Hello from Garland Texas!

[RodRico]

Hello!

After 4 years of math and analysis, I'm just now starting final design of a prototype of a new patent-pending engine design. The prototype will only be 50cc, and I see a lot of helpful information here, so I thought I'd join.

Rod

P.S. You can read a somewhat outdated description and see some equally outdated illustrations of my new engine at https://contest.techbriefs.com/2017/entries/aerospace-and-defense/8090 . The new baseline displaces 50cc with 8 cylinders, each completing 6 full cycles per revolution of the output shaft. I'm currently predicting it will be under 5" in diameter and 4" thick. It should produce on the order of 3.6 HP/7.2 lb-ft torque at 2626 RPM and be well over 50% efficient. It also employs Low Temperature Combustion (LTC) and should produce very little smoke and NOx.

 

[Cogsy]

and be well over 50% efficient.

Are you claiming Carnot efficiency here?

 

[dalem9]

Welcome Rod

 

[RodRico]

Cogsby,

No. The high side temperature in my engine is 2150K and the low side is 288K, so the max theoretical Carnot efficiency is 87%. If it were an Otto Cycle engine, it's theoretical efficiency would be limited to 68% given my compression ratio of 21:1. It's not an Otto or a Diesel Cycle engine, however. It's a hybrid called Homogeneous Charge Compression Ignition (HCCI) which is more efficient than either Otto or Diesel. My calculated efficiency with *estimates* of friction and heat loss is 55%, but I haven't built it yet, so I just say ">50%."

My >50% figure is what I expect after optimization is complete, and that will require a fully instrumented engine (quartz windows and rapid reaction temperature/pressure sensors in the combustion chamber), detailed multi-physics models (COMSOL, CONVERGE, KIVA, etc.), and advanced treatments on the cylinder walls and pistons (lubricity and heat barrier). I can't afford to do all that myself. I believe, however, that if the prototype attains >45% efficiency, I'll be able to attract the funding required to attain the higher figure.

Rod

 

[RodRico]

Deleted duplicate

 

[Cogsy]

I'll take your word on the theoretical Otto efficiency as I can't be bothered doing the math right now and it looks to be a reasonable figure. I had a brief look at the link you posted and was somewhat perplexed to see you refer to the problem of 'constant volume' combustion in the diesel cycle. As I'm sure you're aware the theoretical diesel cycle utilises 'constant pressure' combustion rather than the constant volume of the Otto. The overall feeling I get from your blurb is that you strive for the actual (near) constant volume combustion of the theoretical Otto cycle without flame propagation delays. Added to the inherent efficiency reduction from LTC compared to 'traditional' combustion, combined with the increased friction of twice as many pistons per cylinder and I must say I'm very sceptical of your design achieving such efficiencies.

Having said all that, I'm more than happy to see you produce a running model as it'd be a very interesting engine.

 

[RodRico]

Cogsby,

HCCI is not diesel. The entire charge lights of very quickly. The video at https://youtu.be/oNCBbcINHuk shows just how much faster HCCI combustion is than spark ignition (much less diesel injection). Friction is a function of pressure and contact surface area, not quantity. The total area and pressure of my rings is larger than a single cylinder, but not 12 times greater. Nonetheless, I likely do incur slightly more ring friction on the rings I have. The friction is more than compensated by increased efficiency.

The first answer at https://www.researchgate.net/post/H...ion_engines_achieve_higher_thermal_efficiency (Professor Paul Ronney of USC) gives a great explanation of HCCI efficiency with LTC. It’s worth a read.

I too am excited to see what results I attain. I’ll share my progress and results here as they come in.

Rod