Cooper Welch

Ammonia–hydrogen mixtures are promising carbon-free fuels for internal combustion engines, but their unconventional combustion behavior complicates stable operation and emission control, particularly for NO, N ₂ O, and unburned NH ₃ . To characterize these emissions and their underlying formation pathways, diagnostics with high temporal resolution and strong species selectivity are required. This study employs high-speed, in-situ tunable diode laser absorption spectroscopy (TDLAS) to measure H ₂ O, NH ₃ , NO, and N ₂ O at 1 kHz directly downstream of the exhaust valves of a single-cylinder spark-ignition engine. The technique resolves the temporal emission characteristic of individual cycles and provides insight into how cycle-to-cycle combustion behavior influences pollutant formation. Analysis across the tested operating points shows that increasing hydrogen content improves combustion stability and reduces NH ₃ slip but elevates NO formation. NO correlates positively with mean in-cylinder pressure, whereas N ₂ O exhibits an inverse trend, reflecting their distinct temperature-dependent production and decomposition pathways. During warm-up, the measurements capture a sudden advance in combustion phasing under otherwise constant boundary conditions. Zero-dimensional reactor simulations suggest a plausible explanation, indicating that temperature- and pressure-dependent NH ₃ cracking can increase in-situ H ₂ concentrations and thereby accelerate combustion. By combining cycle-resolved measurements with thermochemical simulations, this work clarifies how transient combustion dynamics, mixture reactivity, and boundary-temperature effects shape the formation of NO, N ₂ O, and NH ₃ in ammonia–hydrogen engines. The results support the development of stable and low-emission operating strategies and suggest that, under sufficiently high temperature, pressure and residence times, the cracking of NH ₃ within the cylinder can provide enough H ₂ to enable stable pure-ammonia combustion.

Cycle-to-cycle variations (CCV) pose significant challenges to the performance and reliability of internal combustion engines (ICE). This study investigates the applicability of information entropy as a diagnostic tool to quantify and characterize CCV in ICE subject to exhaust gas recirculation (EGR). Particle image velocimetry (PIV) and flame imaging were used to measure the flow field and flame behavior. The concept of information entropy is related to flow and flame evolution by calculating the Shannon entropy of the turbulent kinetic energy and flow velocity components to assess their sensitivity to CCV. Shannon entropy was applied to the flow velocity components and the turbulent kinetic energy on the tumble plane, where the horizontal component was identified to correlate with high-speed (HC) and low-speed (LC) combustion cycles both, with and without EGR. The turbulent kinetic energy was found to be major driver of HC cycles without EGR, however, it plays a subordinate role with EGR. The conditional Shannon entropy was then applied to assess local fluctuation of the turbulent kinetic energy during ignition from cycle-to-cycle under the influence of the direction of the horizontal velocity component and the presence or absence of the flame, revealing the areas where turbulent kinetic energy fluctuates strongly between different cycles. The results have potential for both computational and experimental studies of ICE, since the use of information entropy as a diagnostic tool allows for early prediction of HC and LC cycles.

Background: Atomization plays a key role in spray drying, a process widely used in the pharmaceutical, chemical, biological, and food and beverage industries. In the pharmaceutical industry, spray drying is particularly important in the preparation of amorphous solid dispersions, which enhance the bioavailability of active pharmaceutical ingredients when mixed with a polymer. Methods: In this study, a 3D-printed adaptation of a commercial spray dryer nozzle (PHARMA-SD^® PSD-1, GEA Group AG) was used to investigate the atomization of PVP-VA 64 polymer solutions under varying flow conditions using high-speed diffuse back-illumination. Results: Unlike pure water, the atomization process of the polymer solution was governed by viscous effects rather than surface tension, as indicated by stringing effects in the liquid core and the formation of larger droplets. In addition, the classical Ohnesorge diagram accurately predicted the atomization regime with increasing Reynolds numbers and could be modified to reasonably predict the breakup regime by considering the transitions between regime boundaries. Conclusions: The use of such a modified diagram facilitates the efficient selection of viscous fluid solutions and process parameters to achieve complete spray formation.

The work presented in this study aims to understand the spray-wall-flow interaction within a gasoline direct-injection (GDI) engine flow bench under simulated early-injection conditions. The Engine Combustion Network (ECN) Spray G injector is installed in the Darmstadt optically accessible engine flow bench. Under simulated early-injection conditions, the formation of a multi-hole spray and the interaction with characteristic intake flows, such as the intake jet and central tumble flow, are extensively discussed. By reducing the complexity in the number of variables inherent in engine flow and whole-engine simulation, an engine flow bench operating under various mass flow rates is applied in this study. The numerical simulation is carried out using Large Eddy Simulation (LES) under the Eulerian-Lagrangian framework for spray simulation. Experimental data, acquired through particle image velocimetry (PIV) measurements, provides 2-D flow fields on both the central tumble and valve planes, facilitating the validation of in-cylinder flow fields. Furthermore, experimental data obtained through Mie scattering is utilized to investigate spray formation and evolution within the GDI engine, providing the liquid penetration length and liquid spray angle. Comparison between the numerical and experimental data demonstrates several agreements. Moreover, the variation of different spray plumes under different mass flow rates is observed in the case of both experimental and numerical data. Increasing the mass flow rate distorts the overall plume shape and shifts it away from the intake port. This phenomenon is examined by extracting the liquid volume fraction and vapor fields of each plume. Spray plumes encounter different convective disturbances and evaporation due to their local characteristic in-cylinder flow. Furthermore, spray-wall-flow interaction and wall film deposits are observed during the injection. Lastly, the influence of the spray-induced turbulence is analyzed under different mass flow rates.

Control of the combustion process in Spark-Ignition (SI) engines operated with extreme dilution from exhaust gas re-circulation (EGR) represents one of the major limitations in the industrial design of such technology. Numerical approaches able to describe in detail the formation of the early flame kernel become essential to face such an ambitious task. This work presents a RANS-based multi-dimensional model of the combustion process, including an advanced description of the ignition stage to consider its stochastic re-ignitions within the average cycle prediction. The spark-channel is described as a column of Lagrangian parcels that represent early flame kernels, whose growth is controlled by the laminar flame speed and energy input from the electrical circuit. The spatial evolution of each parcel is computed according to a scaled value of the average-flow speed, to mimic the smooth but short elongation of the mean-cycle channel produced by stochastic restrikes affecting the single-cycle arcs. To clarify this phenomenon and assess the proposed CFD method, a series of experiments are performed in a single cylinder SI engine with optical access, running at a low-load cruise-speed operating condition. Increasing EGR levels are tested up to the onset of misfire, with measurements of the secondary-circuit features and of the flame evolution through high-speed imaging. Satisfactory results are achieved in terms of numerical-experimental comparison of the cycle-averaged in-cylinder pressure, discharge parameters, and spatial flame distribution, demonstrating the reliability of the proposed numerical approach.

An optically accessible single-cylinder spark-ignition engine operated under homogeneous, part-load conditions is experimentally investigated using optical and spark diagnostics to evaluate the relationship between the spark, flow, and flame with increasing dilution using several levels of exhaust gas recirculation (EGR). Voltage and current measurements of the secondary spark circuit are compared with simultaneous high-speed spark plasma imaging, particle image velocimetry measurements of the flow field, and burned gas images. Specifically, characteristic restrike cycles and normal cycles are examined under the 0 % EGR and 12.9 % EGR conditions to reveal a relationship between the magnitude and direction of the velocity near the spark plug and the spark’s behavior coupled with that of the subsequent flame propagation. Through the use of conditional statistics and correlation analysis of data sets of all non-restrike and all restrike cycles, the horizontal velocity across the spark gap was identified as a critical quantity in facilitating more stable and faster combustion under diluted mixture conditions.