to start the rollout, they get rewarded by market when they do it because its a fundamentally better product.
My gut feeling is most of these japanese companies are opposed to electrification because of some other ulterior reason, likely because solar may not be viable in that region & their govts might not be so excited about it. In any case they are about to get their ass handed to them by tesla & chinese EVs because EVs are essentially democratizing the automobile development platform due to its simplicity.
> Well was the decision to go all in on a entirely new tech (hydrogen fuel cells) was conscious choice by Toyota or not? So you agree that they have capacity to spend investment dollars, right? Now could they spend maybe an order of magnitude less money on improving ICE, Most definitely yes. Its definitely less costly trying to reinvent and entire new scientific field (fuel cells) than repurposing ice engine as demonstrated by companies I highlighted (& many more).
Toyota spent that money years ago. How is that at all relevant to how much they can spend in 2023?
Financial markets are much tighter, so I doubt they could even spend 20% as much without huge shareholder pushback.
Guys like you are totally deluded. BEVs are the real dead end and waste of resources. It is just replacing one unsustainable idea with another. And it can't even meet the driving needs of everyone anyways.
All car companies will inevitably have to pivot to hydrogen (or efuels or whatever). It is a matter of when and not if. If anything, Toyota is decades ahead of the competition.
Kind of weird article that doesn't talk about either the main benefits or design hurdles. The advantage of the LiquidPiston design is that at the time of ignition, the combustion chamber is a roughly round shape, as opposed to a traditional rotary where it's a long crescent. This should theoretically improve the emissions and fuel economy to be more like piston engines.
I don't think Liquid Piston was talking about a 2-stroke version before. That's news to me, and it seems like it would throw out the efficiency/emissions benefits in exchange for more power. Maybe the author of the article was confused and this isn't actually a 2-stroke design?
The main design hurdle has been longevity. Their prototypes in the past only work for a short time and wear out. That's probably just a matter of doing the necessary R&D to figure out the best alloys to make the engine out, and the best ways to lubricate everything. It's not clear from the article if this new version has this solved so it can last a normal amount of time or not.
This is likely all part of a pump and dump. That's why it's a weird article.
They've been advertising this heavily of all places on instagram and taboola chumboxes. Obviously none of those people need this engine, they're looking for marks.
2 stroke has poor unburned emissions because of mix flow-through when ports are open. If air charge / purge is completed before fuel is injected then that doesn't occur; whether that's diesel or something else is irrelevant.
I thought 2-strokes had poor emissions was the injection of lubrication oil into the air fuel mixture. traditional 2-strokes I'm familiar with pull in air into the crank case (which requires lubrication), then uses a portion of the exhaust stroke to compress the fuel/air creating forced induction. By keeping air out of the crank case and providing lubrication delivery outside of the air/fuel mixture, emissions can be significantly improved. The article claims the design allows external lubrication, but it doesn't say how. I'd like to see how the seals are better than apex seals.
The basic crankcase-scavenged two-stroke suffers from both problems. Typical diesel two-strokes use a separate blower for scavenging, so the combustion air inflow never passes through the crankcase and does not come in contact with the lubricating oil, while the fuel is not injected until after the exhaust is closed.
The engine described here can have its shaft and eccentric bearings externally lubricated, but its apex seals, like those of Wankel engines, seem to be in a situation analogous to that of a piston ring. Unlike either of those, however, they are mounted in the stator, not the moving part, and so may be easier to lubricate precisely.
My 1960s cafe racer (years ago!) had oil injection. Some engines do have oil injection and just inject it into the inlet port, but in this engine it was delivered directly to the crank bearings. From there it was flung all over and ultimately burned. Anyway, as the saying goes on the lost continent of Perl: "There's More Than One Way To Do It".
All the numbers in the article were really small and seemed to aim at use cases that are all about small and reliable. Is anything stopping this from being scaled-up to be a light but very powerful engine for a sports or supercar? This could be a huge innovation in racing if it scaled.
The four strokes of a four stroke cylinder are intake, compression, combustion, and exhaust. That's down, up, down, up. Since there's no down or up in any of this engine's combustion chambers, "strokes" is probably inappropriate.
The strokes have nothing to do with up and down (e.g. flat motors, like a boxer), but to do with compression and expansion. The direction of compression doesn't really matter aside from packaging concerns.
As you said, 4 stroke has intake, compression, combustion, and exhaust. That's expansion, compression, expansion, compression. It fires between compression and combustion.
A 2 stroke motor has compression and expansion. It fires between compression and expansion. Intake, exhaust, and combustion happen during the expansion phase.
A rotary motor is traditionally 4 stroke, and I'm not sure a 2 stroke version is feasible. The LiquidPiston rotary appears to be a 4 stroke to me, despite the article text.
Typical Otto cycle 4-stroke piston engines do two rotations for a single cycle. Wankels are more complicated; each rotor face acts as a separate combustion chamber and all four strokes happen in a single rotation. It looks like the situation is similar with LiquidPiston's implementation.
Ok, so they're "shooting for" a performance of 1hp per 1.57 lbs of engine weight. A Toyota Camry engine produces 1hp for every 1.41 lbs of engine weight. It produces 1ft-lb of torque for every 1.94 pounds of engine weight, compared to 1.58 for the Camry.
How is this revolutionary motor being outdone by a mid-range sedan engine?
> How is this revolutionary motor being outdone by a mid-range sedan engine?
Go ask your Camry engine to make 100% rated power indefinitely, and see how long it holds up. That's the difference.
A typical car engine is designed to make 30-50hp sustained, and occasionally generate more power for reasonably short periods of time.
An aviation engine, generator engine, or any sort of "industrial" engine is going to be able to sit there, making full rated horsepower, for thousands of hours without any trouble at all.
IIRC some automakers do test automotive engines at 100% duty cycle (in a test stand configuration). And more than a few automotive engines are used in slightly modified variants for marine and aviation applications.
As I understand, the reason a typical car engine can’t sit at 100% duty cycle isn’t the engine itself, but usually the cooling and oiling configuration.
100% duty cycle doesn't really exists as stand alone concept. It is always in reference to the application. A typical car engine is at 100% duty cycle at around 30 horsepower, but the engine can produce 200+ horsepower for short bursts (enough to do the 0-60 test that everyone loves to quote). With more cooling you can run more power from the same engine, but the additional stress will mean the engine doesn't last as long before it breaks.
Marine applications generally means salt water, so they will run at higher power is the salt is what gets the engine eventually not the stress of high power output. Airplane engines are expected to be reliable and so they run at relatively lower power output. There are many small niches in between that have their own idea of what 100% duty cycle is.
I agree, it can mean different things. To be more specific, the video I linked says Kia tests at full load, WOT, and maximum engine speed for 300 hours continuously. Then they run it 10-20% faster than the specified maximum engine speed for another 10-20 hours.
This exceeds most definitions of "100% duty cycle".
The first time I learned you can increase, sometimes significantly, the performance of a car by upgrading the oil cooler blew my mind a little bit, but of course in hindsight it makes perfect sense.
I'm aware of some auto engine conversions - the 13Bs out of the RX-7s and related could do it, the older Subaru engines (EA81) would do it, but they're just a small aircraft engine in a car, design-wise...
Looking over the Viking engines, I don't think it's fair to call those "automotive engines," because my read of the description of what they do means they're pulling it apart and replacing an awful lot of pieces. They claim they're "based on" the latest Honda engines, and once you're starting to change the cylinder bore offset, custom hone the cylinders, replace your pistons and conrods, etc, it's no longer a car engine.
If changing those minor attributes makes an engine "not a car engine" then the majority of race cars also don't have car engines.
On their About page, they themselves say:
> Companies like Honda and Mitsubishi have spent millions of dollars refining and testing. We don’t claim that we can outsmart either company when it comes to the design of any internal running component of these engines. We don't change vital engine parameters around and claim we have different models. The compression, etc. is all stock. Every part is OEM Honda / Mitsubishi, nothing is new aftermarket from unknown origins.
> We start with the most up to date year engines with super low mileage, derived from fender benders across the US. When customers want the information about where there engine core came from and how many miles it had - we have all that documentation readily available to show.
Literally, every one of these engines came out of a car. I think that plainly qualifies it as a car engine.
It really depends on the engine, but almost all the general aviation engines you'll find (Lycoming and Continental 4s, and the smaller 6s) are rated for continuous operation at full power, and if they're flown regularly, will typically make well past the 2000-3000 hour TBO (which is a recommendation/expectation, not a legal requirement, though I believe some of the small diesels can't be operated past it).
Our flying club engines in the 172s typically make at least 3000, if not 3500 hours, and I think some of the overhauls at that point have been a "Well... it's still perfectly fine... but..." thing where the board was just starting to get uncomfortable with the hours on it.
And, yes, they spend a lot of time making less than rated power, because of density altitude, but they're still rated for full power operation, and since there's basically no wear going on with an engine in operation (almost all the wear is during starting), there's no real difference there.
It's not until you get into the really large engines where "maximum continuous" is a different thing from "takeoff power." The turbocharged 500s are about the smallest I know of with that sort of rating, and even then I don't think it's all of them. Most of the big radials have that limit, though. If you find a smaller plane with that sort of limit, it's either a possible resonance issue between the engine and prop, or a noise regulation for certification.
> XTS-210 is about the size of a basketball, weighs in at 19 kg (42 lb), and displaces 210 cc.
So you are talking about a 26HP lawn mower.
While the Camry might make more power at its normal size. It would not if you scaled it down to the size of a basketball. I'm guessing it would make 1-3HP at that size.
A Traxxas 5407 TRX 3.3 engine used in RC cars makes 1.42 horsepower, weighs 305 grams, and fits in the palm of your hand.
This is 1hp per 0.46 pounds of engine weight, nearly three times better than the camry engine.
Granted an RC engine runs on a mixture of fuel and nitromethane, and doesn't have any reasonable durability compare to a Camry engine. But it also only costs $200.
You can't just make the Traxxas 18x bigger and get linear performance improvement. Trying to compare power/weight between engines with radically different weight constraints is silly.
Ok, a Kawasaki H2R engine makes 326 horsepower and weighs about 160 pounds running regular fuel. That's almost identical to the Traxxas - 1hp for 0.49 pounds.
my point is that this ratio exists both much smaller and also somewhat larger. it makes sense this same ratio would be possible in the middle of the two as well. also diesels have super/turbo chargers all the time on production engines, why is that cheating?
In a way, sure. Often when a car engine fails people just replace it. If you were to replace all 18 when the first one failed, the same way you would with a regular car engine, it's not 1/18 the MTBF. And if it was just 1 failing prematurely and you replaced only that one, you also see that same dynamic with car engines when a single component of it fails that's worth fixing.
They tend to seize and when they do and you gang them they'll likely break stuff in the other ones unless you add a freewheel or some other luxury like that.
> Granted an RC engine runs on a mixture of fuel and nitromethane
That's a huge difference. The main limiting factor in engine power is mass air flow, not fuel. Engines are as much air pumps as they are containers for extracting expansion from explosions. Nitromethane provides extra oxidizer in liquid form, putting nitro engines in some ways closer to rocket engines in terms of power-to-weight ratio.
I've read about a lot of people complaining about the difficulty of getting the mixture right, perhaps that might be a show stopper for a UAV that must reliably work unattended for a long time. Though the military should also be able to get such mixtures down to a science - so I don't know.
Every motorcycle mechanic I've seen has a sign in the shop: speed costs money, how fast do you want to go. That sign isn't referring to the costs to modify an engine to go faster so much as the cost to constantly rebuild the engine after they modify it to go fast. I've seen two identical engines, one rebuilt to stock and one rebuilt to max speed - the cost for both rebuild jobs was about the same (the parts for speed were more - but not much more compared to the labor which was the same), but the engine rebuilt to stock ran for thousands more hours, while the one rebuilt for speed has the mechanic bragging that it lasted a whole 80 hours!
My dad used to say the perfect race car would explode into a million pieces just after it crossed the finish line. Anything more robust is wasted weight.
Normal cars are designed from wide temperature ranges (something like -30F to 130F), -100 to 14k feet altitude, with a wide range of sand, dirt, snow, ice, hail and a wide variety of roads surfaces and steepness. Generally they seem designed to last 100k miles under normal use and terrible things don't happen if you forget an oil change.
You can do a chip tune that might get you more HP across a wide range of RPMs, but you won't be as robust, will need maintenance more often, and will likely wear through oil, gas, differentials, clutches, and related more quickly.
There's MANY things you can do that all basically come down to burning more gas+o2 in less time. Higher intake airflow (turbo, supercharger, better/missing air filters, scoops, etc), bored out cylinders for more engine displacement, more gas (increased fuel pressure/pumps), increased RPMs, and decreased exhaust pressure (better pipes, decreased or missing cats).
Trick is, more gas+o2 burned = more heat, more wear, more stress, hotter oil, faster clutch wearing, faster tire wearing, and generally faster brake wearing. Turbos are driven by exhaust, spin at crazy RPMs, increase air intake pressure, and generally are harder on the engine and oil and make cooling more of an issue. Higher RPMs require more precise timing, better valves+springs, better balanced cam shafts, etc. So what might seem like a cheap/easy change like increasing turbo boost from 10psi to 15psi might like a good idea, but have major impact on engine life and maintenance costs. A single blown head gasket from the increased temp, increased vibration, and increased pressure can be very expensive.
Much like CPUs of today, cars are generally designed carefully for their performance level and there's less spare performance left to be easily tweaked. Much like how older CPUs could be overclocked for substantial performance gains. Now both cars and CPUs will throttle if they don't have enough cooling or any of numerous other sensors detect potential problems. It's pretty common these days to see a car with 300hp, but 350hp for up to 10 seconds before the sensors reel you back in.
Simplifying things in this comment a fair amount, but...
Extracting more power is, most commonly, a matter of burning more fuel, which requires more oxygen. This increases combustion chamber pressure, which drives the piston down with more force; that force is converted to rotational torque and ultimately drives the wheels harder, pushing the vehicle forward faster.
More oxygen can be added in any number of ways; less restrictive intake/exhaust parts, larger valves, cams that are more optimized for whatever load/engine speed you want to produce peak power (or are more optimized for output than, say, economy or emissions), supercharger, turbocharger.
Adding fuel is more straightforward: A higher capacity pump and/or bigger injectors/carbs.
You can also switch to pistons that will compress the air/fuel charge more. This also increases combustion chamber pressure.
You can also run the engine at a higher speed, which will often warrant different cams, stronger valve springs, etc. May also require bottom end uprated components that can handle that task (connecting rods, pistons, bearings, crankshaft).
On the subject of bottom end components, depending on how much you increase cylinder pressure, you may need to upgrade those.
You can also increase output power by reducing losses - a lighter flywheel is a common example with enthusiasts.
Every single one of these involves a trade-off. A lighter flywheel impacts drivability; removing intake/exhaust restrictions and adding forced induction components will both make more noise; etc.
Right. Generally more air and more fuel, produces bigger explosions and bigger forces, so the engine would output more power and torque.
These greater forces cause more stress to factory engine components, so generally at a certain level you will need to replace engine internals with uprated parts e.g. stronger rods and pistons.
Their target market is the military - which has plenty of kerosene / jet / diesel fuels as part of its standard supply chain. The Camry engine will only run on gasoline - which the military neither carries, nor wants to.
Toyota makes some great diesel engines (they don't put them to the US bound products in general), which could run on jet fuel with some small modifications.
I know this is off-topic, but I'm curious. I always had the impression that even in the US, standard units are used for engineering. Reading about "ft-lb" makes me think I was wrong (and my head hurt, tbh). Do you really compute stuff like torque in imperial units? Don't you need weird factors in every formula to make that work?
There are lots of weird factors in engineering anyway. We have different factors, but there are still factors. Besides, nobody is calculating this, they are measuring and that is just a matter of what label you put on the dial.
Most engineering in the US is done in metric units. Then marketing applies a metric to imperial conversion.
I suspect China does more engineering in imperial than the US, both in total an per capita: most things I buy made in America are all metric (cars are all metric except for parts designed in the 1960s and the adapter bracket to make them fit on a modern metric car). Most things I buy made in China are imperial. I don't really know for sure, but that is my impression of industry.
Torque to power is just (torque * RPM) / (some constant depending on the units inolved). With ft-lbs and horsepower, that constant is 5252; with N-m and kW, it's 9549. The only thing that changes is the constant.
The engineers who do that are using metric. Marketing might do this conversion, but they just plug it into a converter and have no reason to know anything more than bigger is better.
I think the primary advantage is the size (about the size of a basketball) and the number of moving parts (just 2), and also its ability to use a range of fuels.
Confusion is also possibly due to misuse of the term 'rotary'. A true rotary engine turns on its crankshaft. The Wankel is a rotating-sleeve-valve engine.
both seem to disagree with your technical definition. at the very least, the colloquial usage is broad enough that adhering to some archaic technical definition isn't sufficient to explain some confusion.
Surely, I can't be alone in reading this having driven an RX-7, numerous turbos, but no diesels, thinking this is EXACTLY what I need to replace the 310cc single cylinder in my BMW motorcycle that gets 70 MPG consistently, sits comfortably at 70 MPH on the highway, but is slow on the uptake in a crowded on-ramp. I remember the BMW single being a revelation because it's a single, DOHC, eats corn gas for breakfast without indigestion and has plenty of breathing room at the top end of the tach, which is unusual in single cylinders at redline, 10.5K RPM IIRC. One can only hope since one has less-than-zero mechanical engineering skills.
I don't know anyone who has done the rotary or diesel conversion, though I have driven the zero and know another designer who built an electric motorcycle from scratch. When I say from scratch, I mean sketches, solid works, chassis - the whole 9. Of course, this gets easier at the edges where wheels, handlebars, exhaust, lights, and batteries are abundant.
My daily awareness of his progress was working close to his desk at work, so I'm not sure where it's at today though I recall he was about to transition from chassis to engine at the time - 2016. He was definitely ahead of the curve. Sadly, my skills are in things that we have the luxury of pretending are not bound by the laws of physics. ;->
Sounds like it could be awesome for some GA applications given the lack of weight budget and it seems like they did solve the issues with rotaries. Hopefully someone starts cramming them in some experimentals!
General aviation are perhaps the most cautious and wary ICE users around. Most of the engines used in GA, Lycomings and Continentals, are essentially 1960s designs with very well known cost, performance and reliability characteristics.
That is not to say change is impossible, GA's overdue changeover to unleaded gasoline seems like an inevitability. Unleaded gas is already being approved for many of these engines, like new production O-360 engines (which date back to the 1950s.)
> General aviation are perhaps the most cautious and wary ICE users around.
That depends on if you're describing the pilots or the ~manufacturers~ Textron. The experimental fleet has been pretty adventurous and it's a fast growing fleet. I think most of the conservatism in GA ICE tech has been driven by the broader issue of consolidation into a near monopoly on the cheaper end of the market. If you have no competition then why bother innovating?
It starts with GA pilots being very conservative with what kinds of planes they invest in, since planes are huge money sinks already. The old engines have very well characterized reliability and cost, so pilots know what they're getting into and can accurately plan for all their expenses. New planes/engines are proposed fairly regularly, but generally fail because there are too many unknown factors that buyers are wary of.
Actually mounting an engine inside a wheel increases "unsprung weight" which is bad for handling. But putting such small engines near the wheels (but still on the body so the suspension can do its job) that could indeed improve cargo space. Pushing the engine weight outward toward the wheels would also make the vehicle harder to rotate, which is bad for track cars and go carts, but good for passenger and freight vehicles.
You want the unsprung mass to be as low as possible. As in you want the wheels to be much lighter than the rest of the car for a smooth ride. The wheels should bounce around but the rest shouldn't. Newtons law and all.
Putting engines in wheels causes a very rough ride. Even if the engine is light you're still likely creating an order of magnitude more unsprung mass. That's an order of magnitude rougher ride.
Mazda is doing something that I think is fairly novel, which is almost exactly what you've described. They've scaled down the rotary engine from their RX cars to a single-rotor and put it into their new EV (almost tucked into the front wheel well,) and letting it act as a 70ish horsepower generator for the otherwise battery-powered car to extend range.
Mazda really seems like the only company innovating in the ICE space (this, wankel rotary engines, skyactive engines) and their cars look damn good these days too.
On top of that, they make fun cars. With buttons and knobs on the dash!
Agreed, but there's also Koenigsegg, which has managed to eliminate the need for cams, and complete heads from ICEs, replacing them with their 'freevalve' tech (which basically replaces the timing chain with computers so that instead of having one or two modes that a camshaft can opt into, you can precisely dial in bespoke timings for every RPM, or every RPM and speed, or ever RPM / speed / gear combination. They've also practically reinvented the transmission to invent a new transmission that eliminates moving gearsets and gives you a dual-clutchish transmission with a 6 speed manual AND a 9 speed automatic in the same device.
IIRC, the Freevalve tech is like a 30% efficiency hack for any ICE you put it on, and it's a part of how Koenigsegg are managing to squeeze 600 brake horsepower out of just a 2L, 3-cylinder engine.
Wesley Kagan reimplemented their freevalve technology on his Mazda Miata, and it's probably the coolest hobby automotive project I've seen in years. https://www.youtube.com/watch?v=E9KJ_f7REGw
Absolutely love Koenigsegg, and their new engines are probably the current state of the art in (small scale) production ICE engines.
I just feel like Mazda doesn’t get enough credit for the innovation they manage to accomplish at a truly mass produced scale. It's almost like they're too "normal" to get the attention they deserve.
You're right. They might need to bring back MazdaSpeed to get the [gear|petrol]heads back on board, who seem to have either stayed put with Honda/Toyota/Subaru fandom, or to Hyundai for those who haven't. Or just put out another RX.
The tragedy of Mazda is that they already make one of the best cars in the world, but machismo / public opinion prevents too many men from enjoying the full glory of the Miata. But on the other hand, Mazda's refusal to move it beyond 'momentum car' holds it back. If they added ~30-40 horsepower to it, it could legitimately be stealing sales from cars thrice its price.
Agreed. I feel the same way about every programming language beyond assembly. I mean, what's the point of trying something new and different if it isn't immediately better than the competition in every possible metric?
I always wondered why "electric with an onboard generator" didn't take off as a subset of available vehicles. AFAIK, hybrids all work with complex gear boxes to allow the engine to directly power the wheels, while also charging the batteries.
I suspect the answer is because it's more efficient from a MPG perspective to allow the engine to directly power the wheels, at the cost of the extra complexity of gearing. Converting motion to electricity back to motion is lossy, and even more so if you insert battery storage as an additional step.
This was done by BMW for the i3 with REX (range extender) equipped models. To be classified as an EV the gas tank range can’t be greater than battery range. This led to a 2ish gallon tank.
Surely the engineers who came up with this are a lot smarter than myself, but to me it looks like the lower half of the rotor rotates into the combustion and thus has to work _against_ its force. If this is true, I'd assume that this takes away a lot of effectiveness.
It actually happens less on this engine than piston engines because the lobe on the rotor kind of rotates over the combustion chamber for a while instead of moving towards or away from it.
On the other hand, it exposes a lot of surface area to heat, which gets absorbed by the rotor but isn't used to turn the engine. It's a problem it shares with wankel engines. The advantage over wankels is the extra time air and fuel spends burning in the combustion chamber before the chamber volume expands. It means it gets more time to combust evenly which should help reduce both hydrocarbon and nitrogen oxide emissions.
I know this goes towards steam-engine design, but why can't that heat be re-captured as steam? When the engine heat gets above a threshold, inject [distilled?] water instead of fuel.
I'm not sure what you mean -- are you referring to at the end of the combustion cycle during the exhaust phase? If so, then because the exhaust channel is open, the gases in the combustion chamber won't be exerting appreciable force on the shaft/rotor, the gasses will simply escape through the exhaust channel. At least, that's how I see it.
This motor is doomed... dirty exhaust gases exiting through part of the rotor? Only a matter of time before carbon+sludge builds up and the thing is out of balance.
This is one of those designs that works fine initially when everything is fresh.
Diesel piston engines work fine when everything is worn out and full of goo.
The exhaust gas recirculation valve on a modern diesel engine does exactly this. It diverts a portion of the exhaust product back into the intake manifold of the engine to achieve more complete combustion and lower emissions.
Yes, it does result in a buildup of goo in the intake. No, the engine does not run well in that state. That’s what maintenance is for. Clean out the goo every 50,000km or so and it’s fine.
Modern diesels are very reliable machines, just like modern petrol engines. They’re certainly not the robust rocks they used to be, though. High pressure common rail fuel systems, precision injectors and multi stage turbos are standard issue these days and they all require regular maintenance, clean air and clean fuel to operate properly.
> The exhaust gas recirculation valve on a modern diesel engine does exactly this
Anyone who thinks the EGR valve should be made part of the rotating assembly requiring a complete overhaul to clean out, unbalancing the assembly until that occurs, needs their head examined.
I guess the "inside out" is that the rotary block is also the fuel injector? Would have to read more to figure out how they get fuel into a thing moving at thousands of rpm.
A traditional Wankel engine has a rotary block in the shape of a reuleaux triangle moving in a more cylindrical stationary chamber. The "inside out" refers to how this engine is a more cylindrical rotary block moving inside a stationary reuleaux triangle chamber.
They were, I think, imagining placing the fuel injector on the moving part itself (eg the piston) which doesn't makes much sense to do, taking the inside out bit to the extreme.
looks neat and I am in no way any kind of expert; I wonder why there is an external counterweight? It seems to me that the rotating 'piston' has hollow chambers in one side only to allow passage of gases and therefore needs a counterweight to balance it; is there a reason they cannot have some hollows in the other side but not have them connected to the burn chamber so that the piston is balanced by design, and the external weight not required?
My understanding is that everyone acknowledges that rotary engines are great, bt in comparison to piston based engines they have far shorter longevity.
My '88 RX-7's engine went 120k miles before I decided to rebuild it and it still probably had a good 30k miles before it would have 'gone'.
This is completely normal through the 70s and 80s when these engines were popular. We didn't start getting million-miler cars until the Lexus LS400 came out.
The problem with the rotary is heat and the damage it does to other components. The RX-8's engine design was actually bad and doesn't adequately lubricate, but that gets 'fixed' in the last three model years.
The biggest reason that RX-7 owners have seal failures are often due to adding on too much power without adequately upgrading the fuel system. Keep in mind that Wankel engines are absurdly popular in the world of amateur aviation without any of the stigma.
They also have issues meeting emissions targets - both because of the basic design (there isn't the ability to actively control valve timing events), and also because they typically need some sort of lubrication for the combustion chamber. They are similar to two-stroke engines in these respects.
Running them at a pre-determined RPM constantly can resolve lack of VVT, but that limits their applications. New materials for apex seals being researched could alleviate their longevity issues too. But, I have a big soft spot for rotaries and would love to see them applied more :(
I think it's difficult to make a direct comparison because of the way the capacity of the engines is calculated. I know it's "fair" from one point of view, but it's not from another (depending on which team you support).
The only straight-ish comparison I can think of is the Suzuki RE5 vs the GT500, which are same-era motorbikes from the same manufacturer, with roughly the same capacity. The RE5 wins on horsepower (62 vs 44), but weighs about 50kg more.
My near-mint condition 2009 Mazda RX-8 never had a Wankel engine problem (over 100k miles). It would have easily lasted another 5 years without a doubt or hiccup.
Wankels are usually excluded from all engine comparisons, because it's a considered a different class...for piston engine marketing reasons.
I sold off my RX8 in 2018 because my fiancee and I moved to Seattle (passing emissions testing wasn't anything special). We needed the money and we had her car, which was more functional. I do miss it.
More antic-data: i worked with a guy whose brand new RX-8 needed two engines in the time we worked together. Granted, his was a 04 automatic, which is the worst combo. But still, Mazda didn't go out of their way to extend the engine warranties on the early RX-8s for no reason.
Did you happen to have an 08+ model with the updated engine and/or remove teh catalytic converter?
My RX-8 needed a new engine at 50k miles. As you likely know, if you start and stop an RX-8 engine without allowing it to warmup you risk flooding the engine.
In my case, I was taking a trip with my family and my RX-8 was blocking the driveway. We were running late for the flight, so I pulled it out, parked it back in the driveway, and let it idle there for 30 seconds knowing I'm not supposed to shut it down so quickly. But I had people waiting for me and what am I supposed to do, say "Sorry I own a strange car and I need to drive around the block for a bit to let it warm up!".
Of course that flooded the engine, but I didn't know until I got back from the trip. I followed all the instructions to de-flood the engine but it wasn't working for me so I had it towed to Mazda where they probably screwed it up further. It was there 2 weeks before they told me the engine needed to be replaced. They eventually had to fly an engineer from Japan to replace the engine since the dealer apparently had no one capable of dealing with rotaries. I think my car was at the dealer for a good 2 months. Thankfully all covered by warranty.
Long since mattering, but you could move them like this if you started it, rev'd it beyond 4k RPM, and then shut the motor off prior to it dropping below 4k. Basically, the idea was the rotors would force the fuel / oil mixture out of the crankcase and keep the spark plugs from fouling.
I loved my RX-8, but it was a pain in the rear. Switched to a WRX and got 50% better gas mileage, more power, more torque, and way more room. This of course bypassed the need to check / refill the oil every other fill up (aka, every 300-ish miles) all while trying desperately not to burn your hand.
I also experienced this flooding issue. Running it to a high rpm before shutoff to avoid the flooding, was a convenient workaround.
Why flooding the car (or frankly doing anything to my RX-8's engine) would require it to be replaced seems ridiculous. The casing of the engine is a solid piece of steel. Removing the ring gears and shaft (which you have to do for cleaning every 100k mi anyway), there's nothing to break.
Ofc, if you introduce the engine to some exotic combustion or get some foreign material in there, you could scar any part of the casing and that would brick the engine.
They're not great, at all. They have very few moving parts and they are very smooth because there are no reciprocating parts.
Other than that, they have emissions like 2-stroke engines because of the incomplete combustion and we have never been able to devise any kind of material to make the apex and side seals last anything like as long as piston rings.
Piston engines are a terrible way to power vehicles, but everything else we've tried is worse.
Large turbines running at close to rated power actually have pretty good efficiency. Turbines are bad at scaling down to smaller sizes due to e.g. boundary layer friction, and also part load efficiency is poor. Recuperators help somewhat, though still not nearly as good as a piston engine.
Mazda addressed both of those issues, Rotax addressed both of those issues, Norton addressed both of those issues, NSU addressed both of those issues, Comotor addressed both of those issues...
The issues remain fundamental, and largely unaddressed.
I understand this too, however, the technology might be worth revisiting with modern techniques, I understand the power output is 'smoother', which can reduce vibration, some applications might need that?
The problem with rotary engine is that its max power efficiency is at a very narrow rpm range and loses power at most other rpm ranges. This is due to the constant air intake inherent in the design. Piston engine has variable valve air intake to ensure optimal air oil mixture compression to deliver max power efficiency at a long range of rpm’s. That’s why rotary design is not popular for cars.
Mazda is reviving small single cylinder rotary engine design for HEV by running it at a constant speed with max power efficiency to charge the battery.
Some years past, a friend who worked for Mazda explained to me that the engines need to be driven for a bit because until they're warmed up fully there can be a lot of carbon buildup and it needs to be run some amount of time to get the carbon through. Once they're warmed up and running for a bit they're fine. Supposedly it's the short trips of only a few miles that can kill them over time.
Yeah I talked to some race mechanics that said the mazda rotary engines had much better longevity if you really drove the piss out of them. They liked to rev high and hard, which would be basically consistent with that notion.
If we lived in a world of rotaries and BMW came out with the S85 we'd say that piston engines were emotive and fun but too unreliable for mainstream use. When we refer to rotary engines we mostly talk about two generations of one engine from one manufacturer used in sports cars that were designed before emissions targets changed.
That's what they claim, but since this engine isn't in general use yet it's impossible to verify. In the past "supercharged" and "Wankel" have been a combo prone to maintenance issues.
It comes out of the woodwork with a $9 million grant from the US Army, that is true. On the other hand, the article states "LiquidPiston has been working on these X-engines for nearly 20 years now, with numerous prototypes already tested in small planes (see above) and go-karts."
came across this company a few weeks ago. the engine design is neat (who doesn’t have a soft spot for the wankel). while the design is neat, the scammy investors page turned me right off.
Two-strokes are extremely dirty, due to blow-through of the fuel-oil mixture, incomplete/less efficient combustion due to crude fuel metering, and inability to use conventional catalytic converters (due to fouling from the above two points). But they do afford roughly double the power-per-RPM of four-stroke engines, and a further power-to-weight multiplier due to their simpler design.
AFAIK there's nothing mechanically stopping you from scaling a 2-stroke, but it would very quickly render the immediate area noxious.
But they are simple, lightweight, and easy to shrink.
This is actually a really important point as we are trying to clamp down on VOC/NOx emissions. Ignoring CO2, two-strokes emit way more emissions than cars per unit work. But a 4-stroke engine, in addition to expense, does not lend itself to tools like chainsaws. In theory this engine could fill that niche.
The rotary in the article is a 2 stroke design, by my understanding.
Fuel injected 2 strokes have been around for years now. In saws, the Stihl 500i.
Scaled 2 stroke engines, both with and without fuel injection, have also been around some time. The KTM 300 XC is a very modern example with 300cc displacement, so the same general category as the one in the article. Modern outboards on boats go even bigger.
Yes there’s a push on at the moment to retire the fleet of small 2 stroke engines in older garden power tools. Emissions controls have been tightening up on new tools over the years. Electric tools are rapidly displacing them with lower maintenance requirements and less noise.
There’s a lot more to 2 stroke engine development than just saws and lawnmowers from the 80s, though.
Not sure a rotary engine screaming at 6500RPM is comparable here to a diesel with a peak torque at 2000 and peak power at 3600.
> LiquidPiston has been working on these X-engines for nearly 20 years now,
I'm guessing they will never actually release a commercially viable product. 20 years to design an ICE is...too much.