Readers letters
Having over 42 years' experience in the rail industry, I am surprised at the findings of the research by Ricardo Engineering on the fuel usage on Britain’s diesel trains (“Coupled up,” PE April).
Two points stick out. First, the recommendation to revert to a mechanical transmission, and second the lack of any mention of the obvious issue of the high usage of diesel traction over long stretches of wholly electrified routes.
To take the first point, all modern diesel multiple units (DMUs) use either a torque converter type drive, or, for the later Class 22x fleets (the Virgin and Cross Country Voyagers and East Midlands Meridians), a diesel-electric transmission. To revert back to a multi-stage mechanical gearbox and clutch arrangement as was used on the 1950s DMUs would be a retrograde step and not consistent with smooth acceleration and 125mph running.
There does not seem to be any mention of the two additional advantages of DMUs with diesel-electric transmission – the ability to provide rheostatic braking, saving considerable wear and tear on the friction brakes, and the possibility of a hybrid system utilising the electric transmission on the train and the electrification infrastructure where this is present.
This brings me to my second point – the use of diesel traction over long sections of electrified routes, an issue only now starting to be considered with the work being undertaken to look at the feasibility of converting an existing Class 22x to a hybrid system to allow the diesel engines to be shut down when working under the overhead wires. There was no mention of this initiative in the article.
The use of diesel traction over long electrified routes must be one of the most wasteful and unnecessary uses of fossil fuels in existence, not to mention the consequential exhaust emissions. Some of the trains on both the east and west coast main lines and all of the Cross Country trains are diesel powered and many run considerable distances “under the wires”.
Good examples of this are the use of the diesel HSTs (InterCity 125s) out of Kings Cross to Aberdeen, where the first 400 miles to Edinburgh are electrified. Similar examples exist out of Euston with North Wales services running “under the wires” to Crewe and some Cross Country services that run via Doncaster to Newcastle or Edinburgh, again running over extended electrified routes.
Surely this is one area where more urgent research is needed into a cost-effective hybrid system, where the initial outlay in converting the existing diesel-electric multiple units into an electro-diesel configuration would produce large savings in fuel, and with the predicted escalation in fuel costs and consequential benefits to the environment, should pay for itself well within the existing lifetime of these fleets.
A further spin-off would be the possibility of using regenerative braking when electrically powered, further reducing energy consumption.
Reverting back to a mechanical transmission arrangement would effectively slam the door on any potential fuel, emissions and energy savings that could be gained by utilising the already installed, and hopefully soon to be extended, electrification infrastructure.
Steve Beck, Rainham, Kent
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