Modelling of a thermoelectric generator for heavy-duty natural gas vehicles: Techno-economic approach and experimental investigation

Abstract

Global CO2 emissions of heavy-duty vehicles are rising steadily and will continue to increase in the future without the implementation of measures such as technologies to reduce fuel consumption and emissions. In recent years, vehicles with natural gas-powered engines have increasingly been used as an economical and environmentally friendly alternative to diesel engines to reduce emissions. In addition to their lower emissions, these offer a high potential for waste heat recovery. A thermoelectric generator as a waste heat recovery system represents a cost-efficient technology for fuel and emission reduction. Integrated in the exhaust system, some of the otherwise lost heat can be converted to useful electrical energy. The advantages of thermoelectric generators compared to similar systems are low maintenance requirements and therefore a low cost-benefit ratio. This paper presents research on thermoelectric generator systems for heavy-duty natural gas vehicles on multiple levels. As a novelty, a holistic approach is applied, which includes interactions between all its components, all interactions with the overall vehicle system and the total cost of ownership. This approach is combined with a multiphysical numerical simulation model to obtain an economically suitable design. The solution of the simulation study is validated by an experimental investigation using a single channel system with commercially available thermoelectric modules. Approximately 70% of the simulated output power and the calculated efficiency could be measured. The proposed thermoelectric generator solution for heavy-duty natural gas vehicles achieves a peak power of 1507 W and a power density of up to 50 W kg−1. The results indicate a net fuel reduction of −0.54% (gross −1.04%). This is equivalent to a reduction of CO2 emissions of 4.9 (9.4) gCO2 km−1. The maximum system efficiency is simulative up to 4.2% (3.7% experimental). The overall system costs are estimated at 1811 EUR and thus represent a cost-benefit ratio of min. 1.2 EUR W−1. The results exceed the state of the art by more than 84%. The investigated commercially available thermoelectric modules with a power density of 1.1 W cm−2 are currently not application-oriented and are unable to fulfil the economic target of an amortization period of less than 3 years. New approaches are required and discussed. The new solution found with a power density of up to 3 W cm−2 and an efficiency of up to 9% indicates a high potential regarding the future cost-benefit ratio of the technology and will be adopted for further research and development activities.