**Ilya Kulikov \*, Andrey Kozlov, Alexey Terenchenko and Kirill Karpukhin**

National Research Center "NAMI", 125438 Moscow, Russia; a.kozlov@nami.ru (A.K.); terenchenko@nami.ru (A.T.); k.karpukhin@nami.ru (K.K.)

**\*** Correspondence: i.kulikov.mami@gmail.com

Received: 3 April 2020; Accepted: 13 April 2020; Published: 21 April 2020

**Abstract:** This article describes a study that aimed to estimate the fuel-saving potential possessed by the hybridization of conventional powertrains intended for heavy-duty vehicles based on diesel and natural gas fueled engines. The tools used for this analysis constitute mathematical models of vehicle dynamics and the powertrain, including its components, i.e., the engine, electric drive, transmission, and energy storage system (ESS). The model of the latter, accompanied by experimental data, allowed for an analysis of employing a supercapacitor regarding the selection of its energy content and the interface between the traction electric drive and the ESS (in light of the wide voltage operating range of supercapacitors). The results revealed the influence of these factors on both the supercapacitor efficiency (during its operation within a powertrain) and the vehicle fuel economy. After implementation of the optimized ESS design within the experimentally validated vehicle model, simulations were conducted in several driving cycles. The results allowed us to compare the fuel economy provided by the hybridization for diesel and gas powertrains in different driving conditions, with different vehicle masses, taking into account the onboard auxiliary power consumption.

**Keywords:** heavy-duty vehicles; diesel engine; natural gas engine; hybrid powertrain; supercapacitor; fuel consumption; mathematical modeling
