Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Feasibilitystudyonavehicularthermoelectricgeneratorforbothwasteheat recovery and engine oil warm-up Song Lan, Andy Smith, Richard Stobart, Rui Chen ⁎ Department of Aeronautical and Automotive Engineering, Loughborough University, UK HIGHLIGHTS • Developed and validated a bifunctional thermoelectric module model. • Four-quadrant operation diagram was developed to present the bidirectional characteristic of module. • Case study of applying a bifunctional thermoelectric generator to a 2l-diesel engine was carried out. • Faster warm-up effect of engine oil can be obtained by a bifunctional thermoelectric generator. ARTICLEINFO Keywords: Bidirectional thermoelectric module Bifunctional thermoelectric generator Engine warm-up Waste heat recovery ABSTRACT The thermoelectric modules have the bidirectional characteristic, which can work either in power generation modebasedonSeebeckeffectorinheating-coolingmodebasedonPeltiereffect.Inthispaper,afeasibilitystudy isperformedforabifunctionalthermoelectricgeneratorappliedinvehicleengines,whichcanuseSeebeckeffect for waste heat recovery and Peltier effect for engine warm-up. To predict the bidirectional behaviours of the thermoelectric module, a dual-mode thermoelectric module model is developed, and the simulation results for thetwomodes(powergenerationmodeandheating-coolingmode)arebothverifiedwithexperiments.Thefour- quadrant operation diagram of thermoelectric module, which clearly presents the cooling, heating and power generation curves, is produced based on the validated model. A case study of applying a bifunctional thermoelectric generator to a 2l-diesel engine passenger car is then carriedoutbasedonafurtherextendedbifunctionalTEGmodelandanengineoilandcoolantcircuitmodel.The simulation results shows that the optimal engine oil temperature (100°C) cannot be reached in the new European driving cycle for the baseline engine without thermoelectric generator, but it can be reached by both applyingthermoelectricgeneratoroperatinginwasteheatrecoverymodeandenginewarm-upmode.Compared withthethermoelectricgeneratoronlyoperatinginwasteheatrecoverymode,a3-minfasterwarm-upeffectof engineoilcanbeobtainedwhenthebifunctionalthermoelectricgeneratorworksinenginewarm-upmodewith electrical current applied. It also finds out that the electric power generated in waste heat recovery mode at vehicle starting and low vehicle speed phrase is limited. However, a faster warm-up effect (engine oil tem- peraturerising7°Cinthefirst100s)canbeobtainedbyoperatingthermoelectricgeneratorinenginewarm-up modeatvehiclestaring.Theelectricenergyusedinenginewarm-upmodecanberegeneratedinthelaterwaste heat recovery mode. To compensate all the used electric energy in engine warm-up mode, longer time of thermoelectric generator operating in waste heat recovery mode is needed. 1. Introduction In the face of internationally tightened CO 2 emission requirements and regulations, the pursuit of improved fuel economy is becoming an increasingly important objective for automotive manufacturers. Based onthetypicalenergyflowpathofaninternalcombustionengine(ICE), approximately one third of the energy is discharged through the ex- haust flow [1–3]. A thermoelectric generator (TEG) can convert a proportionoftheotherwisewastedthermalenergyoftheexhaustgasto electricity directly for use in the vehicle systems. Due to the significant strides in thermoelectric materials and modules, a number of vehicular TEG prototypes for waste heat recovery (WHR) have been fabricated https://doi.org/10.1016/j.apenergy.2019.03.056 Received 23 July 2018; Received in revised form 28 January 2019; Accepted 7 March 2019 ⁎ Corresponding author. E-mail address: r.chen@lboro.ac.uk (R. Chen). Applied Energy 242 (2019) 273–284 0306-2619/ © 2019 Published by Elsevier Ltd. T