Performance of hybrid electric vehicles with internal combustion engines and heat recovering Stirling engines
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School of Engineering |
Master's thesis
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Ene-39
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en
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75 + [11]
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Abstract
In this master's thesis the performance of hybrid electric vehicles with internal combustion engines and heat recovering Stirling engines were investigated. The performance was mainly investigated from fuel consumption and emission levels aspects. Different power train topologies were studied and compared. The main focus was series-and parallel configurations. The performances of the vehicles are tested by simulation on the new European driving cycle. The simulations are carried out in the Matlab/Simulink-based simulation tool Advisor. Stirling engine models are introduced into the block diagrams of the power trains as Matlab functions. A Carnot efficiency model was implemented for quick feasibility tests. An adiabatic quasi steady state flow model with pressure losses was adopted for more realistic results and for case studies of power trains with the GPU-3 Stirling engine. The biggest reduction in fuel consumption is achieved with the series topology and when the Stirling engine is placed adjacent to the exhaust manifold. It is also easier to integrate a Stirling engine into the series-than the parallel topology. The control strategy of the power train with parallel topology would have to be modified and/or the fuel converter would have to be downsized, due to reduced fuel converter efficiency, in order to attain optimal performance. In both cases acceleration and top speed are affected. For instance, the shifting strategy could be modified so that the fuel converter would be operated with higher efficiency. The temperature drop of the exhaust gases over the Stirling engine results in higher emission levels because the catalytic converter does not get heated up sufficiently to work effectively. This problem can be circumvented by using low temperature catalytic converters, by integrating the converter onto the Stirling engine or by heating the converter electrically. Another solution is to place the Stirling engine after the catalytic converter. This would, according to the simulations, lower the fuel consumption with 12% and the emissions with 3%, 5% and 2% for NOx, HC and CO respectively. These numbers are, due to inaccuracy in the model, too optimistic. The reduction in fuel consumption is lower than for Rankine hybrid systems. The Stirling engine price is also uncompetitive at the moment, but mass production might turn the situation over.Description
Supervisor
Lampinen, MarkkuThesis advisor
Coatanea, EricLarmi, Martti