clean technologies Review A Review of Heavy-Duty Vehicle Powertrain Technologies: Diesel Engine Vehicles, Battery Electric Vehicles, and Hydrogen Fuel Cell Electric Vehicles Carlo Cunanan, Manh-Kien Tran , Youngwoo Lee, Shinghei Kwok, Vincent Leung and Michael Fowler * Department of Chemical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada; [email protected] (C.C.); [email protected] (M.-K.T.); [email protected] (Y.L.); [email protected] (S.K.); [email protected] (V.L.) * Correspondence: [email protected]; Tel.: +1-519-888-4567 (ext. 33415) Abstract: Greenhouse gas emissions from the freight transportation sector are a significant contributor to climate change, pollution, and negative health impacts because of the common use of heavy-duty diesel vehicles (HDVs). Governments around the world are working to transition away from diesel HDVs and to electric HDVs, to reduce emissions. Battery electric HDVs and hydrogen fuel cell HDVs are two available alternatives to diesel engines. Each diesel engine HDV, battery-electric HDV, and hydrogen fuel cell HDV powertrain has its own advantages and disadvantages. This work provides a comprehensive review to examine the working mechanism, performance metrics, and recent developments of the aforementioned HDV powertrain technologies. A detailed comparison between the three powertrain technologies, highlighting the advantages and disadvantages of each, is Citation: Cunanan, C.; Tran, M.-K.; also presented, along with future perspectives of the HDV sector. Overall, diesel engine in HDVs will Lee, Y.; Kwok, S.; Leung, V.; Fowler, remain an important technology in the short-term future due to the existing infrastructure and lower M. A Review of Heavy-Duty Vehicle costs, despite their high emissions, while battery-electric HDV technology and hydrogen fuel cell Powertrain Technologies: Diesel HDV technology will be slowly developed to eliminate their barriers, including costs, infrastructure, Engine Vehicles, Battery Electric and performance limitations, to penetrate the HDV market. Vehicles, and Hydrogen Fuel Cell Electric Vehicles. Clean Technol. 2021, Keywords: heavy-duty vehicles; diesel engine trucks; battery electric trucks; fuel cell electric trucks; 3, 474–489. https://doi.org/10.3390/ cleantechnol3020028 zero-emission vehicles Academic Editor: José-Santos López-Gutiérrez 1. Introduction Received: 24 March 2021 Increasing truck transport demand [1] and greenhouse gas emissions [2] have gar- Accepted: 25 April 2021 nered the interest of many to research alternative powertrain technologies for heavy-duty Published: 1 June 2021 vehicles (HDVs). Objectives to reduce and mitigate emissions across all sectors have been set by many governments regarding the transportation sector. Conventional HDVs dis- Publisher’s Note: MDPI stays neutral proportionately represent the on-road carbon dioxide (CO2), nitrogen oxide (NOx), and with regard to jurisdictional claims in particulate matter (PM) [3]. Medium and heavy-duty vehicles account for approximately published maps and institutional affil- 23% of the greenhouse gas (GHG) emissions in the United States [4]. HDVs also account iations. for approximately 40–60% of the NOx and PM emissions [3]. Climate change, pollution, and the resulting health impacts are some of the major concerns with the rise of these combustion emissions [5]. Therefore, the proposal for lower emission and zero-emission HDVs has been made. Copyright: © 2021 by the authors. A vehicle is classified as heavy-duty if it has a gross vehicle weight rating (GVWR) Licensee MDPI, Basel, Switzerland. greater than 26,000 lbs [6]. The GVWR is the maximum loaded weight of the vehicle, which This article is an open access article is the weight of the vehicle in addition to its payload. HDVs can be further classified distributed under the terms and into two classes, as seen in Figure1. Class 7 vehicles include transit buses, tow trucks, conditions of the Creative Commons and furniture trucks. Class 8 vehicles include semi-tractors, fire trucks, and dump trucks. Attribution (CC BY) license (https:// Class 7 vehicles have a GVWR of 26,000 lbs to 33,000 lbs, and Class 8 vehicles have a GVWR creativecommons.org/licenses/by/ of greater than 33,000 lbs. 4.0/). Clean Technol. 2021, 3, 474–489. https://doi.org/10.3390/cleantechnol3020028 https://www.mdpi.com/journal/cleantechnol Clean Technol. 2021, 3, FOR PEER REVIEW 2 Clean Technol. 2021, 3 Class 7 vehicles have a GVWR of 26,000 lbs to 33,000 lbs, and Class 8 vehicles have 475a GVWR of greater than 33,000 lbs. Figure 1. Classes and applications of heavy-duty vehicles. Figure 1. Classes and applications of heavy-duty vehicles. Conventional HDVs use fossil fuels and an internal combustion engine (ICE) which produceConventional energy to HDVs power use their fossil movement fuels and [7 an]. Most internal HDVs combustion today use engine an ICE (ICE) that utilizeswhich producediesel called energy a compression-ignitionto power their movement engine [7]. due Most to itsHDVs greater today energy use an efficiency ICE that than utilizes gaso- dieselline. However,called a compression many kinds-ignition of emissions engine are due released to its greater during energy diesel efficiency combustion, than such gaso- as line. However, many kinds of emissions are released during diesel combustion, such as CO2, NOx, and PM. Lower emission strategies in HDV technology consist of increasing the COefficiency2, NOx, and or reducing PM. Lower the pollutionemission ofstrategies the conventional in HDV technology diesel truck consist [8], using of increasing alternative thefuels efficiency which produceor reducing fewer the emissions pollution [ 9of], the or usingconventional a hybrid-electric diesel truck powertrain [8], using that alterna- stores tivesome fuels of thewhich energy produce it uses fewer within emissions batteries [9], [10 or]. using These a strategies hybrid-electric work bypowertrain reducing that fuel storeconsumptions some of the or by energy reducing it uses their within tailpipe batteries emissions. [10]. These Examples strategies of lower work emission by reducing strate- fuelgies consumption include reducing or by the reducing rolling resistancetheir tailpipe of theemissions. tires, which Examples increases of lower the fuel emission savings strategiesof the vehicle include and reducing using alternativethe rolling resistance fuels such of as the compressed tires, which natural increases gas the or fuel biodiesel, sav- ingswhich of the produce vehicle fewer and using emissions alternative [11]. However, fuels such zero-emission as compressed vehicles natural require gas or biodiesel a different, whichpowertrain produce as anyfewer vehicle emissions with [11]. an ICE However, will result zero in-emiss tailpipeion emissions. vehicles require a different powertrainThe two as any types vehicle of zero-emission with an ICE will vehicles result that in tailpipe will be emissions. discussed in this review are batteryThe electrictwo types vehicles of zero (BEVs)-emission and vehicles hydrogen that fuel will cell be vehiclesdiscussed (HFCVs). in this review These are vehicles bat- terypropel electric themselves vehicles using (BEVs) electricity and hydrogen and do fuel not requirecell vehicles the use (HF ofCVs). an ICE. These BEVs vehicles and HFCVs pro- pelboth themselves convert the using chemical electricity energy and stored do not in require active materialsthe use of into an ICE. electrical BEVs energy and HFCVs within boththe electrochemicalconvert the chemical cells. Batteriesenergy stored differ in from active fuel materials cells because into electrical batteries energy have the within active thematerial electrochemical stored within cells. the Batteries system, differ while from fuel cellsfuel ce havells because the active batteries materials have continuously the active materialfed into stored the system. within BEVthe system, batteries while are oftenfuel cells composed have the of active lithium-ion materials cells continuously due to their fedhigh into energy the system. andpower BEV batteries density are [12 often–14]. composed On the other of lithium hand,-ion HFCVs cells due often to usetheir proton high energyexchange and membranepower density fuel [ cells12–14 (PEMFC)]. On the dueother to hand, their HFCVs high-power often densityuse proton and exchange cold-start membranecapabilities fuel [15 cells]. (PEMFC) due to their high-power density and cold-start capabilities [15]. Both solutions offer zero tailpipe emissions, however, their well-to-wheels (WTW) emissionsBoth solutions are still highoffer in zero many tailpipe countries emissions, because however, of fossil fueltheir energy well-to generation.-wheels (WTW) WTW emissionsemissions are are still the high emissions in many released countries from because two main of fossil stages: fuel well-to-pump,energy generation. and WTW pump- emissionsto-wheels are [16 the]. Well-to-pump emissions released emissions from aretwo the main emissions stages: well released-to-pump, from theand production pump-to- of energy and the transport of it to the consumer. Pump-to-wheels are the refueling and tailpipe emissions generated when the vehicle is being refueled and used, respectively. Therefore, if the energy to generate the electricity or hydrogen to power the vehicle was uti- Clean Technol. 2021, 3 476 lized fossil fuels, the well-to-pump emissions would be significant. However, if the sources of energy used to generate the