The " Alco Smoke " was due to a lag in the turbocharger. It could not spool up as fast as the fuel injectors were applying a greater stream of fuel; it was kind of like driving your car with the choke on ( too much fuel & not enough air ).
Espee's dual fuel system did have several advantages. The heavy " Bunker C " oil had a higher BTU rating than regular # 2 diesel, offering somewhat better fuel economy. It was also cheaper than diesel, at least at first.
Espee's dual fuel system also had several disadvantages. As noted above, the units still required diesel fuel for starting up the prime mover and supplying heat to coils inside the Bunker C fuel tank. Bunker C was a heavy, tar - like oil which had to be heated before it could be run through diesel injecters. This led to the biggest issue with dual fuel: the requirement to switch back to diesel before shutting off the engine. If the engine was shut off while still running Bunker C, the stuff would harden in the injecters & exhaust, requiring an engine overhaul to remedy.
Other issues with dual fuel included the eventual increase in the price of Bunker C, due to its' use in asphalt roads and roofing shingles. And yes, as Espee retired its' steam era facilities, the availiability of Bunker C oil was limited on the system.
And YES, I will call it Bunker C Oil, just as Joe Strapac does. So there...