Fiber-based sensor for combustion chamber monitoring: manufacturing challenge

The measurement of relevant process emissions is a challenging task, especially when access for measurement technology is limited. One example is the optical combustion chamber monitoring of internal combustion engines. The access is limited and spatial resolution for observation is limited by the possible use of optical elements in the combustion chamber. So far, data acquisition has been realized with the aid of spark plugs with integrated connections to an optical sensor. This optical spark plug has the function of a spark plug and simultaneously enables the detection of light in the engine. The optical spark plug is positioned in the center of the combustion chamber which allows for a symmetrical design for a 360° field of view. Our approach is to build an alternative fiber-based light sensor without the function of a spark plug, because if no ignition unit is installed, there is more space for additional optical elements for higher optical spatial resolution than conventional light sensors with ignition function. The main challenge is the miniaturization of the optical and mechanical set up. Due to the fixed position of the spark plug and the limited access to the combustion chamber, the light sensor must be inserted at an angle into the combustion chamber at a different location, so, the optical system must be asymmetric. This paper presents the results of the design and fabrication of a combustion chamber light sensor with respect to the optical and mechanical challenge of spatially resolved detection of light pulses in a combustion chamber of an engine under an oblique access to the combustion chamber.