Woodward did offer an optional fuel limiter on its PG locomotive governors. It was intended to limit smoke during engine acceleration when the turbocharger was “running behind the engine” so as to speak:
I am not sure when it was first offered, but I’d guess in the early 1960s. Possibly it was developed at GE’s request for the U25B:
The underlying idea was not new; Sulzer had introduced a manifold pressure-operated fuel limiter c.1946 after patenting it in the late 1930s.
I have heard anecdotally that the Woodward device required careful adjustment if it was not to operate too aggressively and so limit steady-state power. One suspects that if this were so, some operators may have chosen to disable it or set it for less-than-desirable fuel limiting under acceleration.
Whether any Alco locomotives fitted with the Woodward PG governor also had the fuel limiter I do not know. From casual observation in Sri Lanka a few years back, I noticed that the M4 class DLW-built DL560 produced a lot more smoke during acceleration than the M8 class MLW-built MX620. The DL560 had the GE 17MG governor, or at least a later DLW iteration of it, which as far as I know did not have any acceleration fuel-limiting device, and was fast-responding. So, one would expect that DL560 fleet to produce a lot of acceleration smoke when the throttle was moved very quickly to Run 8 from a standing start, which looked to be the case in Colombo suburban service. The MX620 had the Woodward PG governor, and its much lesser smoke output suggests that it also had the fuel limiter.
Of the Australian Goodwin-built Alco locomotives, the early DL500s (through to NSWGR 4460) had GE 17MG governors. The later DL500s and I think all of the DL531s and DL541s had Woodard PG governors. The observational evidence suggests that they were not fitted with fuel limiters.
English Electric (EE) had its own governor (without a fuel limiter option), but also fitted Woodward PG and Regulateurs 1100 governors from the 1960s. The latter had manifold-pressure fuel limiting, in this case operated by moving the load control pilot valve sleeve. Later Rocklea-built Australian EEs, from the QR 1600 class onwards, had Woodward PG governors, and this included all of those with the “Australian special” version of the Mark II 12-cylinder engine. My guess is that they were fitted with fuel limiters, but I do not know for sure. But definitely the NZR Di class of 1966 was so fitted.
Re GEs, in its early days, the U26C (NZR Dx class) was known for throwing quite a flame from its stack when working at full throttle. These had Woodward PG governors with fuel limiters; the exhaust flame was a steady-state rather than a transient phenomenon.
The EMD case, with mechanical drive to the turbocharger at lower engine speeds and outputs, has already been mentioned. Two-stroke engines are more difficult to turbocharge as the exhaust gases are much more diluted by scavenging air than in the four-stroke case, and so have a lower energy density. Given that the gas exchange process must take place during the bottom 15% or thereabouts of the piston stroke, excess scavenging air is required. In any event the EMD turbocharger requires mechanical drive at lower engine speeds to provide enough combustion air under steady state conditions, and not just under engine acceleration conditions.
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