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An Evaluation of Turbocharging and Supercharging Options for High-Efficiency Fuel Cell Electric Vehicles

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An Evaluation of Turbocharging and Supercharging Options for High-Efficiency Fuel Cell Electric Vehicles applied sciences Article An Evaluation of Turbocharging and Supercharging Options for High-Efficiency Fuel Cell Electric Vehicles Arthur Kerviel 1,2, Apostolos Pesyridis 1,* , Ahmed Mohammed 1 and David Chalet 2 1 Department of Mechanical and Aerospace Engineering, Brunel University, London UB8 3PH, UK; [email protected] (A.K.); [email protected] (A.M.) 2 Ecole Centrale de Nantes, LHEEA Lab. (ECN/CNRS), 44321 Nantes, France; [email protected] * Correspondence: [email protected]; Tel.: +44-189-526-7901 Received: 17 October 2018; Accepted: 19 November 2018; Published: 3 December 2018 Abstract: Mass-produced, off-the-shelf automotive air compressors cannot be directly used for boosting a fuel cell vehicle (FCV) application in the same way that they are used in internal combustion engines, since the requirements are different. These include a high pressure ratio, a low mass flow rate, a high efficiency requirement, and a compact size. From the established fuel cell types, the most promising for application in passenger cars or light commercial vehicle applications is the proton exchange membrane fuel cell (PEMFC), operating at around 80 ◦C. In this case, an electric-assisted turbocharger (E-turbocharger) and electric supercharger (single or two-stage) are more suitable than screw and scroll compressors. In order to determine which type of these boosting options is the most suitable for FCV application and assess their individual merits, a co-simulation of FCV powertrains between GT-SUITE and MATLAB/SIMULINK is realised to compare vehicle performance on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) driving cycle. The results showed that the vehicle equipped with an E-turbocharger had higher performance than the vehicle equipped with a two-stage compressor in the aspects of electric system efficiency (+1.6%) and driving range (+3.7%); however, for the same maximal output power, the vehicle’s stack was 12.5% heavier and larger. Then, due to the existence of the turbine, the E-turbocharger led to higher performance than the single-stage compressor for the same stack size. The solid oxide fuel cell is also promising for transportation application, especially for a use as range extender. The results show that a 24-kWh electric vehicle can increase its driving range by 252% due to a 5 kW solid oxide fuel cell (SOFC) stack and a gas turbine recovery system. The WLTP driving range depends on the charge cycle, but with a pure hydrogen tank of 6.2 kg, the vehicle can reach more than 600 km. Keywords: turbocharger; supercharger; E-turbocharger; Proton-exchange membrane fuel cell; solid oxide fuel cell; range extender 1. Introduction The Intergovernmental Panel on Climate Change (IPCC) study from 2014 showed that 14% of global greenhouse gas emissions are due to transportation [1]. Since 65% of greenhouse gas emissions are related to CO2, it has become crucial to decrease their global warming impact. Taking well-to-wheel emissions into consideration, electric vehicles reach 180 g CO2eq/km (because of a global 68% electricity production still coming from oil, gas, and coal) whereas fuel cell vehicles (FCVs) reach 127 g CO2 eq/km [2,3]. Even if current regulations only take into account tank-to-wheel emissions, which are null for both of these types of vehicle, some car manufacturers such as Toyota (Mirai), Honda (Clarity Fuel Cell), or Daimler Group (GLC F-cell) are investing in fuel cell technology to Appl. Sci. 2018, 8, 2474; doi:10.3390/app8122474 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2474 2 of 21 Appl. Sci. 2018, 8, x 2 of 21 prepare for an uncertain future. To become a viable solution for transportation, fuel cell vehicles must dealpower with density power challenge densitys challenges.. For instance, For the instance, Hyundai the Tucson Hyundai Fuel Tucson Cell edition Fuel Cellis 300 edition kg heavier is 300 than kg heavierthe gasoline than version the gasoline for the version same output for the power. same output To decrease power. the To weight decrease of thethe weightfuel cell of vehicle the fuel means cell vehicleless fuel means consumption less fuel, consumption,and thus a higher and driving thus a higher range. driving range. ThereThere isis aa largelarge potentialpotential forfor increasingincreasing the thepower power densitydensity byby usingusing aa boostingboosting systemsystem forfor thethe airair supply.supply. AA higherhigher pressurepressure of air means a higher output output power power and and efficiency. efficiency. As As seen seen in in Figure Figure 1,1 ,a arecent recent paper paper from from Honda Honda underline underlinedd that that increas increasinging the pressure ratio from 1.0 to 1.71.7 providedprovided 10%10% moremore outputoutput powerpower [[4].4]. AsAs aa consequence,consequence, itit isis possiblepossible toto reducereduce thethe numbernumber ofof cellscells andand thusthus thethe weightweight of of the the fuelfuel cellcell stackstack forfor thethe samesame outputoutput power.power. GivenGiven thatthat thethe requirementsrequirements differdiffer fromfrom thosethose ofof anan internalinternal combustioncombustion engineengine (ICE),(ICE), thethe choicechoice ofof compressorcompressor typetype mustmust bebe adaptedadapted toto fuelfuel cellcell vehiclevehicle application. application. InIn orderorder toto determinedetermine whichwhich typetype ofof compressorcompressor toto use,use, aa literaryliterary surveysurvey waswas conductedconducted toto identifyidentify whichwhich typestypes ofof fuel fuel cell cell are are relevant relevant to to transportation transportation application. application. ThisThis waswas followedfollowed byby thethe developmentdevelopment of of fuel fuel cell cell vehicle vehicle powertrain powertrain models, models, employing employing co-simulation co-simulation between between GT-SUITE GT-SUITE and MATLAB/SIMULINK.and MATLAB/SIMULINK. Finally, Finally, simulations simulations have have included included driving driving cycle cycle simulations simulations to analyse to analyse the impactthe impact of the of air the supply air supply system system on vehicle on vehicle performances. performances. Figure 1. Influence of the operating pressure on the fuel cell output power. Figure 1. Influence of the operating pressure on the fuel cell output power. 2. Methodology 2. Methodology 2.1. Proton Exchange Membrane Fuel Cell (PEMFC) Model 2.1. Proton Exchange Membrane Fuel Cell (PEMFC) Model A polarisation curve model has been used to model the operation of a monocell pure hydrogen PEMFCA polari with MATLAB/SIMULINK.sation curve model has been The model,used to which model was the proposedoperation byof a Pukrushpan monocell pure [5], hydrogen and was usedPEMFC in the with MATLAB/SIMULINK MATLAB/SIMULINK. environment, The model, is which described was byproposed the following by Pukrushpan equations: [5], and was used in the MATLAB/SIMULINK environment, is described by the following equations: Vcell = Enerst − Vact − Vconc − Vohm (1) −3 RT 0.5 Enerst = 1.229V −=0.85E ∗ 10 −(VT − 298.15− V ) +− V log PH2∗P (2)(1) 2F O2 Vact = v0 + va[1 − exp(−c1∗i)] (3) RT h i V = 0.279 − 0.85 ∗ 10−3(T − 298.15)+ log (P − P ) ∗ 0.1173 ∗ (P − P )0.5 (4) 0 2F H,in sat A,in sat . E = 1.229 − 0.85 ∗ 10 (T − 298.15) + log (P ∗ P ) (2) Appl. Sci. 2018, 8, 2474 3 of 21 h i2 −5 −2 PO2 −4 Va = −1.618 ∗ 10 ∗T + 1.168 ∗ 10 0.1173 + Psat + 1.8 ∗ 10 ∗T − 0.166 h i (5) PO2 −4 0.1173 + Psat + −5.8 ∗ 10 ∗T + 0.5736 i c3 Vconc = i∗ c2 ∗ (6) iL h P c = 8.66 ∗ 10−5∗T − 0.068 O2 + P − 1.6 ∗ 10−4∗T + 0.54 (7) 2 0.1173 sat Vohm = Ri∗i (8) where Vcell is the output tension of the monocell. Enerst is the Nerst potential. Vact, Vconc and Vohm are respectively the activation, mass transfer, and ohmic losses. C1 and C3 are given by a recent paper concerning air supply system control [6] as C1 = 10 and C3 = 2. The total output power of the N-cells’ stack is calculated as: P = N ∗ Vcell∗I (9) The electrochemical reaction is considered as stoichiometric. The system is supposed to run with an excess of air. The current is calculated from the hydrogen mass flow rate, and the excess of air is included in the calculation of oxygen partial pressure. As a result, the PO2 and PH2 from previous equations are calculated by taking the average between the inlet and outlet stack pressure as follows: DmO,out PO2 = 0.5 ∗ (PA,in ∗ 0.21) ∗ 1 + (10) DmO,in DmH,out PH2 = 0.5∗PH,in ∗ 1 + (11) DmH,in where DmO,in and DmH,in are the inlet mass flow rates, and DmO,out and DmH,out are the outlet mass flow rates of oxygen and hydrogen, respectively. PA,in and PH,in are the inlet pressures of air and hydrogen. As seen in Figure2, the MATLAB/SIMULINK model runs as a black box in the GT-SUITE environment. The “PEMFCs_model” refers to the MATLAB function using the model described. The inputs are the inlet mass flow rates (DmA,in, DmH,in), the inlet pressures (PA,in, PH,in), and the required power by the air supply system (Pcomp). The outputs include the outlet mass flow rates ((DmA,out, DmH,out), the outlet air pressure (PA,out), the output produced power, the current, and the electric efficiencies (P, I, Reff , Reff,system). There are different ways of calculating the electric efficiency. In this paper, it is the electric stack efficiency and the electric system efficiency that are considered and calculated as follows [4,7,8]: P R = (12) eff 1.481∗N ∗ I P − Pcomp R = (13) eff,system 1.481∗N ∗ I where N is the number of cells, and 1.481 is the theoretical voltage at the terminals of a hydrogen fuel cell. As seen in Figure3, the GT-SUITE model takes into consideration the air consumed through the stack.
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