[Gerben]

$this->bbcode_second_pass_quote('malcomatic_51', '.')..A combined cycle plant is the most efficient prime mover ever produced by humanity, with a thermal efficiency of over 60%. I think this system has been tried experimentally in truck engines, but like any turbine system, it does not suit varying speeds.
...

[invest_in_politics]

$this->bbcode_second_pass_quote('malcomatic_51', 'B')y the turn of the 20th century the science of thermodynamics was advanced enough that the efficiency of any engine could be predicted fairly reliably just by knowing the maximum temperature and the pressure ratio.

[malcomatic_51]

$this->bbcode_second_pass_quote('invest_in_politics', '')$this->bbcode_second_pass_quote('malcomatic_51', 'B')y the turn of the 20th century the science of thermodynamics was advanced enough that the efficiency of any engine could be predicted fairly reliably just by knowing the maximum temperature and the pressure ratio.

[jbeckton]

$this->bbcode_second_pass_quote('Gerben', ' ')80%+ efficiency should not be very difficult to obtain.

[Gerben]

Never mind that remark (I removed it).

Which doesn't mean it is totally impossible, just impractical in a vehicle. You can use a lot of the waste heat of an engine in a heat engine. The more heat cycles you add, the more heat you can use. The problem is that it's not cost-effective (and adds too much weight on a vehicle).
It's cost-effective in large power plants (Combined Cycle, Gas Turbine + Steam Engine); but not used at lower capacities or with gas engines (less heat and at lower temperatures, because of higher gas engine efficiency). By using a different medium (with a lower boiling point than steam, in a secondairy cycle) you can use more heat.

Some rough estimates:
Combined cycle = ~ 66%
Gas Turbine = ~ 40%
-> Heat Engine = ~ 43%
Gas Engine = ~ 45%
-> Gas Engine + Heat Engine = ~ 69%
-> 2 heat cycles = ~ 82%
In practice you’ll probably need a third cycle and good insulation.

It's all about money (and in vehicles about weight). Luckily energy is still cheap.

[invest_in_politics]

$this->bbcode_second_pass_quote('malcomatic_51', '.')..Being aware of the effort and the vast range of ideas that have gone into achieving the gains we have made in the last century, I am not very excited by anyone who casually claims they can improve efficiency by the equivalent of 50 years' of effort "through minor modifications". I have Googled Tinker and he has a fraction of my own Internet profile - and I am nowhere near being a genius. I'd put him with other minor inventors as seeking attention for a modest idea with perhaps a little promise in it.

[invest_in_politics]

$this->bbcode_second_pass_quote('malcomatic_51', '.')..recollection from historic data held by my former employer Brown Boveri Corporation...

[invest_in_politics]

$this->bbcode_second_pass_quote('malcomatic_51', '.')..Not all engines rely on heat flow. There are isothermal processes that can theoretically be 100% efficient, but they are all too awkward to make as practical engines..

[malcomatic_51]

$this->bbcode_second_pass_quote('invest_in_politics', '')$this->bbcode_second_pass_quote('malcomatic_51', '.')..recollection from historic data held by my former employer Brown Boveri Corporation...

[invest_in_politics]

$this->bbcode_second_pass_quote('malcomatic_51', '.')..No it does not mean I was part of the COLSS development, whatever that was or is...