The latest round of locomotive developments seem to be in part at least, back to the future. This is in terms of locomotives returning to higher speed engines , once shunned in favour of 'mid' speed , marine derived power units. Also we have seen a fragmentation of new types of locomotives, post the mass public purchase of the Class or Type C 66 as it is known across Europe. Quite a few of these have been diesel hydraulic too, especially from Vossloh and indeed Voith of course with their monster.
It seems that there is a new king and queen in the power unit world and they are both v16s with the choice of either Caterpillar from the USA or MTU from the father land. In rail application they run about the same rpm with the former being quoted as having a higher output. It is presumed by the Author that in fact mid speed engines from MAN group, EMD, and GE are no longer in favour due to emissions profile, higher rpm seems to then suit better combustion in smaller cylinderr volumes. Taking this to its extreme the interesting rival from Seimens, the Traxx loco, takes a completely different approach by utilising not just two but up to five power units of presumably automotive origin or smaller industrial marine type diesels, or perhaps based on static generators.
The concept here being that of each power unit is working most of the time at above 80% output when engines are allegedly at their most efficient. You then dial in extra power units as the demand increases. This is no crazy idea because once a load ie train, is started and taken up to a speed of between 40-80kmh it requires far less kilowatt power to maintain rolling, given light gradients of less than 1/110 say. Also a bug bear for low carbon emissions is running empty trains, many of whose rolling stock is restricted to a top speed unloaded of under 120kmh. Some rostered container diagrams vary greatly in actual tonnage to be transported, yet the driver has the same diagrammed time to hold to despite being able to go faster with a better power to weight ratio. Power units of the mid type are as I say allegedly not very efficient below 80% max rpm, but that was probably not the case for the ruston SVT and CSVT whose smallish , multiple turbos provided good fuel economy when only 50% power was demanded.
Given that a major global player in the market, Siemens, is now pushing multi power units as a solution and no doubt presenting lots of figures in endless powerpoint slides to support their teutonic assertions, then it seems inevitable that other loco manufacturers and PU producers will offer the same, most likely in a two or three unit solution.
Post war, the Deutsche Bahn took almost exclusively a ' high speed' motor option with hydro/mechanical transmission. Faced with a very similar practical limit for single drive in the 1950s as with generators, they twinned up with the famous v200 series of locomotives, which influenced of course the BR Western Region most, but is of course a daily fact of life on the remaining high speed diesel lines in the UK, where Intercity 125 HSTs operate with two power cars, effectively a twin engined system. Deltic and Falcon were in the bidding too, but limitied to only 24 locomotives out of many thousands of diesel electric, single power unit locos (ignoring the ill fated 'Claytons' )
In the 1950s then the transmissions only handled about 1.3 kw / 1800 hp of output, with perhaps the best generators from Brush taking towards 1.8. So BR twinned up for their premier high speed passenger routes where 2000 hp was just for starters, they needed really '3000hp under the bonnet' . DB went a little further than BR of course by using twin v16s in the infamous DH4000, v320 which is a mighty bit of oil sloshing kit, being uprated to 3800 hp and still running today in contrast to the single venture prototypes of BR days. The v320 is fitted with twin v16s as against the v 12s of the BR DH and DE 125s . The D1000 'Western' class should have surpassed the performance of several type 4 DEs of the time, but the Voith gearing in the triple convertor was a little high at the top end for the v12s, presumably this hydraulic gearbox was the same as fitted to the v320. It is also revealed now for posterity that Falcon, with the same power units but DE drive was superior in the lickey bank trials. It wouold be interesting to have seen westerns fitted with either 1) Hymek transmissions, with gearing tailored to the engine output 2) the v16 Maybach/ MTU as choice.
DB moved away from twin units quite quickly into the 1960s with the v160 type, fitted with a single v16, and only odd and shorter lived flirtations with a secondary power unit. DB found out of course my own contention that type three power , 1.3kw, was adequate for the typical 300 - 600 tonne trains of the day, and of course today passengers are no heavier, while freight can be handled by multiple locomotives. Later of course there was the demand for ETS (ETH as it used to be called) and trains which were yet faster than steam, so fortuitously MTU could offer far more power from the same footprint v16 over time and the v160 type evolved and dominated much of western german loco hauled transport through the 1960s and 70s.
DB later favoured single power unit locomotives with the v16 in DH going up to 2700hp while then more powerful DE locos were introduced in the late 60s and onward. The same is actually not true in Britain, where firstly IC 125 units are essentially dependent on two power cars, and then of course there was all and sundry rubbish of multiple units with several power units per train. Also DH transmission is by in large restricted to sub 100 mph operations for some reason, but is very useful for lifting heavy loads on gradients and can produce a lighter power car / loco for any given horse power.
In the 1950s the attraction of twin engines was not only overcoming the limitations of transmissions, but also provided a means of redundancy ie back up in break down of one PU or drive system. Back then it was also conceived that single power unit operation on lighter trains or slower sections was perhaps desirable. Indeed Deltics allegedly ran North of Edinburgh on one power unit to Aberdeen as a matter of routine to save on engine hours and probably fuel too. The NBL warships had early reliability issues with their power units, so redundancy helped GWR a bit at least. Wwith subsequent twin engine locos all the way to the hst and its notorious mid eighties reliability issues caused mostly by cracked alloy turbo casings, there is a means of limping home or at least running off the main section before the need for another loco and multiple knock on details on the blocked line.
An internesting historical bit of politics about twin engined trains was that the hst protoype was launched to the public at large, the promotional film was edited carefully to only show a single, leading power car. This was because it was the beginning of the early 1970s oil crisis, and two thirsty power units may have not gone down well during petrol rationing and power cuts. Back to the future once more, fuel costs and taxation rising and te desire for a lower CO2 profile for rail travel, just as with all others. It is a little infair in both respects here. Firstly to do 125mph with a 300 tonne train gross weight, you need 4000hp and then you need another 500 for 'head supply' ie heating, lights, aircon', kettles, and auxilliary loco supply like compressors. Secondly how many car joiurneys saved in the last 40 years since ic 125 came into service? ....with congestion at Sheffield, N. london or Birmingham rendering them much longer and less environmentally freindly.
Now uk rail on diesel lines is 99% mutliple power units. They are being used in the wrong way though. One per carraige often. There is the inevitable loss of efficiency in each transmission, heat inefficiency, and also weight inefficiency due to many duplications of auxilliary equipment. In the three car single unitary train, this is actually arguably less notable while when you reach Six or nine cars you are more efficient again with one or two powerunits in a loco or hst style power cars according to some work done by Virgin trains.
The future looks to the past then but also to the mistakes. Take for example HSTs- ruston paxman delivered high powered yet light V12 valentas. They took on a missive for long distance super expresses, non stop with crew changes under way via the communication doors at the back of each power car. By time of operation, BR had some clowns in their planning dept who decided trains should stop far more often in order to serve a bigger overall potential market per sevice. In one fail swoop they blighted the reliability of the design, and also dammed BR to semi stoppers and journey times often comparable only to normal car journeys door to door. Also while on this specific train-set, they are quite heavy all up and the driving style from a standing start seems to use a lot of energy up getting off their marks, reaching the first electrical gear change with both locos having been run up to near full power. It would seem that v200/western system would be preferable, where only one changing at a time maintains tractive power and hence momentum
There in lies what the usa with conrail and private operators have done with the longest trans rocky mountain freights and dial on power units in 'robots' along the arrangement. Computers have been assisting this since the 1980s. Route mapped performance and power demand is still in its infancy in the uk, where shorter sections between signals and congestion may seem to negate their use. However trains still need to accelerate, cruise and deccelerate. Now they have to keep the Kyoto men happy with co2 output though.
So the body of work is all their in the annals of dieselisation, now we have the technology to move forward, twin engines or not......just one step ahead of the 25kv overhead lines.....