The transition to renewable energy is essential in addressing climate change. While natural gas plays a significant role in this transition, it still produces CO2 emissions. Ammonia (NH3) is being investigated as a promising alternative fuel. However, ammonia combustion presents several technical challenges, such as low flame velocity, limited calorific value, difficulties with flame stabilization, and high NOx emissions. This study examines the impact of ammonia addition to methane, equivalence ratio, and swirl number on pollutant emissions (NO, CO, CH4, and CO2), exhaust gas temperature, and flame stability. Experiments are carried out using a swirl burner with a radial fuel injection in a 1-meter high combustion chamber. The burner consists of two concentric tubes, with the inner tube supplying fuel and the outer tube supplying air. The fuel is injected radially through eight holes at the burner exit. The ammonia fraction ranges from 0 to 100 %, the equivalence ratio from 0.8 to 1.0, and the swirl number from 0.8 to 1.4, with a constant flame power of 10 kW. Emissions of NO, CO, CH4, and CO2 are measured in the dry exhaust gases using a multi-gas analyzer, inside chamber temperatures are measured and the flame structure is analyzed via OH* and NH2* chemiluminescence and velocity measurements by LDA technique. The results show that both the swirl number and equivalence ratio significantly alter flame geometry, affecting combustion zones and flame height. Axial velocity measurements indicate that the recirculation zone shrinks with ammonia addition, while a high swirl number increases axial velocity, promoting ammonia combustion and upstream flame propagation. Up to 30 % ammonia, the flame remains stable, but higher ammonia levels lead to fluctuations in stabilization. High ammonia content in the fuel mixture results in reductions of NO, CO, and CO2 emissions, though there is a potential increase in unburned gases. As expected, the inside chamber temperatures decrease as the ammonia fraction increases.
The kinetics and products of the reaction of OH radicals with ethylene were studied using a low-pressure discharge-flow reactor combined with modulated molecular beam mass spectrometry. The total rate constant of the reaction (k(1)) was determined as a function of pressure (0.4-20 Torr of helium) and temperature (240-1000 K). The title reaction was found to proceed through two channels: adduct forming and H atom abstraction. For the addition channel, the high- and low-pressure limit rate coefficient were extracted from a global fit of the fall off curves observed at different temperatures (present low pressure and available in the literature high-pressure data for the reaction rate constant) with the two-parameter expression k = k(0) k(infinity)[M] / k(0) [M] + k(infinity) x 0.6 ( 1 + ( log ( k(0)[M]/k(infinity)))(2))(-1) : k(0) = 4.6 x 10(-29) (T/298)(-3.9) cm(6) molecule(-2) s(-1), k(infinity) = 8.0 x 10(-12) (T/298)(-1.0) cm(3) molecule(-1) s(-1) in the temperature range 240-470 K. Moreover, this parametrization was found to reasonably reproduce existing measurements of k(1) with N-2 bath gas down to 69 K. The hydrogen atom abstraction channel was found to be the only important reaction pathway at T > 700 K. The rate constant of this reaction channel was determined in the temperature range 375-1000 K, as being equal to the overall rate constant at T > 700 K, and through the measurements of the yield of the reaction product, C2H3 radical, at T = 375-690 K: k(1b) = (1.43 +/- 0.10) x 10(-14) (T/298)(3.96 +/- 0.09) cm(3) molecule(-1) s(-1). This expression was found to describe well earlier shock tube measurements at high temperatures (up to 1930 K) and can be recommended for use in the temperature range 375-1930 K. The rate constants measured in this study for both addition and abstraction channels are in good agreement with available theoretical calculations.
In a diffusive combustion regime, an aluminum droplet undergoing combustion forms an oxide cloud that surrounds the burning droplet. Thorough characterization of this cloud is crucial to the validation of the subsequent modeling. This paper makes a significant contribution to the field by providing an experimental procedure to resolve the spatial temperature profile within the oxide cloud. An electrodynamic levitator is used to observe the self-sustained combustion of aluminum particles with a radius of 35 mu m in atmospheric air, with negligible convective effects. The levitating device is coupled to an optical apparatus that allows for a light extinction method, thereby enabling the determination of size and concentration profiles of the nanometric alumina droplets, as introduced in previous works. The data from the previous study are employed in conjunction with a modulated absorption-emission (MAE) technique to ascertain a temperature profile that does not rely on the grey-body assumption. This technique is further enhanced by an optimization method to account for gaseous phase emissions, which typically hinder conventional temperature evaluation. Consequently, a spatially resolved temperature profile of the oxide cloud surrounding the burning droplet is obtained. Close to the surface of the droplet, a temperature of 2580 K is assessed. Then, a maximum temperature of about 3615 K is measured. As an additional outcome, gaseous emission profiles are obtained for three wavelengths and exhibit a notable correlation with a simulated gaseous suboxide concentration profile. The results presented in this work demonstrate a relatively high degree of consistency with expected temperatures. Novelty and Significance Statement This work presents a novel experimental method to obtain an unique temperature profile surrounding an isolated aluminum droplet in combustion. In conjunction with previous work, a non-intrusive, complete, and instantaneous characterization of the oxide smoke is now made possible, with the addition of the temperature profile to the known alumina particle size and concentration profiles. This comprehensive data set is presented for a fundamental case of a single levitating particle. The incorporation of the temperature profile provides an incomparable insight into alumina condensation processes and a detailed reference case for simulation purposes. The results presented in this work document the intricate condensation process of nanoparticles and highlight the limitations of current simulation methods.
Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a fire suppressant candidate for the use of lithium-ion batteries (LIBs). It is known that the electrolyte components in LIBs are highly flammable, making them susceptible to igniting, whether this is due to a manufacturing fault or an abuse of the LIB itself. To address this risk, the efficiency of BtFEC as a fire suppressant was investigated experimentally in a high-temperature combustion environment, allowing for further refinement and validation of the model. Using a shock tube, BtFEC combustion properties were measured experimentally behind a reflected shock wave, capturing OH* chemiluminescence to assess ignition delay times (IDT) as well as CO time-history profiles through the implementation of laser absorption spectroscopy. Both pyrolysis and oxidation conditions were captured with three equivalence ratios (phi = 0.5, 1.0, and 1.5) for a temperature range of similar to 1200-1650 K at near-atmospheric pressures. In addition, key species measurements were taken using a microflow reactor (MFR) with a controlled temperature profile associated with Fourier transform infrared spectroscopy (FTIR). Key species investigated were BtFEC, CO, CO2, CHF3, CF2O, C2F6, and HF for the temperatures range of 800-1300 K. MFR measurements allowed for a new set of measurements by which to validate the model compared to the previous study [Mathieu et al. Proc. Combust. Inst. 2023, 39, 499] where the first assembly of the model used CO time-history, IDT, and laminar flame speed measurements. Refinement of the model was carried out with new high-level calculations as well as sensitivity, rate-of-production, and reaction pathway analyses using recent reaction rate updates from the literature. The modifications led to improvements in the level of agreement between the kinetic modeling and the new experimental data.
