Lean, mean steam machine
Attempts to break the land speed record for a steam car may not seem much like progress - but the vehicle's designer insists that the speedster is truly innovative. He talks to Lee Hibbert
Glynne Bowsher is no stranger to fast cars. As chief engineer on the successful Thrust land speed record attempt, he created an absolute monster of a vehicle that achieved a ferocious 763mph.
Now, for his next adventure, Bowsher is part of a team trying to break the land speed record for a steam car, which has stood for a century at just over 127mph. On the face of it, this might seem a somewhat more sedate challenge. But Bowsher reckons that, in many ways, it is more difficult than his supersonic escapades.
“Thrust was fairly straightforward once the engine had been established and issues of stability at high speed had been overcome,” he says. “On the steam car record attempt, speed is not such an issue, but there are a host of other technical problems. For instance, the car needs an extremely compact boiler and powerplant. This has proved extremely difficult and has required some advanced thinking. To the layman, this project might seem rather less exciting than previous supersonic efforts, but it’s still a real engineering challenge.”
The current land speed record for a steam-powered car is held by Fred Marriott, who in 1906 achieved 127.659mph driving his Stanley Steamer. In 1985, an unofficial record was set by American Bob Barber who raced along at 145.607mph. Later this year, the British Steam Car Challenge expects to sweep aside historical controversy by thrashing previous efforts and achieving a speed of around 200mph.
The vehicle – called Inspiration – started out as a masters project for graduates at the University of Southampton. It is a rear-wheel powered, rear-engine car whose motive power is provided by a two-stage steam turbine fed by four boilers fired on liquefied petroleum gas. The turbine drives an epicyclical gear train for a wheel speed of 3,000 revs per minute at the target speed of 200mph.
Originally, the students created an aerodynamically efficient design known as the Morelli shape which has proved extremely efficient for traditional four-wheeled cars. But, when Bowsher was appointed chief designer on the project, he spotted some immediate problems.
Wrong shape
He says: “While the Morelli shape was the most aero-dynamically desirable, it did not lend itself to some practical realities of the project. To produce the amount of steam required, the car needs four boilers, each measuring 1.3m in length, and these had to be fitted behind the cockpit. This meant that the Morelli shape – while beautiful – was a non-starter. We have kept the front shape true to the students’ design, but the rear of the car had to change.”
Bowsher is convinced that the aerodynamic goal of a coefficient of drag of 0.2 is within the grasp of the project. The aerodynamics of the car have been extensively analysed with the help of computational fluid dynamics. This simulation helped to validate the design before construction of the body began. “Our performance predictions look spot on,” says Bowsher. “We predict that 200mph is well on the cards.”
In terms of construction, the overall concept is to be spaceframe-with-body. The frame is constructed of square tubing (except the roll hoop), incorporating single-member longitudinal beams. “In the end we chose an aerospace-specification, cold-drawn manganese steel for the spaceframe,” he says. “This high level of specification is required because the spaceframe carries all the load: the boiler system weighs around half a tonne alone. So it needs to be really strong.”
The body shell front is to be made of an epoxy carbon-fibre matrix, while the bodywork from the boiler section rearwards will be constructed of aluminium sheet to cope with heat predictions from the car.
The engine/drivetrain will comprise a Curtiss wheel turbine producing 320bhp, operating at 12,000rpm. The 13-inch diameter turbine is non-condensing and is fed at four nozzles, one from each boiler. The system is total loss, which means that each run will expend the total amount of water carried. Exhaust steam will be vented to the wake of the car. The engine and gearbox sit co-linear with the rear axles. The drive unit consists of an epicyclical gear reduction unit connected to a limited slip differential unit. Output is split across two axles to the drive wheels in the rear.
“We are confident the engine design will give us the power that we need, and then some,” says Bowsher. “We reckon that the car can achieve 200mph operating at around 80% capability. So, if for any reason there is a shortfall, we should have something in hand.”
The design and construction of the boiler system proved an immense challenge. The iterative process of designing the boilers proved to be a time-consuming matter. The original configuration exceeded the team’s space allowances, and subsequent revisions proved to be unusable for other technical reasons.
“The struggle to get the boilers right nearly killed the project,” admits Bowsher. “We thought it was straightforward, so found a company and let it get on with things. But after two years it had nothing to offer us. Over that time my own thoughts had evolved.”
Getting-up steam
The result was a system with four independent boilers, each feeding one of the nozzles of the turbine. The boilers are laid horizontally behind the driver along the longitudinal axis of the car and each is comprised of a matrix of stainless-steel finned tubes set at zigzag angles to help with heat transfer. Each boiler section can be fired independently if necessary. The final design provides the necessary 2MW of heat release.
The fuel is to be liquefied petroleum gas fed into the boilers at a relatively low pressure a little over 2 bar. The system is still under design but it is thought that each burner panel will be independently controlled. This will be advantageous during trials as only the number of boiler sections needed can be fired. Each boiler section is being designed to produce steam at 500psi and 725°F with a mass flow rate of 625 lb/hr.
Safety systems have also been uppermost in Bowsher’s mind, with the driver required to sit in front of the heat output and steam generator. Fire safety is split into two active systems – the boiler section and the driver’s compartment.
The driver’s compartment is sealed from the boiler section by an aluminium bulkhead. In the event of a fire, the driver can activate a suppression system that will flood the compartment with high-pressure nitrogen. At the same time all non-life support systems are shut down. This will drive atmospheric oxygen out of the car to extinguish fires and prevent further combustion.
The boiler section of the vehicle will be protected in a similar fashion. Should the fire-suppression system be activated, the boiler fuel and air are shut off and the boilers and engine compartment are flooded with high-pressure nitrogen.
The vehicle control system includes sensors that indicate the load on each wheel. If the system senses less than 40% of the static load on the front, an alarm is sounded and the engine is shut down. The engine control system includes detection of burner panel flameout. If any one of the burner panels is somehow extinguished or flames out, the system shuts down all of the burners and simultaneously floods the boiler room/engine compartment and burner segments with nitrogen.
Designing and building a vehicle of such complexity has taken its toll on Bowsher. He has no idea how many man-hours he has spent on the project, claiming it feels “like around 90 man-years”.
“At some stages of the project, I have been working 80 hours a week. Maybe I should have retired and dug my garden, but I like a challenge. It’s been time consuming, but I want to see it through to the end.”
An attempt to beat Marriott’s official record is due to take place in the summer, probably in South Africa. A run in the US aimed at beating Barber’s unofficial speed will follow this.
At both attempts, the car will be run up to 25 times, building up speed slowly. “I will be very happy with 201mph and a shade disappointed with 199mph,” Bowsher says.
Bowsher insists that the steam car record attempt is more than just a case of boys and their toys. “There are many reasons for doing it,” he says. “Firstly, it’s a challenge. Sometimes, if you see a mountain, you want to climb it.
“Then there are the technological reasons. The car will use LPG fuel rather than petrol or diesel, so there might be some environmental ramifications down the line. And the engine and boiler are unique, so they might find other applications in the near future.”
© PE Publishing, 22 March 2006
