Particle image velocimetry (PIV) has become a key tool in the internal combustion engines (ICEs) research. This chapter comprehensively reviews the current applications of PIV in ICEs research, particularly in the fuel injection, the combustion processes, and the in-cylinder flow of engines. Detailed insights obtained from PIV measurements have significantly contributed to optimizing engine design, improving combustion efficiency, and reducing emissions. Despite its advantages, PIV technology still faces several challenges, especially in the context of ammonia–hydrogen-fueled engines. Selecting appropriate tracer particles and organizing the complexity in-cylinder flow field pose significant obstacles. Moreover, this chapter explores corresponding measures to address these challenges, including the development of specialized tracer particles, multimodal measurement approaches, and AI-enhanced data processing. These measures have the potential to further improve the accuracy and applicability of PIV measurements in carbon-neutral engines research. This chapter aims to provide researchers and engineers with a comprehensive understanding of the most advanced PIV applications, encountered challenges, and corresponding measures in the field of ICEs research.