We report on essential design elements of optically accessed research engines and describe selected examples of their applications in engine development. Whereas research topics most often address specific generic topics and are focused on comprehensive analysis of selected engine phenomena, the priority in using optical engines for engine development tasks is in providing data relevant for the operation of a normal multicylinder engine. In this latter case, optical engines are only used if their results have such high value that they justify the efforts required to achieve the outcome. Both, research and development applications, benefit from each other as they promote progress in optical engine technology as well as in application of new analysis techniques.