Reduction Of Nitrogen Oxide Emissions Research Articles

Decadal Variabilities in Tropospheric Nitrogen Oxides Over United States, Europe, and China

AbstractGlobal trends in tropospheric nitrogen dioxide (NO2) have changed dramatically in the past decade. Here, we investigate tropospheric NO2 variabilities over United States, Europe, and E. China in 2005–2018 to explore the mechanisms governing the variation of this critical pollutant. We found large uncertainties in the trends of anthropogenic nitrogen oxides (NOx) emissions, for example, the reductions of NOx emissions, derived with different approaches and data sets, are in the range of 35%–50% over the United States and 15%–45% over Europe in 2005–2018. By contrast, the analysis in this work indicates declines of anthropogenic NOx emissions by about 40% and 25% over the United States and Europe, respectively, in 2005–2018, and about 20% over E. China in 2012–2018. However, the shift of major NOx sources from power generation to industrial and transportation sectors has led to noticeable diminishing effects in emission controls. Furthermore, satellite measurements exhibit the influence of NO2 background levels over the United States and Europe, which offset the impacts of anthropogenic emission declines, resulting in flatter trends of tropospheric NO2 over the United States and Europe. Our analysis further reveals underestimation of background NO2 by chemical transport models, which can lead to inaccurate interpretations of satellite measurements. We use surface in‐situ NO2 observations to diagnose the satellite‐observed NO2 trends and find top‐down NOx emissions over urban grids represent the changes in anthropogenic NOx emissions better. This work highlights the importance of comprehensive applications of different analysis approaches to better characterizing atmospheric composition evolution.

Tropospheric ozone changes and ozone sensitivity from the present day to the future under shared socio-economic pathways

Abstract. Tropospheric ozone is important to future air quality and climate. We investigate ozone changes and ozone sensitivity to changing emissions in the context of climate change from the present day (2004–2014) to the future (2045–2055) under a range of shared socio-economic pathways (SSPs). We apply the United Kingdom Earth System Model, UKESM1, with an extended chemistry scheme including more reactive volatile organic compounds (VOCs) to quantify ozone burdens as well as ozone sensitivities globally and regionally based on nitrogen oxide (NOx) and VOC mixing ratios. We show that the tropospheric ozone burden increases by 4 % under a development pathway with higher NOx and VOC emissions (SSP3-7.0) but decreases by 7 % under the same pathway if NOx and VOC emissions are reduced (SSP3-7.0-lowNTCF) and by 5 % if atmospheric methane (CH4) mixing ratios are reduced (SSP3-7.0-lowCH4). Global mean surface ozone mixing ratios are reduced by 3–5 ppb under SSP3-7.0-lowNTCF and by 2–3 ppb under SSP3-7.0-lowCH4. However, surface ozone changes vary substantially by season in high-emission regions under future pathways, with decreased ozone mixing ratios in summer and increased ozone mixing ratios in winter when NOx emissions are reduced. VOC-limited areas are more extensive in winter (7 %) than in summer (3 %) across the globe. North America, Europe, and East Asia are the dominant VOC-limited regions in the present day, but North America and Europe become more NOx-limited in the future mainly due to reductions in NOx emissions. The impacts of VOC emissions on ozone sensitivity are limited in North America and Europe because reduced anthropogenic VOC emissions are partly offset by higher biogenic VOC emissions. Ozone sensitivity is not greatly influenced by changing CH4 mixing ratios. South Asia becomes the dominant VOC-limited region under future pathways. We highlight that reductions in NOx emissions are required to transform ozone production from VOC to NOx limitation, but that these lead to increased ozone mixing ratios in high-emission regions, and hence emission controls on VOC and CH4 are also necessary.

Modeling the decomposition of urea-water-solution in films and droplets under SCR conditions with chemistry in the liquid phase

Due to strict environmental regulations in the automotive sector selective catalytic reduction with urea-water-solution is often used to reduce nitrogen oxide emissions. To improve and solve technical problems, like the formation of solid residuals, detailed simulations of the exhaust gas system are used. Such simulations have high computational needs due to the multitude of different processes involved at strongly differing spatial and time scales. For this reason, simplified or reduced models are applied and urea decomposition is often modeled with a vapor pressure curve fitted to experimental results. This method is incapable of describing the formation of solid residuals. A recently developed chemical mechanism for urea decomposition in the liquid phase is used in this work to simulate the decomposition of spherical droplets and planar wall films of urea-water-solution in exhaust gas. For droplets, the overall behavior with liquid chemistry is similar for the whole range of ambient temperatures. Less ammonia and nearly no isocyanic acid is produced compared to the evaporation model and residuals of liquid biuret and solid triuret remain. For wall films, the behavior as well as the composition of the residuals strongly depends on the temperature. The mechanism predicts the production of a similar amount of ammonia but less isocyanic acid compared to the evaporation model. The remaining mass loss is mostly composed of cyanuric acid. It is found that the process of urea decomposition is much slower with liquid chemistry and complete decomposition only happens at 673 K or above. The analysis of the chemical time scales results in a skeletal mechanism for the droplet decomposition with 6 out of 13 reactions among 7 out of 13 species that can describe the whole process with good accuracy, where the mass of the produced gases deviates by less than 5%.

Investigating the role of fuel injection pressure and piston bowl geometries to enhance performance and emission characteristics of hydrogen-enriched diesel/1-pentanol fueled in CRDI diesel engine.

This paper deals with the effects of piston bowl geometry (hemispherical bowl, troded bowl, and re-entrant bowl) and fuel injection pressure (200bar, 220bar, and 240bar) with hydrogen-diesel/1-pentanol (B20 (80% diesel and 20% pentanol) + 12 lpm of hydrogen) on the emission, combustion, and performance characteristics of a common rail direct injection diesel engine. Re-entrant bowl outperforms hemispherical and troded bowl in terms of brake thermal efficiency (5.67%) and hydrocarbon (8% reduction) with an increase in the fuel injection pressure (240bar) at part and full load. However, with the increase in the fuel injection pressure in the re-entrant bowl, a slight reduction in nitrogen oxide emissions (2%) is observed. With an increase in injection pressure in the case of re-entrant bowls, NHRR (net heat release rate), peak pressure (in-cylinder), and ROPR (rate of pressure rises) all rise significantly by 3.4%, 4.2%, and 2.3%. It is found that changing the piston shape and fuel injection pressure simultaneously is a potential alternative for improving engine performance and lowering emissions.

Electrothermal alloy embedded V2O5-WO3/TiO2 catalyst for NH3-SCR with promising wide operating temperature window

Vanadia-based catalysts are widely used in selective catalytic reduction (SCR) reaction for reducing nitrogen oxides emissions, however, they only exhibit sufficient DeNOx efficiency within a narrow temperature window. In this study, a catalyst embedded with electrothermal alloy was prepared. The catalyst surface temperature could be heated using the electrothermal alloy, in order to widen the operating temperature window of the V2O5-WO3/TiO2 catalyst. Experimental results revealed that the electrothermal alloy embedded V2O5-WO3/TiO2 catalyst can maintain superior NH3-SCR performance and high resistance to H2O in a wide gas temperature range of 100–400 °C by controlling the surface temperature. In the meantime, the NH4HSO4 poisoned catalyst could be efficiently regenerated through electric heating, and NOx conversion can be restored to the level of fresh samples. Additionally, the effect of additives including methylcellulose and glass fiber, on the physicochemical properties of the plate-type catalyst was also investigated, and the catalyst samples were characterized by means of BET, XRD, NH3-TPD, H2-TPR, TG and SEM-EDS. This study proves the electric heating strategy is a promising way to enhance the performance of the V2O5-WO3/TiO2 during wide temperature SCR applications.

Experimental Analysis of the Influence of Exhaust Thermal Management on Engine NOx Emission

Exhaust thermal management is essential to allow engines to meet the Euro VI emissions standards and reducing nitrogen oxide emissions is one of the most important targets being pursued nowadays. Along these lines, in the present study, engine’s thermal performances have been evaluated on the basis of a WHTC test, namely a transient engine dynamometer schedule defined by the global technical regulation (GTR) developed by the UN ECE GRPE group (the GTR is covering a world-wide harmonized heavy-duty certification (WHDC) procedure for engine exhaust emissions). The influence of thermal management on fuel consumption, intake, and tailpipe NOx have been quantitatively analyzed for the overrun state. The results have shown that there can be a strong influence on the after-treatment temperatures and tailpipe NOx. In particular, the average temperature upstream of the diesel oxidation catalyst (DOC) has been found to increase from 245°C to 254°C, the average temperature of the selective catalytic reduction (SCR) to increase from 248°C to 253°C, the SCR’s minimum temperature to increase from 196°C to 204°C, and the peak value of the NOx emissions in the low-temperature region to decrease from 73 to 51 mg/s. However, the influence of the overrun state’s thermal management strategy on the fuel consumption, the air intake, the ammonia storage, the NO2/NOx ratio, and the urea consumption has been observed to be relatively limited.

Effects of air supply optimization on NOx reduction in a structurally modified municipal solid waste incinerator

The reduction of NOx (nitrogen oxides) emission remains the key challenge in the incineration of MSW (municipal solid waste). The flame position, gas temperature and heat load distribution can be optimized by adopting suitable air supply methods, and the NOx generation as well as the NOx emission will be reduced. In this study, numerical models of a 350 t/d MSW incinerator were established to study the effects of different air supply methods (such as different ratios of primary air and secondary air, ratios of secondary air guns, supply methods of over-fired air). Results indicated the combustion state and flowing characteristics were effectively improved, which suppressed the initial generation of NOx and promoted the NOx removal efficiency of SNCR process. Reducing the ratio of primary air could significantly avoid the NOx generation, the initial production of NOx decreased by 8.39% when the ratio of primary air was reduced to 65%. With the arrangement of over-fired air, temperature distribution was more evenly, and significant promotion effects on SNCR (selective non-catalytic reduction denitrification) process were obtained. The maximum SNCR efficiency reached 62.81% with NOx emission at outlet was less than 100 mg/Nm3, which was 23.95% higher than before.

Experimental Approach for Reducing Nitrogen Oxides Emissions from Ammonia–Natural Gas Dual-Fuel Spark-Ignition Engine

Experimental Approach for Reducing Nitrogen Oxides Emissions from Ammonia–Natural Gas Dual-Fuel Spark-Ignition Engine

Influence of the fin to baffle distance on temperature, stress distribution and fatigue life of a cooled Exhaust Gas Recirculation system

Environmental concerns and the decline of Earth's natural resources are among the most prominent issues in today's society, leading to stringent policies regarding commercial vehicle emission products, such as nitrogen oxides (NOx) and carbon dioxide (CO2) emission levels. Aiming to reduce their environmental footprint, car manufacturers have chosen to integrate the Exhaust Gas recirculation (EGR) cooler technology into their vehicles decades ago, as this is a resourceful and effective technique for reducing NOx emissions. This technique is still applied in hybrid cars and is foreseen to be used in future moved vehicles, proving its contemporaneity, adequacy, and relevancy. Nevertheless, this technology requires that different factors be considered during the design phase, such as high gas temperatures, mechanical vibrations, and other loads, as these may affect overall performance and durability. Therefore, this study aims to assess the impact of varying the inner fińs length on the applied loads and how it may affect the EGR Cooler efficiency. To this end, Computer-Aided Engineering (CAE) tools using numerical methods, such as Finite Element Method (FEM) and Finite Volume Method (FVM), were applied. This investigation revealed that varying the inner fi length affects each of the applied loads differently, and increasing the length was shown to improve the heat transfer process of the EGR; however, it also increases the thermally induced stresses at the hottest region, diminishing the fatigue resistance of the component. The advantages and disadvantages of several configurations understudy were addressed in the work carried out.

Combined Effect of a Catalytic Reduction Device with Waste Frying Oil-Based Biodiesel on NOx Emissions of Diesel Engines

Internal combustion engines with application in automobiles and other relevant industries constitute significant environmental pollution via the release of toxic exhaust gasses like carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), and nitrogen oxide (NOx). Engine researchers and manufacturers are challenged to develop external and internal measures to ensure environmentally friendly solutions to accommodate and conform to the growing list of emission standards. Therefore, this work presents an experimental investigation of the NOx emission profile of a diesel engine that is fuelled and fitted with waste frying oil-based biodiesel and catalytic converter. Using a single-cylinder, four-stroke air-cooled CI engine at a constant speed of 1900 rpm and different loadings of 25%, 50%, 75%, and 100%; fitted with a catalytic converter at the exhaust outlet of the engine and linked to a dynamometer and a gas analyser, an experiment was conducted at biodiesel/diesel volume blends of B0 (0/10), B5 (5/95), B20 (20/80), B30 (30/70), B70 (70/30), B100 (100/0); and 30% concentration (v/v), 0.5 litre/hr flow rate of aqueous urea from the catalytic converter. The results show an increasing NOx emission as the biodiesel component increased in the blend. The catalytic converter showed a downward NOx reduction with a significant 68% reduction in efficiency at high exhaust gas temperatures. It is concluded that the combined utilisation of waste frying oil-based biodiesel and the catalytic converter yields substantial NOx emission reduction.

CFD Evaluation of Heat Transfer and NOx Emissions When Converting a Tangentially Fired Coal Boiler to Use Methane

The need to reduce global carbon dioxide (CO2) emissions is driving the conversion of coal-fired power plants to use methane, which can reduce CO2 emissions by >40%. However, conducting gas firing in coal boilers changes the heat transfer profile; therefore, preliminary evaluations using computational fluid dynamics are required prior to conversion. Here, methane was used as a heat input source in the simulation of an existing coal boiler, and combustion, nitrogen oxides (NOx) emission characteristics, and heat transfer profile changes inside the boiler were analyzed. Furthermore, changes in the burner zone stoichiometric ratio (BZSR) were simulated to restore the decreased heat absorption of the furnace waterwall, revealing that air distribution could change the heat absorption of the waterwall and tube bundles. However, this change was smaller than that caused by conversion from coal to methane. Therefore, to implement gas firing in coal boilers, alternatives such as output derating, using an attemperator, or modifying heat transfer surfaces are necessary. Despite these limitations, a 70% reduction in NOx emissions was achieved at a BZSR of 0.76, compared with coal. As the BZSR contributes significantly to NOx emissions, conducting gas firing in existing coal boilers could significantly reduce NOx and CO2 emissions.

Combined effects of various strategies to curtail exhaust emissions in a biomass waste fueled CI engine coupled with SCR system

This study is an exhaustive investigation on engine performance and combustion features of a conventional diesel engine charged with biodiesel produced from biomass waste. Grapeseed oil methyl ester resulted in poor thermal efficiency with enormous quantity of harmful emissions. As an effort to reduce the engine pollutants, Grapeseed oil methyl ester was doped with zinc oxide nano particles, engine cylinder shape modification and exhaust gas recirculation method was used. Hydrocarbons, carbon monoxide and smoke emissions reduced considerably, whereas reduction in nitrogen oxide emissions was low. Selective catalytic reduction technique at optimized mass flow rate of aqueous urea solution minimized the nitrogen oxide emissions by 76.9% compared to grapeseed oil methyl ester without compromise in brake thermal efficiency.

Experimental analysis of C.I. engine using pyrolyzed plastic oil blended with alumina nano additive

The aim of the research work is to study the efficiency of Al2O3 nanoparticle as a blending agent and to test the performance characteristics of pyrolyzed plastic oil in an IC engine at EGR conditions. Al2O3 nanoparticle was synthesized, and discarded plastic was pyrolyzed to prepare plastic oil. Different blends of plastic pyrolyzed oil (P10 to P40) blended using the synthesized nano Al2O3 with commercial diesel were employed in the study. Various factors like Brake Thermal Efficiency (BTE), Brake Mean Effective Pressure (BMEP), Indicated Thermal Efficiency, Mechanical Efficiency, emissions of Carbon Monoxide (CO), Carbon-di-oxide (CO2) and Nitrogen Oxide (NOx) are analyzed and reported herein. A notable reduction in emission was observed with the application of nano additive blended fuel. The results confirmed that the emission of CO was reduced using the P40 blend with 50 ppm of nano additive. In the P30 + EGR blend, a drastic reduction in NOx emission was also observed with the same amount of Al2O3 nano additive. CO2 has been cut down when P30 blend with 50 ppm of Al2O3. The remarkable calorific value, density and viscosity of P30 blend had resulted in highest Brake thermal efficiency (32.11%) and Brake Mean Effective Pressure (6.3 Bar). The P30 + EGR blend resulted in high indicated thermal efficiency in comparison with other blends because of the reduced heat loss in the blend. Diesel showed the highest Mechanical efficiency because of the high ignition delay when compared with the other blends.

Analysis of the NOx storage behaviour during cold start of modern SCR flow-through substrates and SCR on-filter substrates

AbstractSelective catalytic reduction (SCR) systems are the state-of-the-art technology to reduce nitrogen oxide emissions (NOx) of modern diesel engines. The system behaviour is well understood in the common temperature working area. However, the system properties below light-off temperature are less well known and offer a wide scope for further investigations. Vehicle measurements show that under specific conditions during cold start, NOx can be partially stored and converted on on-filter and flow-through SCR catalysts. The purpose of this work was in a first step to analyse the main influence parameters on the NOx storage behaviour. Therefore, synthetic gas test bench measurements have been carried out, varying the gas concentrations, temperature, and gas hourly space velocity (GHSV). These investigations showed that the NOx storage effect strongly depends on the NH3 level stored in the catalyst, GHSV, the adsorbed water (H2O) on the catalyst, and the temperature of the catalyst. Further influence parameters such as the gas composition with focus on carbon monoxide (CO), short-chain hydrocarbons and long-chain hydrocarbons have been analysed on a synthetic gas test bench. Depending on operating conditions, a significant amount of NOx can be stored on a dry catalyst during the cold start phase. The water vapor from the combustion condenses on the cold exhaust pipe during the first seconds, or up to a few minutes after a cold start. As the water vapor reaches the surface of the catalyst, it condenses and adsorbs onto it, leading to a sudden temperature rise. This exothermal reaction causes the stored NOx to be desorbed, and furthermore it is partially reduced by the NH3 stored in the catalyst.

Effect of SCR downsizing and ammonia slip catalyst coating on the emissions from a heavy-duty diesel engine

The combination of diesel oxidation catalyst (DOC), catalyzed diesel particulate filter (CDPF) and selective catalytic reduction (SCR) is the most effective way to reduce particulate emission and nitrogen oxide (NOx) from diesel engines. In this study, the effects of a DOC+CDPF+SCR system on the emissions including carbon monoxide (CO) total hydrocarbon (THC), NOx, particle number (PN) and particle mass (PM) from a heavy-duty diesel engine were evaluated. In addition, the influences of ammonia (NH3) slip catalyst (ASC) coating and SCR catalyst downsizing on the NOx conversion efficiency, nitrous oxide (N2O) emissions and NH3 slip were also investigated. Results showed that the installation of the after-treatment system had negligible effect on the power and BSFC of the engine. The upstream DOC reduced by an average of 97.0% of the CO and 67.5% of the THC, in combination with CDPF, the CO and THC emission further decreased with an average drop of 97.8% and 72.5%, respectively. In terms of particulate emissions, the single DOC reduced 48.0% of the PN and 50.9% of the PM, and the combination of DOC and CDPF led to a reduction of 98.0% in the PN and 96.9% in the PM on average. The SCR was effective in reducing NOx emission, but resulted in higher N2O emission by more than 3 times, meanwhile led to an average NH3 slip of 3.80 ppm. Downsizing the SCR length by 1/3 could still ensure a 91.9% conversion efficiency of NOx, and produced less N2O, but led to an increase of the NH3 slip by 2 times, reaching 7.63 ppm on average. By coating Pt-based ASC catalyst on the back end of the SCR could eliminate the NH3 slip. Considering the cost and performance, the combination of DOC, CDPF and a downsized SCR with ASC coating may be a better choice.

Prediction of Transient NOx Emission from Diesel Vehicles Based on Deep-Learning Differentiation Model with Double Noise Reduction

For diesel engines, accurate prediction of NOx (Nitrogen Oxides) emission plays an essential role in virtual NOx sensor development and engine design under situations of actual road driving. However, due to the randomness and uncertainty in the driving process of diesel vehicles, it is difficult to make predictions about NOx emissions. In order to solve this problem, this paper proposes differential models for noise reductions of NOx emissions in time series. First, according to the internal fluctuation of time series, use SSA (Singular Spectrum Analysis) to reduce the noises of the original time series; second, use ICEEMDAN (Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise) to decompose the noise-reducing data into several relatively stable subsequences; third, use the sample entropy to calculate the complexity of each subsequence, and divide the sequences into high-frequency ones and low-frequency ones; finally, use GRU (Gated Recurrent Unit) to complete the prediction of high-frequency sequences and SVR (Support Vector Regression) for the prediction of low-frequency sequences. To obtain the final models, integrate the prediction results of the subsequences. Make comparisons with five single models, SSA single-processing models, and ICEEMDAN single-processing models. The experimental results show that the proposed model can predict the instantaneous NOx emissions of diesel engines better than the single model and the model processed by SSA, and the differentiated model can effectively improve the execution speed of the model.

Optimization of hydrogen‐enriched diesel/n‐Amyl alcohol‐fueled engine to meet emission standards through varying nozzle opening pressure and static injection timing

AbstractImportant injection parameters such as fuel injection timing (FIT) and fuel injection pressure (FIP) on different piston bowl geometries substantially impact the performance, emissions, and combustion characteristics of a common rail direct injection engine. The aim of this study deals with the effects of piston bowl geometry (hemispherical bowl [HSB], troded bowl [TRB], and re‐entrant bowl [REB]), FIP (200, 220, and 240 bar), and variable FIT (20, 24, and 28°bTDC) with hydrogen‐diesel/1‐pentanol (B20) (80% diesel and 20% pentanol) with a constant flow rate of hydrogen at 12 Lpm. Furthermore, to decrease emission standards and energy consumption, biodiesel and hydrogen are the ideal substitutes for conventional fuels. REB outperforms HSB and TRB in terms of brake thermal efficiency (5.67%) and hydrocarbon (8% reduction), increasing the FIP at full load (240 bar). However, with the increase in the FIP in the REB, a slight reduction in nitrogen oxide (NOx) emissions (2%) is observed. With an increase in FIP in the case of REB, net heat release rate, peak pressure (in‐cylinder), and rate of pressure rise all rise significantly by 3.4%, 4.2%, and 2.3%. NOx emissions are marginally enhanced with higher FIP and advanced FIT. It is found that changing the piston shape and FIP simultaneously is a potential alternative for improving engine performance and lowering emissions.

Integrated effects of SCR, velocity, and Air-fuel Ratio on gaseous pollutants and CO2 emissions from China V and VI heavy-duty diesel vehicles

Vehicle exhaust, an important source of air pollution, is affected by many factors, including driving conditions, combustion efficiencies, and the usage of emission control devices. In this study, the Portable Emission Measurement System (PEMS) was used to test the emissions from China V and China VI heavy-duty diesel vehicles to evaluate the integrated effects of Selective Catalytic Reduction (SCR), velocity, and air-fuel ratio on carbon dioxide (CO2) and nitrogen oxide (NOx) emissions. Our results reveal that the average distance-based CO2 and CO emission factors at high velocities (50–90 km/h) are 25% and 61% lower than those at low velocities (less than 50 km/h). The use of SCR increases CO2 emissions in the range of 70–90 km/h (an average increase of 10.9%). In addition, SCR leads to a 55% NOx emission reduction at low velocities and 89% at high velocities, with an overall average reduction of 84%. We also find that SCR leads to a significant reduction in the correlation between NOx emissions and air-fuel ratio (0.76 vs 0.47 for China V truck; 0.72 vs 0.05 for China VI truck), but it does not cause a drastic reduction in the correlation coefficients between CO2 emissions and air-fuel ratio, which can be used to detect whether SCR is working effectively.

Evaluation of NOx Reduction Effect and Impact on Asphalt Pavement of Surface Treatment Technology including TiO2 and Asphalt Rejuvenator

Nitrogen oxide (NOx), emitted at the highest rate among automobile exhaust gases, is the main cause of air pollution, and various construction technologies are being developed to reduce NOx emissions. In this study, the NOx reduction effect of surface treatment technology for road pavements, and the effect of the photocatalytic reaction on asphalt pavements, were evaluated using a photocatalyst. Three types of titanium dioxide (TiO2) were used as photocatalysts, and an asphalt rejuvenator used to recover aged asphalt was applied as a surface treatment agent. To evaluate the NOx reduction effect, a test device capable of testing large-sized specimens was manufactured and compared with the ISO method, which only allowed the testing of small specimens. In addition, the effect of TiO2 and the asphalt rejuvenator on the asphalt mixture was analyzed through chemical analysis. The test results of the newly manufactured mixed-tank photo reactor showed the same trend as the ISO test results concerning the evaluation of its NOx removal performance. As a result of the performance evaluation of the surface treatment using TiO2, the NO removal rate was up to 7.83% when Anatase-type TiO2 with excellent light efficiency was applied. In addition, when the rejuvenator was used, the oxidation of asphalt, caused by the photoreaction of TiO2, was reduced.

Effects of ammonia energy fraction and diesel injection timing on combustion and emissions of an ammonia/diesel dual-fuel engine

Ammonia has been receiving increasing interest as a hydrogen carrier and carbon-free fuel to tackle the issue of greenhouse gas (GHG) emissions from transportation. In this study, an ammonia/diesel dual-fuel (ADDF) engine is experimentally and numerically investigated, with focus on its feasibility to reduce GHG emissions while achieving a diesel-like efficiency. A single-cylinder, heavy-duty diesel engine is used to investigate the effect of ammonia energy fraction and start of diesel injection (SODI) timing on the combustion performance and emissions of the ADDF engine. Results revealed that due to the low flame speed of ammonia, increasing the ammonia energy fraction decreased the thermal efficiency of the ADDF combustion mode compared to the diesel-only combustion mode. Increasing ammonia energy fraction from 0 to 40% reduced the nitrogen oxides (NOx) emissions by 58.8% at a given SODI due to the effect of the thermal DeNOx process. However, increasing the ammonia energy fraction at a given SODI increased the nitrous oxide (N2O) emissions, which offsets the benefit of lower intrinsic carbon dioxide (CO2) emissions of ADDF combustion and resulted in a higher GHG emission compared to diesel-only combustion. Advancing SODI helped reduce the N2O and overall GHG emissions while achieving a diesel-like thermal efficiency in ADDF combustion mode. The lowest GHG emissions of ADDF combustion achieved by advancing the SODI were 12% lower compared to those of diesel-only combustion. The thermal efficiency of ADDF combustion mode at the optimum point of GHG emissions (i.e., ITE = 37.85%) was slightly lower than that of the diesel-only combustion mode (i.e., ITE = 38.53%). This, however, comes with a benefit of 10% and 20% reduction in NOx and CO emissions, respectively. The unburned ammonia concentration is high (i.e., about 4445 ppm) in the exhaust flow. The reduction of ammonia emissions in the exhaust flow should be further investigated in the future.