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.

 

[BrianPetersen]

That one struck me as an attempt to efficiently extract funds from venture-capital investors.

 

[RodRico]

Mike,

The systems engineer in me won't let me start building without a solid analytical base from which the design is derived. I spend 30 years in that paradigm, and it's always served me well. In any case, I'm done with the thermodynamic analysis and tolerancing is almost complete. Build will commence as soon as I complete the detailed design and test plan, build the shop, procure the tools, etc. I will undoubtedly pend a good deal of time learning all the tools and processes required but hope to have the first prototype in hand by the end of the year.

The Scuderi approach never impressed me. I saw too many problems to beleive it would yield results significant enough to justify the additional complexity. In all honesty, I think the original inventor had his heart in the right place, but his children simply saw it as an opportunity to make money and ended up suckering investors into a quagmire. One thing that triggered my suspicions was the fact that I couldn't find one iota of evidence that there was a reasonably good analytical model underlying the design. Everything was described using adjectives rather than math, and that's a commmon sign of an idea driven by intution rather than an understanding of the actual thermodynamics.

I agree with your assessment of SwRI. Their reports never mentioned what performance they were seeing, only that things were progressing well. Again, if the engine were based on a solid analytical approach, testing would be a series of parameter tests with pass/fail, not a bunch of adjectives indicating this or that is progressing nicely. Their language is a sure sign that it didn't meet any stated requirement and was being continuously revised in hopes of hitting success. That's a teriibly inefficienct and expensive way to develop a design. A paid contractor will never tell you this; they'll just keep doing as you ask and billing you into bankruptcy.

I have consistently said I will accept not one dime from an outside investor until I have results that indicate likely commercial success. Because of this, the entire prototype effort will be done using my own funds. I thus have to keep out-of-pocket costs down, and that's one reason why I work so hard on the System Engineering baseline and small displacement engines that can be inexpensively built and tested.

Rod

 

[hendersdc]

Rod,

I have been following this thread with interest and wish you luck with your design. I know nothing about engine design but I do know a fair bit about machining, I have even used a Tormach PCNC 1100 at a previous job. You will never get acceptable accuracy for your engine out of Tormach machines. They are great for hobby stuff or quick fixes to prototypes where +/- a few thou doesn't matter (which is what we used it for), they are also not nearly rigid enough to work with anything harder than aluminum with accuracy. We ended up selling the Tormach after a year or so and getting a Sharp HMV with 2.5 axis prototrak control and were much happier with the performance but that machine would not be suited for your parts either. I assume you will need tighter tolerances and stronger materials than the Tormach is capable of. I commend you for wanting to learn machining but I wouldn't recommend starting with this project.

The goal of your first prototype is to prove out the design right? If you attempt to make these parts on your own instead of having them made by a machinist the risk is that you will run into issues where you don't know if the problem is with the design or the quality of the parts.

 

[gruntguru]

"Gruntguru,
I mentioned some time ago that I had eliminated the stepped bore."

Sorry. I missed that.

je suis charlie

 

[RodRico]

hendersdc,

Good points all. I do plan to at least get quotes before building anything myself. A good compromise may be align my shaft diameters to what can be bought off the shelf and have the steel parts made for me while I handle the 4032 aluminum (which demands much less tolerance and precision). That way I can still get my hands dirty without too much risk. I'm thinking of using ProtoLabs or Xometry for the steel. Do you have experience with their accuracy and precision?

Rod

 

[hendersdc]

Rod,

If you can tweak your design to use off the shelf precision shaft stock I would highly recommend it. [URL unfurl="true"]https://us.misumi-ec.com/[/url] can also be a good source for semi custom relatively precision parts. For example, you can get a stepped shaft with wrench flats and tapped ends of custom length from them instead of just a basic shaft for relatively cheap.

I have used Protlabs extensively, only Xometry a couple times but they are in the same level in terms of capabilities. Their niche in the market is that they get you parts very fast, they do this by automating as much of the process as possible including the quoting and the generation of the tool paths. They will not match the quality of a good machine shop but they can get you parts in 1 wk instead of 6 wks. If I were making your prototype or something of similar precision needs I would not get my parts from them. They do a decent job for quick fit or function checks but will not give you the tolerances and surface finish quality that you need.

For example, slight gouges into walls at transitions, tool chatter marks, or steps of around 0.005" between coplanar surfaces that were machined using different tools or cut from both sides of the work piece would all be acceptable and expected by them. Parts that may be best made on a lathe with secondary work done on a mill may be done all at once on a 5 axis mill to save time, you won't get adequate circularity or concentricity tolerance out of that approach.

If your design can't accept defects like that (which I expect it can't) I would urge you to go with a local machine shop that can demonstrate experience and good quality on similar parts. Depending on your desired tolerances grinding may also be necessary which is not offered by any vendor that fits in the "rapid" category.

 

[RodRico]

hendersdc,

The misumi site is a great resource, thanks! They even have the stepped shafts I will need to support my tilting bad cam followers (or crowned roller bearings, a prototype option).

Don't FormLabs and Xometry allow specification of surface finish and wouldn't the finer grades eliminate many of the flaws you identify? Also, can't I *specify* use of a lathe where appropriate?

All my precision demands (other than cams and rings) are designed to be handled on a lathe specifically to address circularity/concentricity. The cams are closed NURBS curves that will be ground and polished (likely outsourced). The ring banks may be done on a lathe, but they are a non-gap Dykes design that will likely require fine EDM in the region of overlap (depending on desired spring force, they *may* be large enough to allow milling the overlaps, but even then it will be some fine work).

I have identified a local machine shop that looks pretty qualified (

http://www.northdallascnc.com/).

Thanks for your guidance here!

Rod

 

[hendersdc]

Rod,

No bead blast or polish surface finish step will make up for tool chatter or gouging, the marks are just too deep. You may be able to specify use of a lathe with secondary machining, it has been a while since I have received a part where they used the wrong process. It used to be a much bigger issue when Protolabs didn't have lathes at all.

The shop you linked to looks much more suited for this kind of work, in an area like Dallas you should be able to find dozens of shops that will do great work and I think you will be much happier with the results.

 

[RodRico]

hendersdc,

How could they claim to comply with a surface finish spec if there is tool chatter or gouges the surface? Also, I believe they'd be on the hook for delivered dimensions, concentricity, circularity, and finish, or I could reject the part and stop payment.

I'm goiong to start by talking to local machine shops now. If their quality is high and they're not too far out of bed in terms of cost and schedule, I'll likely go with them.

Rod

 

[SwinnyGG]

How could they claim to comply with a surface finish spec if there is tool chatter or gouges the surface?

This question is a giant quagmire.

Surface finish specs aren't as simple as they seem- this is sort of an inside joke with mechanical engineers actually.

The other thing is, if a rapid shop screws you, what recourse do you really have? Much better to be able to go pound on the door of the guy who owes you good parts.

 

[hendersdc]

The rapid shops tell you what their typical tolerances are and you get what you get. By procuring parts from them you are agreeing that you understand their process capabilities and agree to them. Some will look at drawings and attempt to meet tighter tolerances but there is no recourse if they can't because they did not say they could in the first place. This doesn't apply to gross mistakes like missing holes or parts at 2/3 scale, both of which have happened to me and were corrected by the vendor.

As far as the surface finish paradox you mention, think of a flat surface with some polished finish callout. They can polish the surface they produce but that doesn't mean that it will also be flat.