British Steam Car Challenge 13th June 2007
As you are aware, we decided, after the poor output achieved by our original boiler design, rather than rush ahead with a new boiler, to complete the turbine build and use our original 70% boiler to first confirm that our turbine could produce around 70% of our power requirements! A dynamometer was rented and the complete final drive and turbine assembly was mounted onto it along with the steam supply, control and safety valves. This new assembly was constructed, installed into our test cell and connected to the existing test boiler. A series of tests were carried out and the conditions optimised. However, much to our disappointment we only achieved 40% of our power needs.
At this point in time as I am sure you remember, we had no choice but to stop the vehicle build program, lay off the admin, design and build staff so that the remaining small technical team could focus on trying to resolve the 2 issues fundamental to the design of the car – STEAM & POWER!
We dismantled the boiler and turbine assembly and carried out a lengthy and detailed examination of the various components and after taking advice from our friends at Spirax Sarco (Power Station steam equipment suppliers) regarding the boiler, and advice from our turbine specialist Tim Goldsmith, we concluded that the boiler needed a complete redesign and the turbine was suffering from a serious problem with the steam nozzle design.
To cut a very long story short, our systems engineer Jerry Bliss began researching steam nozzles and came up with several potential designs. He was also able to determine that the nozzle position in the original design was incorrect in relation to the turbine wheels, these errors were corrected by modifications to the turbine and nozzle housings and a completely new steam nozzle system was designed and manufactured, this time with the ability to change the nozzles relatively easily during testing for optimisation purposes.
A crude nozzle tester was also devised by Jerry so that we could sort out the best of the bunch from the designs that we had. This left us with 2 nozzle types and several sizes to manufacture and test.
In the background, while all of this was going on, we made contact with the designer of a recent prototype steam engine commissioned by Volkswagen, by the name of Arne Joergensen. He was asked to predict the performance of our existing boiler design and provide an indication of what could be achieved with design changes.
The results of his analysis of our existing boiler mirrored our test results almost exactly and his estimate of what could be achieved with boiler tube revisions, along with his calculations and explanations, which were laid out in the same format as his analysis of the existing boiler, gave us the confidence to ask him to design a new boiler layout!
While the new boiler design was ongoing, we were anxious to know whether our modifications to the turbine had been successful, so as soon as it had been rebuilt with our redesigned parts we approached our friends at Spirax Sarco and asked them to put us in touch with a “user friendly” power station, so that hopefully we could use their steam supply to test our turbine and, if successful, test our various nozzle designs to find the optimum type and size. They kindly introduced us to Slough Heat & Power and their site engineer (Peter Ward), agreed to a meeting to discuss our requirements. Without too much arm twisting he agreed enthusiastically to help.
The turbine was duly mounted onto a dynamometer complete with the necessary control and safety valves which had been adapted to suit the steam outlet supply at the power station, then it was shipped to the Slough Heat & Power facility. Much to our surprise, the turbine produced too much power for the dyno, so we stopped the test re-engineered the installation onto a larger dynamometer that we rented then went back in December 2006 to the Power Station. With Slough Heat and Power’s assistance we were able to run a complete series of turbine tests to confirm both it’s reliability and a very healthy 350+ bhp.
Early in the New Year 2007, now that we knew we could achieve a more than adequate power output, we began the process of revising the car design to suit the changed turbine and new boiler layout and to try and get back on schedule with the car build. This program continues with the help of sub-contractor technicians. The new prototype boilers have recently arrived and been found to be a massive improvement in performance compared to the original design. However their very output is, in itself producing temperature control and balance issues, so we are working through a test program to understand what additional control systems and/or equipment will need to be put in place to control them adequately so that we can confirm the absolute performance prior to commissioning the manufacture of the new vehicle boilers.
Unfortunately our initial inability to control the boiler has led to substantial damage occurring during the testing of the new prototype. This has not dented our confidence in the new boiler and we are working flat out to improve our control software while building a replacement test piece. It has however prevented Bonneville in August being a possibility. As soon as we have established stable control of the new boiler a revised test and record run schedule will be published.
13th June 2007