The School of Engineering of the University of Glasgow is preparing to embark on a 3.5 year PhD project on "Harvesting energy from engine exhaust gas with a thermoacoustic generator".
The thermal efficiency of modern internal combustion engines is limited to 20-40%. It has been estimated that, for a typical medium-size passenger vehicle in urban traffic conditions, 33% of the thermal energy from fuel combustion within the engine is carried away by exhaust gases and 29% is carried away by cooling water and heat radiation. The temperature of the exhaust gases from internal combustion engines usually vary from 500 to 900 ◦C depending on engine type and operating conditions. This makes the exhaust gases very attractive for energy harvesting applications, and indeed recovery of a part of this energy would make a significant improvement to overall engine efficiency.
A thermoacoustic prime mover is essentially the acoustic equivalent of the Stirling engine. It employs a delicately designed acoustic network instead of a complicated mechanical mechanism to force the gas parcels within the regenerator to experience a thermodynamic process similar to the Stirling cycle. In this way, it can convert thermal energy, especially low grade heat energy, to acoustic power (i.e. very high intensity sound / pressure waves). The acoustic power can then be utilised to drive linear alternators to produce electricity. Thermoacoustic engines have several advantages over conventional Stirling engines such as simplicity (no moving parts), reliability (freedom from maintenance) and low cost.
To push this technology towards the commercialisation, this project aims to address some of the remaining fundamental and technical challenges. Initially an improved model will be developed to optimise whole system, especially the coupling mechanism between the thermoacoustic engine and the linear alternator. The project will then focus on the optimisation of the heat exchanger which extracts heat from the exhaust gases. Novel designs need to be explored and examined, both numerically and experimentally, to minimize the additional backpressure applied to the engine and to ensure that a high degree of heat transfer efficiency is maintained. A prototype of such a thermoacoustic generator will be built and tested during the course of this project and the experimental results will be compared to the simulations in order to further improve the modelling.
Source: University of Glasgow
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