[vlucas]

The money quote, for the TL;DR crowd:

"Duke Engines' 3-liter, five cylinder test mule is already making a healthy 215 horsepower and 250 lb-ft of torque at 4,500rpm – slightly outperforming two conventional 3 liter reference engines that weigh nearly 20 percent more and are nearly three times as big for shipping purposes. With an innovative valveless ported design, the Duke engine appears to be on track to deliver superior performance, higher compression and increased efficiency in an extremely compact and lightweight package with far fewer moving parts than conventional engines."

[noir_lord]

215hp out of a 3 litre is shockingly low except for a naturally aspirated carburator engine from the 80's.

For example the 2 litre 2015 Mondeo Turbodiesel gets 210bhp.

The article is interesting but reads like a marketing release, the weight saving is the interesting take away I think if reliability matches a modern diesel.

[iaw]

I do agree with you but a turbo diesel isn't a valid comparison because it is:

1) turbo charged 2) diesel fueled

An inter-cooled turbocharger setup on this engine would likely net an additional 100 HP without much issue (presuming the sealing issues aren't horrific). Generally 100 HP per litre of displacement is the gold standard for naturally aspirated engines (see Ferrari).

[noir_lord]

I used diesel as historically cc for cc they have lagged behind petrol engines (though that has largely ended).

The turbo is irrelevant though, the IC has a turbo, they work and are reliable the rotating engine doesn't but that doesn't rule out a basis for comparison.

It comes down to fuel efficiency, emissions, maintenance and cost and I can't see this engine winning (for cars).

[iaw]

The turbo is not irrelevant because it has a direct impact on the ratio of power delivery / fuel consumption due to the recaptured energy from exhaust gasses. The volumetric efficiency (ratio of cylinder pressure pre-compression to atmospheric pressure) of engines with turbo-chargers is almost always >1 while the volumetric efficiency of naturally aspirated engines is always (excluding rare high-performance vehicles in specific ranges of operation) <1.

I don't have time to do more thorough research right now, but the Ford Duratec 30 series of engines [1] is roughly comparable in both displacement and cylinder count and produces between 200 and 240 HP depending on configuration which puts this engine slightly ahead of normal engines from a performance perspective (smaller form factor and lighter).

Is there any apples to apples comparison that you can find that actually makes this development look substantially inferior? I get that you used a diesel because historically that gave the ICE an advantage but with modern diesel technology and forced induction they aren't the same animal.

[1] http://en.wikipedia.org/wiki/Ford_Duratec_V6_engine#3.0_L

Edit: changed 'pre-combustion' to 'pre-compression' for clarity on volumetric efficiency definition.

[noir_lord]

In this context it is irrelevant since my comparison was purely one of power output against displacement.

The Turbo allows a given displacement to output more power for a given displacement, indeed volvo have 2 litre putting out 450hp (uses staged turbo's one of which is electrically driven), I wasnt comparing the nearest ICE equivalent to the rotary.

[BrandonMarc]

Curious: what's the alternative to naturally aspirated engines? Space-bound rockets?

[Gracana]

The other side of the coin is forced induction, using a turbocharger or a supercharger or even both. "Natural aspiration" just refers to engine with intake air at atmospheric pressure.