Greenhouse crops represent a significant productive sector of the agricultural system; one of the main problems to be addressed is indoor air conditioning to ensure thermal well-being of crops. This study focuses on the ventilation analysis of solar greenhouse with symmetrical flat pitched roof and single span located in a warm temperate climate. This work proposes the dynamic analysis of the greenhouse modeled in TRNsys, simultaneously considering different thermal phenomena three-dimensional (3D) shortwave and longwave radiative exchange, airflow exchanges, presence of lamps with their exact 3D position, ground and plant evapotranspiration, and convective heat transfer coefficients. Several air conditioning systems were analyzed, automatic window opening, controlled mechanical ventilation systems (CMV) and horizontal Earth-to-Air Heat Exchanger (EAHX) coupled with CMV, for different air volume changes per hour. In summer, the exploitation of the ground allows having excellent results with the EAHX system, reducing the temperature peaks of up to 5 °C compared to the use of CMV. In winter, it is interesting to note that, although the EAHX is not the solution that raises the temperature the most during the day, its use allows flattening the thermal wave more. In fact, the trend is almost constant during the day, raising the temperature during the first and last hours of the day.

Re-ignition of aeroengines under high altitude conditions is of great importance to the safety and use of lean-burn flame. This study is focused on the experimental and numerical characterization of flow dynamics and flame re-ignition in a rectangular burner. A ring-needle type plasma actuator was considered and run by high-voltage (HV) nanopulsed plasma generator. The electrical power delivered to the fluid and an optimal value of reduced electric field (E_N) was calculated considering non-reactive flow. Smoke flow visualizations using a high-speed camera and proper orthogonal decomposition (POD) were performed to recognize the most dominant flow structures. Experimental results revealed the transport effects due to plasma discharge, such as the induced flow, that could have a strong impact on the recirculation zone near the corners of combustor, improving the mixing performance and reducing the ignition delay time. Two different numerical tools (ZDPlasKin and Chemkin) were used to investigate the ignition characteristics. ZDPlasKin calculated the thermal effect and the plasma kinetic of nanopulsed plasma discharge at the experimentally measured E_N. Finally, based on the output of ZDPlasKin, Chemkin estimated the flame ignition at low pressure and low temperature conditions. It was noticed that time required to achieve the maximum flame temperature with plasma actuation is significantly less than the auto-ignition time (‘clean case’, simulation result of the model without considering the plasma effect). Maximum reduction in ignition time was observed at inlet pressure 1 bar (3.5 × 10⁻⁵ s) with respect to the clean case (1.1 × 10⁻³ s). However, as the inlet pressure is reduced, the ignition delay time was increased. At 0.6 bar flame ignition occurred in clean case at 0.0048 s and at 0.0022 s in presence of the plasma actuation, a further decrease of the pressure up to 0.4 bar leads the ignition at 0.0027 s and 0.0063 s in clean and plasma actuation, respectively.

This study investigates the kinetic modeling of CH₄/H₂/Air mixture with nanosecond pulse discharge (NSPD) by varying H₂/CH₄ ratios from 0 to 20% at ambient pressure and temperature. A validated version of the plasma and chemical kinetic mechanisms was used. Two numerical tools, ZDPlasKin and CHEMKIN, were combined to analyze the thermal and kinetic effects of NSPD on flame speed enhancement. The addition of H₂ and plasma excitation increased flame speed. The highest improvement (35%) was seen with 20% H₂ and 1.2 mJ plasma energy input at ϕ = 1. Without plasma discharge, a 20% H₂ blend only improved flame speed by 14% compared to 100% CH4. The study found that lean conditions at low flame temperature resulted in significant improvement in flame speed. With 20% H₂ and NSPD, flame speed reached 37 cm/s at flame temperature of 2040 K at ϕ = 0.8. Similar results were observed with 0% and 5% H₂ and a flame temperature of 2200 K at ϕ = 1. Lowering the flame temperature reduced NO_x emissions. Combining 20% H₂ and NSPD also increased the flammability limit to ϕ = 0.35 at a flame temperature of 1350 K, allowing for self-sustained combustion even at low temperatures.

These days, various national and international research organizations are working on the development of low NO_x combustors. The present work describes the experimental and numerical characterization of flow dynamics and combustion characteristics in a rectangular burner. A ring-needle type plasma actuator was developed and driven by a high voltage nanosecond pulsed generator under atmospheric conditions. Smoke flow visualizations and Proper Orthogonal Decomposition (POD) were carried out to identify the relevant flow structures. Electrical characterization of the non-reactive flow was carried out to predict the electrical power and the optimum value of the reduced electric field (E_N), which is useful for the implementation of a numerical model for the study of plasma-assisted ignition. A detailed plasma kinetic mechanism integrated with all excited species was considered and validated with experimental studies. Numerical modeling of plasma ignition has been performed by coupling ZDPlasKin with CHEMKIN. Energy and power consumption for methane/air plasma actuation is higher than the air plasma actuation. This could be due to the excitation and ionization of methane that required more energy deposition and power. The mole fraction of O atoms and ozone was higher in the air than the methane/air actuation. However, O atoms were produced in a very short time interval of 10⁻⁷ to 10⁻⁶ s; in contrast, the concentration of ozone was gradually increased with the time interval and the peak was observed around 10⁻¹ s. Plasma discharges on the methane/air mixture also produced radicals that played a key role to enhance the combustion process. It was noticed that the concentration of H species was high among all radicals with a concentration of nearly 10⁻¹. The concentration peak of CH₃ and OH was almost the same in the order of 10⁻². Finally, the mixture ignition characteristics under different low inlet temperatures were analyzed for both air and methane/air plasma actuation in the presence of different plasma discharges pulses numbers. Results showed that it is possible to reach flame ignition at inlet temperature lower than the minimum required in the absence of plasma actuation, which means ignition is possible in cold flow, which could be essential to address the re-ignition problems of aeroengines at high altitudes. At Ti = 700 K, the ignition was reached only with plasma discharges; ignition time was in the order of 0.01 s for plasma discharges on methane/air, lower than in case of plasma in air, which permitted ignition at 0.018 s. Besides this, in the methane/air case, 12 pulses were required to achieve successful ignition; however, in air, 19 pulses were needed to ignite.

This study deals with the experimental characterization of the induced flow dynamics by a disk-needle-type plasma actuator driven by a sinusoidal generator and located in a rectangular cross-section burner. Flow characterization was performed using different plasma actuation conditions and standoff distances. Experiments were conducted under non-reactive flow conditions. Electrical characterization was carried out. Airflow behavior was also analyzed using smoke flow visualization. Smoke flow visualization showed the dynamic behavior of the plasma-induced flow. Post-processing of high-quality images was performed by using Proper Orthogonal Decomposition (POD) technique to recognize the dominant flow vortexes and coherent structures. This could support the design of plasma actuation devices in real combustors and be useful for the implementation of numerical models. Moreover, it has been concluded that flow dynamics can be controlled by a variation of the plasma power or the gap distance between two electrodes. Laser Droplet Velocimetry (LDV) was used to investigate the distribution of flow velocities and turbulent kinetic energy (TKE) at different plasma power values of the sinusoidal alternating current generator and standoff distances. From POD and LDV analyses, it has been observed that there is quite a linear relation between the POD energy of the first mode and the maximum TKE. The POD method could be used to identify motions in the flow field carrying the most TKE. TKE peaks are present in the area with the most energetic flow structures, as identified by the POD.