LiquidPiston HEHC engine

[AW111]

Apologies if this has been discussed before : I did search, but only found references to thefuture's bizarre wankel trolling thread. I don't want to go anywhere near that.


LiquidPiston have got some money from DARPA for further developement of their non-wankel rotary.
They make the usual bold claims, but they are doing something genuinely different : constant-volume combustion, then non-burning expansion.
They have a resonable (data free ) overview here.

I would be grateful if any of the powertrain guys here could say whether the revised cycle solves some of the wankel's poor thermodynamic efficiency.

I have no affiliation with LP, and no axe to grind, but I do like novelty .

[stevieturbo]

Would it still not have similar sealing issues that a normal rotary has ?

[AW111]

stevieturbo said:

Would it still not have similar sealing issues that a normal rotary has ?

Probably, although as the combusion chamber is a smallish "pocket" there is probably a different pressure profike across the seals.
I read that the seals are fitted to the housing, not rotor - although that may be for ease of manufacture.

I don't know if "mechanical" issues like seals will be a show-stopper or not, but the combustion cycle looks interesting, and has some theoretical advantages. It remains to be seen whether
a) They get anywhere near their projected combustion cycle efficiency
b) They solve the rotary bugbears of seal wear / leakage, machining cost, and large surface/volume ratio. The combustion design may help with the last of those 3.

There may be other issues - who knows? I remember when lean-burn was the way of the future, except for those pesky NOx emissions.

[stevieturbo]

AW111 said:

Probably, although as the combusion chamber is a smallish "pocket" there is probably a different pressure profike across the seals.
I read that the seals are fitted to the housing, not rotor - although that may be for ease of manufacture.

I don't know if "mechanical" issues like seals will be a show-stopper or not, but the combustion cycle looks interesting, and has some theoretical advantages. It remains to be seen whether
a) They get anywhere near their projected combustion cycle efficiency
b) They solve the rotary bugbears of seal wear / leakage, machining cost, and large surface/volume ratio. The combustion design may help with the last of those 3.

There may be other issues - who knows? I remember when lean-burn was the way of the future, except for those pesky NOx emissions.

Was lean burn not scuppered by the forced legal introduction of catalytic convertors ?

I guess the other limiting factor...if indeed it is a limitation, due to airflow etc, it might be difficult to build a multiple rotor design.
Maybe a single setup makes enough power though ?

[anonymous-user]

Unfortunately "power density" is so far down the list of "important issues we need to solve" that it's almost irrelevant. Add in some completely new, untried technology, and OEMs will be rushing to say "I'm Out"!


Like all "novel geometry" engine designs that have come an gone over the last 100 years, it's solving a problem that isn't really a problem and can still be rendered obsolete and an expensive white elephant by EV technology. The big sea change in IC engines will be cost effective waste heat recovery, rather than any novel combustion architecture imo.

[SuperchargedVR6]

I don't get the intake and exhaust. It seems to draw in unfiltered air and also blast the exhaust out the other side to atmosphere? No headers or intake manifolds etc? I must be missing something obvious lol!

[stevieturbo]

SuperchargedVR6 said:

I don't get the intake and exhaust. It seems to draw in unfiltered air and also blast the exhaust out the other side to atmosphere? No headers or intake manifolds etc? I must be missing something obvious lol!

It would obscure the visual demo if it capped inlet and exhaust

Much the same as 4 stroke demo videos not having inlets and exhausts always shown

[AER]

Apart from the huge asymmetric thermal expansion issues with that rotor, here is the worlds first liquid piston engine!

[davepoth]

AW111 said:

Probably, although as the combusion chamber is a smallish "pocket" there is probably a different pressure profike across the seals.
I read that the seals are fitted to the housing, not rotor - although that may be for ease of manufacture.

IIRC the big issue with the wankel was that the seals got scraped across the housing - this design looks like the seal would be in compression with very little (if any) lateral movement, which should be better.

[AW111]

I'm still trying to get my head around the effects of their constant-volume combustion and then expansion cycle.
I have read some stuff on steam engines that seems similar, as they "inject" steam at high pressure, then allow it to expand and push the piston down.

One thing that springs to mind is that the peak combustion pressure is presumably a lot higher with this method.

[anonymous-user]

AER said:

Apart from the huge asymmetric thermal expansion issues with that rotor, here is the worlds first liquid piston engine!

No thermal efficiency numbers quoted yet either (wonders about surface area to volume issues....)

[AW111]

I doubt it will break into any mainstream application, but there may be a niche at small sizes / low power levels, direct driving something, maybe a portable generator or pump. I think at least some of the Boston Dynamics devices run on hydralics, with what sounds like a 2-stroke running the pump.

I accept that modern 4-stroke engines, SI or CI, are the best there is in oil-based car engines, and they improve year by year. It is a very hard act to beat, and I don't think anything will.

I enjoy looking at different engine designs, unless they are just a mass of wierd linkages, to see if they offer any useful ideas, even if the engine as a whole is fatally compromised.