Efficiency Improvements for Internal Combustion Engines

[Frank Lee]

The "Crower" thing sounds neat and all, but it was patented in 1920 by someone else. That it's been around 90 years and never made it out of the lab begs the question of why?

http://www.freepatentsonline.com/1339176.pdf

[dcb]

It is a good point, that the secondary cycles should not increase the backpressure, as that directly affects the work the pistons have to do. Heat exchangers usually involve some energy losses.

Given the pitiful energy density of hydraulic and power to weight of sterlings (think lots of little sterlings with plenty of surface area connected to a hydraulic cvt), it is looking like the most "feasible" highly efficient vehicle is going to be a (hopefully streamlined) fatass, on two wheels

[NeilBlanchard]

So, why do piston / connecting rod / crankshaft designs seem to hit the efficiency wall at 38%? What is holding them back from getting closer to the 54% theoretical limit? The beginning of this thread has about three new rotary designs -- do any of them look to exceed 40%?

[autoteach]

You seem to be caught on the 38% number, but what of the ones that are rated higher? How about the VAG engines from VW and Audi? And why does the efficiency of very large engines exceed that of smaller ones? Here is a related question to that... Why will a 3 cylinder 1.2l typically have a better thermal efficiency than a 4 cylinder of same size? I would say that there has been a good amount of discussion on why we havent seen this 54% theoretical efficiency, and I dont know what you are looking for in our answers as this is at least the second time you have asked this after getting many answers.

[NeilBlanchard]

What piston engines are higher than 40% efficient in the real world? How long do they take to warm up? Can they have some sort of cogeneration cycle added on that significantly improves that?

[UFO]

Originally Posted by NeilBlanchard

What piston engines are higher than 40% efficient in the real world? How long do they take to warm up? Can they have some sort of cogeneration cycle added on that significantly improves that?

hey, I can answer that:

DIESELS!

Brake specific fuel consumption - Wikipedia, the free encyclopedia

[NeilBlanchard]

What is the most efficient diesel engine?

Obviously, biodiesel would avoid the massive penalty of wasting the majority of energy; because it is short-cycled energy and since it is renewable, it doesn't upset the balance of carbon in the atmosphere.

[autoteach]

Neil, do you refuse to read the links provided?

[NeilBlanchard]

Nope, just missed it...

So, the VW TDI V8 (?) and the Audi TDI are most efficient car engines, then? Do diesels have Start/Stop tech?

Do the EPA rating for diesels take into account the higher BTU's per gallon of diesel?

[autoteach]

So, if the EPA uses mpg for both, but uses mpge for electric, one could conclude that they do not account for the energy density difference. That is their efficiency at constant operation, not using engine stop/start tech.