Twin Engines Drone and Whine Again? The Shape of Diesels to Come

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.....

Locomotives In a Spin> High RPM and Multiple Power Units versus Mid Speed

It is interesting that some things return full circle to the way engineers thought in the late 1940s and into the 1950s when presented with a problem to solve> Back Then it was replacing steam with quite literally,. a turn key solution, while now it is replacing the second generation of 1970s&80s Diesel locomotive with locomotives which can comply to the outrageously strict emissions and noise legislation laid down by the EU commission and also lead by California who have pointed their judicial compliance bow to zero emission locos. This in itself is a farce becuase even diesel loco hauled trains are many hundred times more efficient over any long haul route than the equvalent 20-50 lorry loads or 200 - 300 personal car journeys. Rather than painting power units in locos with the same black brush as mass anarchy transport, they should be setting a sensible level of progress on these fronts, all be that very much quieter locos than we enthusiasts may like to hear pounding the metals..

Today Seimens present a modular power unit loco with possibility for dual power (over head or maybe third rail units top be popped in) and / or battery packs. One key benefit they quote for today's operations is that the locomotive can dial in and out power as it needs it, with the power units then working at their most efficeint peak range more of the time when they are on, thus reducing fuel consuimption and emissions,. In their Marketing PR launch discussion they talk with no reference to the long history of multiple power working doing just this, dialing in more power when needed, while then saving fuel by cutting back on parts of the route which do not need so much horse power. Rail actually requires a large tractive effort to start a train and to take a train up a steep or continous gradient, but since the days of Rocket it has been known that there is a lot of coasting and low tractive effort haulage going on due to the inherent efficiency of running on rails, particularily with roller bearings and optimally loaded axles. Thus you are actually dialing in power a lot more in a train than you are in a lorry which has a lot more relative wind and rolling resistance than a train, and you can times that by as many as 60 in europe for the biggest 2000 tonne trains

I can't remember if the PR release mentioned engine redundancy in case of power unit failure, but this has to some extent been quoted as the reason for multiple engined locos. This may have been at some point someones 'also ran' selling point, be that point made by a supplierr on internally to British Rail western regiona and the Deutsche Banen in particular. In fact the notion is largely a red herring : in the case of the German multi engined V200s/220s and the British Deltics, the attraction was more horsepower per se from a single locomotive within some technical limitations. Interestingly those limitations were quite similar and both technical. In the 1950s there was a desire for light locomotives with 2000kw output approximately to sustain speeds of over 90mph/150 kmh and run ideally cruising at 100mph//161kmh.  The limitation were on both diesel electric and the hydrualic mechanical transmissions at the time.

Both systems were limited to about 2000hp per power unit by technical limitations. Firstly in the electrical generators, where English Electric had a size limitation and a knowledge of flash over (which would later plague the class 50 and competitor's class 47 locomotives ) in the dirty railway environment for the then DC generators. The biggest EE could offer was about 1.75 Mw , brush and AEI offered slightly higher while the American locomotive manufacturers could offer their home market around 2.2 by the early 60s with the larger loading gauge. The DB in Germany had opted for Diesel Hydraulic for their higher speed services and much of their other locomotive provision in the 1950s. The limitation to them was that at that time for the footprint required at least, neither Voith nor Mekhydro could offer power transmissions of over about the same 1.7 mw, or actualy at rail about 1500 hp.

One efficiency advantage of diesel electric in this respect is that a single engine can be employed to deliver the maximum applicable kw to the traction motors at start and low speed in a light weight express locomotive. In the Deltic this means that the power control handle does not activate the second engine until approximately 18 - 22mph is achieved. With the secondengine revving up to deliver power to the same level as the first and then both going onto rev further to deliver 50mph 
, the system as a whole is very efficient for passenger workings because they require exactly this type of acceleration avoiding a field diversion(electrical gear change). A typical 350 tonne passenger express of the late 50s'1960s requires light starting effort and offers actually not very much momentum to push through field diversion  . This explains why the class 50 out accelerates a deltic to over 30 mph, while a class 37 will out accelerate a deltic to 18pmh hands down because it can lay down far higher amps as its single engine is delivering maximum mechanical effort in the first field which dies at around that speed. Both these classes however could be plagued at speeds of under 50mph by trains not having enough momentum to push through the diversion, then meeting a gradient, or by a speed limit or signalling which meant the engine hunted between two gears as a manner of speaking about the automatic detection and switching equipment. The twin engined deltic and presumably Brush "Falcon" overcame this issue by dialling in the power and avoidimg low speed diverts, while the former offered quite low starting effort and maximum continuous effort due to having a lower amps/ higher voltage system (amps are a measure of torque where as higher voltage relates to spinning if you like, groossly over simplified) 

Diesel hydraulics however have a different advantage in having their torque convertor 'half gears' ie slippage in the fluid coupling followed by the married phase, as well as having a range of 'hard ' gears to change up to.  Correctly engineered this makes for a very smooth acceleration with virtually no wheel slip and quite a high starting effort. Both engines can power their respective bogies from a standing start without the typical electric overload of 1950s first generation DE locos, they are designed to be geared correclty for this tractive effort and the limiting factor is how long you can cool the hyrdaulic  transmission oil when it runs in fluid unconnected phase (slipping stator relative to rotor). For all types of trains in fact, a twin engined diesel hyrdaulic has another slight advantage over DE designs of the late 50s at least, and that is that one complete transmission bogie system can be left on maximum power while the other system reves down and changes gear for its next bit of the cherry so to speak, thus the train can be kept at a constant speed if not on a steep gradient. Field weakening on DE is a just a natural physical barrier for the entire system if it is to run smoothly, although a complex out of phase double system coudl be concievable, where the two bogie/traction motor sets are tuned to different field weakenings. Instead as in the deltic, the number of gear changes to 100mph is just three versus effectively six for diesel hydraulics even when they are more powerful as in the german V classes. 

As touched on in the pre amble above, the redundancy of twin engined locos was a secondary selling point in effect then. However it did mean that the most important express services on the GWR and the ECML could limp home at about three quarters speed in the mid 1960s when the whole genre of diesel was still to be proven as a mass produced item. Further into the 1970s, the HST IC 125 sets had two power cars in order to deliver the magic extra thousand over deltic services to go 125 mph., but the betting on effectively two power units per train proved prudent in terms of limping home as both the Ruston Paxman valenta and the Mirrlees power units prove to be less reliable than anticiapted for their service intervals in the reality of the dusty conditions and high thermal cycling loads placed upon them by the nature of having more stop starts than originally discussed with the manufacturers. The 125 was actually designed with train crew changes en route and fewer stations than the deltic and class 52 services they replaced. 

In terms of fuel efficiency then I have not heard of westerns warships havbing one PU shut down, but it happened regularily on Deltics which would have their second engine shut down on the slower Ediinburgh-aberdeen section of the expresses from KX. Presumably after ETH was introduced this required that the second PU be on a heat only selection, revvving not far boave idle I do not know. Deltics did limp home and run light loco on a single PU, and especially with the teething problems with pistons they encouuntered, this became a very fortuitous feature.

In post war Europe and the UK there was still materials rationing and oil was imported from the US and Middle East, so the use of multiple workings, dual or more locomotives is for those historical reasons far less wide spread than it is in the USA/Canada, coupled to a steady decline in freight from the 1960s to the 2000s as the road network improved. The states on the other hand and canada had a heavier loading gauge and bigger, more economic commodity and produce loads to haul by rail and thus it was economic for them to run multiples and 'robot'  locomotive arrangements were widespread by the early 1960s with multiples of up to 4 at the head and more down the train. I do not know of any european robot multiple locomotives apart from shunters like the class 13 and some on the continent, robots being a unit which lacks a proper cab and are only used in multiple with cabbed locomotives leading. By 1960 the BTC/BRB had abandonned through connection doors for locomotive design, although many were in still in production then, and were stipulating that type 4 motive power be above 2700bph and not fitted with multiple working ( a decision reveresed in the class 50 due to the gradients of the WCML and the ambitious timetables laid out in the run up to electrification in order to keep the route competitive in respect of the new M6 /M74 and the advent of the Glasgow Airport-London shuttle. Class 50s were not fitted with these as a response to theirr reliability issues, which were in fact somewhat better than their rival mass priduced brush type 4, which required a massive rectification at a cost of over three million pounds back then. That class 50s were delivered without multiple working cables t first has been cited as being because of availability of the materials at the time, safety testing not being complete, the price of the class 50 running into problems and then this being taken as part of the hire-purchase scheme they were bought on, subject to absolute rquirement for the faster timetables north of Crewe and later Preston)   

So at the end of the day you have to examine what your actual missive for tractive effort and maximum speed is, and in fact this is where DE wins over DH:  For the same horse power and power unit arrangement, " Faclon" was a better performer than the class 52 Western hydraulics with their voith systems. The limitation here was that the v12 MD655 engines were not powerful enough for the  third gear on the Voith transmissions which were presumably very similar to those fitted in the more powerrful German V2xx locos. It may have been possible to have fitted tiwn v16 MD870s or alternatively a Mekhydro gear case could have provided a better matched power deliver for running at over 75mph. The Voith transmission is in theory smoother than the Mekhydro due to it working on a priciple of triple, sequential torque convertors and hydraulic actuation of these three main gears. Although Westerns and of course Hymeks saw a lot of working on relatively heavy freight services, the similarily powered Falcon and the Class 37 EE type 3 both out performed their respective DE cousins in standing lift and progress, all be that with some degree of wheel slip on the EE type 3. Deltics did work a very few freights in their lifetime and heavier night mail/sleepers of over 650 tonnes, famously last year D9000 working some heavy lifts to the rail head due to lack  of class 66s.  Falcon, the class 53 one off from Brush, excelled at both freight and passenger working, and indeed ended its productive life on ore and coal traffic, slugging them around south Wales. Class 50s were designed on out set to be a stop gap passenger loco for the WCML but also then to have the possibility to work higher speed freights of upto 1000 tonnes, being in fact prepared with mounting points for buck eye coupling as if it was going to happen in the 1970s.  

We have then come full circle in which transmission system suits which traction missive: For light passenger trains of 40 mph to 80 mph the vast majority of diesel services in the UK are now sloshing oil over convertors with mechanical hydraulic tranmission. This was a decision taken a very long time ago by some engineers, probably ironically enough, about two or three years after Western Region lost their last main line DH locos. For heavy freight you want to slug it out with 25 tonnes per axle at least and over 3000hp in DE, while also the hands down winner for mixed traffic is the DE too because of the controllability and range of electrical traction systems. This is reflected in the delivery of the latest class of locomotive to the UK, the mixed traffic class 68 which is pretty much the type of locomotive the GWR would have ordered if they had been forced to run with a larger proportion of DE locos. The main point lacking here is that we do not see many multiple power unit locomotives with their specific advantages and redundancy, but that in main part is due to the amount of power available in reasonably sized single power units in mid or higher speed * GM versus Caterpillar, MTU and the most powerful per weight, the VP185 from Rustons /MAN, and also that there has been no specific missive for this type of locomotive. Even in DH we have seen several Vossloh locomotive classes and the Anglo Belgian powered freight class emerge with only single power units. It seems the reliability and modern engine management have by in large rendered twin engines obsolete, where as the Seimens loco can carry up to four power units.