Laser ignition has been discussed widely as a potentially superior ignition source for technical appliances such as internal combustion engines. Ignition strongly affects overall combustion, and its early stages in particular have strong implications on subsequent pollutant formation, flame quenching, and extinction. Our research here is devoted to the experimental investigation of the early stages of laser-induced ignition of CH₄/air mixtures up to high pressures. Tests were performed in a 0.9–l combustion cell with initial pressures of up to 25 bar with stoichiometric to fuel-lean mixtures using a 5-ns 50-mJ 1064-nm Nd:YAG laser. Laser-induced fluorescence (LIF) was used to obtain two dimensionally resolved images of the OH radical distribution after the ignition event. These images were used to produce an animation of laser ignition and early flame kernel development. Schlieren photography was used to investigate the laser-induced shock wave, hot core gas, and developing flame ball. We extend existing knowledge to high-pressure regimes relevant for internal combustion engines.

A new method and workflow to assess outdoor thermal comfort and thermal stress in urban areas is developed. The new methodology is applied to a case of an urban quarter in the city of Graz. The method recognises the significance of detailed and accurate spatially resolved determination of mean radiant temperatures taking into account all relevant radiative components, comprising thermal radiation, as well as global radiation. The method relies on radiometric imaging data that are mapped onto a three-dimensional model. The image data are acquired by means of drones (UAVs) equipped with multispectral and thermographic cameras to capture short- and long-wave radiation. Pre-existing city models and a Monte Carlo raytracing algorithm to perform anisotropic sampling based on a 3D model with human topology are used to determine local radiation temperatures with high spatial resolution. Along with spot measurements carried out on the ground simultaneously, the spatially resolved and three-dimensionally determined mean radiation temperatures are used to calculate thermal comfort indicator maps using UTCI and PMV calculation. Additional ground measurements are further used to validate the detection, as well as the entire evaluation process.

Laser-induced ignition of methane-air mixtures of varied composition was investigated experimentally using nano-second pulses generated by Q-switched Nd:YAG lasers (wavelength 1064 nm, 532 nm and 355 nm) at initial pressures up to 4 MPa. The minimum focal spot diameter was found to be about 20 μm for effective ignition, independent of the laser wavelength, indicating that small impurity particles provide the seeds for laser plasma generation. The minimum laser pulse energy needed for ignition ranged from 2-15 mJ decreasing reciprocally with initial pressure and with fuel equivalence ratio Φ in a mixing of Φ=0.91 to Φ=0.56. Corresponding threshold intensities ranged from 10¹⁰ to 10¹¹ W/cm². In this way, evidence for a non-resonant breakdown mechanism was established. Optical in-situ diagnosis of water vapor concentration covering the whole timespan of the combustion process in a stationary high pressure vessel with four optical windows was performed involving linear absorption measurements over the entire spectral absorption linewidth by rapidly tuned diode laser radiation at 2.55 μm. Additionally, planar laser-induced fluorescence was measured in a time-resolving fashion yielding 3D determination of the OH concentrations during the process. To the knowledge of the authors, these are the first results on laser-induced ignition under laboratory conditions well above atmospheric pressure being relevant for several technical combustion systems.

A novel method to derive surface temperatures from aerial thermography is proposed. Its theoretical foundation, details regarding the implementation, relevant sensitivities, and its application on a day and night survey are presented here. The method differs from existing approaches particularly in two aspects: first, a three-dimensional sampling approach is used to determine the reflected thermal radiation component. Different surface classes based on hyperspectral classification with specific properties regarding the reflection and emission of thermal radiation are considered in this sampling process. Second, the method relies on a detailed, altitude-dependent, directionally and spectrally resolved modelling of the atmospheric radiation transfer and considers the spectral sensitivity of the sensor used. In order to accurately consider atmospheric influences, the atmosphere is modelled as a function of altitude regarding temperature, pressure and greenhouse gas concentrations. The atmospheric profiles are generated specifically for the time of the survey based on measurements, meteorological forecasts and generic models. The method was initially developed for application in urban contexts, as it is able to capture the pronounced three-dimensional character of such environments. However, due to the detailed consideration of elevation and atmospheric conditions, the method is also valuable for the analysis of rural areas. The included case studies covering two thermographic surveys of city area of Graz during daytime and nighttime demonstrate the capabilities and feasibility of the method. In relation to the detected brightness temperatures apparent to the sensor, the determined surface temperatures vary considerably and generally cover an increased temperature range. The two processed surface temperature maps of the city area of Graz are finally used to validate the method based on available temperature recordings.

Proper design of daylighting and electric lighting is of high relevance during the design of a building, affecting both, energy consumption and people’s well-being and health. To be able to assess the impact of different solutions, planners use simulation tools to evaluate the relevant performance indicators. Two reference simulation models are presented – one group office and one factory hall – that are used to describe and compare various lighting simulation tools, including widely used professional software as well as new research tools. Both models are set up including the required information for integrated daylighting and electric lighting simulation and include full spectral characteristics to also allow evaluating non-visual effects. Background information and a detailed description of the models are provided, and example simulation results are presented. The models provide researchers and professionals a means to test simulation tools and investigate their applicability for specific projects.