Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

LiquidPiston – The combustion engine reimagined

invest.liquidpiston.com

Post reply on HN
Print view View original

41–50 of 50 posts

Re: LiquidPiston – The combustion engine reimagined

#41

Post by stefncb »

2-718-281-828 wrote: post #32
stefncb wrote: post #3

Earlier quoted context omitted.

It's effectively an inside-out wankel, so the seals are stationary. This is a much easier problem to solve, and now you don't need to throw oil in the combustion chamber to lubricate the moving seals.

problem one will be balancing forces if combustion is taking place on one side. also i don't see why this should be burning less oil. you are smearing the oil constantly around.

This isn't all that different from a four stroke, at some level. With a piston engine you lubricate from below, the oil never getting above the rings. Practically some does and gets burned away, but that's negligible usually. Anyway, the seals on the liquidpiston engine supposedly do the same, keeping the oil from leaking around the seals (in a significant quantity anyway; I'm sure it's higher than a four stroke though).

Here's what their webpage says:

> The seals do not experience centrifugal forces, and can be lubricated directly by metering small amounts of oil directly to the sealing surface through the housings, which means that oil consumption can be reduced to levels potentially comparable to that of a 4-stroke piston engine (essentially negligible).

Obviously take all this with a grain of salt. I haven't read any practical studies on this.

Re: LiquidPiston – The combustion engine reimagined

#42

Post by ilyt »

zokier wrote: post #25

Apparently they have 210cc 25hp engine available.. is there any reason someone (or they themselves) couldn't throw that into a bike to see how it performs in real-world? There are plenty of 250-300cc bikes around with comparable power ratings, so you'd think it'd be feasible project and a bike sounds much simpler than car/aircraft/etc

Well, if you want Wankel in your bike...

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

Re: LiquidPiston – The combustion engine reimagined

#43

Post by taylodl »

dreamcompiler wrote: post #26
taylodl wrote: post #21

Earlier quoted context omitted.

You're both right. Tesla doesn't make battery cells , they make battery packs. A battery pack is comprised of several battery cells, for example the Model Y has over 4,000 cells in its battery pack.

They certainly appear to be making cells now too. https://cleantechnica.com/2020/09/22/everything-you-need-to-... https://electrek.co/2023/04/21/tesla-update-4680-battery-cel...

Wow! That's huge! They're doing a good job of positioning themselves as being the world's best source of batteries.

Honestly, Tesla Energy is looking to eclipse Tesla as the main source of recurring revenue.

Re: LiquidPiston – The combustion engine reimagined

#44

Post by linuxftw »

ilyt wrote: post #38
linuxftw wrote: post #23

On the one hand, it seems like they have an addressable market. On the other hand, it seems like a scam because they're trying to attract investors with a fancy web page and thin statements about where they're actually selling. The comparison to a 25HP Kholer on the main page is... something. Here's the 'brochure': https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/642... Less than half the torque at more than…

> Less than half the torque at more than double the RPMs. I mean if you double RPM you halve the torque at same power, dunno what's weird here ? It's smaller CC faster rotating engine. > And very low compression, I don't see how this can run diesel. I'm also on "show us the working engine" side but supercharger will also add some heat and pressure to the system it might work?

They're comparing a small engine to a 25HP diesel engine. A 25HP diesel is what powers my tractor, they're really not in the same class as a small 25HP gasoline engine that powers my lawnmower.

If we're comparing the usefulness of an engine, torque is a big part of the equation.

If they can get a small diesel engine for light load applications like generators or small aircraft, that might be a win so the military doesn't have to bring a different type of fuel (gas) or a heavier diesel engine.

But I'm not sure 8:1 compression ratio is enough to operate the diesel cycle.

Re: LiquidPiston – The combustion engine reimagined

#45

Post by basch »

ngvrnd wrote: post #24
Cthulhu_ wrote: post #9

Earlier quoted context omitted.

I think any engine design that was popularized was backed by a car company, even the Wankel engine. If they want to make this design popular, they need to design products around it so their claims are proven. I mean I still don't believe Tesla's primary business model is cars; the competition is outselling them left right and center. Theirs is batteries and charging infrastructure. That's a huge market that can fuel…

I have this feeling that all of Musk's comnpanies are technology development ventures intended to support his primary goal of getting humans to live off-earth. Note: I am not defending his goal, or idolizing him. But consider: boring company: finance learning about tunnel construction; tunnels needed on moon or mars for habitation; solar cells: very useful on moon or mars; hyperloop: finance learning about vacuum sea…

You would need a lot of the same tech to terraform Earth, or make Earth habitable, if it became unso.

Re: LiquidPiston – The combustion engine reimagined

#46

Post by ilyt »

linuxftw wrote: post #44
ilyt wrote: post #38

Earlier quoted context omitted.

> Less than half the torque at more than double the RPMs. I mean if you double RPM you halve the torque at same power, dunno what's weird here ? It's smaller CC faster rotating engine. > And very low compression, I don't see how this can run diesel. I'm also on "show us the working engine" side but supercharger will also add some heat and pressure to the system it might work?

They're comparing a small engine to a 25HP diesel engine. A 25HP diesel is what powers my tractor, they're really not in the same class as a small 25HP gasoline engine that powers my lawnmower. If we're comparing the usefulness of an engine, torque is a big part of the equation. If they can get a small diesel engine for light load applications like generators or small aircraft, that might be a win so the military doe…

>They're comparing a small engine to a 25HP diesel engine. A 25HP diesel is what powers my tractor, they're really not in the same class as a small 25HP gasoline engine that powers my lawnmower.

Their comparison was essentially for mostly-constant RPM usage (generators,UAVs), rather than something more dynamic. Which means they can just peg the engine at most efficient point, just like Mazda's range extender wankel. So yeah, not for tractor-like usages.

> If we're comparing the usefulness of an engine, torque is a big part of the equation.

No, torque on its own is not, else you could compensate with gearing. Power (and in relation, torque) curve is the important one.

The "tractor" like uses want "constant power" across the range, which essentially means flat-ish power curve across whole range[1], and that means torque is dropping fast with RPM. This "theoretical" one liquid piston one is probably classical high-revver curve which is near-constant torque across most of the range and very small range of peak power.

Just the torque number tells very little about that, you need a graph.

* [1] https://www.darksidedevelopments.co.uk/Blog/reading-a-dyno-g...

Re: LiquidPiston – The combustion engine reimagined

#47

Post by ktm5j »

toss1 wrote: post #34
xnx wrote: post #8

Posts on Hacker News related to LiquidPiston go back 11(!) years. The most comments are on this post: https://news.ycombinator.com/item?id=25450477 If this was going to revolutionize anything, it would've happened by now.

Yup Seven-ish years ago while working on a hybrid-powered UAV I was checking out high power/weight engine platforms. I found a significant variety of regular Wankel engines that had MUCH better power/weight ratios and were available for purchase (not "real soon now"). Since power/weight is Liquid Piston's main claim to fame, this is rather important. Today, a quick DDG search similarly returns many Wankel-based engin…

Thanks for this, I really appreciate the real data and perspective

Re: LiquidPiston – The combustion engine reimagined

#48

Post by aredox »

toss1 wrote: post #34
xnx wrote: post #8

Posts on Hacker News related to LiquidPiston go back 11(!) years. The most comments are on this post: https://news.ycombinator.com/item?id=25450477 If this was going to revolutionize anything, it would've happened by now.

Yup Seven-ish years ago while working on a hybrid-powered UAV I was checking out high power/weight engine platforms. I found a significant variety of regular Wankel engines that had MUCH better power/weight ratios and were available for purchase (not "real soon now"). Since power/weight is Liquid Piston's main claim to fame, this is rather important. Today, a quick DDG search similarly returns many Wankel-based engin…

The main selling point of LP would be in durability - I'm sure once liquidPiston patents are expired, better engineering firms will produce better Wankel engines with their design. LP doesn't seem to execute well.

Re: LiquidPiston – The combustion engine reimagined

#49

Post by toss1 »

aredox wrote: post #48
toss1 wrote: post #34

Earlier quoted context omitted.

Yup Seven-ish years ago while working on a hybrid-powered UAV I was checking out high power/weight engine platforms. I found a significant variety of regular Wankel engines that had MUCH better power/weight ratios and were available for purchase (not "real soon now"). Since power/weight is Liquid Piston's main claim to fame, this is rather important. Today, a quick DDG search similarly returns many Wankel-based engin…

The main selling point of LP would be in durability - I'm sure once liquidPiston patents are expired, better engineering firms will produce better Wankel engines with their design. LP doesn't seem to execute well.

>>The main selling point of LP would be in durability

Um, I haven't seen them significantly promote that even rhetorically, much less with data backup. Replacing Wankel's ordinary tip seals with ceramic tip seals (yes, more expensive) and proper lubrication both improves performance and very much extends inter-rebuild time.

I'm definitely interested if you can point me to any data showing LP extended life. Their previous comparisons have been so bogus as to be laughable, such as comparing their weight vs some old military diesel generator-set (and not to the much more relevant Wankel).

>>LP doesn't seem to execute well. Agree - that is the understatement of the year!

Re: LiquidPiston – The combustion engine reimagined

#50

Post by aredox »

toss1 wrote: post #49
aredox wrote: post #48

Earlier quoted context omitted.

The main selling point of LP would be in durability - I'm sure once liquidPiston patents are expired, better engineering firms will produce better Wankel engines with their design. LP doesn't seem to execute well.

>>The main selling point of LP would be in durability Um, I haven't seen them significantly promote that even rhetorically, much less with data backup. Replacing Wankel's ordinary tip seals with ceramic tip seals (yes, more expensive) and proper lubrication both improves performance and very much extends inter-rebuild time. I'm definitely interested if you can point me to any data showing LP extended life. Their prev…

LP doesn't execute well, so I don't think they can have data showing their engine has a better life span (which is dependent on more than just these seals). It just makes sense from an engineering, "first principles" point of view.
Post reply on HN