XTS-210 25hp rotary engine; 1/5th size/weight of diesel piston engines | Hacker News Reader

weight of diesel piston engines

greencarcongress.com

54 pointsmpweiher51 comments

This is a pretty cool engine. 25hp is about 18.75 kW so a really good fit for a 15kW generator (sometimes marketed as "whole house" generators) its high RPM (typical of rotary engines) makes it a good match foundation for a turboprop engine. A pair of these driving ducted fan turboprop engines would give you an excellent long duration drone platform with good payload capacity.

My guess is the Army might be considering them as APUs (Auxiliary power units) on armored vehicles as this would give them long duration "sitting" capability without running the main power plant (but using the same fuel). Similarly bus style RVs could use them to run their in-vehicle electric gear (not a lot of bus RVs are designed for the "dry camping" or boon docking market but it would definitely work well for that.

The next thing they have to figure out I'm guessing is how to make them inexpensively (the Army won't care so much but I don't think the company would survive on just Army contracts).

This would definitely be interesting in an RV, it's way more compact than engines in similarly powerful generators in a vehicle where space is at a premium - and the ability to run off the same diesel fuel as the main engine is a huge plus.

Nit: it's not a turboprop if it's no longer using a turbine.

There is a turbine in the supercharger… does that count?

It's also not a turboprop if it's using a ducted fan. Chuck keeps using that word, I do not think it means what he thinks it means.

Benefit of doubt; they're likely using it as shorthand for 'equivalent to turboprop style/class engine' as an established feature set to have a drop in alternative to.

lol, love this. Yeah, high bypass turbofan was what I was thinking about, and yes those are "jet" engines. Model airplanes use something called an electric ducted fan or EDF[1], and it has the nice properties in that you can run it over a wide range of speeds if desired. The recent Black Sea MQ-9 incident would, in my opinion, turned out differently if that drone used a shrouded engines for propulsion.

[1] https://www.rc-airplane-world.com/rc-jets.html

I updated the trailer to LiFEPO4 this year, Solar is next year. It's REALLY easy to undersell just how many calories are in a gallon of gas. The 5500 watt generator can top off the batteries in 90-120 minutes and the tank is 60 gallons.

This is perhaps not totally relevant, but one fun comparison I like is that a human's total energy expenditure for a year is about equivalent to the chemical energy in a single barrel of oil.

Previously

[Efficient Rotary Engine Lands Million-Dollar Darpa Contract](https://news.ycombinator.com/item?id=9431379) 76 points, 44 comments, 8 years ago

[LiquidPiston: Efficient rotary engine](https://news.ycombinator.com/item?id=11995735) 87 points, 20 comments, 7 years ago

[LiquidPiston's “inside-out” rotary X-Engine wins Army research contract](https://news.ycombinator.com/item?id=25450477) 278 points, 130 comments, 2 years ago

[“Inside-out Wankel” rotary engine delivers 5X the power of a diesel](https://news.ycombinator.com/item?id=35455286) 255 points, 196 comments, 24 days ago

My twitter ads have been flooded by this company liquid piston, it looks cool, but if the use case is to replace small engines also, I need to see a drop in crate replacement for a honda or cheap chinese motor for a generator/atv/scooter.

I love tote-goats, they use the old 5hp engines, if I could get a diesel version that I could use (for farm use and cheap diesel), count me in if it works.

Do the ads want you to buy engines, or invest in the company? Last time[0] I saw this on HN, it appeared very targeted toward military UAV applications rather than anything most consumers would have a use for.

[0] https://news.ycombinator.com/item?id=35455286

Just got one NOW, yes invest. They are still paying to promote their product.

630.7K views, https://twitter.com/LiquidPiston/status/1625932968865693718

"The first major innovation to the internal combustion engine in over 100 years" claimed there suggests they're not familiar with the Wankel rotary engine upon which their design is based; the modern eccentric shaft version first ran in 1958.

It's not just another wankel engine tho, it's significant modification to the idea and comes with few interesting improvements (and some other drawbacks).

Basically, the intake and exhaust is delivered thru the rotor, not ports on the sides, and the seals (the achilles heel of the wankel engines are on the outside of it which in theory would make it possible to both replace them without taking apart whole engine, and oil them directly, without putting oil into fuel.

The bad part of it is that it would probably be pretty hard to make multi-rotor one

I know it's a different and likely improved design, but the claim is "the first major innovation to the internal combustion engine in over 100 years". It would be odd if they didn't consider the Wankel itself a major innovation. The Wankel engine is 65 years old.

Surprising that there's still that much efficiency to be squeezed out of internal combustion engines!

They are squeezing small size out, not efficiency. You can get more power from a small engine, but you trade long term reliability when you do.

Yes. Makes you wonder how real this is. And how long it lasts.

The military might want it for drones. Even if it's only good for an hour, that's a good survival time in modern combat.

They mention "the XTS-210 engine addresses the fuel efficiency, lubrication, and fuel type limitations of the traditional Wankel rotary engine", but while they quote great fuel compatibility, don't waste more words on efficiency and lubrication. So just based on the marketing fluff I expect those two points to still be worse than traditional diesel engines, just good enough for military applications. And given the other advantages the military might be completely ok with a fuel-guzzling hard-to-maintain engine for certain applications, wouldn't be the first time

Dollars to donuts the rotary will be easier to manufacture and maintain than the diesel. It's got fewer parts and the parts themselves are way simpler. Lubrication's easy if you don't care about efficiency or emissions, which the military doesn't.

The military does care about efficiency: higher efficiency means longer range, as we seem to be talking about aircraft / rotocraft applications.

Higher wear is what they care less about: at peacetime, parts can be replaced more often, and at wartime, many will be destroyed before spending up the spec-dictated operation hours.

Right - they care about range, fuel efficiency is secondary at best. WRT this engine, it's too small for anything but a small-mid sized drone. In that context the specific fuel consumption is likely less of an issue as there's some pretty hefty weight and size savings over the comparable piston engine (and they're claiming better fuel efficiency).

The issue with the parts isn't higher wear, it's simplicity. Look at the strain that Ukraine has put on military supply chains. Now take a look at what's involved in building a diesel engine versus a rotary. The rotary engine is a few relatively simple castings*, a piston engine has a ton of small, complex parts. There's no mention if they comparable diesels are two or four stroke, but take a look at a four stroke injection pump and how complex they are (inline pumps are basically mini piston engines). Then take a look at the LiquidPiston motor – at least on one variant they're using the crankshaft for fuel and air delivery. Pretty much everything about it is simpler than a comparable piston engine, and when you've gotta scale up wartime production simpler is better.

* okay so it looks like LiquidPiston is milling everything for the time being.

This is right; the simpler, the cheaper and faster to make, and often the harder to break. Very important in the military.

Delivering fuel and lubrication via the crankshaft is not uncommon in aircraft motors, or was at times of WWII at least. Delivering air this way is indeed novel and impressive.

https://www.liquidpiston.com/how-its-made

If I'm not mistaken there are no apex seals in there – so there's one major weakness eliminated. Regardless of military applications there is some real interesting engineering there.

Since this engine is so much lighter and smaller, you can just have a larger capacity fuel tank and drastically increase the range

Adding in the 2 stroke design and wide ranging fuel compatibility to the above military centric specs, I have to imagine the emissions profile is truly stunning.

I think it probably is real, Mazda has a new single rotor engine they've got in the new MX30 hybrid, it's used to extend the range https://www.drive.com.au/news/2023-mazda-mx-30-r-ev-revealed...

Also discussed 24 days ago:

"Inside-out Wankel" rotary engine delivers 5X the power of a diesel

https://news.ycombinator.com/item?id=35455286 (203 comments)

This is more hype than performance.

When I worked on a hybrid-power multirotor drone about eight years ago, I was checking out Wankel engines for their power-weight ratio, and also came across this Liquid Piston crew. They were supposedly ready to ship Real Soon Now. But worse, their power-weight just didn't compare to Wankel options available then.

Liquid Piston still do not compare on their headline power-weight ratios. They make a lot of claims about 25 HP (18.6kW) and light weight, but don't actually mention the weight, which is down in their spec sheet - 21.2kg dry [0], which is about 0.877kW/kg.

By comparison, just a quick search of small Wankels turns up these:

-- AIE model 225CS outputting 40 bhp / 30kW weighing 10kg = 3.0 kW/kg[1]

-- AIE model 80S outputting 15 bhp / 11.2kW weighing 5kg = 2.24 kW/kg [2]

-- Sorrel Hiperlight Wankel outputting 75 hp / 56 kW weighing 52kg (fully wet with all electric start, reduction drive, and exhaust system, etc. = 1.07 kW/kg [3]

-- Crighton CR700W motorcycle engine puts out 220 hp / 164 kW weighing 43kg = 3.8 kW/kg. [4]

-- Small Nitto NR20-EP puts out 2.24kW / ~3hp weighing 1.466 kg = 1.53 kW/kg. [5]

In short, this is a lot of marketing hype for low pefrofrmance, and they've been working on it since 2003 according to their website.

The sole advantage this engine might have is running on a broader range of fuels including JP-8, but I've seen Wankels setup for a wide fuel range also. If I had a funded task to develop a high power-weight engine, I'd start with the Wankel design, not this one. It is already WAAAY ahead, and there's still a lot of performance left on the table.

[0] https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/642...

[1] https://www.aieuk.com/225cs-40bhp-wankel-rotary-engine/

[2] https://www.aieuk.com/80s-15bhp-wankel-rotary-engine/

[3] http://www.ultralightnews.com/sunfun99/hiperlight.html

[4] https://newatlas.com/motorcycles/dual-rotary-crighton-cr700w...

[5] https://barnardmicrosystems.com/UAV/engines/wankel.html

How much does that metric matter? Especially in the context of hybrids with regenerative braking.

For comparison a Model S weighs over 4,500 lbs.

Power/Weight ratio matters for pretty much everything more than one initially thinks.

People usually think first of adding power as adding performance. But power affects only one parameter - acceleration. In contrast, reducing weight similarly improves acceleration, but also improves turning, and braking performance, and reduces the loads and wear on every other component (the opposite of adding power). And that is just in automotive performance.

As soon as you go to anything that flies, the same effects are just multiplied. Every gram of weight saved is either a 1:1 increase in available payload, or an increase in range and/or fuel that can extend range, and of course still improved performance across the entire envelope.

And the only reason that e-Vehicles get away with such absurd weights is that all that weight can be put low and centered in the suspension so the fundamentals of chassis dynamics is acceptable. They still massively abuse the tires, but with a higher weight distribution would be absolute pigs if no virtually un-driveable.

Of course, any vehicle choosing between a Wankel and this LP thing is not likely an overweight battery-heavy vehicle, so it'll count more. Obviously a 1% saving of 45 pounds on a 4500Lb EV is not going to do a lot, but ... yeah, it's still a key issue.

And this is especially an issue because LP is making it the central claim of their pitch, and it is so easily beaten by much older technology. Makes it seem more like a basis for fleecing investors than a serious entry to improve the state of the art.

I wish they had video of the two-stroke design in operation. There's a bunch of their 4-stroke engines being demonstrated by this youtube channel: https://www.youtube.com/watch?v=TDFAjCOM3iQ This one is interesting as it shows difference between their 4-stroke design and a standard wankel rotary in operation, wondering if the two-stoke variation looks like a combination between the two?

It's rotary. There are no strokes in it.

The manufacturer calls it a two-stroke. Due to the ubiquity of piston engines most people use "two-cycle" and "two-stroke" interchangeably.

It's a comparision to the two stroke cycle. There is no four stroke equivalent for rotaries

Haven't rotary (Wankel?) engines proven to be unreliable?

I love the RX-7 (my dream is to own a FD one day), but IIRC even the more refined Renesis engine on the RX-8 seems to have been proven to be ornery.

I think Mazda has a rotary acting as a range extender in their MX-30 EV. I wonder how that will fare.

Kinda, kinda not, they have been proven to be vulnerable to mishandling. They have few quirks and require a bit different handling than normal engine, which means that someone treating it as any other car. But at some point it will need to have engine out job and replace apex seals.

In motorsports it proven to be very reliable for example.

> IIRC even the more refined Renesis engine on the RX-8 seems to have been proven to be ornery.

Renesis was evolution in performance but IIRC had some quirks that weren't solved because the car stopped being produced. IIRC the modern apex seals with modern materials do a pretty good job. It also have oil metering pump which just...stole the engine oil and put it into fuel (which was required to oil the seals), which means if you were not on top of filling oil up, you could end up starving the engine. It wasn't a good idea either as 2 stroke oil was better for that use case, so many people removed the metering pump and just added some 2 stroke to the fuel tank every time they filled up

The oil metering pump was a simple mechanical device on Mazda Wankel engines up to ~1991 (the first and second generation rx-7, and I presume other models in Japan.) This was replaced by an electronically controlled pump on all the later models. The advantage of electronic control is that it conserves oil at low RPM. Unfortunately, the reliability of the pump (and the wiring) became a problem. With the RX-8, they had to dial back the oil supply to meet modern emissions regulations and this lead to premature wear to a lot of engines. I believe this contributed heavily to dwindling sales and ultimately to the decision to discontinue the RX-8 in 2012.

Yeah, I wonder how they deal with it in the liquid piston engine, emission control gotta be harder with no valves that can be controlled.

What killed the rx-8 is emissions. Wankel engines are very similar to 2-cycle piston engines. Both 2-cycle and Wankel burn oil in order to lubricate their seals. Very difficult to do that and also meet current emissions standards.

The second generation NA 13b engine was probably the most reliable / longest lasting wankel. Easily could go 200k miles without a rebuild. The Rx-8 rarely makes it past 150k due to insufficient lubrication which was required to meet ~2010 emissions standards.

Source: Experience. I've owned five rx-7s and two rx-8s, maintained them myself for the past 23 years.

"Source: Experience. I've owned five rx-7s and two rx-8s, maintained them myself for the past 23 years."

Would you describe the past 23 years as self torture or did you actually enjoy the process?

The only rotary I'd want is some ridiculous 4 router putting down enough horsepower to make me wet myself, and even then I'd probably sell it before I'd need to do maintenance on it.

My 2nd gen RX-7s were a joy to own and not at all difficult to maintain. They lack all creature comforts and practicality, they are loud, not fuel efficient but a lot of fun to drive. The RX-8 is much more refined and actually quite practical except for the even worse fuel efficiency - 16-18mpg just doesn't make sense when my Hyundai gets 45-52mpg.

Wankels . . are a sort of Lovecraftian fever dream that seems to set in upon the brow of mech eng greybeards every now and again. There you are, comfortable mid-career at LockBoNorthRay, but then you have to go open some weird geometry called NECROWANKELCOM from a Forbidden part of the vault and before you know it you're ranting about how four cycle engines are a Jewish plot.

Ok, hyperbole, a bit. But for reals, check out the man himself. It's pretty wild.

From an engineering perspective, there's some hard limits. Heat is going to always be a problem for Wankels due to the low thermal mass of the thing, and, of course, the fact that there's always a power cycle. The actual rotational efficiency is pretty bad, combustion impulse goes towards the center of rotation, some of it goes backwards. Compression is inherently limited from the necessities of spinning a triangle in an circle. It's nearly impossible to lube the thing effectively; early on they tried to intermix oil and fuel only to create a high-revving Soviet-era ecological disaster because Wankels tend to spit fuel before it's done combusting.

I love, love, love cutting Gordian Knots like this, which makes me want to love the Wankel, but at the same time, sometimes Gordian Knots are tied for a reason. High flow, high RPM, low weight, yes all super awesome, but . . honestly, that's called a turboshaft.

I dig this Wankel Rebooty from the Liquid guys, but they also seem to have killed the one solid advantage of the rotary design: its low weight. The thing's a brick. Also, that wobble it has when the rotor engages, do you see the back and forth? That's some weird oscillating vibration there, and I couldn't help noticing what looks like some wicked counterweights. Of course that could be some other doodad I'm ignorant of.

They were easy to modify for more power, but you trade reliability when you do that. People who ran them stock and followed the maintenance plan generally found them reliable.

So the big question is: what’s the fuel efficiency of this thing?

For things that fly, what I’ve seen be more significant is the weight savings (as long as you’re not running too rich).

This would be great for making a light sporting cyclecar around, a category of vehicle that's been sadly neglected this last 100 years.

The problem of (very) light cars is that they can't be strong enough to pass crash tests. 100 years ago regulations around that barely if at all existed.

That would make cool small dual-sport/dirtbike, super-light and "put anything flammable in the tank".

Why did it take them nearly 30 million in grants and 20 years to just now speak about delivering a prototype next year.

Engines can be prototyped on the time scale of months not decades.

Now they are soliciting the public to "invest" in their business.

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