Stagnation Flow Research Articles

Experimental and numerical study of product gas and N2O emission characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow

In order to achieve carbon neutrality, the use of ammonia as a fuel for power generation is highly anticipated. The utilization of a binary fuel consisting of ammonia and hydrogen can address the weak flame characteristics of ammonia. In this study, the product gas characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow were experimentally and numerically investigated for various equivalence ratios for the first time. A trade-off relationship between NO and unburnt ammonia was observed at slightly rich conditions. At lean conditions, NO reached a maximum value of 8,700 ppm, which was larger than that of pure ammonia/air flames. The mole fraction of nitrous oxide (N2O) which has large global warming potential rapidly increased around the equivalence ratio of 0.6, which was attributed to the effect of a decrease in flame temperature downstream of the reaction zone owing to heat loss to the stagnation wall. To understand this effect further, numerical simulations of ammonia/hydrogen/air flames were conducted using the stagnation flame model for various equivalence ratios and stagnation wall temperatures. The results show that the important reactions for N2O production and reductions are NH +NO = N2O + H, N2O + H = N2 + OH, and N2O (+M) = N2 + O (+M). A decrease in flame temperature in the post flame region inhibited N2O reduction through N2O (+M) = N2 + O (+M) because this reaction has a large temperature dependence, and thus N2O was detected as a product gas. N2O is reduced through N2O (+M) = N2 + O (+M) in the post flame region if the stagnation wall temperature is sufficiently high. On the other hand, it was clarified that an increase in equivalence ratio enhances H radical production and promotes N2O reduction by H radical through the reaction of N2O + H = N2 + OH.

Mathematical Study of Heat Transfer in a Stagnation Flow of a Hybrid Nanofluid over a Stretching/Shrinking Cylinder

Mathematical Study of Heat Transfer in a Stagnation Flow of a Hybrid Nanofluid over a Stretching/Shrinking Cylinder

Unsteady MHD oblique stagnation slip flow of Oldroyd-B nanofluids by coupling Cattaneo-Christov double diffusion and Buongiorno model

• Oblique stagnation flow with slip effect under slant magnetic field is studied. • Pressure gradient is gained by solving first order ordinary differential equation . • Thermophoresis and Brownian motion term with relaxation effects are generated. • Approximate analytical solution of unsteady oblique stagnation flow is acquired. Unsteady oblique stagnation flow, thermal and mass transmission of Oldroyd-B nano model through a vibrating tensile plate are investigated, with slip effect and inclined magnetic field. According to the boundary layer flow characteristics, a first-order ordinary differential equation is established to acquire the pressure field. Meanwhile, the heat conduction and Brownian diffusion of Buongiorno model is modified by Cattaneo-Christov double diffusion innovatively, which can produce the thermophoresis term and Brownian motion term with relaxation effects. Convective heat transfer and nonlinear radiation are also considered. The governing equations are changed to time-varying partial differential equations (PDE) via similarity transformation, which is calculated by Homotopy Analysis Method (HAM). The outcomes exhibit relaxation effect first accelerate and then impede energy and mass transfer of fluid. As a result of diffusion of nanoparticles, thermophoresis and Brownian motion give rise to large variations in concentration. Convective heat transfer and radiation can profit to thermal transfer. Changing the angle of inclined magnetic field can flexibly dominate flow velocity of fluid, which can cut down the cost in practice. Velocity slip is an obstacle to fluid flow.

Radial stagnation flow of a micropolar fluid over a twisting cylinder

AbstractAn investigation is accomplished to analyze the problem of radial stagnation flow of micropolar fluid radially impinging over a twisting cylinder. The impact of the twisting rate σ, Reynolds number R on the flow under the concentration of rotation of microelements on the flow is predicted in this research. By utilizing similarity variables, the leading flow equations of micropolar fluid are transformed into ordinary ones. A numerical scheme called the Keller–Box technique is applied to acquire the numerical results. The consequences of the micro rotational components on the twisting parameter are analyzed. Important characteristics of this flow are studied for different values of and σ. The wall shear stresses are also obtained. The interesting feature of axial and azimuthal wall shear stress parameters under the concentration of micro rotation of fluid elements are obtained and discussed.

Numerical Analysis of Nanofluid on Stagnation Flow Past a Stretching Sheet in the Presence of Magnetohydrodynamics (MHD), Convective Heating and Double Diffusive Effects

The article provides a specific section of the model, which incorporates Soret-Dufour and convective heating effects, to emphasise the intricacies of the mathematical model for Nanofluid on stagnation flow towards a stretched sheet in the presence of a magnetic field. The revised governing equations in the form of linear ordinary differential equations were solved utilising shooting methods and a Runge-Kutta-Felhberg-integration technique. The plot used to explain the change in velocity, temperature, and concentration was based on a storey in which different characteristics appeared first on the graphs. Tables may also be used to analyse skin friction and the Nusselt and Sherwood values, both of which are essential in engineering. Following that, we will look at how the new method compares to previously known approaches in a few different situations. The main findings of this investigation are: the velocity profiles are increasing with increasing values of velocity ratio parameter and the reverse effect is observed in presence of Magnetic field parameter. The temperature profiles are rising with increasing the numerical values of Thermophoresis, Brownian motion, Diffusion thermo, Biot number parameters and the temperature profiles are decreasing with increasing values of Prandtl number. Also, the concentration profiles are rising with the increasing values of Thermophoresis, Thermal diffusion parameters and reverse effect is observed in case of Brownian motion parameter.

Residence time distribution and heat/mass transfer performance of a millimeter scale butterfly-shaped reactor

A millimeter scale butterfly-shaped reactor was proposed based on sizing-up strategy and fabricated via femtosecond laser engraving. An improvement of mixing performance and residence time distribution was realized by means of contraction and expansion of the reaction channel. The liquid holdup was greatly increased through connection of multiple mixing units. Structure optimization of the reactor was carried out by computational fluid dynamics simulation, from which the effect of reactor internals on mixing and the influence of parallel branching structure on heat transfer were discussed. The UV–vis absorption spectroscopy was used to determine the residence time distribution in the reactor, and characteristic parameters such as skewness and dimensionless variance were obtained. Further, a chained stagnant flow model was proposed to precisely describe the trailing phenomenon caused by fluid stagnation and laminar flow in small scale reactors, which enables a better fit for the experimental results of the asymmetric residence time distribution. In addition, the heat transfer performance of the reactor was investigated, and the overall heat transfer coefficient was 110–600 W m-2 K-1 in the flow rate range of 10–40 mL/min.

Heat transfer enhancement and entropy generation minimization using CNTs suspended nanofluid upon a convectively warmed moving wedge: An optimal case study

AbstractThis paper aims to examine the effects of singleand multi‐walled carbon nanotubes (CNTs) nanoparticles on heat transfer enhancement and inherent irreversibility in the boundary layer of water base nanoliquid flow over a convectively heated moving wedge with thermal radiation. Manipulation of the angle positioning towards the flow stream provides the opportunity for comparing physical aspects in the flow states, where three main geometries of the well‐known Falkner–Skan problem include: (i) the flat plat (named Blasius flow), (ii) the wedge, and (iii) the vertical plate (named Hiemenz stagnation flow) have been considered to present a comprehensive development of this significant problem. Applying suitable similarity constraints, the model partial differential equations are transformed into a set of nonlinear ordinary differential equations. Solutions are obtained analytically via optimal homotopy asymptotic method and numerically via shooting technique coupled with the Runge–Kutta–Fehlberg fourth–fifth scheme. The impacts of solid volume fraction of carbon nanoparticles along with other germane factors, such as wedge angle, velocity ratio parameter, Biot number, thermal radiation, and so forth on velocity and thermal profiles, Nusselt number, heat transfer enhancement, rate of entropy generation, and irreversibility ratio, are scrutinized via graphical simulations and discussed. Optimization of such entropy developments in the system was found to depend on geometrical (β), dynamical (λ), and thermophysical (Bi, NR, Ec, φ) parameters. The ultimate objective of reducing the energy loss and enhancing heat transference was obtained with the geometrical manipulation of a flat plate case (β = 0). Dynamically (λ = 1) were spotted to exert the best fluidity irrespective of obstacle shapes (wedge or plate) in its way. In thermophysical aspects, reducing the convective heating develops a favorable situation for attaining the optimal balance between energy loss and heat transfer. SWCNT/water could be the better choice with enhanced thermal transference ability and exerts minimal irreversibility to overshadow the influences of all the above‐mentioned factors. The SWCNT suspended nanofluid can provide 12%–64% heat transfer enhancement when compared with the multiwalled CNT nanofluid which ranges from over 11% to 58% heat transference rate.

Mixed convectional and chemical reactive flow of nanofluid with slanted MHD on moving permeable stretching/shrinking sheet through nonlinear radiation, energy omission

Hybrid nanofluids are remarkable functioning liquids that are intended to reduce the energy loss while maximizing the heat transmission. In the involvement of suction and nonlinear thermal radiation effects, this study attempted to explore the energy transmission features of the inclined magnetohydrodynamic (MHD) stagnation flow of CNTs-hybrid nanofluid across the nonlinear permeable stretching or shrinking sheet. This work also included some noteworthy features like chemical reactions, variable molecular diffusivity, quadratic convection, viscous dissipation, velocity slip and heat omission assessment. Employing appropriate similarity components, the model equations were modified to ODEs and computed by using the HAM technique. The impact of various relevant flow characteristics on movement, heat and concentration profiles was investigated and plotted on a graph. Considering various model factors, the significance of drag friction, heat and mass transfer rate were also computed in tabular and graphical form. This leads to the conclusion that such factors have a considerable impact on the dynamics of fluid as well as other engineering measurements of interest. Furthermore, viscous forces are dominated by increasing the values of λ p, δ m and δ q, and as a result, F′(ξ) accelerates while the opposite trend is observed for M and ϕ. The drag friction is boosted by the augmentation M, λ p and ϕ, but the rate of heat transfer declined. According to our findings, hybrid nanoliquid effects dominate that of ordinary nanofluid in terms of F′(ξ), Θ(ξ) and ϕ(ξ) profiles. The HAM and the numerical technique (shooting method) were found to be in good agreement.

A Study of MHD Fluid with Second Order Slip and Thermal Flow Over a Nonlinear Stretching Sheet

An electrically conducted viscous incompressible nanofluid flow caused by the nonlinear stretching surface with stagnation flow has been investigated numerically. The effect of Brownian motion and thermophoresis on the nanofluid is also incorporated. The governing partial differential equations with nonlinear second order boundary conditions are solved by the fourth order Runge-Kutta technique using MATLAB programming. The effect of the radiation parameter (<i>Rd</i>), stretching parameter (n), Brownian motion parameter (<i>Nb</i>), thermophoresis parameter (<i>Nt</i>) on temperature, velocity and mass transfer are shown graphically. The influence of some of these parameters on the local Nusselt number (− <i>θ</i>′(0)) and local Sherwood number (−<i>ϕ</i>′(0)) are shown by the graphs.

Effect of twisted tape inserts on thermal performance of heat pipe evacuated-tube solar thermal collector

The effect of twisted tape (TT) inserts on the thermal performance of a heat pipe evacuated-tube solar thermal collector (HP-ESTC) with an eccentric inlet and outlet developed by the present research team is experimentally investigated. An experimental apparatus was constructed to simulate the flow and heat transfer phenomena inside the manifold header of an HP-ESTC and tested in the laboratory. Based on a comparison analysis between the HP-ESTC with TT inserts and an existing HP-ESTC, it was found that adding TTs enhanced the heat transfer performance by eliminating the stagnation flow region, reducing the degree of flow skewness, and generating rotating flow. Because adding the TT inserts increased the flow resistance, resulting in a greater pressure drop based on the pressure drop experiments, an overall performance analysis considering both heat transfer and pressure drop characteristics was conducted. It was confirmed that applying TT inserts could improve the overall performance by up to approximately 7.7%. To assess the applicability of TT inserts for commercial HP-ESTCs, an HP-ESTC containing TT inserts was manufactured and tested outdoors based on test standards (KS B 8295).

Mass-based hybrid nanofluid model for entropy generation analysis of flow upon a convectively-warmed moving wedge

In this research, the steady incompressible laminar two-dimensional hybrid nanofluid flow upon a convectively-warmed moving wedge with radiative transition has been studied numerically. The nanoparticles are the magnetite (Fe3O4) and the graphene oxide (GO), in two research parts of spherical and non-spherical (brick, cylinder, platelet, and disk) shapes, suspended in the pure water as base fluid. Three main geometries of the well-known Falkner-Skan problem including: (i) the flat plat (named Blasius flow), (ii) the wedge, and (iii) the vertical plate (named Hiemenz stagnation flow) have been considered to present a comprehensive development of this significant problem. The applied methodology is according to the single-phase Tiwari-Das hybrid nanofluid model considering the masses of nanoparticles and base fluid instead the volume concentration of first and second nanoparticles. For the first time, the mentioned mass-based method will be utilized in combination with the entropy generation analysis. The governing dimensional PDEs are varied to a system of non-dimensional ODEs with the use of similarity transformation technique which is then solved numerically through Runge–Kutta–Fehlberg method coupled with a conventional shooting procedure. The effect of the governing parameters on the hybrid nanofluid velocity, the temperature distribution, the skin friction coefficient, the Nusselt number, the entropy generation, and the Bejan number has been investigated and interpreted through the tabular and graphical results. A reliable treatment of the mass-based method for the hybrid nanofluid flow, the heat transfer and especially the entropy analysis is the substantial achievement of the present research; although, the detailed results have been presented and discussed in the article's body. Certainly, new modeling and approaches for the hybrid nanofluid can be dramatically beneficial in the various industries in which the cooling technologies are vital

Numerical analysis of entropy generation and induced magnetic field on unsteady stagnation flow with suction/injection

The core part of current model is to analyze the entropy generation and 2-dimensional unsteady stagnation flow with suction/injection constraint present in the boundary. Further, the induced magnetic field has applied with this flow model, which is formed by the motion of fluid that conducts electrically. The time-dependent partial differential equations (PDE) of the recent model are first converted to non-linear ordinary differential equations (ODE) using suitable similarity variables. We obtain solutions numerically using inbuilt shooting technic. We demonstrate the results using the graphs, tables and discussed them in detail. It is found that as the injection parameter is responsible for the thinning of the boundary layer, induced magnetic boundary layer; Suction, and unsteady constraints decelerate Bejan number; and the unsteady parameter decelerates the profiles and the temperature distributions accelerate by the

Canoeing disturbs riverine benthic invertebrates, but effects are small compared to the impact of water power generation

Canoeing is increasingly popular and disturbance by canoeists has environmental impacts, e.g. on breeding birds. We investigated how trampling by canoeists affects the benthic invertebrate fauna of a mountain river. In reaches around three weirs, where canoeists are forced to leave the river upstream of the weir and to enter the river in the residual flow section downstream, we sampled benthic invertebrates at the exit and entry sites, and at two undisturbed sites directly up- and downstream of exit and entry. All these were compared to undisturbed, free flowing sections further upstream. Compared to the free flowing sections, we observed a strong effect of stagnation (upstream of the weirs) and of residual flow (downstream of the weirs) on the benthic invertebrate fauna: lower abundances, taxa numbers and shares of sensitive taxa, and higher Saprobic indices. Compared to sites directly up- and downstream, habitat composition and benthic fauna of the exit sites were not modified and characterised by sludge and tolerant taxa. However, at the entry sites downstream of the weirs, benthic invertebrate abundances, taxa numbers and shares of sensitive species were strongly reduced, as compared to undisturbed sites directly up- and downstream. We conclude that trampling and pulling boats causes strong but spatially restricted organismic drift and thus effects on benthic invertebrate abundances at the entry sites. In contrast, it is possible for canoeists to leave the boats upstream of the weirs without causing measurable disturbance. Overall effects of canoeing on benthic invertebrates are small as compared to the effects of stagnation and residual flow.

Transport of thermal energy in the magnetohydrodynamic oblique stagnation point flow in a hybrid nanofluid with nanoparticle shape effect

AbstractIn the present paper, the augmented heat characteristics of a hybrid nanofluid which is a blend of Al2O3 (alumina) and Ag (silver) in the host hybrid fluid (C2H6O2‐H2O) (50%–50%) impinging obliquely on an elastic surface with magnetic lines of force are investigated. The properties of the nanofluid are assessed through the computational solutions established with the aid of the popular Runge–Kutta–Fehlberg fifth‐order (RKF 5) numerical technique. Outputs of the analysis reveal that the rate of thermal energy transport in the hybrid (mono) nanofluid is enhanced by 11.5% (5.8%) by using blade‐shaped nanoparticles in comparison to that of the spherical particles. Stream contours of both nanofluids are inclined to the left (right) of the stagnation‐point for positive (negative) values of the stagnation flow parameter.

Zinc oxide–silver/water hybrid nanofluid flow toward an off‐centered rotating disk using temperature‐dependent experimental‐based thermal conductivity

AbstractHerein, the off‐centered stagnation flow and heat transfer of zinc oxide–silver/water hybrid nanofluid over a rotating disk according to the mass‐based algorithm is studied. It is assumed that the nanoparticles have a spherical shape. Also, the velocity slip between the base fluid and nanoparticles is negligible. The Prandtl number is kept constant at 6.2. In addition, it has been used an experimental relation for effective thermal conductivity which is a function of volume fraction and temperature. The governing partial differential equations are converted to dimensionless ordinary differential equation (ODE)s by the similarity transformation method. The simplified ODEs are solved numerically by the bvp4c function from MATLAB which is an efficient and reliable code according to the three‐stage Lobatto IIIa formula. The influence of rotational parameters and both nanoparticles masses on the profiles and quantities of engineering interest are presented and discussed in detail. It is shown that the flow becomes complicated when there is a distance between the flow axis and the disk axis. Under determined conditions for a hybrid nanofluid with 30‐g mass for both nanoparticles and 100‐g mass for pure water, adding 30 g of the second nanoparticle's mass into the base fluid leads to enhance all hydrodynamic quantities of engineering interest by about 4.3%, while dispersing 30 g of the first nanoparticle's mass inside water results in decreasing the similarity temperature gradient at the surface about 3.6%. Also, when the disk rotates faster, the maximum radial velocity near the disk, s′(0) and f″(0) increases.

Classroom demonstration of a stagnation flow using cell phone-captured particle image velocimetry data

Courses in fluid mechanics and aerodynamics often require lengthy and involved mathematical derivations. However, these subjects are also associated with visually appealing flow features. In an effort to provide students with a full appreciation for fluid mechanics, it is desirable to not only provide a theoretical background, but also perform some visual demonstrations; this can be achieved through quantitative flow visualization demonstration. The cost of research-grade equipment is prohibitive for a teaching college, especially if only used for classroom demonstration. This article describes a Particle Image Velocimetry (PIV) demonstration of flow around a vertical plate using widely available cell phone cameras, reducing the cost of the required equipment. The velocity field calculated using PIV analysis was compared to a velocity field predicted using potential flow theory. The two showed an agreement of about 30% – a sufficient accuracy for an in-classroom demonstration. The learning effectiveness of this demonstration was evaluated using course evaluations and an end-of-semester survey. Overall, students expressed their appreciation for added experimental work and visualization to the course curriculum.

Numerical and experimental study of product gas characteristics in premixed ammonia/methane/air laminar flames stabilised in a stagnation flow

The adoption of ammonia/hydrocarbon fuel blends can be viewed as an intermediate step towards a hydrogen economy, hence the characterization of methane/ammonia flame product gas trends is essential for designing combustors for a broader range of low-carbon fuel blends while fulfilling strict NOx requirements. This paper describes the product gas content of laminar premixed ammonia/methane flames for a range of equivalence ratios and ammonia heat ratios ranging from 10% to 60%, using a strain stabilized burner at atmospheric pressure and room temperature. The optimal condition to reduce NOx emissions while maintaining below 100 ppm of unburnt NH3 emissions was found to be at equivalence ratio of 1.20 for higher ammonia ratios, moving incrementally closer over 1.35 as the methane fuel content was increased. Meanwhile, the highest measured NO values were ∼6,950 ppm at an equivalence ratio of 0.9, peaking at heat ratios of 30% to 40% at this equivalence ratio. Detailed reaction mechanisms were evaluated against the experimental data and rate constants of NO production/consumption steps featuring both NH and HNO intermediates and thermal NOx reactions were updated for Okafor's mechanism. Changes in reaction rate constants improved the mechanism accuracy for NO emissions in lean to stoichiometric flames. Meanwhile, in the rich region, modelled NO values were less responsive to changes in reaction constants, suggesting the need for an alternative approach to improve NO predictions for rich, high methane content flames. However, N2O performance in the rich region could be improved, highlighting the significance of the HNO+CO→NH+CO2 reaction.

Quadratic regression analysis of unsteady MHD free convective and radiative–dissipative stagnation flow of hybrid nanofluid over an exponentially stretching surface under porous medium

In this research article, we have analyzed the unsteady MHD free convective stagnation point flow of hybrid nanofluid towards an exponentially stretching surface placed in a uniform porous medium with velocity slip, thermal radiation, Ohmic and viscous dissipations. A convective heating type condition at the surface boundary is incorporated into the system. The base fluid water (H2O) along with alumina (Al2O3) and copper (Cu) nanoparticles is chosen to stimulate the fluid flow. Such flow problem arises in several industrial and engineering processes including aerodynamic heating, polymer processing, etc. By utilizing appropriate similarity transformations, the resulting governing equations along with the boundary conditions are converted into dimensionless forms for numerical computations. For the simulation of transformed highly nonlinear ordinary differential equations, Runge–Kutta–Fehlberg method-based shooting technique is applied. The consequences of physical parameters on velocity and temperature distributions are explored via pictorial representations. The values of the local surface drag coefficient and local Nusselt number for all the implanted parameters are calculated at the boundary and presented through the tables. Further, a regression analysis is performed to estimate the local surface drag coefficient and local Nusselt number and the numerical data are presented in tabular form. Moreover, under some limiting conditions, a comparison of the present results with the available results has also been made and an excellent correlation is observed among the results.

Identifying Stagnation Zones and Reverse Flow Caused by River‐Aquifer Interaction: An Approach Based on Polynomial Chaos Expansions

AbstractFluctuating stream stages and peak‐flow events can significantly influence the interactions between streams and aquifers and modify the hydraulic gradient, the flux exchange and the subsurface flow paths. As a result, stagnation zones and reverse flow may appear in different parts of an aquifer and at different times. These features of the flow field play a relevant role in the transport, transformation, and residence time of solutes, pollutants, and nutrients in the subsurface. However, their identification using numerical models is complex not only because of highly nonlinear dynamics, but also due to significant uncertainties in the model input data which propagate into the quantities of interest. In this work, we use an approach based on polynomial chaos expansions to map the probability of occurrence of stagnation zones and reverse flow during a flood event. We quantify the propagation of uncertainty into the groundwater flow field due to the applied river boundary conditions. Then, we evaluate the responses of the posterior probabilities in an element‐wise fashion using a set of flow classification criteria and kernel density estimations. The proposed methodology is flexible because it employs a nonintrusive pseudo‐spectral technique and, consequently, it can be applied straightforwardly in preexisting models. The regions near the confluence of two streams in the studied area are prone to present transient stagnation and reverse flow.

Numerical analysis of NOX formation in CO2 diluted biogas premixed combustion

A further investigation of premixed biogas combustion towards the NOx formation is presented in this study. The purpose of the simulation is to determine the addition of CO2 in biogas fuel to the combustion behavior of premixed biogas on NOx formation, and to determine the occurrence of NOx in the pre-mixed biogas combustion. In this study, the Counterflow Premixed Flame class is used where this class is based on the One Dim class which is the basis for simulations with a 1-dimensional domain. The Counterflow Premixed Flame class uses an axisymmetric stagnation flow domain which has been written based on the equations. Cantera uses Newton's method to solve them. Completion is carried out in two stages. The first stage is to solve the solution using the equilibrium at each z coordinate point that has been determined. Many estimation starting points are determined from the start of the program. The second stage is the recalculation process at each point and then subdivided to get a smoother solution. The premixed excess CO2 biogas fuel and air combustion analyzed using a 1-dimensional numerical study. The diluted CO2 mass fraction ranged between 0–40 %. The CH4/CO2/air volume flow rate was maintained in ±L/min. The analysis implements the 1-D Counter Flow approach. Two counterflow nozzles were 20mm in diameter and the flame stagnation point at 10 mm. The results show that NOx mass fraction formed only on a fuel-lean mixture of CH4/CO2/air and its values decreased along with CO2 added. The addition of CO2 could reduce the NO species mass fraction down to 18 %, and NO2 reduction down to 7 %. This is mainly caused by a decreasing heat release rate of NO+N↔N2+O, N+O2↔NO+O, N+OH↔NO+H, and N+CO2↔NO+CO reactions. The N+CO2↔NO+CO reaction increased as CO2 was added but its values were not as much as the decline of three other reactions