SRS/LIF-Messungen zur Charakterisierung rußarmer dieselähnlicher Flammen von alternativen Kraftstoffen und n-Heptan

• SRS/LIF-measurements for the characterization of low-sooting diesel-like flames of alternative fuels and n-heptane

Schulz, Christian; Grünefeld, Gerd (Thesis advisor); Pitsch, Heinz Günter (Thesis advisor)

Aachen : Wissenschaftsverlag Mainz GmbH - Aachen (2019)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Technischen Thermodynamik 22

Dissertation, RWTH Aachen University, 2019

Abstract

One of the main tasks in the development of modern diesel engines and alternative diesel fuels is the reduction of pollutant emissions, especially soot and NOx. For obtaining a deeper understanding of pollutant formation processes laser-optical measurement methods are quite suitable. Nitric oxide (NO) can be detected by laser induced fluorescence (LIF) in the UV-range. However, up to now evaluable NO-LIF measurements in the core of classical diesel jets were lacking. One basic reason is typically severe light attenuation of laser light and fluorescence emission which is to a large extend caused by soot. Newly developed alternative biofuels are also optimized to produce little soot. Also modern combustion regimes with enhanced premixing, e.g. PPCI or PCCI, show a reduced sooting tendency, but may in theory exhibit significant NO-concentrations inside the flame. Hence, in this work the measurement of NO-LIF in low-sooting diesel-like internal combustion of alternative fuels is examined. Therefore an optimized measurement approach with excitation by light of a KrF* excimer laser and 1-d spatially and spectrally resolved emission detection from combusting jets in a high-pressure vessel is used. Thereby reliable and evaluable NO-LIF signals can be measured for the first time in the core of diesel-like flames. Light attenuation is found which is lower than in classical diesel flames but still significantly high. Because for the quantification of NO-LIF, a precise knowledge of light attenuation of laser light and fluorescence emission is necessary, as another focus of this work the behavior of light attenuation in the UV-range in low-sooting diesel-like flames is studied in detail. By evaluating the N2-SRS induced by the KrF* laser, values of UV-light attenuation close to the premixed burn early in the combustion cycle can be determined for the first time. Furthermore, the feasibility of a thermometry method based on the evaluation of the ratio of Stokes-to-Anti-Stokes N2-SRS is demonstrated since temperature is also an important input parameter for NO quantification. Finally, the possibility of quantitative measurements of O2 by SRS in the core of diesel-like jets is investigated.

Institutions

• Chair and Institute of Technical Thermodynamics [412110]