Approximately half the thrust of BLOODHOUND SSC is provided by a EUROJET EJ200, a highly sophisticated military turbofan normally found in the engine bay of a Eurofighter Typhoon.
Although at first sight very different from the diesel or petrol engine in your car, a gas turbine, or jet engine, is still an internal combustion engine. Air is sucked into the engine, it is compressed, fuel is added which then burns, and this expands pushing the exhaust out of the nozzle producing thrust.
At its simplest level the jet engine can be split into four basic sections, an intake which channels the air, a compression stage to raise its pressure, a combustion stage where the fuel is added and an exhaust stage where energy is extracted to drive the compressor and the remainder comes out as thrust.
There are four main classes of jet engine;
These were the early jets with all the intake air going through the engine core. They were noisy and not very efficient.
These have replaced the turbojets, and come in two flavours. The high bypass turbofan (pictured left) is typically seen under the wings of airliners and has a large fan at the front of the compressor stage housed in a nacelle. The advantage of the high bypass engine is that instead of generating all its thrust by accelerating a small amount of air by a large amount, it gets the same momentum change by accelerating a large body of air a small amount, as only 10% of the intake flow goes through the engine core. These are quieter and more efficient, and are great for sub sonic airliners. The second type of turbofan is the low bypass engine, where a significant portion of the intake air goes through the engine core (around half). This type of engine can work at a much greater range of Mach numbers and altitudes, and is typically found in combat aircraft. The bypass air is used to dilute the hot exhaust, reducing noise, but also provides an oxygen rich mixture that additional fuel can be added to provide extra thrust with reheat.
Here a jet engine is used to drive a propeller through a reduction gearbox driven off either the compressor or a power turbine.
like the turboprop, power is taken from a gearbox driven by a power turbine. This is typical of the installation found on helicopters, and also for industrial and marine applications.
Going through the stages of the engine section by section:
This is the front of the engine, and is concerned with the sucking and squeezing of the air into the engine. It can be split into two sections, the Low Pressure Compressor and the High Pressure Compressor. The LP Compressor does the initial work of taking the air from the intake and increasing its pressure by a factor of about 4:1, then feeding this air either to the engine core, or around the bypass duct. The bypass air misses out the HP Compressor and Combustor, and rejoins the core flow at the jet pipe, some of it is diverted and used to pressurise the bearing chambers and cool various engine components.
The air which travels through the engine core next goes through the HP Compressor which will raise its pressure a further 6 times, again some of this air is bled off for cooling various hot end components, though the term cooling is relative as now the air temperature is over 500oC and we haven’t even got to the bit where we add the fuel.
The combustor is where fuel is added through a ring of sprayers which, after starting with an igniter plug, is self sustaining until the fuel supply is cut off. The temperature of the flame is over 2000oC – well above the melting point of the alloys that the casing is made from, so bleed air is used to provide a cooling flow, and to prevent the flame from touching the casing.
The flow from the combustor is now fed through two turbines, their purpose is to extract energy from the exhaust gasses and drive the LP and HP compressors. The turbines consist of alternate stationary and rotating aerofoil section blades. The stationary blades, known as guide vanes are attached to the engine casing, the rotating blades are mounted on the turbine disc which is attached to a shaft driving the compressor. Again these are operating in conditions far exceeding the melting point of their alloys, and need active cooling from bleed air fed through internal passages.
To give an idea of just how much energy is needed to drive the compressor, for a jet engine producing around 60kN of thrust, something in the order of 35,000hp is needed to drive the HP compressor. To put this into perspective the total thrust of the engine is equivalent to 40,000hp, so, almost half the power of the jet is being used to drive its own compressor, with the remainder coming out of the nozzle as thrust.
The exhaust gasses now exit the turbine and pass through the jet pipe to the nozzle, the purpose of the nozzle is to control the flow out of the back of the engine. On the EJ200 this nozzle can adjust its area to match the engine requirements, both to increase the thrust of the engine, but also to help control engine surge.
On this engine additional fuel can be injected into the jet pipe and burns with the aid of the oxygen rich bypass air, this is known as reheat, and provides a significant extra push, the maximum dry (non-reheated) thrust of the EJ200 is 60kN, but start chucking a few gallons of fuel into the exhaust and this increases to a maximum wet (reheated) thrust of 90kN.
There are three main issues with the integration of an EJ200 into the BLOODHOUND SSC (if you’re of an engineering bent, please feel free to replace the word “issues” with “challenges” or “opportunities”).
Probably the most significant issue is with the electronic control of the engine. As designed, the EJ200 is a fully integrated component of the Eurofighter Typhoon, and has a highly sophisticated engine control and health monitoring system that is in constant conversation with the aircraft. Should it feel unhappy with the answer it gets to some of its questions then it will set the engine to a safe mode with greatly reduced thrust. The challenge (or opportunity) will be to convince the engine it is happily sat in a Typhoon engine bay, and that going at Mach1.4 at an altitude of 130mm is a sensible thing to do. But flippancy aside, the electronic control of the engine and ensuring it is getting the correct data, is a major part of the integration into BLOODHOUND SSC.
Secondly, and linked to the engine control issue is the design of the intake. This has to be able to deliver the correct "quality" of air to the compressor face to avoid any chance of the engine experiencing a surge. Surge is when the compressor stage of the engine stalls, resulting in a reversal of flow through the engine, an extremely violent and damaging event. Jet engines have a defined surge margin, this ensures they are never run in regions of their operational envelope where surge could be an issue. This margin includes allowances for many parameters such as intake icing, bird ingestion and unsteady flows brought about by rapid manoeuvring. Hopefully most of these won’t be relevant to our installation of the EJ200, so we have cashed in some of this margin for increased performance. However, this all depends upon our confidence of the intake performing as it should, hence the extensive CFD analysis, as we don't have the opportunity for a lengthy development programme.
And finally, access. Due to what we’re trying to achieve with BLOODHOUND SSC the niceties of packaging the EJ200 in a maintenance friendly environment cannot be achieved within the vehicle constraints. What we can do, is ensure all vital engine systems are accessible for safety checks prior to a run, and certain additional tasks can be achieved within the car confines, such as oil and hydraulic level check and replenishment. However most tasks normally considered possible and routine within the engine bay of a Typhoon may well require us to remove the engine. The hope is that by using the onboard engine health monitoring we will be able to predict and plan such maintenance requirements.