Rotary engine breakthrough (?)

[rv6ejguy]

As we've seen from comparisons, the EFI is not a lot better than a well sorted mechanical FI at "normal" cruise power settings. More of the gains come from advancing ignition timing to the proper figure when LOP.

Forget the airframe as that doesn't enter into BSFC numbers. While I'm not at liberty to release all the details about Dave's engine and some of the dyno testing it's undergone at this time, feel free to work out the approx power and BSFC yourself from the MAP and rpm shown in the screenshot vs. the fuel flow. AFR was 16.7 in this screenshot. It's presently a 10 to 1 engine with ported heads and revised cam timing. This is not even optimized. An AFR of 17.5 to 18 would give slightly better BSFC figures.

A new engine is in the works, upping the CR a couple more points again.

The big issue with TE and the Wankel is the high surface to volume ratio and high heat losses.

Make sure any flight testing comparing piston and Wankels are both using optimized leaning techniques and optimized fuel and spark control, otherwise the results aren't very meaningful.

I've never seen or read anything reputable from car, airplane or dyno testing that Wankels are anywhere close to modern SI piston engines in BSFC under similar running conditions. The RX8 was abysmal in the real world as were all the previous iterations. (I know, I've owned a couple of them) If you have some data you'd like to share, please do. I'd be very interested.

For military use, certainly heavy fuels makes tremendous sense no matter which engine design is being used.

 

[PMD]

Ah but those boat anchors with 10-12 to 1 CRs, when equipped with EFI/EI are capable of showing BSFC figures almost the same as the current crop of aero CI engines. One of our testers is showing better than .36 running LOP in cruise.

View attachment 67544

EFI Lycoming 360 in an RV4. 6.2 gph (37.2 PPH) truing 197mph.

The flash point of diesel or jet fuel is well below the exhaust temperatures in CI engines. Jet aircraft burn really good when they crash too. That's a weak supposed advantage IMO.

In North America, the CI aero engines currently available show no reduction in overall costs per flight hour mainly due to their high initial and maintenance costs: http://www.aviationconsumer.com/issues/48_8/avionicsreport/Diesel-Reset-Improved-Economics_6962-1.html

CI engines are not detonation limited but they certainly are limited by the physical strength of the engine. I don't see any CI engines approaching the 1000hp/L specific outputs that SI race engines achieved 30 years ago.

Ross, I would dearly LOVE to see modern electronic ignition and injection on certified boat anchors, but since I am these days kind of in that part of the world, and down to the age where I might have another 10 years of medicals left in me, I will not hold my breath. My ground-bound time is around both CI and SI stuff all with direct injection, and the gap in BSFC is indeed narrow now, but still a nod to the CI not only for efficiency but for stupidly simple and cheap it is to just dial in as much horsepressure as the cylinder head studs will contain.

On race engines: Yes, there have been some pretty big numbers from the "SI" crowd - but I will point out that when you get into the 1000 BHP/Litre engines, their service life is measured in mere minutes and their main SI component - the spark plugs - are no longer involved after the first second under full boost, so they are actually CI engines when you get right down to it.

There are two things that CI can do that SI just simply can not: #1 is the process is not cylinder pressure limited, whereas an aspirated charge meets its limit by that definition. The second is the ability to rate shape the injection process to tailor the BMEP curve to match the most favourable geometry during the power stroke. You might come close at some RPM on a gasser./SI, but in a diesel, you can simply do it at ANY RPM. In an aviation sense, that simply means direct drive is easy, vs. a severe limit on SI engines unless they are far larger in displacement than needed for the tiny continuous outputs used in aviation.

My real world example is of course the now two generation out of date tech used in the SMA 305. Look at what Soloy has been doing by performing a proper install in a C182 - hardly the most aero package in the industry. The range goes from mediocre to best-in-the-industry simply by using the right engine tech and fuel at the real world stage of develoment available to we mere mortals (albeit, as you pointed out, mere mortals with a pretty healthy bank account). AND: it only needs 5.0 litres of hardware to do it, wheras the Lycosaurus need nearly 9.

 

[rv6ejguy]

Ross, I would dearly LOVE to see modern electronic ignition and injection on certified boat anchors, but since I am these days kind of in that part of the world, and down to the age where I might have another 10 years of medicals left in me, I will not hold my breath. My ground-bound time is around both CI and SI stuff all with direct injection, and the gap in BSFC is indeed narrow now, but still a nod to the CI not only for efficiency but for stupidly simple and cheap it is to just dial in as much horsepressure as the cylinder head studs will contain.

On race engines: Yes, there have been some pretty big numbers from the "SI" crowd - but I will point out that when you get into the 1000 BHP/Litre engines, their service life is measured in mere minutes and their main SI component - the spark plugs - are no longer involved after the first second under full boost, so they are actually CI engines when you get right down to it.

There are two things that CI can do that SI just simply can not: #1 is the process is not cylinder pressure limited, whereas an aspirated charge meets its limit by that definition. The second is the ability to rate shape the injection process to tailor the BMEP curve to match the most favourable geometry during the power stroke. You might come close at some RPM on a gasser./SI, but in a diesel, you can simply do it at ANY RPM. In an aviation sense, that simply means direct drive is easy, vs. a severe limit on SI engines unless they are far larger in displacement than needed for the tiny continuous outputs used in aviation.

My real world example is of course the now two generation out of date tech used in the SMA 305. Look at what Soloy has been doing by performing a proper install in a C182 - hardly the most aero package in the industry. The range goes from mediocre to best-in-the-industry simply by using the right engine tech and fuel at the real world stage of develoment available to we mere mortals (albeit, as you pointed out, mere mortals with a pretty healthy bank account). AND: it only needs 5.0 litres of hardware to do it, wheras the Lycosaurus need nearly 9.

This is a homebuilt forum where we can fly non certified engines. I wasn't aware you were referring to certified engines. In any case there are certified FADEC SI aircraft engines and they have been around for some time, however like the certified aero diesels, they are expensive. If you knew what the FAA demands on the electronics and wiring side to certify ECUs, you'll know why that is.

I was referring to the mid eighties F1 engines, not Top Fuel engines as far as the top level of SI engine development. Certainly they still use the plugs to initiate combustion events.

The fact that CI engines are not detonation limited is a moot point since they cannot hope to approach either the specific output levels nor the the power to weight ratios of SI engines. This has lots to do with the dynamics of the diesel combustion process and their inability to work at high revs efficiently. You better look at the peak and average torque figures on a modern small SI turbo engine- as low as 1200 rpm in the auto world- as low or lower than their CI counterparts. This is mainly due to variable geometry turbos. CI engines can't hope to match the area under the curve of modern SI turbo engines running similar manifold pressures.

Don't compare atmo SI engines to turbo CI engines. It's not apples to apples. Take the turbo off any diesel and you will have the definition of a boat anchor...

 

[tspear]

Getting back to rotaries.
Anyone know any heavy fuel ones which are close to the efficiency of a traditional engine?

Tim

 

[Winginit]

I was wondering if anyone knows the appx weight of some of the new Ford (or Chevy) 4 cylinder turbo engines compared to a rotary. Might not some of this new breed of turbocharged engines be worth looking into ? I haven't kept abreast of the rotary engines, or even heard much about them of late. Always kinda thought they would be a good choice, but then there always seemed to be a solved problem followed by a new one.

 

[rv7charlie]

As we've seen from comparisons, the EFI is not a lot better than a well sorted mechanical FI at "normal" cruise power settings. More of the gains come from advancing ignition timing to the proper figure when LOP.

Forget the airframe as that doesn't enter into BSFC numbers. While I'm not at liberty to release all the details about Dave's engine and some of the dyno testing it's undergone at this time, feel free to work out the approx power and BSFC yourself from the MAP and rpm shown in the screenshot vs. the fuel flow. AFR was 16.7 in this screenshot. It's presently a 10 to 1 engine with ported heads and revised cam timing. This is not even optimized. An AFR of 17.5 to 18 would give slightly better BSFC figures.

A new engine is in the works, upping the CR a couple more points again.

The big issue with TE and the Wankel is the high surface to volume ratio and high heat losses.

Make sure any flight testing comparing piston and Wankels are both using optimized leaning techniques and optimized fuel and spark control, otherwise the results aren't very meaningful.

I've never seen or read anything reputable from car, airplane or dyno testing that Wankels are anywhere close to modern SI piston engines in BSFC under similar running conditions. The RX8 was abysmal in the real world as were all the previous iterations. (I know, I've owned a couple of them) If you have some data you'd like to share, please do. I'd be very interested.

For military use, certainly heavy fuels makes tremendous sense no matter which engine design is being used.

I can't see how anyone can derive BSFC numbers from an a/c in level flight, without knowing with precision the exact weight of the plane, density altitude, temperature, humidity, etc, and most important, the actual drag of that a/c, including its cooling drag. How can I look at the EFIS numbers for HP & ignore a/c weight and drag? Would those fuel flow and speed numbers numbers look the same if the engine was transplanted to my very draggy RV-4? (Obviously, a rhetorical question.) If he's got 'uncorrected' numbers from dyno runs, that's a different story.

"The big issue with TE and the Wankel is the high surface to volume ratio and high heat losses." I thought I mentioned that.

"I've never seen or read anything reputable from car, airplane or dyno testing that Wankels are anywhere close to modern SI piston engines in BSFC under similar running conditions. The RX8 was abysmal in the real world as were all the previous iterations. (I know, I've owned a couple of them) If you have some data you'd like to share, please do. I'd be very interested." What would a Lyc look like in an EPA city driving cycle? Multiple issues that show up with rotaries in cars fade or disappear when they're used in a/c. One obvious problem is sticking seals, caused by injecting crankcase motor oil as a 'top lube' (apex seal lube) in the cars and then operating them in a low power, urban driving environment. Never done in a/c use. Fliers use 2 stroke oil; either mixed with fuel or injected using an adapter with the stock oil injection pump. There are multiple documented cases of tearing down aviation-use rotaries after many hundreds of hours, and the seals were as free in their grooves as the day the engine was assembled. For real world examples: I've flown two separate flights in my Lyc powered RV-4 with Tracy Crook's (Real World Solutions) Renesis powered RV-4. Same flight profile, departing and landing at the same airports. Tracy is actually an efficiency 'nut', and I'm not afraid to lean my Lyc to its limit (it is a 'stock' engine; carb and mags). On both occasions, Tracy burned about 10% more fuel than me, but he was running ethanol laced mogas. I was running *premium*, *non-ethanol* mogas. The ethanol alone would account for most of that spread. A more typical Lyc driver would have easily burned through the rest, because he'd be afraid of burning valves. Yes, the Lyc would do better with modern engine control, but my comments were intended to compare typical rotaries in a/c to typical Lycs in a/c.

Now, what were we discussing?

 

[dino]

European automakers are redirecting research and developement away from diesel. The driving force behind CI is fading in the wake of emission scandals.