As a means of exploring the use of optical imaging techniques in the study of engine flow and combustion problems, we have applied several imaging techniques in different laboratory engines and engine flow simulators. Two single cylinder research engines were employed: a sidewall-valved engine and a square piston engine. Additional observations were made of the free jet flowing from a liquid fuel injector, the intake valve air flow in a steady flow facility, and the mixed fuel/air intake flow following the impingement of a fuel spray on the backside of a valve.We used the planar imaging of laser induced fluorescence from OH to mark the position of the propagating flame front in the engine. These results are compared to similar data obtained using a Mie scattering technique employed in an earlier study. In addition, we used laser induced fluorescence imaging of nitrogen dioxide to observe the intake valve flow in a flow stand and schlieren flow visualization to observe liquid fuel sprays, valve flow, and flame propagation. Both planar imaging of Mie scattering and schlieren photography were used to observe liquid fuel sprays and the qualitative aspects of fuel-air mixing during intake valve flow.Our results illustrate that if the optical access to the engine or simulator can be accommodated, the various imaging techniques can be very useful in allowing the observation of the important flow and combustion processes occurring in an engine. Furthermore, in some cases several different techniques are capable of providing the required information.