arXiv subjects

J. A. van Oijen

Publications and source records attributed to J. A. van Oijen.

4 recordsLinked to original sources

arXiv2025

Validation of a Reynolds-averaged numerical simulation environment to simulate high-pressure, auto-igniting hydrogen diffusion flames

The hydrogen (H2) fueled direct-injection (DI) compression-ignition (CI) argon power cycle (APC) is an attractive technology to counteract the mismatch between energy demand and supply from renewable energy sources. The development of the APC, as well as air-breathing DI CI H2 engines, can be advanced by computational fluid dynamics (CFD) models. Reynolds-averaged Navier-Stokes (RANS) combustion models are an effective approach to predict global in-cylinder variables such pressure and heat release rate. However, validity of this method to simulate the complex phenomena associated with high-pressure, auto-igniting hydrogen jets is not ensured due to the underlying model assumptions. In this study, a RANS CFD environment using two commonly used eddy-viscosity models and the Reynolds stress model (RSM) is extensively validated. Combustion is modeled with a detailed chemistry model. First, hydrogen distributions in non-reacting jets are compared against literature data to assess the accuracy of the models on turbulent mixing at high pressure. Subsequently, the capability of the model to simulate auto-igniting jets is assessed by comparison with reported measurement data of closed-vessel experiments at high pressure. Ignition delay times, pressure rise profiles, and heat release rate profiles are compared for different ambient temperature and oxygen concentration. Adequate agreement is found for the diffusive combustion phase for all models, despite the lack of turbulence-chemistry interaction in the combustion model. Trends with ambient temperature and oxygen concentration were well predicted and the best agreement is found for the RSM.

physics.flu-dyn↗

arXiv2025

A zero-dimensional global conservation model to determine non-ideal nozzle conditions for gas injections

To reduce computation times of simulations involving gas fueled internal combustion engines (ICEs), a model is developed that determines non-ideal nozzle exit conditions to spare expensive simulations of internal injector flows. The model, to which we will refer as the Global Conservation Model (GCM), computes nozzle exit values based on reservoir conditions, and a discharge and momentum coefficient. These coefficients can be obtained via common flow bench experiments or a validated numerical simulation setup. Furthermore, it allows to use real gas thermodynamics which is often needed for ICE applications. The model is validated for three commonly used injector types, injection pressures up to 300 bar, subsonic and choked injections, and at flow bench and engine conditions using numerical simulations. If real gas thermodynamics is applied, differences with the simulated nozzle conditions are typically within 1.5% uncertainty, which is within the typical range of experimental momentum flow measurements found in literature. Differences in mass and momentum flow obtained by the numerical simulations between flow bench and engine conditions are negligible, indicating that flow bench measurements can be applied to engine conditions. Once an injector is characterized for mass and momentum flow, applying the GCM can reduce computation times by more than a factor 8, while accurately simulating the spatial and temporal jet development. With the reduction in computation time, the GCM reduces costs associated with numerical simulations and accelerates research and design of efficient and low-emission gas fueled ICEs.

physics.flu-dyn↗

arXiv2023

Numerical determination of iron dust laminar flame speeds with the counterflow twin-flame technique

Iron dust counter-flow flames have been studied with the low-Mach-number combustion approximation. The model considers full coupling between the two phases, including particle/droplet drag. The dispersed phase flow strain relations are derived under the assumption of low Reynolds number conditions. The importance of solving a particle flow strain model is demonstrated by comparing three different models: a free unstrained flame, a counter-flow flame where particle flow strain is assumed equal to gas flow strain and one case in which the particle flow strain is solved. All three cases showed preferential diffusion effects, due to the lack of diffusion of iron in the fuel mixture, e.g. DFe,m = 0. The preferential diffusion effect causes a peak in the fuel equivalence ratio in the preheat zone. At the burned side, the combined effect of strain and preferential diffusion showed a decrease in fuel equivalence ratio. Inertia effects, which are only included in the resolved particle flow strain case, counteract this effect and result in an increase of the fuel equivalence ratio at the burned side. A laminar flame speed analysis is performed and a recommendation is given on how to experimentally determine the flame speed in a counter-flow set-up.

physics.flu-dyn↗

arXiv2023

On the surface chemisorption of oxidizing fine iron particles: insights gained from molecular dynamics simulations

Molecular dynamics (MD) simulations are performed to investigate the thermal and mass accommodation coefficients (TAC and MAC, respectively) for the combination of iron(-oxide) and air. The obtained values of TAC and MAC are then used in a point-particle Knudsen model to investigate the effect of chemisorption and the Knudsen transition regime on the combustion behavior of (fine) iron particles. The thermal accommodation for the interactions of $\mathrm{Fe}$ with $\mathrm{N_2}$ and $\mathrm{Fe_xO_y}$ with $\mathrm{O_2}$ is investigated for different surface temperatures, while the mass accommodation coefficient for iron(-oxide) with oxygen is investigated for different initial oxidation stages $Z_\mathrm{O}$, which represents the molar ratio of $\mathrm{O}/\left(\mathrm{O} + \mathrm{Fe}\right)$, and different surface temperatures. The MAC decreases fast from unity to 0.03 as $Z_\mathrm{O}$ increases from 0 to 0.5 and then diminishes as $Z_\mathrm{O}$ further increases to 0.57. By incorporating the MD-informed accommodation coefficients into the single iron particle combustion model,a new temperature evolution for single iron particles is observed compared to results obtained with previously developed continuum models. Specifically, results of the present simulations show that the oxidation process continues after the particle reaching the peak temperature, while previous models predicting that the maximum temperature was attained when the particle is oxidized to $Z_\mathrm{O} = 0.5$. Since the rate of oxidation slows down as the MAC decreases with an increasing oxidation stage, the rate of heat loss exceeds the rate of heat release upon reaching the maximum temperature, while the particle is not yet oxidized to $Z_\mathrm{O} = 0.5$. Finally, the effect of transition-regime heat and mass transfer on the combustion behavior of fine iron particles is investigated and discussed.

physics.flu-dyn↗