I need your vote for a new Rotary HCCI engine ! 4

[RodRico]

Fellow engineers,

This post promotes my design, but it's also informative for those curious about new developments in engine design, so I hope it's OK. Please accept my apologies if not.

I have submitted my patent pending design for a "Hybrid Miller Cycle Rotary HCCI Engine for RQ-7 Class Drones" in the "Create the Future" contest. You may find it by googling the engine name above or by visiting

https://contest.techbriefs.com/2017/entries/aerospace-and-defense/8090.

Preliminary analysis indicates power density (3 HP per pound) and efficiency (45% with 0.300 BSFC) comparable to a turbofan when operated at full equivalency. When operated in Low Temperature Combustion (LTC) mode, the engine still produces nearly 1 HP per pound but creates very few emissions. Because of its small 10" diameter and 6.5" thickness, multiple engines can be arranged in a clover-leaf pattern around a common shaft to yield 380 HP in a 24" by 6.5" volume. Another set of engines can be arranged behind the first to yield 760 HP in 24" by 16" volume. Note it's not mechanically efficient to add a third engine set due to limitations in my design.

I would greatly appreciate your support of my contest entry. Viewing my entry helps, but voting for it (which requires simple e-mail verification) helps even more. As it stands, I'm only one vote ahead of a "free energy" device ! That's just wrong ! Please circulate the link as widely as possible and encourage all your engineering friends and colleagues to help me win this contest! If I win the contest 100% of the money will go to funding 3D modeling of CFD/Combustion/Heat Loss by a consultant.

Thank you very much for your time and any support you can offer. If you have questions or comments, please post them here or on the contest site and I will answer them to the best of my abilities. I view criticism as being more valuable than praise when it comes to design, so don't hesitate to challenge my design (but please keep it respectful per normal engineering tradition).

Respectfully,

Rod Newstrom

P.S. Some may wonder why I targeted my contest entry at military drones. I would have preferred to emphasize the efficiency and low emissions qualities of my engine when operating in Low Temperature Combustion (LTC) mode. I targeted the military application instead because the administration wants to zero funding at the DOE/ARPA-E (who would normally fund such advances) while simultaneously increasing military budgets. I mention the RQ-7 drone, an unarmed surveillance drone, specifically because my engine fits in the volume and weight envelope of its current engine (the AR-741 Wankel), and the Army issued a Request For Information in 2016 for a replacement engine.

 

[RodRico]

Grunt,

My numbers are still shifting as I finalize the detailed design. Tolerances and other practical matters are driving the design a bit. I *think* I'm about done.

The current specs as of the end of my workday today are 49.5cc with diameter of 5.3" and thickness of 2.3". Current performance is 3.2 HP and 6.3 lb-ft of torque at 2626 RPM with 57% efficiency (I prefer to say >50% since my FMEP of 4.62 bar is pretty coarse). My calculated BMEP is 3.8 bar for a single power stroke of a single cylinder. The engine has 8 cylinders and each completes 6 power strokes per revolution. All figures are calculated at 18,000 foot altitude. At lower altitude, I *could* move more air mass and create more power, but I'm not designing for those loads at present (I currently vent excess intake pressure).

I got through the calculations for the centrifugal fan integral to the rotor. I calculate a need for 48 CFM of airflow at altitude to carry waste heat and analysis indicates the fan will produce 113 CFM. The fan will, however, knock about 0.5% off efficiency.

As I said, I *think* the magnitude of changes should settle down now as I have everything incorporated and most of it toleranced now.

I'm not taking on investors until after I have a prototype with measured performance indicating the engine shows substantial gains over existing products already successful in the marketplace. With this approach, I don't have to worry about wasting other people's money *and* can value the company higher (thus giving up far less equity per dollar of investment).

Rod

 

[gruntguru]

What does 57% efficiency mean? Is it mechanical efficiency, BTE, ITE?

50% is not realistic for BTE or even ITE.

je suis charlie

 

[RodRico]

gruntguru,

My estimates are based on calculation of Work, IMEP, FMEP, and BMEP, so efficiency is Brake Thermal Efficiency. Note that my compression ratio is 23.2:1 so the classic auto cycle thermal efficiency limit (1-1/CR^(y-1))for this engine is 69%, so my 57% figure includes 12% efficiency loss from the ideal.

As I previously mentioned, my estimates only use mathematic estimates for FMEP and heat loss, so I'm really only hoping for >50% at the shaft output during prototype measurement. Since the shaft is turning at no more than 2,626 RPM, the engine will drive propellers directly with no reduction gear or propel a scooter using a 100/90R14 tire to 52 MPH without a transmission.

The chart below shows an HCCI engine attaining 57% efficiency at around 8 bar (

https://energy.gov/sites/prod/files/2014/03/f8/deer10_johansson.pdf).

Rod

 

[gruntguru]

"only hoping for >50% at the shaft output during prototype measurement."

You clearly have no idea of the magnitude of that claim.

Link Scroll down to the list of the most efficient engines. Do you see any small engines? How many engines do you see with greater than 50% BTE?

I will take a wild guess and say that the best efficiency ever seen in an engine with 6cc per cylinder displacement or less would be of the order of 25%. HCCI will add a bit and cam actuated pistons will subtract somewhere between a "bit" and a "lot".

je suis charlie

 

[RodRico]

gruntguru,

I'm intimately familiar with the state of the art in efficiencies. I'm also intimately familiar with the differences between math models and measurements of real production quality hardware. You're guessing the math is off by 52% while I'm guessing it's off by 7%. Only measurements will tell, but I seriously doubt anyone would even bother with the math if it were routinely off by 50%. My figure of 7% is much closer to what most folks claim for math models. Maybe it will be 14%, but I doubt it will be much worse than that,

I'll share results as they come in. It will be quite some time, however, as I have no experience with casting and CNC tools and will be learning a lot along the way.

Rod

 

[BrianPetersen]

Do we have any guesses about what the real-world thermal efficiency is going to be?

My guess is 0. The engine won't start due to leakdown and heat losses that never allow the charge to reach ignition temperature. Maybe I'm wrong.

 

[RodRico]

Brian,

Are you having a bad day? You don’t usually troll.

Rod

 

[gruntguru]

"I'm intimately familiar with the state of the art in efficiencies. I'm also intimately familiar with the differences between math models and measurements of real production quality hardware. You're guessing the math is off by 52% while I'm guessing it's off by 7%. Only measurements will tell, but I seriously doubt anyone would even bother with the math if it were routinely off by 50%. My figure of 7% is much closer to what most folks claim for math models. Maybe it will be 14%, but I doubt it will be much worse than that,"

14% sounds realistic - 14% TE - if Brian is wrong and you can get it to start. You will of course begin with a single cylinder test bed?

It won't be the math that's off. It will be the assumptions on which the the math is based. When the numbers look too good to be true they usually are. A good engineer will go back and try to find why he is predicting TE which is twice the state of the art.

Please don't take my criticisms (nor Brian's I'm sure) as knocking for knocking's sake. I genuinely like to see people with ideas succeed. Listening to people who know can save time and effort. If your engine consultant really is an expert he will be asking the same questions as Brian and myself.

je suis charlie

 

[SwinnyGG]

Rod,

I'd encourage you to take a step back here.

You are making VERY bold claims. Very bold.

You should expect skepticism.

Whether you realize it or not, you are basically saying "My engine is going to obliterate the efficiency performance of every small-scale internal combustion engine ever conceived, AND it is going to do it without any previous design iteration or physical testing, AND it is going to do it on the first try".

There is some possibility that you've cracked the code and you are right- but you are not the first person to make claims like this about some new, radical engine design. If your design is successful, you will be the first to really succeed.

Based on the long history of wild claims, and the long history of development invested in the technology you are trying to beat, the data indicates that the odds are not in your favor.

I think everyone on this thread wishes you success- but that doesn't mean we believe (yet).

 

[RodRico]

All,

I wrote a long and detailed response then lost it somehow just as I was about to click "Submit Post." I'm not going to redo it. I'll just say that I have been through all my numbers repeatedly and so has my consultant. Heck, he didn't even want to accept a contract from me at first saying "I don't want to waste my time or your money." I begged him to at least take a look, and he's now cautiously optimistic. One reason he came on board is I can explain what's different about my engine from other approaches to HCCI and how those differences result in improved performance. Note, by the way, that both Wärtsilä and Mercedes have broken 50% efficiency, and Hyundai thinks they're going to get there as well (

https://www.motor1.com/news/184754/hyundai-future-powertrain-efficiency-plan/).

None of these engines use HCCI, and I've already posted links to articles showing many respected experts predict similar efficiencies using HCCI.

Everyone keeps harping on small displacement. I know full well the problem of having a high surface area relative to volume in regards heat loss. Nobody is considering other factors, however... Opposed pistons help offset the impact of small cylinders by yielding a minimal surface area combustion chamber and use of small steel pistons in steel cylinders with a modified Dykes ring minimizes crevice volume. Folks predicting it won't start due to heat loss are alluding to problems in engines using flame propagation, and don't seem to understand how HCCI differs from flame driven combustion.

I've know since day one the odds are not stacked in my favor; history (and YouTube) are littered with failed engines based on differing architectures substantiated with wild claims and no test data. I was downright pessimistic until my engine consultant came back with "I think you're onto something" along with his first batch of comments and suggestions. We're now on our third pass.

I never said I expected this to work on the first try. I've always said I'm planning a series of critical experiments and hardware measurements that will be used to inform design iterations. My consultant is helping me design the test plan based on his long experience in bringing new engine architectures up from scratch. I've said many times that I am fully prepared to encounter an insurmountable problem that may cause me to abandon the whole project. I haven't yet, but I'm only now preparing to enter fabrication and test of the first experiments.

Finally, I have also said many times that I value criticism. I've accomplished a number of things everyone thought were impossible (first Polyphase Channelizer in an FPGA, first digital Radar Warning Receiver, first ADC/DAC with 30 GHz bandwidth, first Digitally Beam-Formed Ultra-Wide Band multi-beam radar array). All of these firsts had a few things in common. First, I was a neophyte in the subject areas and taught myself what I needed to come up with them; it was my new look based on an understanding of first principles rather than established practice that allowed me to see the problem differently. Second, my preliminary design and analysis were all redone by experts (at my request), and they all came up with similar answers; the final design was always very similar to my proposed preliminary design. Third, all of them took years to get working in real life. Finally, none of them would have been possible without the criticism, comment, and refinement of my team. Every award and patent granted were awarded to the team not me alone.

I value constructive criticism, and most of you, including Brian, have been constructive. Brian's last comment was uncharacteristically blunt, uncivil, and short on details. That's why I assumed he had simply suffered a bad day. What does one do with a comment like "you're going to fail" with no detail? Nothing. I don't hold it against him as anyone can scroll up and see that last comment was uncharacteristic of his usual posting.

Rod

 

[BrianPetersen]

Yup, sorry, bad day. That, in combination with the extravagance of your claims.

I would encourage the use of a single-cylinder test bed. I would encourage scaling up that cylinder by some suitable factor (perhaps 2 or 3 on linear dimensions - 8 to 27 on volume ... but only the same 2 or 3 on linear length of piston-ring leakage path!) I would encourage trying to make use of existing bits and pieces from other engines wherever you can. Substitute an external scavenging blower - even if it's not propelled by the engine itself - use something you can get off the shelf or adapt easily. Anything you can do to simplify to the bare minimum and "modularize", so that if you find out that something has to be done differently, you can do it by changing one part (or a minimum of parts) as opposed to restarting from scratch.

You need to prove out what it takes to make your combustion system work ... or learn that it won't, as the case may be.

One thing common to high-efficiency internal combustion engines has been large displacement per cylinder. I am aware of no exceptions. The automotive industry seems to be converging on per-cylinder displacements around 500cc give or take, as a reasonable balance between thermal efficiency (better with larger, fewer cylinders turning slower), smoothness (better with more, smaller cylinders), power to weight ratio (better with more, smaller cylinders that rev higher), and durability (better with large cylinders turning slowly). Engines in over-the-road trucks are commonly around 2 litres per cylinder in displacement ... slightly more efficient, but the sheer size and poor power-to-weight ratio would be unacceptable in an automotive application. Engines in motorcycles are commonly much smaller (100 - 300cc per cylinder is a common range) in the interest of power-to-weight ratio, but they are unremarkable in terms of efficiency.

These lessons have already been learned and are free knowledge!

 

[RodRico]

Brian,

I'm going to run combustion tests on a single stationary cylinder driven by rotating cams. I plan to use external pumps to move oil and air through the engine (necessary because the centrifugal pumps incorporated in the rotor won't work with a stationary cylinder). I will be injecting air and fuel in a mixing chamber that's pressurized using an external pump to simulate my pump piston.

Ecotec in-line 4 engines use a cylinder with an 88 mm bore. The two top rings are each 1mm thick. I use a cylinder bore of 15mm and have total ring thickness of 1 mm. Due to HCCI, my engine likely runs higher peak pressure than the Ecotec, but I have a larger ring contact area relative to bore (and smaller piston/wall clearance due to my use of steel pistons and cylinder liners). If anything, I'm worried about excessive ring friction. I'm using a gapless Dykes ring to help deal with the friction problem while still handling the high pressures (The upper sealing diameter of Dykes rings readily expands under pressure).

My volume to surface area is pretty high compared to large cylinders, but that's already accounted for in the heat transfer analysis (see

https://www.researchgate.net/public...asurements_of_Instantaneous_Surface_Heat_Flux

and note I'm using the Hohenberg method).

I'm leaning toward spin-casting my rotor specifically to keep iteration time down. I will print the model using a 3D printer, install the machined cylinder liners, then fill it with refractory slurry as it spins about its center. Once the refractory hardens, I'll burn out the 3D print, put the mold back on the spin table, and pour molten 4032 aluminum through the center. A similar process will be used for the two side housings. I will then use CNC to clean up the castings. This process will take some work to get right, but it will allow rapid iterations and significantly reduce machining time during later production (if any). The most complex assemblies will likely be the cams themselves as they need to be ground with great precision then finely polished. I may have to send them out to cam shop.

I want to keep the engine and motoring dyno very small and comparatively inexpensive so I can ship it to evaluators and let them make their own measurements... nobody believes without making their own measurements.

Rod

 

[BrianPetersen]

What's wrong with just modifying the piston or cylinder head of a simple two-stroke engine of some sort (chainsaw?) to see if your combustion system is viable?

A mixture of air and fuel (and residual exhaust after the engine starts) doesn't care about the mechanics of the mechanism that's doing the compressing.

A little bit of smart mechanical design could even achieve the adjustable compression ratio that I think you're going to need.

 

[gruntguru]

Perhaps discuss the following statement with your engine expert.

"Draw a P-V diagram for your proposed cycle. Design the engine to produce that P-V relationship WITHOUT the stepped bore and staggered piston size. ie reduce the bore and increase the stroke for the larger piston (or the reverse for the smaller piston). The resulting engine will retain all the P,V,Torque relationships without the added cost and detrimental geometry of the stepped bore."

je suis charlie

 

[gruntguru]

"One thing common to high-efficiency internal combustion engines has been large displacement per cylinder. I am aware of no exceptions. The automotive industry seems to be converging on per-cylinder displacements around 500cc give or take, as a reasonable balance between thermal efficiency (better with larger, fewer cylinders turning slower), smoothness (better with more, smaller cylinders), power to weight ratio (better with more, smaller cylinders that rev higher), and durability (better with large cylinders turning slowly). Engines in over-the-road trucks are commonly around 2 litres per cylinder in displacement ... slightly more efficient, but the sheer size and poor power-to-weight ratio would be unacceptable in an automotive application. Engines in motorcycles are commonly much smaller (100 - 300cc per cylinder is a common range) in the interest of power-to-weight ratio, but they are unremarkable in terms of efficiency.

Brian. It is many years since I read a piston engine text - I think the last time was Taylor. Link (Jump to P 488 for a discussion of cylinder size effects.) While Diesel engines experience increasing efficiency with increasing cylinder size (diminishing returns but apparently without limit), spark ignition engines seem to have an optimal size range - mainly due to detonation/CR limitations imposed by larger bore. Reducing cylinder size permits higher CR which offsets the increased heat loss to some extent. Not sure how this principle will transfer to HCCI engines but I suspect the absence of knock will mean best efficiency would occur at some larger (than SI) cylinder size - with an upper limit imposed by structural considerations under the extreme pressure (and rate of pressure rise) conditions of HCCI.

je suis charlie

 

[RodRico]

Brian,

I have no worries whatsoever that my combustion scheme "will work." It's not really a "scheme" but the well understood compression ignition. Heck, one research group made HCCI occur with a 3mm bore (

http://www.mrzgroup.umd.edu/pdfs/2003_C&F_aichlmayr.pdf)

and no piston rings (just a small air gap)! There's not much point in me proving I can make HCCI occur using a non-representative method of mechanization; my design concept requires use of unconventionally small steel pistons (to handle immense HCCI peak pressure) driven in a non-sinusoidal fashion (cams vs a crank), and that's what needs to be tested.

I know some feel I should build a larger engine, but from my perspective, the smaller one has equal value even if it has lower efficiency than a larger one; knowledgeable reviewers obviously know there's a bit of a penalty for being so small and will adjust their expectations accordingly. The smaller engine however, vastly simplifies and lowers the cost of fabrication and test; I can use a smaller mill (Tormach PCNC-440 vs 770), smaller electric motor/generator in my dyno, lower power dissipation in the dyno load, etc. It also reduces the footprint of my workshop and yields an engine more easily shipped to reviewers and independent testers (which is absolutely essential IMHO).

Gruntguru,

I mentioned some time ago that I had eliminated the stepped bore. I did so because A) it's not needed in the multi-cylinder radial with a moderately high mass flywheel (inherent to the spinning rotor) combined with the inherent torque advantage of the outer piston even with equal bore and B) it adds risk due to heat/pressure concentration and tighter tolerances. In this equal-bore configuration, the real value of the inner piston of the opposed pair is the fact that it has lower mass and can thus be snapped through it's compression stroke more quickly combined with the ability to rotate the inner cam phase to mechanize variable compression according to knock sense angle.

Rod

 

[BrianPetersen]

From glancing through that paper, it appears that they used a free-piston configuration. In that situation, the compression ratio can vary, and when combustion occurs, it spikes the cylinder pressure and that's the end of compression. It's a little different if a mechanism is forcing the piston to continue compressing. Nevertheless, "it can work", look at model aircraft glow-plug engines ... although those need help, in the form of the glow plug, to get started. Those aren't known for their fantastic thermal efficiency, though.

 

[BigClive]

The "diesel" variety of model engine don't need a glow plug - they use ether in the fuel which self-ignites fairly easily. Adjustable CRs up to about 40:1. They are notably more economic of fuel use and have a quieter exhaust note.

 

[RodRico]

Brian,

The test isn't really a free piston configuration, it's a classic shock tube. The data was collected to evaluate whether a micro-free-piston engine would combust, however, so you're correct in that regard.

I've changed the design a bit a long while ago to stop continuing compression after combustion. The air pump compresses the charge to slightly above 1 atm (pressure regulated), the expansion piston compresses the charge 3.9:1, and the compression piston then compresses another 6:1 (23.2:1 total). The total compression time is shorter than the fuel's ignition delay regardless of RPM, and the sum of compression time plus hold time is greater than ignition delay at all RPMs. The charge is at 900K at the end of compression, more than enough to initiate combustion, and the temperature of the rotor is regulated. I *may* have to add heaters to the rotor for cold start in cold temps (depends on what's happening to wall temperature during cranking).

All of my analysis is based on the paper "A reduced chemical kinetic model for HCCI combustion of primary reference fuels in a rapid compression machine" (

http://james-keck-memorial-collecti...kaAyalaKeck-CombustionFlame-133-467-2003.pdf)

which combines chemical kinetic analysis with measurements from a Rapid Compression Machine (RCM) having a 25.4mm bore (Table 1). A description of the RCM mechanism used in the paper is provided in section 2.3 of another paper (

http://www.kones.eu/ep/2012/vol19/n...2_NO_4_VOL._19_ISSN_1231-4005_Lezanski2.pdf).

Note I will use a precisely mixed batch of reference fuels during initial testing so I can remove fuel variance/uncertainty from the equation.

The relevance of small RC engines that run using compression ignition isn't their efficiency but the mere fact that they were successful in attaining auto-ignition in a small bore. Efficiency is a measure of the quality of the process, and it entails a lot more effort than is usually applied to model engines.

Rod

 

[MikeHalloran]

I think it's time for you to stop analyzing and build something.

Before that, do read up on the Scuderi engine, which may serve as a cautionary tale.
AFAIK, there was one prototype, that ran just well enough to say that it ran, before the inventor died.

His children devoted their efforts to raising money, and dispensing it, some unwisely, but I think a lot of the money went to SwRI, which did a crapload of simulations, and produced a bunch of bulky and impressive reports, all of which were interpreted to mean that the engine might do magical things, if only SwRI did some more research, and so forth.

I am related to the Scuderi family, and asked questions. I could never get a straight answer about whether SwRI actually built and tested an actual engine, so I suspect not, and I'm aware of no record of such an engine ever showing up at a drag strip, or in a pleasure boat, or even in a bicycle.







Mike Halloran
Pembroke Pines, FL, USA