The options for how to use the exhaust energy recovered through a turbine can be categorised as:
1. Turbo-charging: use of turbine extracted energy to pressurise the intake charge
2. Turbo-compounding: use of turbine extracted energy to contribute directly to crankshaft work
3. Turbo-discharging: use of turbine extracted energy to depressurise the exhaust manifold.
Turbo-discharging is a novel approach that can better utilise the energy recoverable by a turbine mounted in the exhaust flow of an ICE - allowing the depressurisation of the exhaust system to reduce engine pumping work, reduce hot residual gases in the cylinder and improve fuel efficiency.
- The turbine outlet pressure and temperature is lower meaning that the turbine can recover significantly more energy than with a conventional turbo-charging or turbo-compounding system
- Initial estimations have shown an increase in engine torque of 7% and a 6% increase in fuel efficiency
- Significant reductions of in-cylinder hot residuals that contribute to the efficiency limiting engine knock boundary
- In combination with an exhaust heat exchanger, a unit of turbine recovered energy can contribute to more than one unit of additional crankshaft work
- Turbo-discharging technology can also be implemented with a single stage turbo-charger, thus giving the same torque curve as a two stage turbo-charging system whilst offering additional fuel economy benefits.
With a combined annual petrol and diesel consumption of 11 billion litres within the UK alone it comes as no surprise that Internal Combustion Engines (ICE) are one of the most widely recognisable power generation devices globally - powering almost all of our vehicles such as cars, trains and ships, whilst also being an integral part of Combined Heat and Power (CHP) systems and other land-based energy generation systems.
Despite their popularity, traditional ICEs tend to offer low efficiencies - for every litre of fuel placed into the engine most will only convert up to 30% of the fuel into usable work. The remaining 70% of the energy contained in fuel is wasted on friction, heat losses, incomplete burning and other inefficiencies.
Demand for Efficient Internal Combustion Engines (EICEs) has increased significantly due to industry requirements and regulation, with a global EICE market value of £80 billion - the trend towards greater efficiency has enabled technologies such as the turbo-charger to become widely used by ICE manufactures.
Turbo-chargers are forced induction systems which compress air entering into the engine through the use of turbines, by utilising the heat energy of the exhaust gases. They introduce significant volumes of air into the engine cylinder allowing more fuel energy to be released, which in turn boosts performance. This increase in power output allows engines to be downsized, thereby offering improved power-to-weight ratios and overall vehicle efficiency. Due to increasing pressure to ensure ICEs become more efficient it has been predicted that the market value for turbo-chargers is expected to reach £8.4 billion within the next 5 years, with an estimated 39 million units sold annually. Traditionally turbo-charged engines offer a fuel economy benefit of approximately 15% while also enabling improved performance - this is quite significant when taking into consideration the low efficiency of ICEs.
Over the past century there has been considerable research focused around the utilisation of exhaust gases within ICEs to allow for higher efficiency, turbo-charging has thus far been the most established method of utilising exhaust gases. However, our technology with the support of the EPSRC, TSB and Royal Academy of Engineering focuses on a fundamentally new concept; turbo-discharging.