Dataset of numerical assessment on the combined effects of non-thermal plasma and water addition in hydrogen combustion.

A comprehensive experimental and kinetic modeling study of flame speed and ignition delay time in n-hexane-based mixtures

This study investigates the effects of ignition timing and excess air ratio on combustion and emission performance under lean-burn conditions using a small-bore intake manifold injection natural gas engine test bench. Results indicate that as the excess air ratio increases, ignition delay period and the combustion center shift backward; combustion duration first shortens, then lengthens; NOx emissions initially rise, then decrease, while THC and CO emissions first decrease, then increase; COVIMEP increases, and effective thermal efficiency first rises, then falls. As ignition timing advances, the ignition delay period shortens and the combustion center advances; the combustion duration first shortens, then lengthens; NOx emissions significantly increase, CO emissions slightly decrease, then increase, and THC emissions vary under different excess air ratios; COVIMEP decreased initially, then increased, while effective thermal efficiency rose initially, then decreased. Compared to stoichiometric combustion, lean-burn technology combined with ignition advance improved engine thermal efficiency, reaching a maximum of 40.47% at an excess air ratio of 1.4.

The development of computationally efficient kinetic mechanisms for alternative fuels remains a critical bottleneck for large-scale CFD simulations in engine design. This work presents a novel integrated data-driven workflow that automates kinetic mechanism development by coupling chemical lumping, skeletal reduction, and parameter optimisation within a unified framework, demonstrated through a compact OME2 combustion mechanism. Using the SciExpeM data ecosystem, the workflow automatically manages mechanism construction, reduction, and optimisation with minimal manual intervention. The approach treats aggressive skeletal reduction as the foundation for two-stage optimisation, where temporary accuracy loss is systematically recovered through targeted parameter adjustment within physically consistent uncertainty bounds. The integrated workflow achieved a decrease in the number of species from 150 to 55 using DRGEP-based reduction, followed by evolutionary parameter optimisation through OptiSMOKE++. Comprehensive validation against experimental data spanning ignition delay times, jet-stirred reactor speciation, and laminar flame speeds demonstrated reliability across operating conditions relevant to compression ignition engines (650–1700 K, 1–50 atm, ϕ = 0.3–2.0). The optimised mechanism successfully recovered the accuracy lost during reduction, particularly in the critical intermediate temperature regime (770–910 K). The integrated workflow further improved the traditional size-accuracy trade-off through systematic parameter recalibration, achieving computational efficiency for CFD applications while maintaining chemical fidelity comparable to detailed mechanisms. This methodology establishes a foundation for rapid development of compact kinetic mechanisms for alternative fuels with automated workflows ensuring physical consistency.

The H-abstraction reactions by small molecule radicals constitute a critical step in the low-temperature chain propagation during 3-pentanone oxidation. This work presents a kinetic investigation of H-, CH3-, NH2-, HO2-, OH-, and NO2-mediated H-abstraction from 3-pentanone, employing CCSD(T)/CBS calculations integrated with RRKM and TST. Sixteen reaction channels are explored to elucidate the reaction mechanisms. All reaction pathways exhibit energy barriers within the range of 1.1-37.2 kcal/mol. The H-, CH3-, NH2-, and OH-mediated H-abstractions are exothermic, whereas those by HO2 and NO2 are endothermic. For H, CH3, NH2, HO2, and NO2 radicals, the barrier heights increase from the 1-site to the 2-site, while the opposite trend is observed for OH. The prevailing reaction site of 3-pentanone migrates from one site to another with increasing temperature. The OH process displays the lowest barriers, leading to the highest rate constants, while the NO2-mediated pathways are kinetically unfavorable. Furthermore, the integration of calculated data into the 3-pentanone oxidation model improves predictive accuracy in matching ignition delay times measured in experiments. The sensitivity analysis identifies dominant consumption pathways and key reactions in 3-pentanone oxidation.

In the pursuit of cleaner and more efficient internal combustion engines, dual-fuel strategies combining diesel and hydrogen are gaining increasing attention. This study employs detailed computational fluid dynamics (CFD) simulations to investigate the behaviour of pilot diesel injections in dual-fuel diesel–hydrogen engines. The study aims to characterize spray formation, ignition delay and early combustion phenomena under various energy input levels. Two combustion models were evaluated to determine their performance under these specific conditions: Tabulated Well Mixed (TWM) and Representative Interactive Flamelet (RIF). After an initial numerical validation using dual-fuel constant-volume vessel experiments, the models are further validated using in-cylinder pressure measurements and high-speed natural combustion luminosity imaging acquired from a large-bore optical engine. Particular attention was given to ignition location due to its influence on subsequent hydrogen ignition. Results show that both combustion models reproduce the experimental behavior reasonably well at high energy input levels (EILs). At low EILs, the RIF model better captures the ignition delay; however, due to its single-flamelet formulation, it predicts an abrupt ignition of all available premixed charge in the computational domain once ignition conditions are reached in the mixture fraction space.

One of the challenges of applying Prognostics and Health Management (PHM) in industrial systems is the lack of labelled training data including anomalies and faults. This study proposes training data generation by a physics-based numerical model and uncertainty quantification (UQ) considering input uncertainty and model form uncertainty, and demonstrates the proposed methodology in a spacecraft propulsion system. A one-dimensional numerical model of the spacecraft propulsion system has been developed in which ignition delay and trapped bubble dynamics are modeled. Sources of uncertainty originating in input variables of the numerical model are identified by domain experts. The probability distributions of them are modeled as uniform distributions, and training data are generated through the propagation of these probability distributions using a Monte Carlo approach. The generated training data were compared with available experimental data and showed good agreement in time-series and frequency-domain response. The 95% confidence interval (C.I.) of total uncertainty, integrating input uncertainty and model form uncertainty, was evaluated through UQ. The generated data enables the use of unsupervised methods for anomaly detection. The C.I. can be used as the normal space for anomaly detection.

Trimethyl phosphite (TMPI) is an organophosphorus compound of growing interest in the contexts of fire safety and energetic materials. Yet, its gas-phase combustion kinetics remain largely underexplored. We develop a TMPI kinetic mechanism from first-principles quantum chemistry and master-equation (RRKM/MESS) calculations, supported by reactive molecular dynamics (ReaxFF-MD) to map early time bond activation and product growth. The potential-energy surfaces include C-O and P-O homolysis, hydrogen-atom abstraction (HAA) by Ḣ, ȮH, HȮ2, ĊH3, and CH3Ȯ, and O2, intramolecular H-transfer, and key association or isomerization steps. Thermochemistry (ΔHf°, S, cp) and NASA polynomials are provided for all P-bearing intermediates. The model reproduces the expected Arrhenius behavior of ignition delay times (IDTs) for TMPI/air across a temperature range of 900-1500 K and pressures of 1 and 10 bar, with φ values ranging from 0.5 to 2.0. Increasing temperature and pressure shorten the IDT, with richer mixtures igniting faster. Sensitivity and flux analyses identify high-temperature chain branching (H + O2 ⇌ O + OH) and control of the HO2/OH pools as primary rate-controlling features, while TMPI-radical reactions that convert radicals to stable products inhibit ignition. Flux maps show HAA-initiated TMPI_R as the universal entry to the radical pool and reveal PO2 as a central hub that feeds PO, HOPO/HOPO2, and ultimately PO3. Hybrid NVT+NVE MD trajectories further indicate an earlier onset of decomposition under adiabatic conditions, consistent with the rapid amplification of radicals once local hot spots are not thermostat-damped. The resulting mechanism and thermochemical set provide a consistent foundation for modeling phosphite oxidation and for comparing phosphite, phosphate, and phosphonate chemistries in fire-inhibition strategies.

<div>This study investigated the combustion processes in hydrogen dual-fuel operation using hydrotreated vegetable oil (HVO) and diesel fuel as pilot fuels. The visualizations of hydrogen dual-fuel combustion processes were conducted using hydroxyl radical (OH*) chemiluminescence imaging in an optically accessible rapid compression and expansion machine (RCEM), which can simulate a compression and expansion stroke of a diesel engine. Pilot injection pressures of 40 and 80 MPa and injection quantities of 3, 6 mm<sup>3</sup> for diesel fuel and to match the injected energy, 3.14, 6.27 mm<sup>3</sup> of HVO were tested. The total excess air ratio was kept constant at 3.0. The RCEM was operated at a constant speed of 900 rpm, with in-cylinder pressure at top dead center (TDC) set to approximately 5.0 MPa. Results demonstrated that using HVO as pilot fuel, compared to diesel fuel, led to shorter ignition delay and combustion duration. OH* chemiluminescence imaging revealed that longer ignition delays observed with diesel fuel resulted in pilot mixture ignition downstream near the piston bowl wall, followed by flame propagation into the hydrogen–air mixture. In contrast, the shorter ignition delays characteristic of HVO caused the pilot mixture to ignite between the injector and the piston bowl wall, with subsequent flame propagation into the hydrogen premixture.</div>

Hypergolic aluminized fuels with rocket-grade hydrogen peroxide: A comprehensive study of the ignition delay, energetics, thermo-physical properties, mechanical properties and storability

This study differs fundamentally from prior investigations on WPO-diesel and WPO-DEE blends by combining combustion-resolved experimentation with predictive modeling, thereby advancing WPO utilization from empirical testing toward optimization-oriented engine integration. It examines the performance, combustion, and emission characteristics of a single-cylinder variable compression ratio (VCR) diesel engine fueled with ternary blends of diesel, waste plastic oil (WPO), and diethyl ether (DEE). WPO was produced via catalytic pyrolysis of LDPE waste and blended with diesel at 15%, 20%, 25%, and 30% by volume, while DEE was maintained at a constant 10% to improve ignition quality, volatility, and atomization. Engine tests were performed at a constant speed of 1500 rpm under variable loads ranging from 2 to 12 kg to evaluate the influence of blend composition and operating conditions on brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), combustion development, and regulated emissions (CO, HC, NOx, CO₂). The D65B25DE10 blend (65% diesel, 25% WPO, 10% DEE) demonstrated the best overall performance among the tested fuels, achieving a 22.22% reduction in CO and an 11.88% reduction in HC emissions compared with diesel, although BTE decreased by 6.93% and BSFC increased by 6.03% at full load. Combustion analysis revealed extended ignition delay and higher peak cylinder pressure for higher-WPO blends, while DEE improved vaporization and supported more complete oxidation. To complement the experimental work, a feed-forward artificial neural network (ANN) model with a 6-12-6 architecture was developed using blend ratio, load, compression ratio, and speed as inputs to predict BTE, BSFC, and emissions. The ANN achieved strong correlation with experimental data (R2 > 0.97), confirming its suitability for performance prediction and blend optimization. The combined experimental and computational approach offers a comprehensive framework for evaluating WPO-based fuels, extending beyond previous binary blend studies by revealing the synergistic effects of DEE in ternary blends and establishing a robust ANN model for predictive optimization. This methodology demonstrates the potential of WPO-based fuels to reduce fossil diesel dependence while promoting sustainable waste-to-energy utilization.

Increasing the initial velocity of large‐caliber, high‐mass projectiles remains a persistent challenge in military weapon design. To address this, we developed a novel main–auxiliary chamber configuration based on the balanced gun concept. An internal ballistic model incorporating this dual‐chamber structure was established to evaluate its ballistic performance. By comparing the internal ballistic characteristics of the proposed design with those of a conventional balanced gun, we analyzed its acceleration capabilities. Additionally, we examined the effects of ignition delay time, auxiliary chamber charge mass, and shell mass on the internal ballistic behavior of the new structure. The results demonstrate that the dual‐chamber balanced gun can significantly enhance the projectile′s initial velocity without exceeding the maximum allowable chamber pressure. Specifically, within a suitable range of ignition delay times, reducing the delay leads to increases in both the projectile′s initial velocity and the peak pressure in the auxiliary chamber. Furthermore, as long as the maximum pressure in the auxiliary chamber remains within safe limits, increasing the propellant charge improves projectile acceleration. Lastly, provided the structural integrity of the shell is maintained, reducing the shell mass of the auxiliary chamber further enhances the initial velocity. These findings offer valuable insights for both the theoretical study and engineering design of large‐caliber balanced guns aimed at achieving higher muzzle velocities.

Experimental and kinetic modeling study on laminar burning velocities and ignition delay times of NH3/PODE3 blends

A numerical toolkit for the ignition delay time and ignition probability density predictions based on instantaneous mixing fields in OpenFOAM

Enhancing the operability of next-generation combustion devices with emerging fuels at near-limit conditions requires the development of innovative ignition strategies. To address this need, a new modular plasma-coupled rapid compression machine (PRCM) featuring a mono-piston, single-stroke configuration was developed to support auto-ignition, conventional spark-ignition, and non-equilibrium plasma-assisted ignition studies within a single experimental platform. The PRCM attains end-of-compression pressures up to 70bar and temperatures up to 1200K, enabling systematic investigation of ignition phenomenon and the effects of non-equilibrium plasmas on fuel reactivity at regimes inaccessible to previous platforms. A high-voltage pulse generator delivers up to 20kV pulses at repetition rates up to 100kHz, producing kilohertz repetitive nanosecond pulsed (KRNP) discharges at elevated pressures in the combustion chamber. Integrated diagnostics include high-speed pressure transducers and optical access to enable time-resolved measurements of ignition delay, burn rate, and kernel and plasma morphology to probe for plasma-combustion coupling. Initial benchmarking with methane and n-butane mixtures demonstrated good agreement with auto-ignition data from the literature, validating the PRCM's functionality and measurement fidelity. Preliminary KRNP studies at 10bar revealed a nearly 20% increase in burn rate compared to conventional spark ignition for n-butane, highlighting the efficacy of pulsed plasma in enhancing fuel reactivity and ignition kernels. This novel experimental facility offers a versatile, high-fidelity platform for investigating the fundamental processes by which non-equilibrium plasmas initiate, control, and accelerate combustion. These insights are expected to guide the design of optimized plasma-based ignition strategies for advanced air-breathing propulsion and power systems.

ABSTRACT In the aircraft engine, auxiliary power unit and other areas, hot surfaces are generated due to fuel combustion, power transmission and other reasons. Meanwhile, these areas may have the potential for oil leakage. When the leaked oil contacts these hot surfaces, it may be ignited to form a fire, threatening the aircraft’s safety. In this paper, evaporation and ignition experiments of oil leakage on a flat hot surface were carried out, and the vapor plume movement and flame propagation characteristics were investigated. Furthermore, the relationship between the hot surface temperature and the ignition core height and ignition delay time was studied. By the PIV technique, the velocity distribution of the vapor plume was studied. The flame transient development process and the flame propagation speed were quantitatively analyzed. The results show that the vapor plume velocity increased rapidly with height, then remained relatively stable, and eventually decreased gradually. Overall, the plume velocity shows a “cap-shaped” horizontal distribution. After ignition, the flame first expands in a spherical shape and then propagates in the vertical direction. The vertical upward propagated flame velocity is greater than the downward, and the corresponding velocities are 100.6 ~ 496.42 cm/s and 66.71 ~ 192.51 cm/s, respectively.

Biomass-derived nanoparticles offer a safer alternative to metallic oxides, yet their use in diesel–biodiesel blends remains limited. This study explores the catalytic effect of corn stover–derived nanobiochar (NBC) on the performance, combustion, and emissions of Croton macrostachyus (CMS) biodiesel, compared with Al₂O₃ and TiO₂ nanoparticles, at 2700 RPM and 0–80% load. The novelty lies in revealing NBC’s influence on CP, apparent HRR, and ID period in CMS biodiesel blends. Experiments were conducted using six fuel blends: B20 (20% CMS biodiesel + 80% diesel), B20NBC30, B20NBC50, B20NBC75 (with 30, 50, and 75 ppm NBC, respectively), B20A50 (with 50 ppm Al₂O₃), and B20T50 (with 50 ppm TiO₂). The result shows that the NBC additive reduced the NOx, CO, and HC emissions by up to 9.8%, 8.4%, and 27.3% respectively, and BSFC by 2.2% and increased BTE by 2.6% compared to the B20. Conversely, TiO₂ and Al₂O₃ were more effective in reducing HC emissions, achieving reductions of 45.9% and 29.5% respectively, while reducing BSFC and increasing BTE compared to NBC additive. In addition, B20NBC50 exhibited an average reduction in cylinder pressure (CP) of 0.5%, heat release rate (HRR) of 517.51 J/oCA with a 2.7% increment and the shortest ignition delay (ID) and advanced start of combustion (SoC) compared to the B20, B20NBC30, and B20NBC75, that makes NBC at 50 ppm as the optimum concentration. NBC reduced NOx due to its higher specific heat capacity, while Al₂O₃ and TiO₂ increased it, demonstrating NBC’s advantage and potential as a sustainable, biomass-derived alternative to metallic nanoparticles.

An X-type rotary engine (XRE) that utilizes a High Efficiency Hybrid Cycle, combining high compression ratio with constant-volume combustion, could be considered an attractive option for both improved combustion efficiency and decreased emissions. However, research on optimizing its combustion in XREs is still limited. The optimization of ignition strategy can be beneficial for enhancing combustion performance and especially for reducing the unburned region due to the particular recess chamber. In this study, a three-dimensional CFD model of the XRE was developed and verified. A numerical study was conducted to analyze how ignition number, ignition location, and asynchronous ignition on combustion characteristics and energy losses of the XRE. Results showed that the twin-spark scenarios had a significantly higher flame propagation speed than the single-spark scenario due to the formation of larger flame fronts. The twin-spark plugs arranged along the rotor rotating direction (Case A1) had maximum peak pressure and indicated thermal efficiency, which increased by 19.6% and 9.8%, respectively, over the single-spark scenario. However, Case A1 produced higher NOx emissions and had the highest heat transfer losses, which boosted by 14% over the single-spark scenario. For this twin-spark arrangement, advancing the ignition of the leading-spark plug (L-plug) significantly reduced ignition delay and combustion duration, as well as boosted the pressure rise rate, peak pressure, and combustion efficiency at the price of a smaller increment of NOx and CO emissions. Notably, advancing the L-plug timing drastically decreased exhaust losses, but had only a minor impact on heat transfer losses. Thereby, it is recommended to set the L-plug timing in advance for practical engineering applications.

This study investigates the macroscopic kinetics of hydrogen and ammonia oxidation under high-pressure conditions to compare their ignition characteristics, activation energies, and sensitivity to mixture composition. Experiments were conducted in constant-volume and flow reactors over a pressure range of 3–10. MPa and a temperature range of 550–850 K. Hydrogen exhibited significantly shorter ignition delays, reaching as low as 0.14 seconds at 800 K and 10 MPa, compared with 0.35 seconds for ammonia under the same conditions. The activation energy for hydrogen oxidation averaged 171,000 J/mol, whereas that for ammonia was approximately 209,000 J/mol, indicating a higher ignition threshold. The peak pressure during ignition for hydrogen mixtures exceeded 11.5 MPa, whereas that for ammonia mixtures peaked at 8.9 MPa. Hydrogen also exhibited higher concentrations of reactive radicals (H and OH), which explains its more intense chain reaction. Empirical global reaction equations were developed for both fuels, with deviations of up to 10% relative to experimental values. These findings provide a reliable basis for the kinetic modeling of combustion systems operating at high pressures with hydrogen, ammonia, or their mixtures.

ABSTRACT This study investigates the effect of aluminum (Al) and ammonium perchlorate (AP) particle sizes on the combustion characteristics of nitrate ester plasticized polyether (NEPE) solid propellants. Thermogravimetry-differential scanning calorimetry (TG-DSC), a laser ignition test system, high-speed camera, and spectroscopy were used to investigate the thermal decomposition, ignition delay times, and burning rates with different particle sizes. The results show that while the particle sizes of Al and AP have a minimal impact on the thermal mass loss process, they significantly influence the heat absorption and insulation processes. At 0.1 MPa, the ignition delay time of NEPE propellant with 3 μm Al particles is reduced by approximately 23.4% compared to that with 30 μm Al particles. As the AP particle size increases from 200–300 μm to 300–400 μm and further to 400–500 μm, the combustion flame intensity gradually increases. However, the increase in combustion spectral intensity is relatively minor when the AP particle size increases from 200–300 μm to 400–500 μm, and when the Al particle size increases from 3 μm to 30 μm. These findings enhance the understanding of the combustion mechanism of NEPE propellants.