15. Hydrogen-Fueled Spark Ignition Engines: Understanding NOx Formation and Mitigation Through Engine Design Innovations

Hydrogen as an alternative fuel in spark ignition engines presents a promising avenue for achieving sustainable transportation. However, the combustion characteristics of hydrogen often result in elevated nitrogen oxide (NOx) emissions. This book chapter delves into a comprehensive exploration of diverse control methods aimed at mitigating NOx emissions in hydrogen-fueled spark ignition engines. The chapter embarks on an analysis of the combustion intricacies of hydrogen, elucidating its propensity for high-temperature combustion and the consequent NOx formation through thermal and prompt mechanisms. It subsequently delves into a detailed investigation of multiple control techniques, including Variable Valve Timing (VVT), Injection timing, Ignition timing (IT), Exhaust Gas Recirculation (EGR), and Engine design optimization. These methods are scrutinized for their potential to modulate combustion parameters, thereby managing temperatures and curbing NOx. A focal point of the chapter is the role of direct injection of hydrogen, which allows for precise control over mixture distribution and combustion phasing. This technique proves instrumental in mitigating NOx by facilitating leaner combustion and controlling heat release. Each strategy's advantages, challenges, and integration feasibility are evaluated. The synergy between these control methods and their potential for simultaneous NOx reduction and efficient engine operation is thoroughly discussed. In summation, this chapter synthesizes a spectrum of control strategies encompassing VVT, Injection timing, Ignition timing (IT), EGR, Engine design, and Direct-injection (DI) hydrogen, all directed at abating NOx emissions in hydrogen-fueled spark ignition engines. It serves as a pivotal reference for researchers, engineers, and policymakers invested in advancing clean and sustainable hydrogen technologies.