A Hydrogen-Assisted Ammonia-Fueled Otto Engine Scenario for 100% Carbon-Free Mobility in Heavy-Duty Vehicles: A Perspective on Stratified Charge, Water Injection, EGR and Turbocharger

<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt;text-align:justify;line-height:normal"><span style="font-size:12.0pt;mso-bidi-font-size:11.0pt;font-family:&quot;Times New Roman&quot;,serif">Global decarbonization targets (IMO2050, EU Euro VII, EPA 2027) mandate the phase-out of carbon-based fuels inheavy-duty transportation. This study develops a holistic conceptual systemarchitecture for a hydrogen-assisted ammonia-fueled spark ignition (SI) Ottoengine that offers 100% carbon-free operation, addressing the structurallimitation of diesel engines that remain dependent on pilot fuel when operatingwith low-reactivity fuels such as ammonia. The original contribution of thisstudy is structured around three main axes. First, it balances ammonia's lowlaminar flame speed (≈ 0.07 m/s) and narrow combustion range with hydrogen'shigh reactivity (≈ 2.65 m/s) through a stratified charge strategy. Second, itcontrols the high-temperature conditions that inevitably result fromhydrogen-assisted combustion through the integration of water injection, cooledexhaust gas recirculation (EGR), and turbocharging. While water injectionserves thermal balancing and knock suppression functions, EGR limits thermal NO_xformation, and the turbocharger compensates for ammonia's low volumetric energydensity. Third, hydrogen functions as a reactivity regulator that governscombustion kinetics, while the interaction between ammonia slip and NO_xin the exhaust line creates an internal selective catalytic reduction (SCR)mechanism without requiring an external reducing agent. This study presents asystem-level conceptual framework and a guiding engineering paradigm for thecarbon-free transformation of internal combustion engines in heavy-dutytransportation. The proposed architecture combines fuel preparation, combustionmodulation, thermal management, and emission control strategies within a singleintegrated framework, establishing a conceptual foundation for future research.<o:p></o:p></span>