Ecological Paradox in the Reuse of Internal Combustion Engines from Scrapped Vehicles for Electric Power Generation—Circular Economy Potential Versus Emission Certification Barriers

Concepts such as reuse, repurposing, upcycling, remanufacturing, and re-powering can be applied to the reuse of combustion engines from passenger cars and trucks in stationary or mobile machines, such as power generators. Technical, economic, environmental, and research analyses indicate that such solutions may be justified; however, their implementation is limited by homologation and emission regulations. In most countries, there are no specific rules governing emissions from power generator engines, while in the European Union, such engines are categorized as mobile generators (portable or trailer-mounted) subject to Stage V (Reg. 2016/1628/EU), stationary generators (permanently installed) subject to the MCP Directive (2015/2193/EU), and emergency generators (limited operation) partially exempt from MCP but requiring registration. Consequently, engines recovered from road vehicles do not meet formal or technical emission compliance requirements for power generators and can only be used under conditional approval for research, experimental, or temporary purposes. This reveals a paradox of modern environmental policy: although reusing functional engines from dismantled vehicles could embody the principles of a circular economy, restrictive emission standards (Stage V, MCP, NSPS) effectively prevent such technological recycling. Addressing this issue requires legislative action and the development of simplified testing methods for used engines in new applications. This article is the first to systematically demonstrate that current Stage V, MCP and NSPS emission frameworks create a regulatory paradox that prevents the circular-economy reuse of functional automotive engines, and it proposes a dedicated secondary type-approval pathway enabling their legal and environmentally controlled application in power generators.