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Over to Captain Deltic for an update from the cutting edge of internal combustion
An issue still to be resolved is the power rating for HST2. The equation to be solved includes the cost of energy, the market and the laws of physics as they relate to top speed and acceleration.
Since Greater Western will be the dominant user, the distances and traffic volumes are such that there is little commercial benefit in running faster than the existing 125mile/h. Thus acceleration, rather than top speed, is the determinant and the key parameter is horsepower per tonne (hp/tonne). A 100mile/h Class 55 Deltic plus 8 was around 9hp/tonne – we don't need to be precise.
An existing 8 car IC125 is just under 11hp/tonne. In contrast, the current 125mileh diesel multiple units with 750 Cummins horses under each vehicle come in at about 15hp/tonne. In an increasingly energy conscious world I am not alone in deeming this excessive.
We can see how power and weight relate from a recent study based on putting the latest version of the 14 litre Cummins NT855 engine under a Class 158. Driven hard the performance would not be far short of a Class 22x. This is a reminder that the current generation of lard-butt DMUs from Bombardier and Siemens carry around 10 tonnes per vehicle more than a Class 158.
Inspired by the 18 cylinder version of the Paxman (now MAN B&W) VP185, I once fantasised a 10 car super HST2 with 4,000hp at each end, matching the performance of the 125mile/h DMUs. Back in the real world, with a 125mile/h HST2 running on increasingly expensive oil, similar performance to HST should be adequate.
If we assume that someone can build a 26m long coach at 40 tonnes and keep to the 69 tonnes of the existing Bo-Bo HST power car, we get something like
Table 3. But the odds are that the HST2 builder will have lardbutt tendencies, in which case, the 1800 rev/min ratings of the potential engines have enough in hand to give 10.5hp/tonne for 45 tonne coaches and 80 tonne power cars
|
Cl 55+8 |
HST 2+8 |
HST2 2+8 (1) |
HST2 2+8 (2) |
Super HST (3) |
Installed power hp |
3300 |
4500 |
5000 |
5500 |
8000 |
hp/tonne |
9.2 |
10.8 |
10.9 |
12.0 |
14.3 |
hp/seat |
8.6 |
10.4 |
10.2 |
11.2 |
12.1 |
1) 2500hp ratings at 1500rev/min
2) nomina;2750hp ratings at 1800rev min
3) VP185 18 cylinder. 4000hp at 1800rev/min
|
|
Power hp |
|
|
Cylinders |
1500rev/min |
1800/rev/min |
MAN B&W VP185 |
12 |
2493 |
2760 |
MTU 4000 R41 |
16 |
2278 |
2680 |
Cummins QSK60 |
16 |
2250* |
2700* |
Tier 2 Rating. Available from 2007.
Table 3 gives the ratings of the three engines in the running for current HST re-engining and HST2 .
Cummins' QSK60 appears to have missed the re-engining market due to caution, subsequently unfounded, over running at the 1500rev/min required by the HST electrical equipment. But given the performance of the horizontal QSKs under the 125mile/h DMUs and Cummins' reputation engine should not be written off for HST2.
Cummins will quote firm prices for parts overhaul and the QSK is also cheaper on first cost than the other two. To get the power needed for HST2, we will have to wait for the Tier 2 QSK60, expected to be available from the start of 2007. The maximum traction rating quoted in the Tier 2 announcement is 2500hp, but my chums in Daventy reckon it could be pushing 2700hp if needed.
MAN B&W offer what long term readers will know as the Paxman VP185. It was love at first sight when we met at Colchester in January 1994, but the curse of Almost (anag) struck and Paxman's product support and development was feeble, alienating the key customer Great Western who is now besotted with MTU.
However, performance of the trial engines was good enough to attract other operators and today 30 are in service in the UK , including 18 on MML. As the proven product, the good news is that operators know what it actually delivers in terms of costs and fuel and oil consumption. The bad news is that it can never be as good as an engine with no HST experience, which clearly has no faults or problems.
Alstom sold its diesel activities to MAN B&W of Germany who are now planning to transfer manufacture of the VP185 to a partner abroad – possibly in Korea or China . But at least the German owners have spent some money on what is now an 11 year old design. Two Mk 2 versions are running comparative trials on Great Western against the MTUs and three are in service with MML.
Backed by long term service experience, the VP185 is a safe bet for HST1 re-engining. GNER could be the next customer with a requirement for 25-34 engines under its franchise commitment. If Greater Western changes hands the new franchise owner might prefer to cling close to nurse. So I might have been premature in discounting the VP185 for HST2.
Last December I had a jolly day out at Brush in Loughborough where the first MTU 16V4000 R41 engine was lowered into an HST power car. The pair of MTU re-engined power cars are now running on Great Western and a recent e-mail from a chum in white overalls waxed lyrical about the fuel economy and low oil consumption of the new engines.
Technically the MTU is more modern than the MAN B&W, the key advance being the use of common rail fuel injection (see the Instant Expert box).
Instant Expert – Common Rail Injection
When I was sweating over hot diesels, and until relatively recently, each cylinder of an engine had its own injection pump operated by a separate cam on the camshaft. Each time the cam came round a piston in the injector was forced upwards, spraying the fuel at high pressure into the cylinder. A common rail engine has a single high pressure pump which feeds an accumulator – the ‘common rail' - running the length of the cylinder block. Each injector is fed by a pipe from the rail and is controlled electronically. Thus, instead of the injection timing being fixed by the camshaft, it can be varied electronically to optimise combustion for economy and emissions. Actually, fuel consumption and emissions are inimical. To reduce nitrous oxides (NOx) you have to sacrifice combustion efficiency and produce more carbon dioxide. Fuel consumption is measure in grammes of fuel needed to produce 1kW of power for an hour (gm/kWh) which is known as the Specific Fuel Consumption (SFC). A 1960s vintage English Electric RK – as in the Class 37 – used 228 gm/kWh at full load, although we called it 0.375lb/hp hr in those days. By the time the RK went into the Class 56, the SFC was down to 220 gm/kWh. And the next version, in the Class 58, was around 205 gm/kWh. Before the SFC wars were overtaken by emissions, the Mirrlees engine in the Class 60 had got down to 195gm/kWh. But now, a compromise figure seems to be around 210gm/kWh. And in the HST context, the original Valenta was quoted at 221gm/kWh. Now all these figures are at full power and engineers look at SFC as a curve across the engine speed range, which improves as power and speed rises. So you are going to be hard pressed to get much more than 10% fuel savings in IC125 where the control lever is more of an on/off switch. Obviously electronic injection can produce a better compromise and common rail fuel systems are the way forward. The Tier 2 version of the Cummins QSK60 will be fitted with the Bosch common rail system, which means that the VP185 will be lagging when it comes to fuel consumption. According to Informed Sources the two common rail technology engines predict a 10% reduction compared with the Valenta. A recent consultant's study quotes a reported 8.3% for the VP185 which correlates with Paxman's claimed 8.5%. However, some Informed Sources have said that %5 would be more typical.
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While the MTU is the engine of the moment, it is not the ‘wundermotor' the First Great Western hype might suggest. The maintenance schedule hints at latent fragility.
Now, I am all for cosseting engines. As Steve Hannam showed with the foster Yeoman Class 59s, daily TLC is effort well spent. But there is a difference between spotting oil dribbles before they become leaks and looking for potential trouble
Overall, there is not much between the three engines, they all run to 25,000 hours between major overhauls, with mid-life overhaul around the 12,500 hours mark – 15,000 for the VP185. You can find my report on the first strip of a VP185 at 25,000 hours in the August 2001 Informed Sources in the Alycidon Rail archive.
But it's the intermediate work between the mid-life and major attention that raises my oily eyebrow. The maintenance schedule for the MTU requires an oil change and tappet attention every 2,000 hours – that's about four months in an IC125.
At 6000 hours the injectors are inspected, but the engine also has to have an endoscope inspection. Then there is a turbocharger overhaul at a very inconvenient at 10,000 hours which, according to informed sources cannot be extended to, say, 12,000 hours to match the mid-life overhaul periodicity.
Talking of turbochargers, I may have given the impression that the VP185 lacks sophistication. In fact, in this department, it has found the holy grail of diesel techies in the form of self regulating two stage turbo-charging. This is why the engine gives so much power, while the use of multiple automotive turbos cuts cost and simplies replacement.
Anyway, back to the MTU. Why does it need an endoscope examination at 6,000 hours? As a veteran of endoscopy I know it is not something you do lightly.
In my case I am on a 3 yearly cycle. Why three years? Well, presumably, three years is long enough for any benign polyps that grow in my colon to be removed, but not so long than they can go malign again. So what is it that MTU are afraid they might see developing at 6,000 hours?
As remarked above, HST design and specification is going to be much, much more difficult the second time around. Watch this space