Numerical assessment of water injection for improved thermal efficiency and emissions control in a medium-duty hydrogen engine for transportation applications

Abstract

[EN] The existing political environment and the growing worries about climate change have resulted in the imposition of stringent regulations on traditional propulsion systems reliant on fossil fuels. While new technologies are being investigated to substitute internal combustion engines, their current technological advancement necessitates further development and refinement in order to emerge as a viable alternative to the conventional internal combustion engine. The utilization of hydrogen-powered internal combustion engines has showcased their ca-pacity to rapidly achieve complete decarbonization in the transportation industry. However, these engines continue to encounter limitations regarding their operational range that need to be addressed. The utilization of EGR for controlling combustion instabilities and mitigating NOx formation still has significant limitations in operating at high engine loads, mainly affecting the boost requirements for reaching high power densities. The present work evaluates the potential of substituting the EGR dilution with a water injection system for reaching full load operation on a conventional diesel engine, assuming the minimum modifications required for it to work under H2 combustion. The study is carried out assuming a multi-cylinder engine representing the medium-to high-duty transport sector. The evaluation includes a comparison of the engine performance and emissions obtained when using EGR and water injection at full load, comparing the requirements of the boost system for both strategies to reach power densities of 24 bar of BMEP equivalent to modern diesel applications. The results show that WI allows for significantly reduced boost pressure requirements lowering intake pressure by up to 1 bar, while achieving very similar engine efficiency and a reduction of NOx emissions around 80%, resulting a similar effectiveness compared with EGR. Additionally, WI provides additional prevention against undesired autoignition.