• Energy Research

Abstract Premixed flame characteristics play a crucial role in most advanced combustion applications, such as gas turbines, aircraft combustors or internal combustion engines. The laminar burning velocity is one key parameter to determine the stabilisation and propagation of premixed flames. This study examined the influence of high pressures on the laminar burning velocity of biofuels and the correlation between laminar burning velocity and pressure. The investigated biofuels were pure ethanol as the state-of-the-art surrogate, pure iso-butanol as a possible alternative and several blends of ethanol/iso-octane. Due to the usage of two methods to measure the laminar burning velocity – the Heat Flux burner and the closed combustion vessel – a comparison was added for atmospheric conditions. The measured laminar burning velocities were conducted for equivalence ratios from 0.7 to 1.3, a pressure range from 1 bar(a) to 15 bar(a) and 373 K. The results were further compared to existing numerical mechanisms and literature data. The numerical mechanisms reveal prediction performances in the range of 0.2 cm/s (0.4%) and 5.2 cm/s (16.2%) for dedicated mechanisms and equivalence ratios between 0.9 and 1.1. The two methods show deviations of the laminar burning velocities between 2.3 cm/s (4.9%) and 6.7 cm/s (11.4%).

Abstract The substitution of gasoline with bio-ethanol is an intended way to reduce the climate impact of the traffic sector. To extend the knowledge of fundamental flame properties of ethanol/iso-octane flames and improve the numerical predictions for the effect of ethanol blending in internal combustion engines, measurements of the laminar burning velocity of established blend ratios of ethanol and iso-octane were carried out and compared to existing numerical mechanisms. The measurements were carried out with the Heat Flux burner, with thermocouples of type E at the burner plate, which was adapted with an evaporation unit based on direct vaporization to investigate the liquid fuels. The preheating temperature ranges from 298 K to 373 K and the pressure is atmospheric. First measurements of the laminar burning velocity of ethanol/air and iso-octane/air flames were carried out for validating the system. A good agreement with available literature data could be achieved for the investigated equivalence ratios from 0.7 to 1.4. Furthermore laminar burning velocities of different iso-octane/ethanol/air blends, namely E10, E24, E40 and E85, are presented. Through variation of the preheating temperatures (298 K, 323 K, 348 K and 373 K) the temperature dependency could be analyzed. The uncertainty analysis of the measurements has been revealed. Numerical simulations were carried out using different chemical mechanisms for ethanol/air flames, iso-octane/air flames as well as various fuel blends and preheating temperatures and are compared to the experimental data. The agreement is evaluated through a classification of the discrepancy between both.

Abstract In this study, a robust and efficient decentralized fuel processor based on the direct autothermal reforming (ATR) of biogas with a nominal production rate of 50 Nm3/h of hydrogen and a plant efficiency of about 65% was developed and tested. The ATR unit is composed of a structured catalyst support for the biogas reforming close coupled to a catalytic wall-flow filter to retain eventual soot particles. The performance of the conventional random foam and homogeneous lattice supports structures for the production of hydrogen from the ATR reaction was investigated. 15–0.05 wt%-Ni-Rh/MgAl2O4-SiSiC structured catalyst and LiFeO2-SiC monolith were selected for the conversion of biogas to hydrogen and for the syngas post-treatment process, respectively. For all the experiments, a model synthetic biogas was used and the catalytic activities were evaluated in three different experimental facilities: lab bench, pilot test rig and demonstration plant. High methane conversions (>95%) and hydrogen yields (>1.8) reached in the lab bench were also achieved in the pilot and demonstration plant operating at different GHSV. Results of duration test using a foam coupled to the filter has demonstrated that the pre-commercial processor is reliable while offering a satisfactory reproducibility and negligible pressure drop. A thermodynamic equilibrium and a cold gas efficiency of 90% were reached for an inlet temperature of 500 °C, O/C: 1.1 and S/C: 2.0, as predicted with the Aspen simulation.

Abstract In this paper the results of the operation of a pilot-plant with a hydrogen output of 50 Nm³/h are discussed. This plant shows the possibility of distributed production of hydrogen for the powertrains based on hydrogen. The focus of the investigations is the long-term behavior of the novel Nickel-based catalyst. This includes experimental studies of the impact of the start-up sequence on the reforming performance after the necessary activation of the catalyst. Additionally the prospective demand of hydrogen requires an analysis of the start-up time of the plant. The focus was a short start-up time without harming the catalyst.