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Blast from • the past

17th December 2009
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Page 56, 17th December 2009 — Blast from • the past
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Gas turbines are used for many applications aircraft, ships, tanks, and stationary generators to name a few but they've never really caught on for road vehicles. That's not to say they haven't been tried in trucks, nor that development isn't ongoing.

Words: Cotin Barnett

The roots of the gas turbine

go back to 0AD, when Hero of Alexandria invented the aeolipile, a reactive steam turbine that converted heat into rotary movement. But it was seen purely as a toy and it was another 1,500 years before Ottoman scientist Taqi al-Din built a working steam turbine to power a roasting spit, although Leonardo da Vinci had drawn a similar design 50 years previously The gas turbine, as we know it today, was patented in 1791 by Englishman John Barber.

An automotive application for the gas turbine was first conceived by Rover, in an amazing piece of diversification for what was regarded as the most quintessentially conservative of motor manufacturers. However, it's not so strange when you realise that Rover was contracted by the government in 1939 to assist with developing and manufacturing Frank Whittle's nascent jet engine. Three years later, having become the leading developer of jet engines, Rover decided to leave the world of aero engines and effectively did a swap with Rolls-Royce for the V12 Meteor tank engine, developed from the legendary Merlin.

Move into cars

Shortly after the war ended, Rover began to develop the gas turbine as a car engine, with financial backing from Leyland Motors. The story of the road cars from JET 1 in 1950 to the T4 Le Mans contender in 1965 is enough for a book of its own, but it eventually became one of high performance allied to high fuel consumption, and the concept quietly faded away from the car scene.

Although Ford and Volvo made abortive attempts to create gas turbine trucks, probably the best known are the Leylands built in the late 1960s and early '70s. The first example was revealed at the 1968 Commercial Motor Show at Earls Court, London.

The background to Leyland's gas turbine project is not dissimilar to today's engineers, looking for ways to provide adequate cooling for the next generation of Euro-6 engines. In the '60s, demand was growing for more power, but existing cab dimensions were hampering progress. The bright idea was to try the now neglected Rover engine, in which Leyland Motors still had a stake, in an Ergomatic-cabbed 4x2 Super Comet. Part of the thinking was that the gas turbine's characteristic of producing maximum torque at stall better suited a truck application. The installation was matched to an epicyclic gearbox from the company's bus range. This is the example still in its Leyland Motors livery, which is currently in storage at the British Commercial Vehicle Museum, in Leyland, awaiting a full restoration hack to running order.

Although a bit short of power, it was considered a partial success and encouraged development work on a larger engine more suitable for truck use.

When this unit appeared, it was in the 6x4 Lynx/Bison chassis, newly developed for the Leyland 500 engine. As well as being physically larger than the car-derived unit, it included the heat exchangers essential to improve the gas turbine's thermal efficiency Power output was 350hp, with scope to develop to 400hp. Transmission was again a bus-derived epicyclie, but with extra electronic fully-automatic control. The AEC Mandator V8's walk-through Ergomatic cab was used, with external modifications by Range Rover and Rover SD1 stylist David Bache.

Weight penalty

Although the engine now produced adequate power, with the addition of the heat exchangers, its weight was nearer 900kg than the target 450kg. rather too close to the 1,000kg of the conventional 680 engine. Five examples of this model were built. The first one, shown at Earls Court in 1970, and a second development truck, were kept in-house. After development support from Shell, Esso and Burmah Castro!, the oil companies had the final three. The final chapter was a mocked-up version on the 1972 Marathon chassis, which is now owned by the Coventry Transport Museum.

So what went wrong? Well, for a start, it was a hit late. By the time it was ready, the turbocharger was making its presence felt on diesel engines, vastly increasing their power/weight ratio and thermal efficiency. With the gas turbine engine ending up heavier than expected, the difference was too small.

But most of all, it was too thirsty. At the end of the day, fuel economy depends on thermal efficiency. Heat lost is heat that isn't converted to power. The amount of heat that could he exchanged within the Leyland gas turbine was limited by the materials available on the day. While components made of unobtainium were theoretically available, their prohibitively high cost and dramatically short service life made them impractical for production purposes. The fact that the oil companies baulked at the consumption tells it all, really.

And so ends the story of gas turbine engines in trucks... or does it? •

Tags

Organisations: Earls Court
Locations: London, Alexandria

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