Deltic Rebirth? The Opposed Piston Engine Strikes Back?

I "stumbled upon" in my own way, the "new" breed of opposed piston engines which are allegedly being funded by the Bill Gates Foundation. They are two stroke turbo diesels which use a double cylinder per bank, with long conrods connecting the outer piston effort to a common single axis crank shaft.
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Although this approach solves the "problem" of reconciling forces* at both ends of each cylinder into a single power stream, it does still have the main inherent emissions issues of a swept port,  two stroke design  ( * in the Napier Deltic this  necessitated an expensive gear box which reverses the one gear lower sump shaft with the other two while then marrying all three axis to a single power output shaft)  

The main issue is that lubrication oil from the piston side walls and the sumps or injection sprayed "dry sumps" ends up exiting with the exhaust and burns partially, or worse, builds up (especially after time on idle )around both the exhaust and the air intake vents/ports and then leads to incomplete combustion when injection and final compression to ignition happens. Incomplete ignition is one thing usually completely avoided in four stroke diesels and modern 2 stroke traditional cylinder head motors like the EMD 645 derived engines.

Deltic pistons are more complex than traditional pistons because they require oil routing in order to effect cooling of the piston. In the absence of a heat dissapating cylinder head with water cooling or oil cooling channels in such heavy casting, then much of the heat from ignitions builds up on the piston heads and in napier's development process they identified that this needed oil cooling for the piston heads:  which means even more lub' oil than  the spray injected crank ends and bearings area can gather in the legnth of the cylinder where it meets the pistons. Inevitably some of this lub oil migrates along the piston head and is swept into the combustion area of the cylinder and exhaust chambers. The air intake side is under positive pressure by super charging (roots blower in a deltic) and turbo charging, and this stops build up to some extent at the lip of the intake but that may exacerbate migration of oil into the cylinder due to this positive pressure.

This oil migration to the combsution area of the cylinder is limited by the piston rings around the top third of the piston head however they do not provide a complete scraping or sealing when they sweep over the "gas"  ports.

One way of further reducing oil ingress to combustion areas is to then add more piston rings along the head and /or an oil scavenging scraper collar which is a consumable part fitted to the piston's base and scraping a swept path at a desirable D400s /BR Class 50, one reason they were too effective in preventing oil getting to the piston walls were it is needed.  In a swept port dry sump two stroke engine with oil cooled piston heads such a collar may well work quite well, and may be something which can be fitted from the crank case inspection points in a larger engine or by at least avoiding taking the pistons out as a outward end extra ring would otherwise.

Deltic "clagg" ie smokey exhaust  was always a feature of the power units when they were first revved from idle. All the excess lub' oil suddenly gets heated and blown out, some burning and there is also a lot of water vapour formed if the exhaust collective is cold , leading to plumes of white to grey smoke steam with a rancid smell. Add a little incomplete combustion of diesel from the air- in-port side issue and you get nasty deltic clagg, not good if you ever want to hear that Napier drone in new locomotives, gun boats etc.

Under way however, as you will see in the opening credits of the 1960s classic 'Get Carter', the deltic power units produced quite little smoke in service life.  So at 1500rpm lub oil was not able to build up due to the scraping of the piston and higher positive pressure on the intake side.

General motors EMD have overcome much of the issue with swept air ports while also steadily increasing the volume and pressure of air which is aspirated by/into the cylnder. So it is not a wild goose chase to clean up a deltic.

One approach is to use a different porting and exhaust rooting design, where you may have a positive pressure at the crucial timing points when the piston sweeps. Another is altering porting design , perhaps with multiple ports, which resist ingress of lub oil.

Alternatively the most complex which is not soild state, ie it requires new moving parts, is to utilise a rotating valve mechanism on the exhaust port which allows for the port to be shut when the piston is sweeping it (or if exposed to the crank case side on an imaginery longer stroke design). This could be a fairly simple cam lobe type arrangement on a single shaft per bank of cylinders, where the valve is wheel like and has an open side cut which is designed to be timed in with necessary exhausting. Alternatively a camshaft lobe  valve actuation could be used, if then introducing a degree of complexity into otherwise an elegant design with a high degree of "solid state" solutions.

Another alternative is to reduce the amount of lub oil needed to lubricate the walls of the piston and to dissapate the heat of combustion from the piston head. Here in Napier's day there was nothing available apart from metal with the best qualities to work with oil cooling, but now ceramic piston heads, rings and cylinder liners are realisable. The deltic has modest piston sizes, modest compression and kw/cylinder and a design which lends itself to cooling circuit improvements in the cylinder linings and design of the triangular engine "block".  All these point to use of low lubrication ceramics as a possibility.

I prefer the idea of the following set of " solid state" technolgies over cam shaft valve systems:

1) ceramic piston heads and rings
2) oil blocking and scraping system on the crank side of the piston which prevents most crank case oil from entering the swept area and reaching the gas ports or combustion area of the cylinder.
3) a high tech solution for the small amount of piston wall and conrod pin which need lubrication: perhaps using low pressure diesel injection, or a complete burning lubricant or a non burning synthetic lubricant.
4) Twin scrolled air intakes which are thus always providing a positive pressure at the in-port side, even at idle from super and turbo charging
5) a design for exhaust manifold which enables a slight positive back pressure on the exhaust port when it is being swept such that it presses lub' oil away.

Deltic - Dinosaur or Died too Early?

I remember deltics well of course, even if i had a fleeting relationship to them in their BR service swansong when I was a nipper. Deltics weren't a locomotive you just saw and heard, you felt their power and prescence.

By the last old days of 1980 the deltic reign had ended. All be that ten years after the anticipated life time on  the ECML metals. Just as with the pacific steam locos the deltics replaced, they themselves were superceded . They had become dinosaurs.

Or had they? In reality the fleet got a stay of execution in 1978 and ploughed on with various east coast and the final rather ill suited liverpool - newcastle semi fast diagrams. Rationalised with two of their brethren becoming parts bins,  the rest in reality kept as an exhibition fleet into 1980.

The remarkable thing is that the remaining  locos have survived much longer in preservation: now more than half as long again as their active service wijth BR. The "third age" of the deltics with proffessional management and main line certification.

What then for the alternative history where BR or a private body supported their utility say another decade in service?

Well if privatisation had been happening in the 1970s then gyou can bet that they would have been. A private railway would not have invested in a hundred 56s and the entire class 58. Standardisation versus reliability was a BR mantra , the opposite has been seen across europe and the usa. So the brush type 4 and its under delivered promise and poor reliability would have stopped the later builds. Class 50s would have been sent back to by then GEC leaving deltics, peaks and the more reliable hydraulics to be the main 100mph service providers outside HST diagrams.

Another alterntaive future would have been re-engining.  By 1980 the Ruston Paxman Valenta would have been available in either a v8 at 1650bhp or a v16.  Twin v 12s could maybe fit in a deltic, giving them thus standard units to hst and an RA 6 not to mention 4000 bhp plus!

Maybe other improvements to lub oil and piston / crank systems in the deltic power unit could have made them less smokey and extended service interval to over 3000 hours. Or a turbo version tuned for efficiency.

Whatever the locos when compared to ageing 45s and dodgey engined 47s , deltics were only a tad more smokey and it was burnt oil not spewing diesel and lub. They werent the only relics of the rush to dieselise which were environmentally non PC even by the mid eighties.

Where would they have worked?

If there had been a gap for them to work in an extended lifetime, then it would have been in the west country that they would have thrived. Well into the 1980s there were enough north to south west diagrams with loco change from WCmL or the need for speed from Newcastle or York right through.

However there were also 50 class d400s and seemingly endless ETH peaks in the post oil-sloshing GWR. Not to mention duffs a plenty, one fails send out another until you are down to 47/3s and ice cold trains!

Deltics had higher ETH capacity than 50s and arguably better performance in the 85 to 110 mph range. However it was only the eastern depots, Paxman colchester and donnie works who had the expertise needed in the early 80s in order to keep an ageing fleet going.  Newcastle could then have been a centre for diagrams NE-SW with temporary stabling and driver training only at brum and bristol.

As a small, specialist fleet though there could be a case for remote allocation of servicing.

My own choice would be phasing out 50s over to HGR and including an upgrade to their eth. Thus allocating them to semi fast passengers, over night sleepers and speedlink on the ecml,. Then having 15 deltics allocated to Doncaster with a preserved demo fleet of four to newcstle and haymarket for railtours.

The donne main liners would actually work the west country with extensive drijver training for the wcml to Sw services during the day and the brum and newcastle sleepers at njight. This would be only to 1986 when boilered "bedz" were finally erradicated and enough hsts were released from ecml electrification to free up class 50 to take over any remaining GwR services in their new proven and fully rectified guise.

Deltic Top Speeds

I was just having a little google about for any facts on the highest ever recorded top speed of a Deltic locomotive.

Well there were plenty of " i heard from..:" ,  or "read somewhere" from neds and "needle off the scale" from actual ECML drivers.

Also there are a few HST idiots who think deltics were a bit rubbisy and needed to be withdrawn for the zinging vermin to take over. The Deltic loco fleet was a small fleet of locos, the smallest of any commissioned main line diesel loco, and was built to supply the top express services on the ECML with improved running times on diagrams as a stop-gap for a decade while electrification was completed on the WCML and later the ECML in that timescale. Improved diagrams over exisiting sulzer powered type 4s entailed sustained 100mph operation on the new continuously welded sections. "3000 HP was needed under the bonnet" as the quote goes.  So that the deltics lasted 21 years in mainline express service is to their credit.

Top speed however is much more a matter of debate, and you then encounter the "short mile" calculation error etc. Firstly let us agree on one thing : 100mph was the maximum permitted speed and not that capable of being achieved. A loco being driver limited in those days means that a higher velocity could be envisaged and that as said above 100mph was the desired cruising speed.

DP1 , the deltic prototype had been uprated in some ways and had safety clearance for 105mph in fact, probably giving this leeway for driver error in maintaining an average of 100mph. That production locos could have been designed slower is not really a consideration if in fact DP1 was not all highly over engineered in terms of electrical equipment.

Throw the next thing into the higher than 105mph camp for them to fight with: The power units were not always set correctly to their top rpm. The non turbo deltic engine 18 cylinder, was rated at 2200hp-2500hp for the admiralty for use in MTB's, first tested in former E boats versus their much larger Merceded engines. These Power Units (PU) ran at 2000 rpm where as the production deltic locos' PU's ran at 1500rpm....ish ...it would appear that the rev limiter was not so finely adjusted and after some improvements to the design and materials during the first 6 years of loco's life with for example variation in the piston head materials, then it would have been ill advised to deliver an engine running a little below 1500rpm or banging off a rev limiting ceiling perhaps so to speak.

It is alleged that D9009 had a fault in this setting while under the cherised protection of the deltic-preservation-society, with an actual power output of c. 2000hp for one of the two PU's!

"secret trials at 3600hp" stories abound when I was a lad too, and have perpetuated on the internet. There probably i some truth in either collusion between fitters or the manufacturer and some managers with an interest more in timings than reliability and service interval! If you rev two car engines to the same relative difference of 500rpm in a deltic, then you hardly really could tell the difference  i'd say.

So here we come to a double ten percent club: firstly you have the permitted top speed being 105 in the prototype, so you could argue that a 10% safety margin was established above this: that being the 115.5mph.

114 mph seems to be quoted often on the internet and IIRC from deltic "men" in their light tweed jackets as they condescended to scurry around the ScR in post deltic 1980s.

Throw in then a second 10% in: 10% more power per PU due to slight misalignments in the limiter governor and Napier or the ertswhile Findsbury park fitter not wanting to disappoint with lower than desired power output. So 3630hp. More importantly actually in the highest field diversion a higher rpm will create a higher voltage with decreasing amps, so that is actually quite important for peak speed running: being able to extend the range before weak field is encountered by applying a higher voltage.

So now we do indeed come up to the possibility that standard deltics pushing out 3300hp, about 1.8kw at rail, could do 114 mph with their ETH off WHILE, an inadvertantly uprated deltic could then go over 120 mph.

You could just ask drivers if they had physically more power handle to pull on, but the situation is more complex due to field weakening, the electrical control system in DE locos and the momentum of the train.

The only real way is to look at timings from fast runs and deduce then the speed troughs for slowing to stop at stations and then be able to back calculate particular speed peaks which relate to the track conditions being straight and probably down hill. With runs of under an hour for 100 miles between stations it is obvious that a higher peak has been hit and maintained for a substantial period in order to allow for the acceleration and braking periods.

I'm of the opinion that a deltic did physically do 120 mph for a mile at least somewhere but however I think the 128.8 quote is probably a miscalculation based on short miles MSTS or whatever they are called.

The top speed for 37s has been quoted in pairs to me as being 114 mph noted by milepost timings on the great eastern, and 116 anecdotally. What speed they ran 37s to propell the APT stock on the ECML during high speed experiments is another story perhaps in the mythology of the blue and yellow railway.