Fuel effects on NO formation in diesel-like jets in a vessel

We demonstrated recently that NO concentration measurements are feasible even in the core of largely non-sooting diesel-like jets by combined laser-induced fluorescence (LIF) and spontaneous Raman scattering (SRS). However, the question arises whether previous findings hold also for other diesel-like jets. The current study focuses on fuel effects. In the previous NO measurements, n-heptane was used. It is replaced by pure di-n-butylether (DNBE) and a tailor-made blend of 50% DNBE and 50% n-octanol. These fuels are promising biofuel candidates and lead to an interesting variation of mixing during combustion (MDC). The determination of NO concentrations turns out to be generally feasible with the blend on the jet centerline in the quasi-steady phase of the injection event. The corresponding uncertainty is about ± 28 %. By contrast, some of the NO-LIF measurements in sooting DNBE jets are discarded, primarily due to increased light attenuation. For the remaining NO concentrations with DNBE the corresponding uncertainty is about ± 40 %. For the blend, results indicate that NO formation is very similar to the one in the n-heptane jets. Thus, the net effect of changed volatility and oxygenation is seemingly weak. By contrast, quasi-steady centerline NO concentrations are apparently significantly affected by MDC for pure DNBE. Relatively high NO concentrations are observed in this case, although products of highly fuel-rich fluid parcels are also present there. This study indicates the importance of MDC in such jets.