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ArticleOpen Access http://dx.doi.org/10.26855/ea.2026.06.007

Internal Combustion Engines Emissions—A Review

Mircea-Tudor Grapini*, Nicolae Burnete

Department of Automotive Engineering and Transport, Faculty of Automotive, Mechatronics and Mechanical Engineering, Technical University of Cluj-Napoca, Cluj-Napoca 400641, Romania.

*Corresponding author: Mircea-Tudor Grapini

Published: June 3,2026

Abstract

Global ecosystems and public health face increasing risks from climate change, primarily driven by greenhouse gas emissions from fossil fuel combustion. The automotive sector accounts for more than 70% of greenhouse gas emissions within the transportation sector, marking it as a primary focus for environmental impact studies. This research examines the ecological consequences of internal combustion engines, which discharge a complex mixture of regulated pollutants—including carbon monoxide, nitrogen oxides, hydrocarbons, and particulate matter—alongside unregulated toxins such as nitrous oxide, hydrogen cyanide, and volatile organic compounds. These substances pose significant long-term threats to both human health and atmospheric integrity. Analysis high-lights the vital role of stringent emission standards, including EURO regulations and modernized testing protocols like the Worldwide Harmonized Light Vehicles Test Procedure and Real Driving Emissions, in minimizing hazardous outputs. While advancements in engine architecture and aftertreatment technologies have been substantial, critical challenges persist regarding cold-start inefficiencies and the suppression of ultrafine particles. Simultaneously, the shift to low and zero-carbon fuels, such as hydrogen, ethanol, methanol, and biodiesel, is highlighted as a feasible route to sustainable mobility. When combined with lean-burn techniques and sophisticated engine designs, alternative fuels provide significant reductions in both regulated and unregulated emissions. They also have improved combustion characteristics and fewer adverse effects on the environment. The transportation industry can drastically lessen its environmental impact by combining alternative fuels, efficient combustion techniques, and strong emission control technologies with a supportive legislative framework. Achieving climate goals, enhancing urban air quality, and moving closer to a sustainable mobility future will all depend on these actions.

Keywords

Internal combustion engines; climate change; alternative fuels; regulated and unregulated emissions; emission control; hydrogen

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Copyright

© 2026 by the author(s).
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND) license, which permits non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited and is not modified or adapted.
https://creativecommons.org/licenses/by-nc-nd/4.0/

How to cite this paper

Internal Combustion Engines Emissions—A Review

How to cite this paper: Mircea-Tudor Grapini, Nicolae Burnete. (2026). BInternal Combustion Engines Emissions—A Review. Engineering Advances6(2), 105-120.

DOI: http://dx.doi.org/10.26855/ea.2026.06.007