Boiling point

Civilisation is steam-powered. Steam generates four-fifths of the world’s electricity and provides the heat for most chemical production. But for a few quirks of fate — international depressions and world wars — it would probably be the main power source for getting us around.

Back in the early days of the car, three technologies were running level with each other as the power train. Electricity was one option, internal combustion engines were another. Steam, however, was in the lead. Over a century of steam-engine development meant that refined, compact engines could be built, incorporating systems such as electromechanical burner control and key ignition. The mechanics were simple, with no need for gears or alternators; unlike hand-cranked petrol engines, they were easy to start; they were safe. A steam engine once powered the fastest vehicle in the world.

But over the years, internal combustion engines overtook steam, with the development of electric starter motors and the fast-track engineering of two world wars securing the primacy of petrol. Now, steam propulsion is seen as a relic; a thing for hobbyists and enthusiasts to tinker with in sheds. However, the spotlight might be swinging back to steam. A UK team is developing a highly advanced steam-powered car to break that old speed record, the oldest land-speed marker still on the books. Although the 1906 Stanley Steamer’s 127mph was soon outstripped by petrol, then gas turbines, rockets and jets, no steam-powered car has ever run faster, according to FIA rules.

Meanwhile, the car industry’s search for greater efficiency and new ways to drive cars is also looking at steam technologies. Could a new age of steam be on the way?

The steam-powered land-speed record sounds like a contradiction in terms — a high-tech car, with a steam engine? But steam technology is anything but old-fashioned. The steam turbines that generate most of the world’s electricity are the epitome of cutting-edge computerised optimisation, materials science and manufacturing techniques. The car designed for the challenge, a sleek form called the Inspiration, all fins and bulges in a British racing green livery, is powered by a steam turbine that drives the rear wheels directly; this, said Matt Candy, team manager and chief engineer, was borne out of the need to keep the design as simple as possible.

‘The origin of Inspiration was a Master’s thesis at Southampton University in the late 1990s,’ said Candy. ‘Originally, the stimulus was just to look at this eccentric record and see why nobody had tried to beat it, and a paper exercise to design a car that could,’ he added. The benchmark for steam speed is actually 145mph, set by a steam turbine car called the Steamin’ Demon in 1985; this isn’t an official record, because the car only completed one run, rather than the two along the same course within an hour as stipulated by FIA rules.

The Southampton project, run by Dr Neil Richardson and championed by Inspiration’s driver, Charles Burnett, a powerboat champion and nephew of Lord Montagu of Beaulieu, was based on a reciprocating engine, the traditional kind of steam engine with pistons and valves. Indeed, there is no reason why such an engine couldn’t have propelled a car to the 170mph that is the Inspiration team’s target. After all, it’s only recently that modern train locomotives beat the 125mph mark set by the Mallard locomotive, now at the National Railway Museum in York. ‘You really could call it either way at the speeds we’re looking for,’ said Candy. ‘But when the time came to make a decision, we went for the turbine option. They’re so well understood, and it was seen as easier to manufacture a turbine. That leads you down a certain route, because the water rate, the amount of steam we have to produce, is enormous. But it’s still easier to make a lot of steam really fast than to build a complicated reciprocating engine from the ground up. The parts count for the turbine engine is just so much smaller.’

Having decided on a steam turbine, the team then had to work out a way of generating the steam. ‘We need to manufacture 40 litres/min, at 400°C and 40 bar,’ he added. ‘In power- generation terms, that’s nothing, but in a small, portable system that needs to go on wheels and keep moving, it’s a formidable goal.’

In this, the format of the record was an advantage, because the car only needs to run for three minutes. ‘We need a long track, about six miles, because the car is slow moving when it starts off. But that still reduces the amount of resource — water and fuel — that the car needs to carry. That sets you down the road to the design, which is a total-loss, monotube boiler system,’ said Candy. This means that the steam produced by the car’s boilers — it has 12, each the size of a suitcase — is all either sent through the turbine or exhausted, rather than being condensed to recover the heat.

‘It would have been nice to have had fewer, larger boilers,’ he added. ‘But the development of boilers is very time and resource intensive, and once we’d developed these 3.5-litre monotube boilers, which worked well, we decided to just use those for our steam generation. It led to a large burden on the control side for the car, but with regards to innovation, the way we came up with the combination of diameters and materials for the boiler internals was a major feat. In a monotube boiler you
start with cold water and take it through the stages of wet steam, saturated steam through to superheated steam all in a continuous tube, and you have to make sure they don’t burn out.’

Another deciding factor in the boiler was the way the heat is applied. ‘We use a thing called a Bekaert mat, which is a metal fibre mat. We use propane as the heating material, starting as a liquid, so we heat that up. Then we use a 300W electric fan to mix it with LPG at 5g/sec, and we pass it through this mat. That gives you a very even heat source across the whole area and a very small flame length. The temperature at the front of the flame is 1,050°C, and our exhaust temperature is 150°C, so we need to get the remaining 900°C into the water as efficiently as possible. This also means controlling the speed of the water, plus its entry and exit into the various stages of the boiler as it goes through its different states, and then insulating the system to keep that heat inside.’ This is not only vital for safety, it is also necessary so that electrical equipment can be operated in close proximity to the burners and boilers.

In terms of design, the car is a hybrid. ‘We concentrated on making the car as light as possible, even though it is 25ft long, weighs three tonnes and has 12km of tubing on board,’ said Candy. The original design for the car was very slippery and streamlined, and the nose section remains from that previous design, but other aspects have changed. ‘Once we had decided on the boilers, we packaged them in the middle of the car, which meant we had to extrude the middle section to reduce the impact on the drag, so we have that very parallel-looking section. That altered the centre of pressure and the centre of gravity, so we needed to add the big rear fins to keep it planted and keep it in a straight line,’ he added.

It’s the control systems, however, which are probably the most complicated technology. ‘We have to keep all 12 boilers balanced as the car starts up,’ explained Candy. ‘We have 130 sensors on the car, monitoring the water in, the steam pressures and temperatures, and the control system works off those.’

Although the car only runs for three minutes, it takes nine to warm it up to the right steam pressure, so for this time it uses external water and fuel supplies and is entirely computer controlled. While the car is warming up, the water is pumped in via a positive displacement fire engine pump, but while the car is running, it uses a pneumatic controller; the computer has to switch seamlessly from one to the other. ‘As we start up, we unplug the oil coolers, the gas in, the water and air in. The last thing to be unplugged is the computer cable. All software was developed in house, and it has a lot of work to handle.’

The team is now fine tuning the design after running tests last autumn, and is hoping to go for the record at Edwards Air Force Base in California in early summer. The publicity from this, Candy hopes, will allow Inspiration to be used to attract attention to recruit young people into engineering. He also hopes that it will highlight the potential of steam in automotive systems.

In this, it appears, the automotive majors have beaten him. Projects at Honda and BMW, are both looking at exploiting steam to improve the efficiency of their petrol and diesel engines, producing very different ‘steam hybrid’ systems.

At its most basic, an internal combustion engine can be seen as a big lump of hot metal producing hot gas. That heat comes from burning the fuel, but it is entirely wasted. ‘Two-thirds of the energy contained in petrol is lost via exhaust emissions and cooling water, and the heat drop in cooling water has to be disposed of via the radiator,’ said Raymond Freymann, head of research and development at BMW. So how can that energy be harnessed?

Steam, of course, is one answer. Use the energy to boil water and raise the steam to high pressure, and it can be used in all sorts of ways. BMW is developing a system called the Turbosteamer to exploit this, which uses steam power to add additional drive to the engine and to generate electricity.

The system, which has been under development since around 2001, uses two heat exchangers in the exhaust line. A series of pumps pushes water through these at 40 bar. Even if the engine is only running at moderate revs, the temperature of the water goes up to 550°C. ‘This steam flows into an expander machine, which drives a rotary piston engine coupled to the crankshaft,’ said Daniel Kammerer, working with the research and development team in Munich. The steam is then condensed and returns to the heat exchangers.

A second circuit in the system uses ethanol instead of water as its working fluid, exchanging heat with the cooling water, the hot steam circuit, and the cooler end of the exhaust line to heat it right up to 150°C. This also passes through an expander and is converted to rotation. The system can produce around 10kW of power and could improve the efficiency of the engine by some 15 per cent, BMW believes. ‘We have about 10 years to go on the project,’ added Kammerer. Honda, meanwhile, is using a technology closer to that of the Inspiration — steam turbines. This is more of a conventional hybrid in that it uses a combination of ICE and electric motor drives. The system uses the exhaust gas heat to convert water in steam in the same way as the BMW system. It then drives a turbine with the steam, generating electricity to keep the car’s battery pack charged.

The system incorporates its steam generator into the exhaust catalytic converter, using the heat generated by the exhaust gases that are reacting over the catalyst to heat the water. A steam-control system keeps the temperature between 400-500°C, and at 7-9MPa pressure. The system, according to Kansaku Yamamoto, development team leader, could produce three times the energy of a regenerative braking system; when he presented a paper on the technology at a hybrid vehicles symposium last year, he indicated that it could improve efficiency by some 13 per cent. This, he said, wasn’t enough for it to be considered for production, but the research is ongoing to wring more efficiency from the system.

It may be a staging-post on the way to fully electric cars, but that’s a long road and there’s plenty of room for new technologies on the way. It looks as if steam, at high speeds and low, could regain its place on the roads.

The BMW Turbosteamer system uses steam power to generate electricity and give additional drive to the engine

Key:

1 Radiator/temperature condenser; 2 Pump; 3 Steam generator; 4 Steam generator/high-temperature condenser; 5 Super heater; 6 Steam generator; 7 Low-temperature expander; 8 High-temperature expander

Red pipe - High-temperature cycle
Blue pipe - Low-temperature cycle
Green pipe - Water-cooling cycle