An active flow turbocharger being developed at Imperial College by Ricardo Martinez-Botas is designed to make better use of wasted exhaust-gas energy from an internal combustion engine.
If that energy could be recovered, the efficiency of the engine would be significantly increased.
’A normal turbocharger takes some of this energy that would otherwise be wasted to the atmosphere, but not all of it,’ he explained. ’The turbocharger is designed for a steady-state operation, whereas the exhaust gases increase and decrease at the rate of the engine reciprocation. The idea is to oscillate the turbocharger’s variable geometry and synchronise it with the engine exhaust to get better energy recovery from the pulsating exhaust flow.’
It uses a fast actuated nozzle to follow the exhaust pulse, reducing the turbine inlet area periodically to increase exhaust-gas pressure.
The potential for increasing engine efficiency is substantial and even greater when coupled with advances in internal combustion engines.
’We are going to see ever smaller engines in cars as we move towards low-carbon vehicles,’ he said. ’These are going to be downsized engines, with a one-litre engine giving the same performance as a two-litre engine using current technology, or perhaps a five-litre engine could be reduced to 1.9 litres. But the key thing is the driver experience and response should be the same.’
Patents have already been applied for and Martinez-Botas has just received a significant grant from EPSRC/TSB to support a detailed feasibility study on a prototype. ’We believe the path for commercialisation of this technology will be through licensing it to an engine developer or a turbocharger developer, and they will then manufacture and implement the technology,’ he said. ’We’ve already carried out testing and simulations, but the key issue now is how to implement it in an engine.’
He is already talking to potential partners, but they have all come back with similar questions in relation to material limitations, reliability and fatigue failure. ’It has been recognised as a sound idea and the grant from EPSRC/TSB will provide the bridge funding for us to test its reliability in use,’ he said.
This sounds like a break through, all the best to the developers.
This is not new technology, more resurrected technology, but one with the potential to be developed into a working piece of equipment rather than a concept.
The future for all vehicular transport, apart from pure electric, seems to be hybrid. This includes even diesel railway locomotives and possibly ships.
This allows an engine to be sized on the basis of the average maximum demand required, possibly half or less of the present output. Any demand lasting less than half an hour can be supplemented by the batteries so that even hill climbing flat out up the alps is unlikely to exceed this as there are bends and eventually you reach the summit.
It allows an engine to run at a constant speed and power output while charging the battery and then cut out until required again. This means that the engine doesn’t need to be designed for part load operation or for variable speeds. Possibly a gas turbine might be viable because they can be very small under these circumstances.
No gearbox is required, whether manual or auto and four wheel drive would be normal because each wheel can have its own motor.
Brakes will last far longer because regenerative braking will be used for all except the most sudden emergency stops.
For short distances the engine won’t be required at all because the battery can be charged from roadside points.
Do we need more development on normal types of engines?
Archie
From the model I note no insulation on the manifold or inlet pipe to the turbocharger; that is a real waste of convertible energy. Insulation on these surfaces significantly increases the energy and power available that can be recovered. The author/inventor can email me for more details.
variable blade geometry applications are good to optimise systems.so ,in deed a good idea. since the turbo charger increases the inlet air intake pressure,why not lhave a intake tank that is fed by the turbo charger. then will not the speed of the turbo and air intake pressure become independant of each other ????
On the idea of an in line reservoir tank lets look at the numbers.
Lets look at a small engine 1Ltr.
rotating at 1200 rpm which equates to 600 inlet valve openings per min. = 10 openings per second.
So how large would the reservoir have to be to give any significant time period of storage.
10 valve openings per second, 1ltr intake on each valve opperation so 10Ltr resivoir gives 1 second assuming the presure drops from 2 bar to 1 bar, or 100ltr gives 10 seconds extra inlet pressure support. Not a lot for a very large tank.
Further the turbocharger could go in to surge ie the pressure in the tank could be grater than the pressure which the turbocharger can support. It would make the control and opperation very difficult. If the turbo where to go into surge then the turbocharger life would be greatly reduced and the stored energy would just go in reverse ie back through the turbocharger. The engine would sound like a big old steam engine gasping for air each time there was a back flow through the turbocharger. A really bad thing to have on an engine inlet system is a large stored volume as it makes matching the turbo to the engine more difficult under transient conditions, which in a car is most of the time when driving around town.
The challenge will be to control temperatures in these rapidly-moving small components.
Turbos, especially small petrol engine applications, are very near the limits of the materials. If they go outside the limits, material lives rapidly collapse, so creating a serious risk to reliability and whole-life costs.
Best wishes with the project anyway.
Being one of the developers of this technology, I will attempt to answer some of your concerns.
With respect to Simon Martin’s remark that this is resurrected technology, well, it is not. This is a novel concept which has not been attempted before. A principal element of the idea is not new, namely, varying the turbine inlet area to achieve as nearly optimal flow conditions for the turbine as possible. This principal, however, as originally conceived and as applied in variable geometry turbos today is one of matching the turbine inlet area to the prevailing (average – and this is the key word in this discussion) flow conditions of the moment. These conditions will vary when the accelerator pedal is pressed further or released and/or there is a gear shift. All of these cases will impose a change in the – average – exhaust flow conditions through the turbocharger turbine. What no turbocharger system can at present do (outside of this proposed Active Control Turbocharger –ACT) is to vary the turbine inlet area according to the changes in exhaust flow characteristics (i.e., in pressure, temperature and mass flow) as a result of the rapid opening and closing of the valves. As a gentleman above mentioned there is a large number of exhaust valve operation per second. These can reach well over 100Hz (or 100 opening and closing periods of exhaust gas flow release into the manifold pipe feeding the turbine). What present turbine of the variable geometry or any other variety ‘’feel’’ is a steady stream of exhaust gas. However, the pressure, temperature and mass flow variations within a second of turbine exhaust flow are enormous. As an example, a turbine might receive 0.3kg/sec of ‘’average’’ exhaust flow of an average pressure of 1.4 bar. If a closer look is taken, it will be realised that this 1.4 bar pressure is not steady at all but is varying from nearly atmospheric (1.0 bar or thereabouts depending on the atmospheric conditions at that location) to 2.0 bar. Now, this fluctuation in pressure levels from 1 to 2 bar is occurring 100 times per second. The average flow from this fluctuation is 1.4 bar and it is what a conventional variable geometry system will take into account in order to provide an optimal setting of the inlet area. However, by fluctuating the area at this rate (yes, 100 nozzle guide vane openings and closings does sound farfetched but a significant frequency range has already been demonstrated with the ACT prototypes we designed and have tested), one can capitalise on the significant energy content at the lower pressure levels of the pulse. The idea is to try and raise this average pressure of (in this example 1.4 bar to as nearly the peak of the individual pulses (of this example) as possible. As in this case, the pulse amplitude is from 1 to 2 bar, then the goal would be to attain an ideal 2 bar of average pressure. Can it be achieved n practice? No, since the very low pressure levels when the exhaust valve is closed (atmopsheric) can not provide enough energy at the turbine inlet for the nozzle to increase the pressure levels (and, therefore, the turbine power output) to as high a level as 2 bar. However, as anyone who has ever dealt with variable geometry devices for turbines knows, they are incredibly capable of increasing the power (and turbine rotational speed) with minimal amounts of inlet pressure present. In other words, this new technology aims at increasing the instantaneous exhaust energy levels available at the turbine as close to the peak pressure levels of the exhaust pulse rather than utilising the average of energy in a wildly fluctuating exhaust energy environment as today’s variable geometry turbochargers do.
Apologies, for the long introduction to the idea, but it is not an entirely instinctive topic as one has to be very familiar with the precise exhaust flow characteristics to realise significant energy potential for power recovery by the turbine, “hidden” there.
With respect to Archie Campbell’s remark on whether we need more development on normal types of engines, the answer has to be: yes. There are still areas of the powerpack of today where there is more than sufficient room for improvement. Hybrids and electrics are here, no doubt (indeed our research team is involved in demonstrating the significant potential for endurance increase from electric vehicles – check today’s news in the Engineer for the Racing Green Endurance project), but they are not yet viable for the large scale replacement of the fossil fuel driven engines of today and the traditional technologies will have to continue improving for a few decades to come, especially in view of the ever stringent emissions regulations coming into force every few years. Boosting technologies (such as the various forms of turbocharging, discussed here) are some of the key technologies that have played and continue to play an even greater role today in allowing OEMs to design engines that align with these regulations.