The TOWB 011-4 optical diagnostics test cell is equipped with a Constant-Volume Combustion Chamber (CVCC) designed for high-pressure, high-temperature spray and combustion studies. The chamber is a certified vessel rated to 120 bar test pressure and 80 bar working pressure, featuring multiple quartz optical windows for high-speed shadowgraph, Schlieren, and vaporisation imaging. It supports inert environments up to 30 bar and temperature-controlled operation up to 500 °C, with integrated pressure/temperature transducers and fully conditioned gas and purge lines. The CVCC is synchronised with a high-pressure common-rail injection system and external timing hardware to enable microsecond-accurate triggering for repeatable research-grade experiments on spray development, atomisation, ignition processes, and fuel behaviour.

The optical diagnostics system includes a Photron FASTCAM SA-X2 high-speed camera with spectral sensitivity from 400–900 nm and a Tokina macro lens for high-clarity imaging. For non-reactive operation, the camera records at 45,000 fps (512×512 px) with a 2.5 µs shutter and 0.07 mm/px resolution. Reactive studies use frame rates up to 144,000 fps (512×136 px) and 3.75–5.3 µs exposure for soot and ignition-related measurements. Full-plume luminosity imaging is performed at 19,200 fps at 896×792 px with 7.5 µs exposure. The system is fully synchronised with injector and DAQ hardware through TTL triggering for accurate timing of spray and combustion diagnostics.