Team

We are faced with the urgent need to reduce CO2 emissions, an issue that affects a wide range of technologies with economic and social significance. One of the major contributors to CO2 emissions over the next decades are internal combustion engines, so reducing their emissions is imperative. Furthermore it is mandatory to improve internal combustion engines with respect to fuel efficiency and low local emissions like NOX and hydrocarbons.

To address these issues, a comprehensive understanding of the underlying physical and chemical processes is necessary. Recent advances in the automotive industry have led to the downsizing of the internal combustion engine geometry, which increases the surface-to-volume ratio of the engine. To this regard, near-wall reactions become increasingly important for flame quenching and unburned hydrocarbon emissions. In combination with numerical simulation research in this field leads to improved combustion efficiency and engine development.

An optically accessible research engine with a quartz-glass liner and piston window is used to investigate flow and combustion processes in a SI or DISI engine. The wide optical access allows for high resolution optical measurements in a large cylinder region. The methods used to measure scalar fields are laser induced fluorescence (LIF), e. g. to investigate the gas temperature, air-fuel mixture, and the flame progress, as well as the use of thermographic phosphors to determine wall temperatures. Finally particle image velocimetry (PIV) and particle tracking velocimetry (PTV) is applied to capture the flow down to the velocity boundary layer.

Measurements of the instantaneous interaction between the flame and the wall temperature are used to study near-wall processes in the optical engine. Thereby the 2D temperature distribution at the piston wall is captured by the temperature dependency of the phosphorescence decay following the excitation of a thermographic phosphor layer with a laser. High resolution velocity measurements allow for an analysis of the boundary layer flow and subsequent improvement of wall models used in numerical simulations. Cycle-to-Cycle variations (CCV) of local gas temperature differences are studied by means of laser induced fluorescence (LIF). The interaction between a direct-injected fuel spray, the flow and the subsequent evaporation and mixing of wall films is investigated with PIV and LIF. Both SO2-LIF and Mie scattering measurements allow to track the flame evolution and determine factors responsible for CCV at different engine speeds and loads.