I'll guess 20-25%.
Al Krug's table is available on the Wayback Machine -- it says an F7 or SW1500 burned 93 gallons per hour in Run 8.
https://web.archive.org/web/20100529204212/http://www.alkrug.vcn.com/home.html
Last month on my way to our 15th Cotton Belt Regional Railroad Symposium I encountered four southbound Union Pacific trains between Brinkley and Pine Bluff. Three were parked on the mainline with their crews staring at red blocks. The fourth was walking its train over the Arkansas River Bridge and into Pine Bluff Yard. It doesn't matter how a locomotive is built if it is standing still. Later at the Arkansas Railroad Museum a retired SSW/SP/UP hoghead told me that as long as the trains are parked it was considered running time and not dwell time.
Ed in Kentucky
Erik_MagI'd wonder if some improvement could come from turbo-compounding, with the turbine(s) driving an alternator(s). The electronics associated with the alternator would impose the optimal load on the turbine, with the electric power put on the same bus as the main alternator. The induction compressors would also derive power from the bus, allowing for faster spool up.
I believe F1 is using similar tactics with their turbocharged hybrid gas engines, which have 'motor generators' that are driven by heat (MGU-H) and kenitic (MGU-K) energy. The total package of 1.6L engine displacement is reported to put out over 1000 HP from both ICE and Electrical outputs.
Never too old to have a happy childhood!
I'd wonder if some improvement could come from turbo-compounding, with the turbine(s) driving an alternator(s). The electronics associated with the alternator would impose the optimal load on the turbine, with the electric power put on the same bus as the main alternator. The induction compressors would also derive power from the bus, allowing for faster spool up.
Vastly, with the advantages of EFI and more broadly FADEC being examples.
On the other hand 'progress is not always forward' most particularly with respect to pollution control, where fuel efficiency in particular can take remarkable hits and maintenance cost can metastasize.
As I have noted, it would not be difficult to make diesel prime movers much more thermodynamically efficient with better regulatory common sense combined with adoption of larger-mass-flow SCR.
How much more efficient are modern diesel locomotives compared to their first generation counterparts?
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