Higher Nitrogen Oxides Research Articles

Association between exposure to combustion-related air pollution and multiple sclerosis risk.

Smoking and occupational pulmonary irritants contribute to multiple sclerosis (MS) development. We aimed to study the association between ambient air pollution and MS risk and potential interaction with the human leukocyte antigen (HLA)-DRB1*15:01 allele. Exposure to combustion-related air pollution was estimated as outdoor levels of nitrogen oxides (NOx) at the participants' residence locations, by spatially resolved dispersion modelling for the years 1990-18. Using two population-based case-control studies (6635 cases, 8880 controls), NOx levels were associated with MS risk by calculating odds ratios (OR) with 95% confidence intervals (CI) using logistic regression models. Interaction between high NOx levels and the HLA-DRB1*15:01 allele regarding MS risk was calculated by the attributable proportion due to interaction (AP). In addition, a register study was performed comprising all MS cases in Sweden who had received their diagnosis between 1993 and 2018 (n = 22 173), with 10 controls per case randomly selected from the National Population register. Residential air pollution was associated with MS risk. NOx levels (3-year average) exceeding the 90th percentile (24.6 µg/m3) were associated with an OR of 1.37 (95% CI 1.10-1.76) compared with levels below the 25th percentile (5.9 µg/m3), with a trend of increasing risk of MS with increasing levels of NOx (P <0.0001). A synergistic effect was observed between high NOx levels (exceeding the lower quartile among controls) and the HLA-DRB1*15:01 allele regarding MS risk (AP 0.26, 95% CI 0.13-0.29). Our findings indicate that moderate levels of combustion-related ambient air pollution may play a role in MS development.

Flame and emission characteristics of preheated ammonia combustion based on chemical reaction network

Ammonia (NH3) is an ideal fuel for achieving decarbonisation in energy production and industrial combustion, but suffers from low flammability and high nitrogen oxides (NOx) emissions in combustion. Preheating of NH3 can lead to stable combustion of NH3 and reduce nitric oxide (NO) emissions. In this study, the special combustion characteristics of the fuel preheated flame were investigated. Combustion, optical temperature measurement and gas measurement systems were set up. The flame images were captured and the flame temperature distribution was reconstructed by experiment. The temperature field in the longitudinal profile at the flame centre was divided into 11 temperature regions. Computational fluid dynamics (CFD) was carried out on the preheated NH3 combustion to analyse the distributions of components and velocity vectors. Then, a chemical reaction network (CRN) with 10 perfectly stirred reactors (PSR) was constructed based on the temperature field reconstructed by experiment and the distributions of components and velocity vector by CFD simulation. The temperature, the concentration of products and reactants, intermediate product components and reaction pathways were analysed by the CRN method to investigate the jet combustion characteristics of preheated NH3 combustion. Experimental and CFD simulation results showed that differently coloured regions appeared in the upstream of the pure NH3 flame, and the high-temperature region was widely distributed in the temperature field. CRN simulation results showed that the formation of special flame characteristics was associated with the generation of large amounts of hydrogen (H2) and water (H2O), and the reactions of NH2 with NH2 were the most dominant generating pathway of H2. Reaction pathway analysis of NH3 showed that H and OH radicals were most relevant to the production of NO, while NH2 radicals were most relevant to the consumption of NO in preheated NH3 combustion.

Flame and emission characteristics from NH3/CH4 combustion under ultrasonic excitation

As a high energy density hydrogen-rich carrier, ammonia (NH3) is a highly promising carbon-free fuel. The large-scale industrial application of NH3 is limited by its low reactivity and high NOx emission. In this work, the flame and emission characteristics of ammonia/methane (NH3/CH4) non-premixed combustion were investigated under ultrasonic excitation. An experimental system was designed and built, including non-premixed combustion system, loading ultrasonic system, deflectionmography temperature measurement system and flue gas measurement system. Combustion and measurement experiments at different ultrasonic frequencies and NH3/CH4 blending ratios were carried out. Flame images and flue gas species concentrations under ultrasonic excitation were acquired. The 3-D temperature field was reconstructed. The influence of ultrasonic excitation at different frequencies on flame characteristics, flame temperature field and emission characteristics of the combustion process was analysed. The mechanism of NH3/CH4 combustion enhancement and emission reduction was revealed when the flame was ex-cited by ultrasonic waves. Results showed that part of the hydrocarbon fuels was replaced by NH3 to reduce CO2 emission. The height and color of the NH3/CH4 flame were changed and the high temperature area of the flame gradually expanded as ultrasonic acted on the flame. As ultrasonic frequency increased, the emission concentrations of unburned CH4, unburned NH3, and NO decreased significantly. The flame was ex-cited by ultrasonic waves, which reduced its local equivalent ratio, improved combustion efficiency and suppressed NOx generation.

Selective non-catalytic denitrification of biomass combustion flue gases (synthetic mixture)

Despite many benefits of agricultural biomass utilization as an energy source, there are certain disadvantages such as the possible high emission of NOx. The NOx emission represents one of the key challenges for agricultural biomass use as a fuel. The experimental denitrification chamber was used to evaluate the impact of initial NO content, NH3:NO molar ratio, flue gas temperature, and the temperature difference between two denitrification chamber sections on NOx reduction using ammonia aqueous solution. The optimization of experimental conditions was done in the NO concentration range from 200-800 ppm, NH3:NO molar ratios from 0.31-3 and second chamber section temperature range from 770-67?C. The denitrification process under controlled conditions is the starting point for the optimization of the secondary denitrification technique of selective non-catalytic reduction SNCR process on real-scale plants combusting biomass or any other fuels with increased NOx emission.

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.

Investigation on combustion characteristics and gas emissions of a high-pressure direct-injection natural gas engine at different combustion modes

In the present study, the potential of natural gas pre-injection, mixing-limited combustion, and slightly premixed combustion modes were evaluated to achieve high thermal efficiency and low nitrogen oxides and carbon monoxide emissions. To this end, a dual direct injection model was established to perform numerical simulations. The obtained results revealed that in the natural gas pre-injection mode, the optimized natural gas pre-injection proportion and injection interval between the end of natural gas pre-injection and the start of diesel injection can significantly reduce carbon monoxide emissions and improve indicated thermal efficiency with a slight increase in nitrogen oxides. In the mixing-limited combustion mode, combustion phasing and indicated thermal efficiency are not sensitive to the variations of the injection interval between diesel and natural gas. Moreover, a larger injection interval between diesel and natural gas is beneficial to reduce carbon monoxide. In the slightly premixed combustion mode, as the injection interval between diesel and natural gas decreases, combustion phasing delays, carbon monoxide emissions reduce, and nitrogen oxides emissions increase first and then decrease. Advancing the start of natural gas injection increases maximum pressure rise rate and nitrogen oxides in both natural gas mixing-limited combustion and slightly premixed combustion modes but decreases carbon monoxide dramatically. The natural gas mixing-limited combustion mode has more potential to meet carbon monoxide limits imposed by the Euro VII standard with no need for extra after-treatment devices while improving thermal efficiency.

Sm-modified Mn-Ce oxides supported on cordierite as monolithic catalyst for the low-temperature reduction of nitrogen oxides

Nitrogen oxides (NOx) are typical atmospheric pollutants that harm the environment and human body, and selective catalytic reduction (SCR) with NH3 is one of the most effective technologies to deal with NOx emissions at present. In this work, a monolithic catalyst, Sm-modified Mn-Ce composite oxides (Sm-MnCe) supported on cordierite (CC), is prepared by impregnation for the first time, and their denitration (de-NOx) performance in NH3-SCR reaction is evaluated in detail. The results show that 0.1Sm-MnCe/CC (Sm/Mn mole ratio is 0.1) has the best de-NOx efficiency with above 80 % NOx conversion from 60° to 270°C, and the high NOx conversion can be maintained within 15 h in the presence of 100 ppm SO2. It is found that appropriate introduction of Sm increases the specific surface area and acid sites, improves the redox environment, elevates the content of Mn4+ on the catalyst surface, which are conducive to the improvement of catalytic activity. In addition, the interaction between active components (Sm, Mn and Ce) also plays a positive role for the excellent de-NOx activity. It is revealed by in-situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) that the NH3-SCR reaction over the 0.1Sm-MnCe/CC catalyst follows Eley-Rideal (E-R) and Langmuir-Hinshel (L-H) mechanisms. This work provides ideas for the preparation and modification of monolithic catalysts, which is conducive to promoting the practical industrial application of low-temperature SCR de-NOx technology.

Enhanced combustion of ammonia engine based on novel air-assisted pre-chamber turbulent jet ignition

Ammonia has demonstrated great potential for achieving zero carbon emissions from internal combustion engines. However, the application of ammonia in engines faces the risks of ignition failure, low burning rate, and high nitrogen oxides emissions. Pre-chamber turbulent jet ignition (TJI) can provide multi-point ignition and fast combustion. Thus, in this study, a novel self-designed air-assisted pre-chamber apparatus is proposed to optimize the engine performance and combustion in a spark-ignition ammonia engine. The effects of high-reactivity pre-chamber fuels, including hydrogen, gasoline, and methane, on the performance of a TJI engine are investigated for the first time. The results show that, in the TJI mode considering the pre-chamber fueled with high-reactivity fuels, both the indicated mean effective pressure and indicated specific fuel consumption are improved compared with those in the spark-ignition mode. The enhanced combustion process involving shortened ignition delay and combustion duration is achieved by using the TJI mode. Double-peak phenomena are observed in both the pressure and heat release rate curves. In the TJI mode with the pre-chamber fueled with hydrogen, an optimal engine performance involving a high indicated mean effective pressure, low fuel consumption, and low coefficient of indicated mean effective pressure variation is obtained. Moreover, both peaks of the heat release rate are higher, and the ignition delay and combustion duration are further shortened owing to the jet effect produced by hydrogen combustion in the pre-chamber. Low NOx and NH3 emissions are observed in the TJI mode, particularly when the pre-chamber is fueled with hydrogen.

Effect of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and CeO&lt;sub&gt;2&lt;/sub&gt; Nano-Additives on Performance and Emission Characteristics of Diesel Engine Fueled with Neem Oil-Biodiesel

Due to the rapid depletion of petroleum reserves, many countries recommended the use of vegetable oils as diesel engine fuel. The best way to use edible and non-edible oil as a diesel fuel is to convert it into biodiesel. Biodiesel is a fuel which can be used instead of diesel fuel as an alternative for the existing system of CI engines. The usage of biodiesel causes a few disadvantages like high nitrogen oxides, utilization of high fuel and higher density. To conquer these problems some promising nano-additives are identified for having been used in the production of biodiesel. However, the addition of Nanoparticles will possibly enhance the performance and reduce the emissions. Therefore, the present investigation focuses on the influence of Al2O3 and CeO2 nano-additives on the performance and emissions characteristics of CI engine fueled with methyl esters of Neem. As nano-additives Al2O3 and CeO2 contain high oxygen content, it leads to complete combustion of fuel thereby increasing performance and reducing the oxide formation. In the experimentation, 50ppm, 100ppm of Al2O3 and CeO2 nano-additives were mixed in methyl esters of Neem. Subsequently, the fuel blends of Neem biodiesel (B20N) alone and Neem biodiesel with 50ppm, 100ppm of Al2O3 and CeO2 nano additives in CI engine were employed. The results revealed that, there is a increase in the break thermal efficiency and decrease in specific fuel consumption for B20N and B20N additive blends. Significant reductions in the parameters like CO, UBHC and NOx emissions are attained at B20N in conjunction with 50ppm, 100ppm of Al2O3 and CeO2 Nano-additives blends as compared with diesel. However, there is a slight increase in NOx emissions for B20N and and additive blends.

Hydrogen and dual fuel mode performing in engine with different combustion chamber shapes: Modelling and analysis using RSM-ANN technique

This study investigates the impacts of hydrogen (H2) induction along with injected liquid honne biodiesel (BHO)/uppage biodiesel (BUO) as secondary pilot fuel in diesel engine. The effects of compression ratio (CR), hydrogen fuel flow rate (HFR) and different combustion chamber shapes in dual fuel (DF) mode were investigated. In the first phase of experiments, the effects of three different CR (15.5, 16.5, and 17.5) on engine efficacy and emission were presented. In the second phase, the effects of three HFR (0.1, 0.17, and 0.24 kg/h) on engine efficacy and emission, as well as the maximum possible HFR were reported. In the last phase, performance with different combustion chambers i.e., Hemispherical Combustion Chamber (HCC), Toroidal Reentrant Combustion Chamber (TRCC), and Toroidal Combustion Chamber (TCC) at maximum possible CR and HFR was highlighted. The study revealed that for knock free operation of the DF engine, the highest probable HFR was 0.24 kg/h at a CR of 17.5, fuel IT of 27obefore top dead center (bTDC) and injector opening pressure (IOP) of 250 bar. The toroidal re-entrant combustion chamber (TRCC) shape yielded 8%–12% better brake thermal efficiency (BTE) with lower emissions but 20–29% higher oxides of nitrogen (NOx) at 80% load in DF mode as contrasted to the single CI mode. Both peak pressure (PP) and heat release rate (HRR) were 12–15% higher. Response surface methodology (RSM) was used to design the experiments and to carry the optimization process. Artificial Neural Network (ANN) was used to forecast the performance and emission behaviors of the test engine. The findings demonstrated that RSM and ANN were excellent modelling techniques with good accuracy. In addition, ANN's prediction performance (R2 = 0.975 for BTE) was somewhat better than RSM's (R2 = 0.974 for BTE). Both the techniques were found to be successful in terms of agreement with experimental findings with ratios varying from 95% to 98% respectively. The prediction of BTE and NOx was also carried using different machine learning algorithms. It can be seen that R2 value for these models were slightly lower than ANN and RSM models indicating good predicting capability of ANN modelling.

Increased diurnal difference of NO2 concentrations and its impact on recent ozone pollution in eastern China in summer

Nitrogen dioxide (NO2) is a key tropospheric O3 precursor. Since 2013, efforts to decrease air pollution in China have driven substantial declines in annual NO2 concentrations, whereas ozone (O3) concentrations have increased. Based on nationwide NO2 observations and a regional air quality model (WRF-CMAQ), we analyzed trends in the diurnal difference (DD, the difference between nighttime and daytime concentrations) of NO2 concentrations across eastern China and in five national urban agglomerations (UAs) from 2014 to 2021, and explored the factors underlying such changes and the potential impacts on O3 pollution. We found that the observed DD of NO2 has increased in most cities and UAs, and that this trend can be primarily attributed to changes in anthropogenic emissions, based on comparison with DDs simulated with fixed anthropogenic emissions, which generally showed much weaker trends and little interannual variation. A sensitivity analysis using the WRF-CMAQ model was conducted to investigate the impact of a modified diurnal cycle of nitrogen oxides (NOx) emissions on O3 concentrations. The result revealed that enhancing the DD of NO2 would increase O3 concentrations in the morning and the daily maximum 8-h O3 concentrations in the cities with high NOx concentrations, as well as downwind areas of cities, indicating that greater DDs in NO2 is one of the reasons that have led to the enhanced China's O3 pollution in recent years.

Polyol-Mediated Synthesis of V2O5-WO3/TiO2 Catalysts for Low-Temperature Selective Catalytic Reduction with Ammonia.

We demonstrated highly efficient selective catalytic reduction catalysts by adopting the polyol process, and the prepared catalysts exhibited a high nitrogen oxide (NOX) removal efficiency of 96% at 250 °C. The V2O5 and WO3 catalyst nanoparticles prepared using the polyol process were smaller (~10 nm) than those prepared using the impregnation method (~20 nm), and the small catalyst size enabled an increase in surface area and catalytic acid sites. The NOX removal efficiencies at temperatures between 200 and 250 °C were enhanced by approximately 30% compared to those of the catalysts prepared using the conventional impregnation method. The NH3-temperature-programmed desorption and H2-temperature-programmed reduction results confirmed that the polyol process produced more surface acid sites at low temperatures and enhanced the redox ability. The in situ Fourier-transform infrared spectra further elucidated the fast absorption of NH3 and its reduction with NO and O2 on the prepared catalyst surfaces. This study provides an effective approach to synthesizing efficient low-temperature SCR catalysts and may contribute to further studies related to other catalytic systems.

Effects of Nitrogen Oxides on the Production of Reactive Oxygen Species and Environmentally Persistent Free Radicals from α-Pinene and Naphthalene Secondary Organic Aerosols.

Reactive oxygen species (ROS) and environmentally persistent free radicals (EPFR) play an important role in chemical transformation of atmospheric aerosols and adverse aerosol health effects. This study investigated the effects of nitrogen oxides (NOx) during photooxidation of α-pinene and naphthalene on the EPFR content and ROS formation from secondary organic aerosols (SOA). Electron paramagnetic resonance (EPR) spectroscopy was applied to quantify EPFR content and ROS formation. While no EPFR were detected in α-pinene SOA, we found that naphthalene SOA contained about 0.7 pmol μg–1 of EPFR, and NOx has little influence on EPFR concentrations and oxidative potential. α-Pinene and naphthalene SOA generated under low NOx conditions form OH radicals and superoxide in the aqueous phase, which was lowered substantially by 50–80% for SOA generated under high NOx conditions. High-resolution mass spectrometry analysis showed the substantial formation of nitroaromatics and organic nitrates in a high NOx environment. The modeling results using the GECKO-A model that simulates explicit gas-phase chemistry and the radical 2D-VBS model that treats autoxidation predicted reduced formation of hydroperoxides and enhanced formation of organic nitrates under high NOx due to the reactions of peroxy radicals with NOx instead of their reactions with HO2. Consistently, the presence of NOx resulted in the decrease of peroxide contents and oxidative potential of α-pinene SOA.

Direct Ammonia Fuel Cells

Ammonia will be utilised as a key energy vector for storage and long-distance transport in the developing hydrogen economy. Direct ammonia fuel cells (DAFCs) have the potential to decrease the process complexity of current fuel cell technology and therefore increase overall efficiency and unit footprint where implemented. In this paper, current DAFC technologies are explored, such as solid oxide, alkaline and ammonia borane fuel cells. From this, it is shown that solid oxide fuel cells with oxygen conducting electrolyte (SOFC-O) have high experimental power outputs of 1100 mW cm–2 but have disadvantages of high nitrogen oxides (NOx) production, lower fuel utilisation and low efficiency. Alkaline and ammonia borane fuel cells are of lesser interest due to complex ammonia pretreatment, high NOx production and lower power outputs of 450 mW cm–2 and 110 mW cm–2, respectively. Solid oxide fuel cells with proton conducting electrolyte (SOFC-H) seem to have the most potential due to high theoretical power outputs, high efficiency, increased fuel utilisation and low NOx production. DAFC technology has yet to reach full commercialisation, but as the hydrogen economy develops the potential benefits of DAFCs in complexity and footprint reduction will drive further investment and development, particularly in the shipping sector.

Single-particle volatility and implications for brown carbon absorption in Beijing, China

Aerosol volatility has a substantial impact on gas-particle partitioning, aging process and hence brown carbon (BrC) absorption. Here we analyzed single-particle volatility in winter in Beijing using a thermodenuder coupled with a single particle aerosol mass spectrometer along with a suite of collocated measurements. Our results showed that elemental carbon, metals, organic nitrogen (ON) were the dominant low-volatility components. The ON-containing particles accounting for 50 % of the total low-volatility particles comprised mainly ON-organic carbon (ON-OC) particles which were associated with biomass burning and significantly enhanced during polluted periods with high relative humidity and nitrogen oxides (NOx) levels. By analyzing the relationship between single-particle volatility and BrC, we found that semi-volatile particles related to fossil fuel combustion contributed dominantly to the light absorption of BrC (~50 %). Comparatively, the low-volatility and semi-volatile particles related to biomass burning contributed 21–35 % and 10–15 %, respectively to the BrC light absorption. Our results demonstrated that single particles from different sources with different volatility showed different impacts on BrC absorption. Although low-volatility organic aerosol accounted only for ~16 % of the total ambient organics, they can contribute as much as ~30–40 % to BrC light absorption in winter in Beijing.

Experimental investigation on performance, combustion and emission characteristics of nanoparticle blends with diesel as fuel in a CI Engine

The present work has discussed the following characteristics like performance, combustion and emission characteristics of blends of aluminum (Al), zinc oxide (ZnO) and its mixture of nanoparticles at different ratios with diesel tested on a stationary direct injection compression ignition (CI) engine at five different loads. The fuels have been made by blending of nanoparticles with diesel at different concentrations. The results have shown that the Nano fuels have given lower brake specific fuel consumption (BSFC), higher brake thermal efficiency (BTE) and air-fuel ratio when compared with diesel. In combustion analysis, the Nano fuels have given higher heat release rate, crank angle 50 (CA50) and lower ignition delay when compared with diesel. In emission analysis, the Nano fuels have given higher nitrogen oxides (NOx) and lower carbon monoxide (CO), hydrocarbons (HC) and smoke emissions when compared with diesel. The fuel properties of nano fuels have shown that the kinematic viscosity, calorific values have been higher and flash point, fire point, density have been lower when compared with diesel.

Experimental mild conversion of a lean burn natural gas engine with SCR to a hydrogen engine: NOx and GWP potential for marine applications

Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

Understanding of combustion characteristics and NO generation process with pure ammonia in the pre-chamber jet-induced ignition system

As a favorable hydrogen carrier, ammonia (NH3) has great potential to achieve the goal of carbon neutrality in engines. However, it has several limits on the combustion in engines such as low laminar burning velocity (LBV), high ignition energy, and high nitrogen oxide (NOx) emission. It needs to employ an appropriate method for its utilization in internal combustion engines. The pre-chamber jet-induced ignition combustion mode which has been widely studied is an effective way to enhance the ignition and improve the combustion process of the mixture in the main chamber, especially under the lean-burn condition. To investigate the combustion effectiveness and NOx generation process of ammonia in this combustion mode, a three dimensions (3D) computational fluid dynamics (CFD) model coupled with a reduced ammonia reaction mechanism was established based on the constant volume combustion chamber (CVCC). The visualization experiments with jet-induced ignition combustion were conducted and used to validate the accuracy of the CFD model. The effect of equivalence ratio swept from 0.65 to 0.9 in the main-chamber was numerically studied in detail. The results indicated that the pre-chamber jet-induced ignition combustion mode can effectively improve the low flammability of ammonia and accelerate the combustion rate in the main chamber. The study of equivalence ratio sweeping demonstrated that a higher equivalence ratio leads to a higher combustion rate and lower NO and NO2 products, simultaneously. The increased equivalence ratio with more NH2 and NH radicals is beneficial for the NO reduction reaction and inhibits the oxidation reaction of NO → NO2. It reveals that a relatively high equivalence ratio in the lean-burn condition might be favorable for ammonia combustion.

Improved Nitrogen Oxide Removal from Simulated Flue Gas by Modified Peanut Shell Chars Through Acid Pickling and Nitrogen Doping

Peanut shell char with high alkali metal and ash content was used in this study to remove nitrogen oxide (NO) from simulated flue gases. Effects of acid pickling and nitrogen doping of the biochar (BC) materials on the removal selectivity were investigated in a fixed bed reactor. Results show that CaO, MgO, SiO2, AgO2, CuO, and so on contained in the ash of peanut shell are not conducive to the pore development of biochar and grafting of nitrogen-containing functional groups during the nitrogen doping process. Ash pickling improves the development of pore structure, and decreases the ratios of H/C, O/C, and (O+H)/C. The NO ratio and reaction selectivity of biochar follow the order as pickling treatment (BC-A) > raw peanut shell char (BC) > nitrogen doping treatment (BC-N). Through a combined effect of ash pickling and nitrogen doping, BC-A-N has the highest NO removal ratio and reaction selectivity because of the improved pore characteristics and introduction of nitrogen-containing functional groups.

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.