  Citation: Laurén, M.; Goswami, G.; Tupitsina, A.; Jaiswal, S.; Lindh, T.; Sopanen, J. General-Purpose and Scalable Internal-Combustion Engine Model for Energy-Efficiency Studies. Machines 2022, 10, 26. https:// doi.org/10.3390/machines10010026 Academic Editor: Francesco Castellani Received: 16 November 2021 Accepted: 27 December 2021 Published: 30 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). machines Article General-Purpose and Scalable Internal-Combustion Engine Model for Energy-Efficiency Studies Mika Laurén 1, * , Giota Goswami 2 , Anna Tupitsina 3 , Suraj Jaiswal 2 , Tuomo Lindh 3 and Jussi Sopanen 2 1 Department of Mechanical Engineering, Turku University of Applied Sciences, 20520 Turku, Finland 2 Department of Mechanical Engineering, Lappeenranta University of Technology, 53850 Lappeenranta, Finland; giota.goswami@lut.fi (G.G.); suraj.jaiswal@lut.fi (S.J.); jussi.sopanen@lut.fi (J.S.) 3 Department of Electrical Engineering, Lappeenranta University of Technology, 53850 Lappeenranta, Finland; anna.tupitsina@lut.fi (A.T.); tuomo.lindh@lut.fi (T.L.) * Correspondence: mika.lauren@turkuamk.fi; Tel.: +358-44-907-2058 Abstract: Hybrid powertrains that combine electric machines and internal-combustion engines offer substantial opportunities to increase the energy efficiency and minimize the exhaust emissions of vehicles and nonroad working machines. Due to the wide range of applications of such powertrains, simulation tools are used to evaluate and compare the energy efficiency of hybrid powertrains for application-specific working cycles in virtual environments. Therefore, the accurate modeling of the powertrain components of a hybrid system is important. This paper presents an agile calculation tool that can generate realistic fuel consumption data of a scalable diesel engine. This method utilizes a simple efficiency model of the combustion and crank train friction model to generate the fuel consumption map in the operating area of a typical diesel engine. The model parameters are calibrated to produce accurate fuel consumption data in the initial phase of system-level simulations. The proposed method is also validated by using three real engine datasets, and the comparison of results is presented. Keywords: internal combustion engine; modelling; powertrain developing; nonroad mobile machinery 1. Introduction Increasingly tightening emission regulations and energy-efficiency demands are key drivers for the electrification of transportation and nonroad mobile machines. Hybrid elec- trical vehicles (HEV) provide the potential to reduce fuel consumption and consequently diminish CO 2 emissions, since the workload of the machine is distributed between an internal-combustion engine (ICE) and electrical energy storage. HEV powertrain compo- nent designs can be studied through the simulation models of different vehicles and mobile machines. In energy-efficiency studies, accurate fuel consumption of the ICE in static loading condition is needed. Therefore, special attention should be paid to the efficiency and specific fuel consumption maps of diesel engine operation to aid in the estimation of fuel consumption in the system’s dynamic simulation [1]. The topology selection and dimensioning of hybrid powertrain components of offroad vehicles, such as agricultural tractors [2,3], different loaders [4], and forest machines [5], is a challenging task. The varying working operational profiles and demands of auxiliary devices of these vehicles make it difficult to evaluate the performance, fuel consumption, and feasibility of different control strategies of the vehicle under design. Simulators that can be used to evaluate and study these characteristics were introduced in previous studies [6]. Such simulation models are capable of simulating standard work cycles, testing powertrain components such as combustion engines, energy storage, and electrical drives, and changing the topology of the vehicle. In typical combustion engine models, many parameters are determined on the basis of measurements. However, if efficiency maps and specific fuel consumption maps are avail- able, a relatively simple simulation model can be created without relying on measurements. Machines 2022, 10, 26. https://doi.org/10.3390/machines10010026 https://www.mdpi.com/journal/machines