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INFORMED SOURCES May 2007

IEP highlights diesel limitations

Why electrify? IEP's power options provide the answer

There is a disturbing tendency to apportion technical equivalence to the choice between diesel and electric traction for the future railway. Even my old and wise chum Tony Mercado, who brought Pendolino into successful service and now heads West Coast Train Care, used a screen in a presentation to a recent Conference on the work of the System Interface Committees (SIC) which read ‘Modern diesel and electric are similar, so no clear performance benefit.

And this was in the context of future electrification. But you buy electric traction because of what it makes possible, not as an either/or. As the industry seems to have forgotten the basic arguments for electric traction which were debated with some heat 50 years ago, let's go back to basics as they apply to IEP.

Table 1 Diesel and electric traction power densities

Power density

What matters in traction is how much power you can fit into the maximum axle load. IEP is expected to have distributed traction. This means that the diesel engine or transformer will feed inverters under motored coaches.

So with the inverters and the traction motors a given, the amount of power you can fit in the train is determined by the mass of the transformer or the diesel traction package.

Table 1 compares diesel and electric power packages on the common basis of kW per tonne. This probably flatters the diesel because both of the transformers are quite specialised.

For example the Class 91 had no fewer than five tertiary windings, one to feed tilt packages, were the Mk 4 coaches ever to be converted. The locomotive specification also included hauling heavy trains over Shap, the demanding overload conditions also adding weight.

Similarly, the Class 390 transformer has its share of special requirements. To improve the waveform of the output, the secondary windings have a higher than normal reactance, which requires more iron than a transformer optimised for efficiency. As I said earlier, engineering is an art.

Dry

In the case of the diesel engines all the weights are ‘dry', that is less oil and coolant. And coolant represents a significant contribution to the mass of the power pack. And thanks to Cummins for weighing a dry QSK60 engine especially for this article.

Table 2 shows another example of engineering as an art.

‘Cooler group', describes the complete package of radiator, fans and drives. The Brush cooler group being fitted to the GNER IC125 power cars is simpler than the Voith unit adopted by FGW. But it contains nearly twice the coolant. More coolant represents an insurance policy on the hottest days, since it can absorb more heat before tripping the over-temperature switch and derating the engine.

Table 2

Thus the dry V16 MTU 4000 Series engine, which could power IEP, has only 40% of the power density of a transformer with a 50% higher rating. But when you add in the weights of the cooler group and the alternator, the power density falls to a mere 20% of that of the transformer.

Also in the table you can see the same sums for the bare Cummins QSK19 in the Class 22x Diesel Electric Multiple Units and the complete power pack. Note that the power density of the smaller installation, at 106 kW/tonne, is less than that of the MTU because of the scale effect on the auxiliaries. The raft supporting the engine and its associated kit also adds weight.

Table 3 is a back of the envelope analysis of what the 2MW (2700hp) diesel traction package for the IEP might weigh. Again, this flatters the diesel somewhat, because I have used Class 43 equipment weights. increasing the engine output from 1.68MW in the Class 43 to 2MW in IEP would produce more waste heat and require a larger cooler group.

Note, too, the weight of the fuel carried. Only 40% of the energy in this 4.68 tonnes will appear as power at the alternator by the end of the day.

Table 3

2MW diesel traction equipment weights

Hard way

So, the diesel IEP is doing it the hard way. All the transformer needs is a Vacuum Circuit Breaker
(VCB) and a pantograph. No fluids, no reciprocating bits, no pre-heating before you can start, no fuelling on depot, no range issues, much less maintenance and no emissions at the point of use.

And yet DfT thinks diesel, oops, self propelled, traction is the future. It is to cheer up these diesel-heads that I have added a couple of alternative power units to Table 1. Actually, the CT18-52 at 2500hp was reckoned to be the best of the breed, but I digress.

Emission

Which brings us to another challenge to the diesel engine. IEP is to be greener than Trafalgar Square on St Patrick's day. And one of the essential requirements is compliance with the Class IIIB emissions limitations in the European Community Directive 2004/26/EC . This directive covers engines for ‘non road mobile machinery' and includes railcars and locomotives.

These emissions regulations are being introduced in stages. Class IIIB, when applied to diesel locomotive engines, will come into effect at the end of December 2011.

Under the Directive, engines for rail traction are divided into three power ranges, up to 560kW (750hp), from 560kW to 2MW (2,700hp) and engines over 2MW. In general the regulations are eased slightly for emissions of hydrocarbons and oxides of nitrogen for the bigger power units.

Even Capt Deltic has yet to get his head more than partially round Class IIIB and how it is to be met. The big engine manufacturers say they are working on it and have announced variations of existing engines which will comply. But ask for details and they go all coy.

What is clear that Class IIIB has upsides and downsides. All will be explained in a future column. Meanwhile it remains an unknown for the bidders.

Electric traction, on the other hand gives you more of what you buy traction for. And in the case of IEP provides a higher power train and, with the electrical equipment distributed along the vehicles. all the space between the vestibules ‘furnishable'.

In a rational world the wires would even now be marching westwards and IEP would be a modern electric train. Meanwhile, the Informed Sources electrify petition is past the 3,000 mark on its way to 5000 signatures by the end of July. If you still haven't signed up, the modern railway needs you at http://petitions.pm.gov.uk/Electrify/

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