ically coupled internal combustion engine that starts to decelerate as soon as you lift off. The EJ200 is a digitally controlled jet engine, which was designed to be used in a fighter plane, not a car. This means that certain functions aren’t ideal for use in Bloodhound without some modifications. If the EJ200 loses its connection to its control unit, it is designed to continue operating so that the aircraft doesn’t stop flying. However, in Bloodhound the opposite is required, so that the car doesn’t career off into the desert. To prevent this there is a mechanical fuel cut of lever in the cockpit. With a jet there is constant acceleration to terminal velocity, so knowing the optimum split second where to lift off needs the superhuman reactions of a jet pilot like Andy Green. And yes, you can practice these procedures, but even with a programme as well organised as Bloodhound SSC, the opportunities to do multiple high-speed practice runs are relatively limited. Another significant technical challenge is to deliver enough fuel to the rocket to make optimum use of its power. The auxiliary power unit (APU) for Bloodhound drives the rocket oxidiser pump, which supplies 800 litres of high test peroxide (HTP) to the rocket at 76 Bar (1000psi) in just 20 seconds, which is why the design of the pump is so vital. This is equivalent to 40 litres (over nine gallons) every second. Currently the auxiliary power unit is a 550bhp Jaguar Supercharged V8 engine. The rocket will be a single monopropellant unit for the initial high speed runs (up to 800mph) and then a cluster of three hybrid rockets for the 1,000mph runs, both developed by Norwegian rocket specialist Nammo. The Jaguar engine has to sit next to the HTP tank, but it’s vital that the heat from the engine doesn’t transfer to the HTP itself to prevent it exploding. The engine’s exhaust is therefore covered with a ceramic coating which 22 February 2018 reduces its surface temperature by at least 30%. In an effort to make this situation safer, more compact and to improve weight distribution the Team is investigating using electrical power for the HTP pump. An electric motor would be significantly smaller than the current APU and provide greater flexibility in the location of other components within the car. It would also offer a great opportunity to showcase the potential of an electrical automotive powertrain. “Bloodhound has always sought to push the boundaries of technology. However, when the Team last looked at an all-electric solution for the APU, suitable motors did exist, but the battery technology was not mature enough to provide a realistic packaging solution," says Mr Chapman. "Since those early discussions, two things have happened – the Team has developed the pump, improving its efficiency dramatically, and battery technology has moved on immeasurably, to a point where a packaged solution can be developed. When we first examined this option we thought we needed about ½ tonne of batteries. Now, solid state batteries and super capacitors are much lighter. This is where road cars are going so we need to evaluate it. “The Bloodhound Project never stops developing and we are always looking at emerging technologies," continues Mr Chapman. "An investigation into an electric APU powertrain will allow the Project to maintain currency with the direction of automotive technology and in addition allow us to showcase the potential that exists today.” The switch to using an electric unit within the car’s powertrain has been made possible by the increase in power and reliability of batteries over recent years, alongside a reduction in cost. For Bloodhound, one of the greatest challenges is accommodating all the components, including multiple braking systems and engines, and their fuel/power supplies. A petrol engine APU is not only larger than the equivalent electrical unit would now be, but also requires the relationship between the engine, clutch, gearbox and pump to be fixed as a single entity, along with the need for a closely positioned air intake, fuel and oil system. Conversely, although the position of an electric motor still has to be fixed relative to the pump, the remainder of the system – including the motor controller, battery packs and so on – can be more flexibly positioned within the car, and even separated if necessary. This gives far more packaging opportunities for the engineers within the car. “So we can move the centre of gravity if we need to as the speeds increase,” says Mr Chapman. “Flexibility in packaging is the biggest benefit of the electric solution.” One of the early aero problems was caused by the rear suspension shock wave producing huge rear supersonic lift. The ability to re-trim the car by moving the batteries could prove beneficial in this regard. SPECIAL FEATURE
EN-Feb18-eMag
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