Formation Of Nitrogen Oxides Research Articles

Experimental support for a new NOx formation route via an HNNO intermediate

Achieving minimal levels of nitrogen oxides (NOx) during combustion is a major constraint in the design of advanced high-efficiency engines. NOx can be formed during combustion of any fuel—including those without fuel-bound nitrogen—in air, where radicals can attack molecular nitrogen (N2) present in air to break the strong NN bond to ultimately form NOx. Paramount to the goal of minimizing NOx formation is knowledge of the fundamental routes by which the strong NN bond in N2 can be broken. Historically, there have been four known routes for breaking the strong NN bond in N2 to ultimately form NOx. We have recently posited that another route—mediated by an HNNO intermediate—may also play a role, particularly at the high pressures and low peak temperatures relevant to high-efficiency, low-NOx engines. Our previous theoretical and modeling studies show HNNO to be a major product of the N2O + H reaction at high pressures and low temperatures; once formed, HNNO is likely to react with radicals in barrierless reactions that would occur quickly and with high NOx yields. In the present paper, we report measurements of H2, O2, H2O, N2O, NO, NOx, and NH3 in jet-stirred reactor experiments for an H2/O2/N2O/NO/N2/Ar mixture that specifically target HNNO pathways. Importantly, we observe significant formation of NO and NH3—both of which provide signatures of the HNNO mechanism that are not predicted by previous models without it. Flame simulations using a new sub-model describing pressure-dependent formation and consumption of HNNO show these pathways to be among the most prominent formation routes at high pressures and low peak temperatures. However, exact quantification of the role of HNNO in NOx formation and quantitative predictions of NOx in general require more accurate rate constants for both HNNO pathways and mixture rules for pressure-dependent reactions.

EXPERIMENTAL STUDY WITH DIFFERENT STRATEGIES AND AIR-DILUTION USING OPTICAL SI ENGINE FUELED WITH HYDRATED ETHANOL

Several dilution conditions techniques are used in internal combustion engines to increase fuel economy and reduce pollutant emissions, primarily nitrogen oxide (NOX), which are generated by the thermal pathway. Among the techniques, we can highlight air dilution (lean combustion) and exhaust gas recirculation (EGR). The control of these operations using different types of fuels and biofuels and their peculiarities, are of fundamental importance to remove the maximum efficiency from the process, generating the lowest level of emission and respecting the current legislation. Although several studies have achieved interesting results for reducing emissions and knocks thanks to the dilution of the air, it has been observed that the diluent without oxygen is more efficient. Although air dilution has a slightly lesser effect than EGR, this mode of operation can help to understand the dynamics of engine load dilution, mainly due to the complexity of EGR tests on research engines. Therefore, as a background, tests were carried out experimentally with air dilution in order to understand the behavior for the prediction of future tests with EGR. The tests were performed with hydrated ethanol and speeds of 1500 rpm and 2500 rpm. It was possible to observe that with increasing dilution, there is a gradual increase in the variability of the burn and its displacement to the region close to the inlet valve. It was observed that the dilution provided a decrease in the formation of NOX and CO and an increase in hydrocarbon emissions. Increased rotation due to increased turbulence causes changes in emission values.

A comparative study of oxidation of pure ammonia and ammonia/dimethyl ether mixtures in a jet-stirred reactor using SVUV-PIMS

Oxidation of pure ammonia or ammonia/dimethyl ether (NH3/DME) mixtures in O2/Ar in a jet-stirred reactor (JSR) at atmospheric pressure was experimentally studied using a synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and a gas chromatograph (GC) to analyse the reaction intermediates and product species. Particular attention was given to the effect of DME addition on NH3 → NH2, a critical step that initiates NH3 oxidation and subsequent formation of nitrogen oxides. The initial mole fraction of NH3 was set to 0.01, and for the NH3/DME mixture, the NH3/DME molar ratio was set to 1. The experiments were performed at two equivalence ratios of ϕ = 1.0 and 0.2 in the temperature range of 500 – 1100 K. A kinetic model for NH3/DME oxidation was developed and kinetic analysis was performed. It was found that the addition of DME significantly promotes the NH3 to NH2 pathway and the mechanisms of this promotion effect are different at low and high temperatures. At a low temperature (∼ 600 K), NH3 → NH2 is mainly promoted by OH radicals produced from the DME low-temperature chain-branching reactions, while at a high temperature (∼ 1000 K), mainly by OH radicals produced from the reactions consuming HO2 and H radicals, which were formed from DME high temperature oxidation. At T > 800 K with ϕ = 0.2, the addition of DME promotes the formation of nitrogen oxides, however, at a low temperature of 600 K, the addition of DME only promotes the formation of N2O and NO2 but not NO. A reaction pathway analysis indicates that the oxidation of NO into NO2 at low temperature is promoted by HO2 and CH3OCH2O2, the intermediate products from the low temperature oxidation of DME.

On the role of HNNO in NO[formula omitted] formation

The formation of nitrogen oxides (NOx) during combustion is a topic of substantial fundamental and practical interest, given the complex nature of its formation kinetics and the fact that, as a highly regulated pollutant emission, it is a major constraint in engineering design. To date, there are four known mechanisms by which the strong N–N bond can be broken to facilitate NOx formation from N2 present in air. Here we posit and explore the possibility of a new NOx formation route mediated by an HNNO intermediate whose reactions with common combustion species break the N–N bond. Altogether, we present results from master equation (ME) calculations for HNNO formation from H + N2O (+M), ab initio electronic structure and RRKM/ME calculations for HNNO + O2, and simulations of NO profiles in freely propagating flames using a newly constructed HNNO kinetic sub-model. Our ME results for the H + N2O reaction indicate that HNNO is the favored product channel at lower temperatures and higher pressures – e.g. favored over all other products up to ∼1100 K and over NH + NO up to ∼1500 K above 10 atm. Our ab initio electronic structure calculations for trans-HNNO + O2 show a barrier for abstraction to HO2 + N2O of 18.2 kcal/mol and a barrier for addition of 27.0 kcal/mol to form an HN(OO)NO which can decompose to NO + HNO2 over a barrier of 32.3 kcal/mol (cis-HNNO + O2 shows similar reactivity). Altogether, our rate constant calculations and kinetic modeling, which also includes estimated rate constants for HNNO + radical reactions, suggest that HNNO + O2 mainly recycles HNNO back to N2O but is sufficiently slow that the primary fate of HNNO in many combustion situations likely involves reactions with radical species, which appear likely to occur quickly and with high NOx yields.

ВЛИЯНИЕ ИНТЕНСИВНОСТИ КРУТКИ ВОЗДУХА В ВИХРЕВЫХ ГОРЕЛКАХ НА ВЫДЕЛЕНИЕ ОКСИДОВ АЗОТА В ПРОМЫШЛЕННЫХ ТРУБЧАТЫХ ПЕЧАХ

An important task in the design and operation of industrial furnaces is to reduce the formation of harmful substances, in particular, nitrogen oxides (NOx), directly at the source of their occurrence. One of the promising methods of reducing the concentration of NOx in the gas emissions of furnaces is the use of vortex burners with a twist of the flow, providing better mixing of combustion products, thereby reducing the maximum local temperatures in the furnace and equalizing the temperatures over the working volume. However, the available information on the effect of vortex formation on the intensity of nitrogen oxides release is extremely contradictory – depending on the design of the burners and the furnace, the twist of the flow can both increase and decrease the formation of nitrogen oxides. Moreover, single burners have been studied at least in some way from the point of view of NOx release, but their interaction with each other in large-volume furnaces has not been practically investigated and requires additional study. By numerical experiments conducted on the basis of the mathematical model developed by us, it is shown that the smallest release of nitrogen oxides is ensured by the use of burners with a twist of the air flow (oxidizer), as well as their combination with two-stage combustion when the burners are located in the same horizontal plane. It is shown that the combined use of these two methods reduces the release of nitrogen oxides in the furnace by more than a factor of ten.

Effect of the Specific Features of the Torch Aerodynamics on the Integrated Efficiency of the Multifuel Boiler

This scientific paper gives the literature review emphasizing that the overwhelming majority of the operated boilers are equipped with vortex burners. These burners are characterized by an increased NOx formation, low operation reliability of screen tubes and convective heating surfaces, small maneuverability range and insufficient economical indicators. The defining role of the aerodynamic organization of the furnace processes affecting the operation efficiency of the boilers was shown for the case of the combustion of the energy fuels of a different type. Hence, the problems of an increased reliability, maneuverability, environmental safety and economical operation of the boilers are rather topical. The above problems faced by Ukraine today have been essentially exacerbated due to the fact that most boilers of the thermal power plants have a depleted resource and the production of new boilers (especially high power boilers) was actually stopped. The use of vortex burners with the traditional counter layout on the two opposite furnace walls is peculiar for the overwhelming majority of modern high power boilers in Ukraine and abroad. In this case, the central zone of the furnace is designed to provide the collision of the burner torches of opposite walls and a high-temperature burning core is created. In the case of gas –oil boilers, the availability of the high-temperature core results in an intensified formation of the thermal nitrogen oxides and a decreased operation reliability of the metal of furnace screens. The torch throw onto the side furnace walls during the combustion of fuel oil results in an essential decrease of the operation reliability of the screen tubes due to a high-temperature hydrogen sulfide corrosion. This paper highlights the issues of the effect of the specific features of the torch aerodynamics on the integrated efficiency of the boiler operation and the optimization of the layouts for the combustion of energy fuels in the multifurnace boilers for further reconstruction of the boilers to reduce the emission of harmful substances, increase reliability and economicity of their operation and enlarge the steam load carrying range.

METHODS TO REDUCE NOX FORMATION DURING GAS COMBUSTION IN BOILERS

A study of reduction of nitrogen oxides emissions using various methods and their combinations on operational typical steam and water heating boilers of Ukraine during combustion gas fuels was conducted. The experimental research of the power steam TGMP-314 boiler showed that when volume thermal stress of the firebox was reduced to qv » 0.09 MW/m3 (55 % of the nominal power), and the flue gas recirculation factor r = 17 %, the nitrogen oxides emissions were reduced by 75 % and they almost meet the requirements of the IED directive. This measure to reduce emissions of nitrogen oxides is also possible for other types of boilers, and it is advisable to implement for those combustion plants with an excess capacity of about 40–50 % and which have exhausted their factory-designated resource. On the water heating boiler KVGM-180, equipped with standard gas recirculation smoke exhauster, the research was conducted with aim to reduce of NOx emissions at combustion natural gas with recirculation of flue gases into the blowing air. NOx emissions were reduced by 67% to European standards, and the concentration of carbon monoxide in flue gases was below СО≤100 mg/Nm3 (at 3% O2) by a recirculation factor was of about r = 30%. The standard burners in the KVGM-180 boiler are two flow of air and can be considered a type of staged combustion burners. That is, in this case, a combination of the staged combustion burners and flue gas recirculation into blowing air was used. The research of combustion a methane and carbon dioxide mixture in the ratio of CH4 (76 %) and CO2 (24 %) (biogas) with regard to reduce the formation and emissions of nitrogen oxides in the DKVR-6.5-13 steam boiler was conducted. The obtained level of NOx in the flue gases is within the range of 63–76 mg/Nm3 (at 3 % O2), which fully complies with the EU standards for the operation of CP from 1 MW on natural gas and other gas fuels. Bibl. 34, Fig. 3, Tab. 1.

IR-spectroscopic study of complex formation of nitrogen oxides (NO, N2O) with strong Lewis acid sites and the reactivity of adsorbed species in CO and CH4 oxidation

The formation of complexes and transformations of nitrogen oxides (NO, N2O) on strong Lewis acid sites of HZSM-5, H[Ga]ZSM-5, ZnO/HZSM-5 zeolites and dealuminated mordenites was investigated by diffuse-reflectance IR spectroscopy. Adsorbed N2O that is formed by disproportionation of NO is capable of oxidizing CO and CH4 molecules to CO2. The behaviour of strong Lewis acid sites in zeolites and cationic forms of zeolites in the NO disproportionation and CO or CH4 oxidation was comparatively studied.

Effect of a Taper Intake Port on the Combustion Characteristics of a Small-Scale Rotary Engine

Taper intake ports are effective in improving the charging efficiency of small-scale rotary engines (REs), but it is unclear how their structural parameters affect the in-cylinder flow field and combustion characteristics. For this reason, the effects of the diameter-length ratio (D/L) of an intake port on the in-cylinder flow field and combustion characteristics of a small-scale RE were numerically investigated by utilizing a three-dimensional computational fluid dynamics (CFD) model. The results showed that the in-cylinder pressure of the RE did not follow a simple single-directional trend with the D/L of the intake port, but it was divided into three levels, where the peak in-cylinder pressure was at its maximum at the D/L of 0.6 and at its minimum at the D/L of 0.8. The gas flows in the intake port with different values of the D/L were all unidirectional, and they made a difference in the vortexes formed on the leading side of the combustion chamber of the RE, which was the main factor affecting the in-cylinder combustion performance. The vortexes formed on the leading side of the combustion chamber with D/L = 0.6 were maintained for a long period of time, thus promoting the propagation of flame and advancing the center of gravity of combustion. So, the heat release rate and combustion efficiency in the cylinder were increased at the price of a larger increment in nitrogen oxide formation.

RESEARCH OF A HIGH-EFFICIENCY CHARGE AIR COOLER

Currently, internal combustion engines have become widespread as sources of mechanical energy in many areas of human activity. It is the internal combustion engines that were and remain the most widespread in transport, where, as a rule, strict requirements are put forward for the mass-dimensional characteristics of the engines and the power plant as a whole. In order to meet these requirements, there is a constant increase in the level of forcing of the engines. For diesel engines, the most common technical measure that provides an increase in the level of engine forcing with almost unchanged weight and dimensional characteristics is an increase in supercharging pressure. However, as a result of air compression, its temperature increases, which is proportional to the degree of increase in air pressure in the compressor. An increase in air temperature causes a decrease in the mass charge of the cylinders, and therefore, a significant deterioration in the fuel combustion process. It also causes an increase in the level of maximum temperatures of the cycle, which in turn causes an increase in thermal loads and the rate of formation of nitrogen oxides in diesel cylinders. The above determines the urgency of the tasks of implementing effective charge air coolers in modern high-pressure transport diesel engines. This technical problem can be solved using air or liquid coolers. The article considers a liquid cooler, because compared to an air cooler, it can be made more compact, allows to achieve a much smaller length and volume of the intake tract, as well as to simplify the layout of the intake tract as part of the power plant as a whole, which is a priority for diesel engines. The article considers the influence of the design parameters of the supercharged air cooler on its overall characteristics and the hydraulic resistance of the supercharged air flowing through the cooler. Thus, the article provides data indicating the possibility of making a compact, highly efficient supercharged air cooler while maintaining its hydraulic resistance at an acceptable level by choosing rational parameters.

Numerical and experimental investigation of surface-stabilized combustion in a gas-fired condensing boiler

Gas-fired condensing boilers are widely used in domestic heating. However, emission of nitrogen oxides (NOx) remains a concern due to their adverse environmental effects. Employing lean premixed surface-stabilized combustion, ultra-low NOx generation is achievable.We studied NOx formation in realistic, axi-symmetric condensing boiler setups featuring lean combustion of methane stabilized by a porous cylindrical burner using a dedicated numerical model. To accurately represent the physical conditions, our model comprises most notably laminar combustion using a GRI-3.0 kinetic mechanism, a volumetric heat transfer coefficient for heat exchange inside the porous solid, conjugate heat transfer at the gas-solid interface and radiative heat exchange between burner surface and combustion chamber wall. A comprehensive assessment included validation of individual model aspects against literature data, a mesh study and validation with experimental measurements from a full-scale condensing boiler setup. Our findings suggest that the effective diffusion due to dispersive flow in porous media is critical for accurately capturing the reaction zone, thus preventing overprediction of flame temperature and NO concentration.The dependencies of NOx generation and heat release parameters on varying parametric and geometric configurations of the setup were assessed in a comprehensive numerical parameter study. We found that NO emission increases in a near-linear way with firing rate, while radiation efficiency decreases. At constant input power, NO emission rises with increasing equivalence ratio alongside radiation efficiency and peak flame temperature. By optimizing inflow uniformity, peak temperatures can be reduced by 9%, leading to significantly lower NOx generation without affecting the heat flow rate.

Stable and clean co-combustion of municipal sewage sludge with solid wastes in a grate boiler: A modeling-based feasibility study

Municipal sewage sludge not only has very high moisture content and low heating value but also carries lots of nitrogen, making it difficult to attain stable and clean co-combustion with municipal solid waste (MSW) in existing MSW incinerators. Blending other high-heating value solid waste as assistive fuel in co-firing of sewage sludge and MSW is considered feasible to improve the combustion stability and meanwhile maintain the disposal capacity of the incinerator. This paper numerically investigates MSW co-firing with sewage sludge and industrial solid waste in a moving-grate MSW boiler with a capacity of 750 t/d. The co-combustion stability and nitrogen oxides (NOx) emissions are among the main concerns, different blends of the three solid wastes and under-grate primary air (PA) distributions are probed and compared. First, a validated in-house bed model, comprehensively describing the solid fuel conversion process and heat and mass transfer phenomena on moving grates, is extended to include NOx formation and employed to simulate the combustion of various blends on the grate. Then, the fuel bed model is iteratively coupled with the simulation of the freeboard of the boiler, which is performed using ANSYS Fluent. For the various blends investigated in this study, co-combusting up to 25.6 wt% sewage sludge, with about 14.4 wt% industrial solid waste and 60 wt% MSW in the existing boiler, is feasible and recommended. By properly tuning the under-grate PA distribution, the stable, efficient and clean combustion of the feedstock blend has been achieved. Compared to the original PA distribution, up to 11.54% reduction of NOx emission from the boiler is attained, because of the enhancement of nitric oxide (NO) reduction reactions with ammonia (NH3) and char. At last, an in-depth analysis of co-combusting the recommended blend using the new PA distribution is elaborated. This study provides a valuable reference and guideline for stable and clean co-combustion of sewage sludge and MSW in existing incinerators.

Analysis of NO Formation and Entropy Generation in a Reactive Flow

A comprehensive investigation of turbulent combustion is accomplished to study the relationship between nitrogen oxide (NO) formation and entropy generation distribution in a non-premixed propane combustion. The radiation heat transfer and combustion are simulated, employing the discrete ordinates model and laminar flamelet model, respectively. A post processing model is employed to estimate the NO formation rate. The present results of NO species formation, mean temperature and velocity are compared with the existing experimental data, and good agreements are obtained. It is shown that the main region of total entropy generation rate and NO formation rate is at the same axial position. The entropy generation distribution may be defined as an index by which the combustion region and main region of NO formation are predicted. However, total entropy generation rate is more sensitive to high temperature (1500–1930 K) than that of NO formation rate. With an increase of 28.7% in temperature, the entropy generation and NO formation rates rise by 900% and 127%, respectively. The occurrence of chemical reactions plays the major role in the generation of entropy.

Effect of the Active Metal on the NOx Formation during Catalytic Combustion of Ammonia SOFC Off-Gas

Catalytic combustion of hydrogen and ammonia containing off-gas surrogate from an ammonia solid oxide fuel cell (SOFC) was studied with a focus on nitrogen oxides (NOx) mitigation. Noble and transition metals (Pt, Pd, Ir, Ru, Rh, Cu, Fe, Ni) supported on Al2O3 were tested in the range of 100 to 800 °C. The tested catalysts were able to completely convert hydrogen and ammonia present in the off-gas. The selectivity to NOx increased with reaction temperature and stagnated at temperatures of 600 °C and higher. At low temperatures, the formation of N2O was evident, which declined with increasing temperature until no N2O was observed at temperatures exceeding 400 °C. Over nickel and iridium-based catalysts, the NOx formation was reduced drastically, especially at 300 to 400 °C. To the best knowledge of the authors, the current paper is the first study about catalytic combustion of hydrogen-ammonia mixtures as a surrogate of an ammonia-fed SOFC off-gas.

Exploring reaction mechanism for ammonia/methane combustion via reactive molecular dynamics simulations

Ammonia has gained growing attention as a carbon-free fuel. However, extensive studies are still needed to clarify and complete reaction mechanisms for ammonia combustion over a wide range of conditions. In the present study, a series of reactive molecular dynamics simulations that could reproduce the ammonia/methane (NH3/CH4) combustion in air at high temperature and pressure conditions were conducted. Results show that high temperature accelerates the consumption of NH3 and affects the yield of nitrogen oxides (NOx). Meanwhile, high pressure accelerates the NH3 consumption, which could be partly attributed to the frequent energetic collisions, and influences the formation of NOx. To understand the mechanism for NOx formation, the reaction pathways of NH3/CH4 combustion at high pressures were generated by tracing the trajectories of reacting atoms. Results suggest that high pressure complicates reaction pathways of NH3/CH4 combustion as it enhances the molecular/atomic collisions. By comparing with five popular NH3/CH4 combustion mechanisms, new intermediates and elementary reactions revealed by this study are identified. The activation energies for a few featured elementary reactions are calculated as well. The activation energies obtained from the present study agree with previous results from combustion kinetics studies. The present study demonstrates the feasibility to generate reaction network via tracing the atomic events in a reacting system and that the reactive molecular dynamics is a cost-effective tool in revealing in-depth reaction mechanisms under extreme conditions.

Анализ эффективности использования восстановителя оксидов азота отработавших газов дизелей

The relevance of the article is due to the need to radically improve the environmental performance of automobile diesels. The most significant gaseous toxic component of spent diesel engines are nitrogen oxides. The mechanisms and models of nitrogen oxides formation in the diesel combustion chamber are considered. The analysis of methods for reducing the emission of nitrogen oxides with diesel exhaust gases has been carried out. The most effective method of their purification from nitrogen oxides is the use of SCR technology, in which an aqueous urea solution is supplied to the diesel exhaust system. At a temperature of about 130 °C, urea decomposes into ammonia and carbon dioxide. Ammonia released from urea reacts with nitrogen oxides of exhaust gases, reducing them to nitrogen. A method for calculating the urea supply to the diesel exhaust system has been developed. Tests of the YAMZ-6566 diesel engine equipped with the SCR system were carried out. With an excess urea ratio of 1.03, the efficiency of the SCR system ranged from 89 to 100 %, depending on the operating mode of the diesel engine.

Impact of Boundary Condition and Kinetic Parameter Uncertainties on NOx Predictions in Methane–Air Stagnation Flame Experiments

Abstract A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modeling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for nonintrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane–air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the six boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only, provide validation targets for modeling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.

Effect of high compression ratio on improving thermal efficiency and NOx formation in jet plume controlled direct-injection near-zero emission hydrogen engines

The Plume Ignition and Combustion Concept (PCC) developed by the authors significantly reduced nitrogen oxide (NOx) emissions in a direct-injection hydrogen engine under high-load operation. With PCC, a rich fuel plume is ignited immediately after completion of injection in the latter half of the compression stroke to reduce NOx formation. Simultaneously, high thermal efficiency was also achieved by mitigating cooling losses through optimization of the jet configuration in the combustion chamber. This basic combustion concept was applied to burn lean mixture in combination with the optimized hydrogen jet configuration and the application of supercharging to recover the power output decline due to the use of a diluted mixture. As a result, a near-zero-emission-level engine has been achieved that simultaneously provides high thermal efficiency, high power output and low NOx emissions at a single-digit ppm level [1]. In this study, a high compression ratio was applied to improve thermal efficiency further by taking advantage of the characteristics of hydrogen fuel, especially its diluted mixture with a high anti-knock property. As a result, NOx emissions at a single-digit ppm level and gross indicated thermal efficiency of 52.5% were achieved while suppressing knocking at a compression ratio of 20:1 by optimizing the excess air ratio and injection timing, and increasing power output by supercharging.

Introducing new lightning schemes into the CHASER (MIROC) chemistry–climate model

Abstract. The formation of nitrogen oxides (NOx) associated with lightning activities (hereinafter designated as LNOx) is a major source of NOx. In fact, it is regarded as the dominant NOx source in the middle to upper troposphere. Therefore, improving the prediction accuracy of lightning and LNOx in chemical climate models is crucially important. This study implemented three new lightning schemes with the CHASER (MIROC) global chemical transport and climate model. The first lightning scheme is based on upward cloud ice flux (ICEFLUX scheme). The second one (the original ECMWF scheme), also adopted in the European Centre for Medium-Range Weather Forecasts (ECMWF) forecasting system, calculates lightning flash rates as a function of QR (a quantity intended to represent the charging rate of collisions between graupel and other types of hydrometeors inside the charge separation region), convective available potential energy (CAPE), and convective cloud-base height. For the original ECMWF scheme, by tuning the equations and adjustment factors for land and ocean, a new lightning scheme called the ECMWF-McCAUL scheme was also tested in CHASER. The ECMWF-McCAUL scheme calculates lightning flash rates as a function of CAPE and column precipitating ice. In the original version of CHASER (MIROC), lightning is initially parameterized with the widely used cloud-top height scheme (CTH scheme). Model evaluations with lightning observations conducted using the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) indicate that both the ICEFLUX and ECMWF schemes simulate the spatial distribution of lightning more accurately on a global scale than the CTH scheme does. The ECMWF-McCAUL scheme showed the highest prediction accuracy for the global distribution of lightning. Evaluation by atmospheric tomography (ATom) aircraft observations (NO) and tropospheric monitoring instrument (TROPOMI) satellite observations (NO2) shows that the newly implemented lightning schemes partially facilitated the reduction of model biases (NO and NO2), typically within the regions where LNOx is the major source of NOx, when compared to using the CTH scheme. Although the newly implemented lightning schemes have a minor effect on the tropospheric mean oxidation capacity compared to the CTH scheme, they led to marked changes in oxidation capacity in different regions of the troposphere. Historical trend analyses of flash and surface temperatures predicted using CHASER (2001–2020) show that lightning schemes predicted increasing trends of lightning or no significant trends, except for one case of the ICEFLUX scheme, which predicted a decreasing trend of lightning. The global lightning rates of increase during 2001–2020 predicted by the CTH scheme were 17.69 % ∘C−1 and 2.50 % ∘C−1, respectively, with and without meteorological nudging. The un-nudged runs also included the short-term surface warming but without the application of meteorological nudging. Furthermore, the ECMWF schemes predicted a larger increasing trend of lightning flash rates under the short-term surface warming by a factor of 4 (ECMWF-McCAUL scheme) and 5 (original ECMWF scheme) compared to the CTH scheme without nudging. In conclusion, the three new lightning schemes improved global lightning prediction in the CHASER model. However, further research is needed to assess the reproducibility of trends of lightning over longer periods.

Investigation of the combustion process of activated fuel in an automotive diesel engine

BACKGROUND: Intensive development of the transport sphere and the extension of the fleet of tractors and cars, as well as the tightening of standards and requirements in the field of exhaust gas emissions have resulted in increased requirements for the combustion process. This problem can be solved by improving the working process in the engine by preheating the fuel to 300 C in the high pressure fuel supply system. Under external thermal influence, the conditions of mixture formation are improved, an increase in the rate of preflame reactions and a positive change in the dynamics of the combustion process are observed. When potential energy of hydrocarbon molecules increases in the activated complex system, energy is redistributed among active molecules. Along with this, the rate coefficient of a chemical reaction increases due to the concentration of foci of hydrocarbon molecules that have reached the energy barrier.
 The object of research is the process of diesel fuel combustion at preliminary external influence on it.
 AIMS: The aim is to study the combustion process of a motor-tractor diesel engine upon fuel activation. Development of a scheme of individual phases of the activated diesel fuel combustion of depending on the temperature at heating.
 METHODS: Theoretical study and analysis of the combustion process of thermally preprepared fuel for an automotive diesel engine. Theoretical determination of the dependence of the rate of formation and concentration of toxic components and dispersed particles on the rate constant of direct and reverse chemical reactions, as well as on the activation temperature of fuel at emission in exhaust gases.
 RESULTS: The actual coefficient of molecular change of the working mixture increases when diesel fuel is activated. The rate of formation of total nitrogen oxides and hydrocarbons increases by 1.79% and 3.66%. The proportion of unburned carbon in the combustion process on activated fuel varies within (24) %.
 CONCLUSIONS: Theoretically, a scheme for changing individual phases of the activated fuel combustion process by time and temperature has been developed. Fuel heating accelerates the pre-flame preparation in the liquid phase, shortens the duration of the rapid gorenje phase. The concentration of toxic indicators depends on the constant of the chemical reaction rate and the activation temperature of the fuel.