What if the textbooks are right?

[CARN0T]

have you ever built an engine?
have you ever modified an engine? such as converting it to run on alcohol or methane?
is this just a paper analysis?

That's a fair question.  I have never built an engine.  The last time I worked on an engine (a lawnmower), I destroyed it.  I am a physicist, and I recognize my shortcomings here.  (I have designed and built machines previously, and I know how tough it can be.)  Up until a year ago, I had a partner on the design work.  He had rebuilt hundreds of engines (mostly diesels) and has some engine inventions of his own.  He got a good job and the work came to a halt.  Two weeks ago, I filed a provisional patent application (at the urging of my patent attorney).  My goal now is to put together a good team, with adequate funding, and build a prototype to test and refine.  The target compression ratio is 40.  This should be enough to come very close to the desired 60% efficiency.  As I'm sure you understand, there is a lot more to the problem than just raising the compression ratio.

Ernie Rogers

[fritznien]

what is required Is a miller or Atkinson cycle engine. keep the compression, its limited by the gasoline. but up the expansion ratio.

[CARN0T]

Hi, Carnot! <SNIP>
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I'm very skeptical about reaching 60% of efficiency with a "carefull design" of an ICE...
There is still a "Carnot limit" >> u=1-Tc/Th, <SNIP>
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Good luck!

Thanks, Spinner, for the very well-thought-out response.  As just mentioned above, my target compression ratio is 40.  Let's try that in the formula, with the specific heat ratio k = 1.35.  The formula again--

   Eff = 1 - 1 / R_c^k-1

putting in 40 for R_c and 0.35 for k-1, I get--

   Eff = 0.725

This is the indicated efficiency without thermal and mechanical losses.  If we lump these losses together as the "mechanical efficiency," then the allowed mechanical efficiency is Eff_M = 0.83 or better.

There's the tall order that I face, to hold all of the practical losses to 17%.  Well, frankly, I don't know if I will succeed.  IF I can build an engine that runs well at that compression ratio, then I am assured that it will far exceed any (small) engine currently in production.  (Note that some very large piston engines (i.e., Sulzer) have already achieved 55% efficiency.)

Ernie Rogers

[WilbyInebriated]

That's a fair question.  I have never built an engine.  The last time I worked on an engine (a lawnmower), I destroyed it.  I am a physicist, and I recognize my shortcomings here.  (I have designed and built machines previously, and I know how tough it can be.)  Up until a year ago, I had a partner on the design work.  He had rebuilt hundreds of engines (mostly diesels) and has some engine inventions of his own.  He got a good job and the work came to a halt.  Two weeks ago, I filed a provisional patent application (at the urging of my patent attorney).  My goal now is to put together a good team, with adequate funding, and build a prototype to test and refine.  The target compression ratio is 40.  This should be enough to come very close to the desired 60% efficiency.  As I'm sure you understand, there is a lot more to the problem than just raising the compression ratio.

Ernie Rogers

thanks for your honest and candid answer ernie. what would be the best place to stay up to date on your project, this thread or your blog?

[CARN0T]

what is required Is a miller or Atkinson cycle engine. keep the compression, its limited by the gasoline. but up the expansion ratio.

Hello, Fritz,

I agree with your thinking.  Actually, I think most efforts today to increase efficiency of an engine involve direct injection into the cylinder.  This allows the compression ratio to be increased no matter what fuel you use, but with a price in combustion complexity.  And, as you say, the expansion ratio is the key to high efficiency.  At my blog ( http://www.ernsblog.com ) I derive the efficiency equation for an engine as a function of several parameters, including the compression ratio and the "Atkinson ratio."  I define the Atkinson ratio as the expansion ratio divided by the compression ratio.

Slight correction-- the equation at the blog is for an Atkinson-Diesel, where the Diesel cycle has the classical definition of heat input at constant pressure.  I have previously looked at the Atkinson-Otto cycle, but found that less interesting.

Ernie Rogers