The field of Virtual Reality continues to evolve to provide an ever-greater sense of immersion to the user. However, VR experiences are still primarily constrained through the human senses of vision and audition, with some interest in haptic (mainly vibrotactile) applications. Only recently have olfactory displays- technologies that generate and deliver scent stimuli- been examined to provide the sense of smell to the human olfactory organ in virtual environments. This paper presents a classification and review of olfactory-enhanced virtual reality systems, particularly those that deployed a Head-Mounted Display (HMD) or Cave Automatic Virtual Environment (CAVE) system. In addition, the paper provides a discussion of the various technological and design challenges for developing an olfactory display suitable for enhancing virtual reality experiences. Finally, the paper proposes future perspectives on the field and includes a table summarizing the characteristics and features of the reviewed systems.

虚拟现实领域不断发展，为用户提供了前所未有的沉浸感。然而，VR 体验仍然主要受到人类视觉和听觉的限制，对触觉（主要是振动触觉）应用也有一定兴趣。直到最近，嗅觉显示（产生和传递气味刺激的技术）才被检查，以在虚拟环境中为人类嗅觉器官提供嗅觉。本文对嗅觉增强虚拟现实系统进行了分类和回顾，特别是那些部署了头戴式显示器（HMD）或洞穴自动虚拟环境（CAVE）系统的系统。此外，本文还讨论了开发适合增强虚拟现实体验的嗅觉显示器的各种技术和设计挑战。最后，本文提出了该领域的未来前景，并包括一个总结所审查系统的特征和特点的表格。