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.

 

[gruntguru]

"gruntguru, the bores are stepped because that was required to ensure the reverse torque generated by the ignition piston during combustion is less than the forward torque of the expansion piston during combustion. This is only an issue during starting. Once the engine is running, the rotational inertia of the rotor is sufficient to prevent engine reversal.

Yes, the stroke of the ignition piston is very short. It's only purpose is to initiate ignition (it's my spark plug so to speak). When the ignition process starts, the larger piston is at TDC, so there's very little volume in the larger bore cylinder and the entire combustion chamber is defined by the smaller cylinder's volume. At this point, the charge temperature is just 100K below auto-ignition temperature. The ignition piston then performs a full stroke as the expansion piston begins moving slowly away to start its expansion stroke. The speed at which the expansion piston moves is determined by its bore vs that of the ignition piston and the radius of its cam versus that of the ignition piston, factors relating to prevention of reverse rotation. The final factor is the angle of contact (mechanical advantage) of the cams associated with each piston. Because the expansion piston has great advantage in its product of bore and lever length (cam radius), it can have a much more shallow cam angle with less displacement and lower speed. As a result of these dynamics, the expansion piston doesn't move far as the ignition piston rapidly approaches and the resulting compression ratio is very high, sufficient to cause auto-ignition. This is the most difficult part of the design to understand. Hopefully my explanation helps. Let me know if I failed."

There are several misconceptions in your analysis of velocities, pressure, torque and mechanical advantage.

Everything you need to know is contained in a volume/crankangle diagram regardless of how many pistons are doing the displacement or what their relationship to the crankshaft ("mechanical advantage") is.

"I will develop different sizes based on demand, but only *after* this one is in production"

Your design will never get into production. You have a great deal of talent and energy - I strongly suggest you get a mechanical engineering degree or enlist the help of someone who has one.

je suis charlie

 

[RodRico]

Guru,

You *could* say "Your explanation makes no sense to me because... Can you address this and clarify?" rather than take the stance that *I'm* an idiot because *you* don't understand.

Yes, PV work is a complete description that encompasses mechanical advantage. In this case, however, we're not discussing the work of a single piston but that of two subjected to the same combustion pressure and controlled by independent cams (or cranks if you prefer). Thus it's convienient to talk of the forces each applies to the ouput shaft. You know full well (I assume) that both approaches are valid, it's just easier to visualize it using force applied to levers.

The faster piston, by definition *because* it's moving faster, has greater mechanical advantage on the output shaft. At the same time its smaller bore results in less surface area (square inches), so combustion gas pressure (pounds-per-square-inch) produces less pound-force on the lever. Thus, though its mechanical advantage is greater, it exerts less torque on the output shaft.

To make it even simpler, imagine I'm trying to turn a shaft one way using a lever and you're trying to turn it the other way. My lever is shorter but the pressure I apply is normal to the lever. You have the longer lever but the force you apply is at an angle far from normal. Thus, even though your lever is longer, a given force applied to your lever will produce less torque on the shaft than if that same force is applied to mine, so I will win. I want *you* to win, however, so I need you to apply more force on your lever than I do to mine. In the engine, both pistons are exposed to the same combustion pressure but the force applied to their respective levers differs according to their bore. I arrange the bores such that you get more force and win.

Hopefully this clarifies whats going on for you.

Rod

 

[MacGyverS2000]

Dan - Owner

http://www.Hi-TecDesigns.com

 

[SwinnyGG]

The faster piston, by definition *because* it's moving faster, has greater mechanical advantage on the output shaft.

It appears to me that you're confusing mechanical advantage with velocity ratio. They are not the same thing.

 

[RodRico]

JgKRI,

Velocity Ratio and Mechanical Advantage are the same in an ideal system (efficiency=100%). I wasn't analyzing detailed machine performance (and never mentioned efficiency), I was only explaining its operation *in theory*. I'm sorry if you found it confusing.

Rod

 

[BigClive]

Rod - I find the whole thing hard to make a judgement on as it is so complex - more and simpler diagrams and drawings are needed - at least by me.

 

[gruntguru]

Rod. I did not say your explanation makes no sense to me. I said it is flawed.

The statement below tells us everything we need to know. If a single piston is connected to a mechanism which produces the same Volume/theta diagram as your multiple piston layout - the result will be the same. There is no need for the extra complexity. Similarly there is no need to "step" the bores to prevent reversal. The actuation mechanism can be tuned for any desired piston-motion profile so the desired rate of volume change can be produced regardless of bore size. Likewise any volume/theta profile can be produced with a single piston layout (With identical torque profile).

"Everything you need to know is contained in a volume/crankangle diagram regardless of how many pistons are doing the displacement or what their relationship to the crankshaft ("mechanical advantage") is."

je suis charlie

 

[RodRico]

BigClive,

The contest only allows 3 illustrations and 500 words. I'm traveling Europe for the next couple of months, but plan to put up my own website when I'm back home. I'll post a link in the forums when done.

Thanks for taking a look !

Rod

 

[RodRico]

Gruntguru,

Granted, I could replicate the volume/theta diagram with one pistion, but it would result in autoignition occuring while compression was still increasing just as with commonplace detonation. With two pistons, I can initiate autoignition with both moving in the same direction (toward BDC expansion) as long as I ensure forward torque dominates.

This conversation would be much easier face-to-face over a beer !

Rod

 

[BrianPetersen]

One of the problems with HCCI is that autoignition happens whenever it wants to happen. If that happens when the net volume is decreasing (it makes no difference whether it's one piston or two or whether they're the same area) there is going to be net reverse torque while the engine has to continue to compress the already-detonating charge. If this happens soon enough before effective TDC (minimum net volume - doesn't matter how it's arranged) your engine is going to have a bad day.

 

[3DDave]

It would have been much clearer if there was a 2-D graph of all the operating characteristics against angle. I can't help but think this was generated at some point, but maybe it's trapped in a spreadsheet.

 

[RodRico]

Brian,

We don't seem to be converging on agreement. Let's suspend the discussion until I have time to generate some figures annotated with forces.

3DDave,

Yes, it would be clearer. I maintain the whole design and analysis in Excel (from which I export parameters and dimensions to Solidworks). Cams are designed on one tab, side port timing on another, volume and surface area on a third, and PVT thermodynamics on a fourth. There are plots of every aspect over a full cycle in 0.5 degree steps. I'm in Europe at present and can't access them until I get home.

Rod

 

[gruntguru]

Definitely be easier over a beer. You don't need figures annotated with forces.

Its all in the V/Theta diagram. Likewise if you take the next step and draw a P/V diagram you can see the work and recognise whether it is negative or positive - regardless of how many pistons, what size and which direction they are travelling.

Volume decreasing -> work (and torque) is negative.
Volume increasing -> work (and torque) is positive.


je suis charlie

 

[BigClive]

Whether it works well or - you can still make a million dollars out of it. Promote it hard enough and somebody will invest - plenty of other people have done this - I can think of half a dozen at least. If you can make a running prototype - even better. Bill Gates has invested more than $30,000,000 (total investments are over $60,000,000) in the OPOC engine - which (to me at least) doesn't seem to be anything new.

 

[RodRico]

Grunt, I have PV diagrams and calculate work in 0.5 degree steps. I suspect the communication breakdown is occuring in my use of terms here.

BigClive, I'm not out to make millions, I'm out to make a better motor. If money comes in as a result, great. I would feel terrible if I wasted others' money on nothing.

Rod

 

[Lou Scannon]

Volume decreasing -> work (and torque) is negative.
Volume increasing -> work (and torque) is positive

gg, I expect you're referring to the compression and expansion phases.
Yet as you know, work can be negative during {at least part of) the induction stroke (but not necessarily). I can't think of any mainstream examples where the work is positive during the exhaust stroke, though certainly two-stroke extraction systems and exotic race headers strive in this direction.
...Or did I misunderstand something?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[gruntguru]

Hemi - "I almost added "assuming positive pressure at all times". Should have.

je suis charlie

 

[RodRico]

gruntguru,

I had a moment on a computer in London and drew this up for you. It's the simplest explanation I can provide.

 

[BrianPetersen]

Ooooh, so it's a variable compression ratio mechanism.

 

[RodRico]

Brian,

The shaft angle at which it crosses autoignition threshold is optimized using knock sensors much like a spark engine varies ignition timing. Neither is properly called "variable compression ratio."

Rod