Quote:
Originally Posted by Hersbird
Right, the gas turbine is always at max efficiency, the diesel sometimes. Plus you are comparing old gas turbines to the most modern diesels. There are modern turbines that do as well or better then the most modern diesels and they are getting better all of the time as they are more widely used in ships.
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Please show me the "modern turbine" that can improve on current thermal efficiencies of diesels. I have already defined this as the simple cycle gas turbine and not the combined cycle turbines you are thinking of. The Nikola truck does not seem to have a steam turbine hanging off the back of the gas turbine exhaust. The steam turbine would be exceedingly large and it's start up would be excessively long.
Turbines are ideal where power to weight is at a premium. Modern turbines have the ability to run at higher temperatures and compressor pressures but are still limited to around 40% TE. Yes, you can hang pre-compressors and thermal recuperators and such but now your small compact turbine is big and clunky for just a few percent gain. Capstone only claims about 35% TE for it's simple cycle micro turbine. Such a turbine would be ideal for a class 8 tractor with hybrid electric drive but not because it is more fuel efficient than current diesels but because it's small size and weight allows you to transfer more payload to your battery and fuel.
The advantage of gas turbines in aircraft is self explanatory. Nothing beats the power to weight advantage. But, small aircraft engines that are diesel are making a comeback for their fuel efficiencies and reasonable costs.
And you are making the assumption that diesels lose great efficiency when at part "throttle". They do not. They do not have throttles and can be optimized for part load efficiencies. The BFSC map of a diesel is far larger than that of a gas turbine or a spark ignition reciprocating engine.
Yes, I am familiar with super-critical CO2 turbines but these are more suited to larger power generators found on ships or land. An experimental system leverages the high quality heat of turbines (little heat is lost to cooling and friction) by running a gas turbine exhaust into a steam turbine whose exhaust powers a super-critical turbine. The thermal efficiencies are pushing 70%. Exciting stuff but not applicable to a class 8 tractor drive.