Decrease In NOx Emissions Research Articles

Investigation of high percentage of dimethyl ether on biodiesel usage in a diesel engine

Demand for cleaner energy sources both as additive and alternative fuels that can substitute or contribute to the usage of conventional fuels is growing. Researchers have mainly focused on improving or finding a renewable fuel from vegetable oil or addition of chemicals and alcohols for IC engine. This study analyzed the effects of a high percentage of dimethyl ether (DME) combined with biodiesel in a diesel engine. Transesterification method was selected for conversion of pure safflower oil to biodiesel. DME was blended with biodiesel at concentrations of 50% and 25% on a volume basis, respectively. Engine performance and emissions tests demonstrated that the thermal efficiency values were increased at high load operation when the engine was fueled with high percentage of DME. Furthermore, compared to conventional diesel, there has been a notable decrease in NOx emissions. Nevertheless, the introduction of DME blend had negligible effects on CO2 emissions. However, when using a high ratio of DME blend, HC emissions were found to increase, whereas a low ratio of DME blend resulted in decreased HC emissions. Apart from these, some irregularities were observed both on heat release rate and cylinder pressure especially for 50% of DME usage. Finally, the values for both brake-specific fuel consumption and mass fuel of DME-blended fuels were deteriorated.

Vehicle emission models alone are not sufficient to understand full impact of change in traffic signal timings

Few studies have considered the real-world impact of changes in traffic signal timings on air pollution and pedestrian exposure with most only drawing their conclusion from vehicle emission models alone. Here, we consider two distinct cycle timings at a junction in London, UK, model the impact using a traffic microsimulation and a NOx emissions model, and compare these results with NOx and other air pollution measurements collected during a two-week field study at the junction.Our models predict that extending the cycle time leads to a 23% decrease in NOx emissions within a 15 m radius of the junction itself. When the wind direction was such that our sensors were downwind of the junction a 21% decrease in traffic and background-adjusted NOx concentrations were seen, suggesting that the intervention was successful. However, when the sensors were upwind of the junction, we observed an increase of 23% in adjusted NOx concentrations. Similar patterns were found for the other pollutants NO2, lung deposited surface area, black carbon and CO2 we measured. This indicates that meteorology was by far the greatest determinant of roadside concentrations during our two-week study period.Looking at pedestrian exposure for pedestrians waiting to cross the road, we found that their NOx exposure increased by 46% as waiting times to cross the road increased and that potential small reductions in air pollution were offset by increases in waiting times on the main road.The study demonstrates the need to go beyond assessing the impact of hyper-local traffic interventions on vehicle emissions. Real-world trials over extended periods are required to evaluate the impact of meteorology and changes to air pollution concentrations and pedestrian exposures.

Enhancing diesel engine performance and emissions control with reduced Graphene oxide and Non-Edible biodiesel blends

The growing concern about environmental degradation and the depletion of fossil fuel supplies has prompted experts to investigate alternate and sustainable transportation energy sources. In these circumstances, biodiesel made from renewable feedstock has emerged as a viable environmentally friendly alternative to conventional diesel. This study thoroughly examines the performance and emission characteristics of a 4-stroke diesel engine running on biodiesel blends, including reduced graphene oxide (rGO) nanomaterial. The non-edible biodiesel from the Jatropha curcas plant is utilized, and it is blended in various ratios with conventional diesel, ethanol, and nanomaterial rGO to improve performance and emissions parameters. Torque increased by up to 17 % in rGO DJE02GO25 at 3500 rpm, while Brake Power decreased by 6.3 % in rGO DJE01GO25 at 2600 rpm. Brake Thermal Efficiency decreased by 12.5 % in rGO Blend 1 at 2600 rpm, and Brake-specific fuel consumption decreased by 16.5 % in rGO DJE02GO25 at 3500 rpm. CO2 emissions decreased up to 19.71 % in rGO Blend 10 at 2600 rpm. HC emissions decreased to 94 % in rGO blend 8 at 3500 rpm. Finally, NOx emissions decreased up to 84.78 % in rGO Blend 1 at 2900 rpm. The current study reveals that after adding rGO nanomaterial in biodiesel, there is a significant decrease in NOx and HC emissions.

The effects of water injection inside an internal combustion engine regarding NOx emissions

Abstract In this paper we present the influence of water injection on NOx emissions and the performance of a gasoline engine subjected under light to medium loads. The test bench used for measurements has a 4-cylinder, 1.6-liter engine and operates with a wasted spark configuration. Water is injected upstream of the throttle valve through a single injector mounted in the intake runner. The injection timing and amount of water injected inside the engine have been controlled by NI CompactRIO hardware device by the aid of an in-house algorithm implemented in LabView. Water is injected twice at each rotation of the crankshaft in order to have water in all cylinders. The injection of water is done at a fix angle, one time at 0°CA and the other at 360°CA, only the amount is varied from 10% to 45% of the total fuel fraction injected. The results showed that at an amount of water of about 25% of the total fraction of fuel injected, it produced a considerable decrease in NOx emissions, while keeping engine performance unchanged.

Using observed urban NOx sinks to constrain VOC reactivity and the ozone and radical budget in the Seoul Metropolitan Area

Abstract. Ozone (O3) is an important secondary pollutant that impacts air quality and human health. Eastern Asia has high regional O3 background due to the numerous sources and increasing and rapid industrial growth, which also impacts the Seoul Metropolitan Area (SMA). However, the SMA has also been experiencing increasing O3 driven by decreasing NOx emissions, highlighting the role of the local in situ O3 production on the SMA. Here, comprehensive gas-phase measurements collected on the NASA DC-8 during the National Institute of Environmental Research (NIER)/NASA Korea–United States Air Quality (KORUS-AQ) study are used to constrain the instantaneous O3 production rate over the SMA. The observed NOx oxidized products support the importance of non-measured peroxy nitrates (PNs) in the O3 chemistry in the SMA, as they accounted for ∼49 % of the total PNs. Using the total measured PNs (ΣPNs) and alkyl and multifunctional nitrates (ΣANs), unmeasured volatile organic compound (VOC) reactivity (R(VOC)) is constrained and found to range from 1.4–2.1 s−1. Combining the observationally constrained R(VOC) with the other measurements on the DC-8, the instantaneous net O3 production rate, which is as high as ∼10 ppbv h−1, along with the important sinks of O3 and radical chemistry, is constrained. This analysis shows that ΣPNs play an important role in both the sinks of O3 and radical chemistry. Since ΣPNs are assumed to be in a steady state, the results here highlight the role that ΣPNs play in urban environments in altering the net O3 production, but ΣPNs can potentially lead to increased net O3 production downwind due to their short lifetime (∼1 h). The results provide guidance for future measurements to identify the missing R(VOCs) and ΣPN production.

Spatiotemporal Distributions and Variations in Summertime Ozone Photochemical Production Regimes over Shanxi

Satellite-based formaldehyde（HCHO）columns and tropospheric nitrogen dioxide columns were observed using the Ozone Monitoring Instrument（OMI），and groundbased observations of ozone（O3）for May-August from 2013 to 2022 were connected to calculate the threshold values of the HCHO to NO2 ratio（FNR）in Shanxi Province. Then，the spatiotemporal distributions and variations in summertime ozone photochemical production regimes were analyzed. The results showed that：① The volatile organic compound（VOC） -sensitive regime area（FNR < 2.3）was obviously reduced，while the VOCs-NOx transitional regime（FNR between 2.3-4.1）area increased in the early years and then decreased， and NO x -sensitive regime area expanded significantly in summer from 2013 to 2022 over Shanxi Province. ② The increased summertime FNR during 2013 to 2019 was associated with the co-effect of increased HCHO columns and decreased tropospheric NO2 columns. The Shanxi Province was generally under an NOx regime since 2016，which reflected the remarkable effect of NO x emission reductions；however，there was a shift from a VOC-sensitive regime to a VOCs-NOx transitional regime，in which O3 pollution aggravation was widespread under the background of decreased NOx emissions. The decrease in O3 concentration during 2020 to 2022 followed the synergistical declines in HCHO columns and tropospheric NO2 columns. ③ The O3 weekend effects were reversed in Linfen and Yuncheng but were persistent in the other nine cities. Satellite-based weekend HCHO and NO2 levels were higher than those on weekdays in some cities of Shanxi Province，indicating that the O3 weekend effect was not only dependent on the changes of precursors emissions but was also closely related to O3 photochemical production sensitivity. The results indicated the necessity of simultaneous controls in NOx emissions and VOCs emissions for ozone abatement plans over Shanxi Province. In addition，Taiyuan，Yangquan，Yuncheng，and Jincheng should continue to promote reduction in NOx emissions.

Ammonia energy fraction effect on the combustion and reduced NOX emission of ammonia/diesel dual fuel

With stringent regulations of internal combustion engine on reducing CO2 emission, ammonia has been used as an alternative fuel. Investigating how engine-related performance is affected by partial ammonia replacement of diesel fuel is essential for understanding the combustion. Therefore, in this study, a three-dimensional numerical simulation model is developed for the burning of two fuels of diesel and ammonia based on relevant parameters (i.e., compression ratio, load, ammonia energy fraction, etc.) in a lab-made diesel engine. The consequences of load and compression proportion on combustion and pollutant emissions are investigated for ammonia energy fractions between 50% and 90%. When the ammonia portion rises, the increased ammonia equivalent ratio causes ammonia to move away from the dilute combustion boundary and accelerates the combustion rate of ammonia. An increase in compression ratio significantly increases the specified thermal performance and combustion efficacy. When the compression ratio is 16, as the ammonia energy fractions increases, due to the increase in the proportion of ammonia, that is, the proportion of nitrogen atoms increases, more NOx is generated during the combustion process. When the ammonia substitution rate is 90%, as the compression ratio increases, the cylinder pressure and temperature increase. The combustion efficiency of ammonia increases, generating more NOx and NOx emissions can reach 0.66 mg/m3. At a compression ratio of 18, the NOx emissions can reach 1.59 mg/m3. However, under medium and low load conditions, as the ammonia fraction increases, the total energy of fuel decreases, and the combustion efficiency of ammonia decreases, resulting in a decrease in the heat released during combustion and a decrease in NOx emissions. When the ammonia substitution rate is 90% and the load is 25%, NOx emissions reach 0.1 mg/m3. This research provides theoretical suggestions for the profitable and use ammonia fuel in internal combustion engines in a clean manner.

Optimization of engine performance, emission and combustion parameters by using mixed nonedible oil biodiesel with nano-additives using hybrid techniques

The current study is focused on three nonedible oils resource such as Ceiba pentandra, Mahua longifolia, and Azadirachta indica mixed together in a specific proportion for biodiesel production. The produced biodiesel serves as an alternative fuel source for operating a variable compression ratio diesel engine, addressing escalating environmental pollution and stringent emission standards. A nano-additive comprising CaO–TiO2 is incorporated into biodiesel blends to enhance engine performance and mitigate emissions. The matrix undergoes experimentation and validation using Box-Behnken Design, Deep Belief Network, and a hybrid DBN-based Arithmetic Optimization Algorithm to optimize engine parameters for achieving higher brake thermal efficiency, lower emission rates, and reduced brake-specific fuel consumption. All the experiments are conducted by varying the engine load, speed, quantity of nano-additives and biodiesel blend. The final empirical model is more significant for DBN with a regression coefficient greater than 0.99. The converged optimized input parametric ranges are load 60 %, biodiesel 25 %, nano-additive 20 wt% and engine speed 1400 rpm. When comparing diesel fuel with CaO–TiO2 biodiesel, the proposed method resulted in significant improvements, including a 41 % reduction in brake-specific fuel consumption, a 32 % decrease in CO emissions, a 25 % decrease in NOX emissions, and a 16.9 % increase in brake thermal efficiency.

A numerical investigation on the effect of altering compression ratio, injection timing, and injection duration on the performance of a diesel engine fuelled with diesel-biodiesel-butanol blend

Abstract Using renewable fuels for diesel engines can reduce both air pollution and dependence on fossil fuels. A computer simulation was constructed to predict the performance, combustion characteristics, and NOx emission of a diesel engine fuelled with diesel-biodiesel-butanol blends. The simulation was validated by comparing the modeling results against experimental data and a good agreement between the results was found. The fuels used for the validation were diesel (B0), biodiesel (B100), diesel-biodiesel blend (B50), and two diesel-biodiesel-butanol blends with 45% diesel-45% biodiesel-10% butanol (Bu10), and 40% diesel-40% biodiesel-20% butanol (Bu20) by volume. Experimental results showed that the addition of butanol reduced NOx emissions but deteriorated the engine performance. The aim of the current work was the numerical optimization of the different parameters to enhance the engine performance while using butanol to decrease NOx emissions. The engine compression ratio (CR) varied from 14 to 24, in increments of 2. Fuel injection timing (IT) was retarded from 30° before top dead center (bTDC) to 5° bTDC in increments of 5o. Also, the fuel injection duration (IDur) was extended from 20° to 50° in increments of 10°. Results showed that the increase in CR improved engine performance for the two investigated fuels, Bu10 and Bu20. The maximum engine brake power (BP), thermal efficiency (BTE), and minimum brake-specific fuel consumption (BSFC) of 1.46 kW, 32.3%, and 0.273 kg/kWh respectively, were obtained when the Bu10 fuel was injected at the optimum conditions of 24 CR, 15°bTDC IT, and 40° injection duration (IDur). Under these optimum conditions, the BP, BTE, and BSFC improved by 3% to 3.5% for Bu10 and Bu20 fuel blends compared to the base engine conditions of CR of 22, 30° IDur, and 10° bTDC IT. The heat release rate during the premixed phase increased when the IT was advanced, while the mixing-controlled combustion phase was enhanced when the IT was retarded. NOx emissions increased with increasing the CR, while both the increase in IDur at constant IT and the retard of IT decreased engine NOx emissions. At the optimum conditions, the NOx emissions for Bu10 and Bu20 were further decreased by 2.2% and 0.9% respectively compared to the experimental results at base engine conditions. Retarding the injection timing from 15° bTDC to 5° bTDC at a CR of 24 and IDur of 40° caused the NOx emissions for Bu10 and Bu20 to decrease by 16%. When the injection duration was increased from 20° to 50° at a CR of 24 and an IT of 15°bTDC, the NOx emissions for Bu10 and Bu20 decreased by 12.3% and 11.8% respectively. The addition of butanol to the diesel-biodiesel blend at optimum conditions showed results comparable to pure diesel, with a decrease in NOx emissions.

Combustion characteristics of premixed ammonia-hydrogen/air swirl flames at elevated pressure

Ammonia (NH3)-hydrogen (H2) blends which are obtainable by NH3 cracking can be an eminent carbon-free fuel. To provide a valuable database for the practical application of cracking-based NH3-H2 fuel, the effects of pressure on the combustion characteristics of premixed NH3-H2(-nitrogen (N2))/air swirl flames are investigated in terms of H2 mole fraction in the NH3-H2 blend and fuel-equivalence ratio. Extinction mechanisms at fuel-lean and rich flames are the same for both normal and elevated pressures, though only the blowoff is observed for elevated pressure. With increasing pressure, fuel-rich limits are generally extended but fuel-lean limits are reduced, NOx emissions decrease and the condition of the maximum NOx emissions moves towards fuel-richer condition. Flame visualization exhibits the shifted main reaction zone upstream, the increased flame wrinkling and the reduced OH and NO intensities with increasing pressure. Dilution effects of N2 at elevated pressure become remarkable compared with those at normal pressure.

Global health benefits of shipping emission reduction in early 2020

The impact of COVID-19 lockdown on the absolute concentration of air pollutant has been widely investigated, whereas the impact of lockdown on global shipping-related air pollutants still remained poorly understood because the contribution of individual source cannot be observed directly. In our study, we employed an efficient chemical transport model (GEOS-Chem) to quantify the shipping-related PM2.5, NO2, and O3 levels in early 2019 and 2020, and assessed the impact of COVID-19 lockdown on global shipping-related air pollutants and health effects. The result suggested that shipping-related global PM2.5, NO2, and O3 levels reduced by 14%, 85%, and 1%, respectively. Furthermore, the decreasing ratios of air pollutants in difference regions often suffered from large spatial discrepancy. PM2.5 and NO2 levels in China, India, Europe, and the United States decreased by 6.5% (NO2: 9%), 7.4% (8%), 11% (8.6%), and 15% (10%), which could be caused by dense shipping activities during the non-lockdown period. For O3 concentrations, the shipping-related concentrations in China, India, Europe, and the United States showed 0.7%, −12.9%, 16.6%, and −4.8% during lockdown period, respectively. The relatively slight O3 reduction might be linked with more significant decrease of NOx emission than VOCs. The changes of air pollutant concentrations inevitably led to the variations of health benefits. Globally, the all-cause mortalities caused by shipping-related PM2.5 exposures reached 40,464 (95% CI: 26,546, 54,382) and 39,035 (95% CI: 25,135, 52,935) cases in early 2019 and 2020, respectively. The combined health benefits of PM2.5, NO2, and O3 linked with shipping emission reduction in China, India, Europe, and the United States reached 476 (95% CI: 131, 822), 3341 (95% CI: 3,177, 3505), 2194 (95% CI: −970, 5358), and 311 (95% CI: 242, 379), respectively. Our study confirms the potentially considerable effects of shipping emission on multiple air pollutants and health impacts, which could provide valuable information for air quality management.

Effect of antioxidants on CI engine characteristics of safflower biodiesel with varying fuel injection pressures

A product of microorganisms, crop plants, and animal-based oil, biodiesel holds excellent promise as a sustainable energy resource and a solution to the world's rising energy issues. Biofuel resembles the qualities of fossil diesel, while it is also proven to be a greener fuel and viable alternative. To enhance the properties of biodiesel, the additives, mainly antioxidants, were added to the 20 % blend of safflower biodiesel (B20) at various injection pressures (190, 200, and 210 bar). At a concentration of 1000 ppm, the antioxidants, namely BHA (butylated hydroxy anisole) and BHT (butylated hydroxytoluene), were added to the B20 blend of higher IP. Investigation on the effects of antioxidants with biodiesel on the performance and emission characteristics were tested in CI diesel engines at different injection pressures (IP). The findings from this study indicate that antioxidants added to biodiesel significantly improved the engine's performance. Higher IP resulted in higher BTE (1.6 %) with lesser emissions of CO (33.33 %), HC (10 %) and smoke (19.5 %) than diesel. But it emits higher NOx emissions (2.5 %). The addition of the antioxidant BHA showed a decrease in NOx emissions by 5 % to higher IP. Thus, the safflower biodiesel B20 added with antioxidant BHA will likely be a tremendous alternate fuel for the CI engine.

Ozone Pollution in the North China Plain during the 2016 Air Chemistry Research in Asia (ARIAs) Campaign: Observations and a Modeling Study

To study air pollution in the North China Plain (NCP), the Air Chemistry Research in Asia (ARIAs) campaign conducted airborne measurements of air pollutants in spring 2016. High pollutant concentrations, with O3 &gt; 100 ppbv, CO &gt; 500 ppbv, and NO2 &gt; 10 ppbv, were observed. CMAQ simulations with the 2010 EDGAR emissions capture the spatial and temporal variations in ozone and its major precursors such as NO2 and VOCs, with significant underestimation. Differences between CMAQ simulations and satellite observations reflect changes in anthropogenic emissions, decreased NOx emissions in megacities such as Beijing, but slight increases in other cities and rural areas. CMAQ also underestimates HCHO and CO, suggesting adjustments of the 2010 EDGAR emissions are necessary. HCHO/NO2 column ratios derived from OMI measurements and CMAQ simulations show that VOC-sensitive chemistry dominates the ozone photochemical production in eastern China, suggesting the importance of tightening regulations on anthropogenic VOC emissions. After adjusting emissions based on satellite observations, better model performance was achieved. Because of the VOC-sensitive environment in ozone chemistry over the NCP, the underestimation of anthropogenic emissions could be important for CMAQ simulations, while future study and regulations should focus on VOC emissions with continuous controls on NOx emissions in China.

The effect of fusel oil and waste biodiesel fuel blends on a CI engine performance, emissions, and combustion characteristics

In this study, experimental engine tests were conducted to investigate the combustion, performance, and emission characteristics of a diesel engine using a fuel blend composed of diesel, biodiesel, and fusel oil. In the study, which was carried out by using fuels obtained from different wastes together in a diesel engine. Seven different fuels were prepared for experiments by adding waste cooking oil (30% and 50%) and fusel oil (5% and 10%) by volume to commercial diesel fuel. The tests were carried out on the Lombardini LDW 1003 engine, a three-cylinder diesel engine, at four different engine loads (10, 20, 30, and 40 Nm), and a constant speed (2000 rpm). The experimental results revealed that the use of WCO generally led to increased NOx emissions which generally decreased with the fusel oil addition to the fuel mixture. Considering diesel fuel as a reference at maximum load conditions, there was a 12.63% increase in NOx emissions with 50% WCO. A 2.45% decrease in NOx emissions was achieved by adding 10% fusel oil. Furthermore, HC emissions decreased with the addition of both fusel oil and WCO at all load levels. When diesel fuel is taken as a reference at maximum load conditions, a 90% reduction in HC emissions was achieved by adding 50% WCO, and a 50% reduction in HC emissions was achieved by adding 10% fusel oil. Additionally, when diesel fuel is taken as a reference at maximum load condition, it was observed that a 0.05% increase in the maximum cylinder pressure value with the addition of 50% WCO and a 2.09% increase in the maximum cylinder pressure value with the addition of 10% fusel oil.

Experimental investigation of engine performance and emissions, and characterization, of waste transformer oils and diesel blends with biodiesel produced from olive oil wastes in a CI engine

In this study, five different fuel blends were prepared by mixing biodiesel obtained from olive oil wastes using transesterification method, waste transformer oil, and Euro diesel in different ratios. The important physicochemical properties of the prepared fuel blends and produced biodiesel were determined by gas chromatography, Fourier transform infrared spectroscopy, and thermogravimetric analysis/differential scanning calorimetry analyses, and their characterizations were carried out. Then, the effects of the prepared fuel blends on engine performance and emission characteristics were investigated in a compression ignition engine. The experiments were performed with five different fuel blends (TD30, TD30B10, TD30B20, TD30B30, and D100) at 1000, 1500, 2000, and 2500 rpm. At all speeds, each fuel blend produced an average torque value that was highest for D100 fuel and lowest for TD30 fuel The average BP value produced by each fuel at all engine speeds was highest in D100 fuel and lowest in TD30 fuel. The results of the experiments showed that there was a 23.98% decrease in the average NOx emissions of TD30 fuel blend compared to the average NOx emissions of D100 fuel at all engine speeds. It was observed that all important fuel properties such as density, kinematic viscosity, and pour and cloud points of all fuel blends met the fuel standards.

Effects Analysis of FAME on the Engine Characteristics of Different Polymerized Biofuels in Compression Ignition Engine

Environmental pollution caused by marine engines fueled with fossil fuels is a matter of growing significance. The search for renewable and clean energy sources and improvements in the way fossil fuels are burnt aims to reduce the environmental impact of these engines. For this purpose, fatty acid methyl esters were produced from pure canola oil using KOH-assisted methanol-based transesterification with a maximum yield of 90.68 ± 1.6%. The marine engine’s model was created with CONVERGE software, followed by experimental verification. This paper examines the blended fuel characteristics of a diesel engine with biodiesel blends (0%, 5%, 10%, and 15%) at different loads of engines (50%, 75%, and 100%). It also explores the variation in these characteristics of B10 (10% biodiesel–diesel blends) at three different load conditions and four different EGR rates (0%, 5%, 10%, and 15%). The results indicate that the addition of biodiesel to diesel fuel reduces CO, HC, and soot emissions, while increasing NOx emissions. Additionally, the EGR rate decreases NOx emissions but results in higher levels of soot, CO, and HC emissions. Finally, response surface methodology was used to elicit the engine’s characteristics. It was determined that the optimum experimental operating conditions were 100% engine load, 6.9% biodiesel addition, and 7.7% EGR. The corresponding BTE, BSFC, NOx, and HC emissions were 38.15%, 282.62 g/(kW-h), 274.38 ppm, and 410.37 ppm, respectively.

SUSTAINABLE PERFORMANCE: ENHANCING CI ENGINES WITH GREEN-SYNTHESIZED NANOPARTICLES AND BIODIESEL

This study investigates the potential of green-synthesized nanoparticles (NPs) doped with a 20% biodiesel blend to enhance the performance and emissions characteristics of a compression ignition (CI) engine. The green synthesis of NPs offers an environmentally friendly alternative to conventional methods, while the addition of biodiesel provides a renewable fuel source. Experimental trials were conducted using various concentrations of NP-doped biodiesel blends in a CI engine. Performance parameters such as brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), and exhaust gas temperature (EGT) were measured. Additionally, emissions profiles, including smoke intensity, carbon monoxide (CO), oxides of nitrogen (NOx), and unburned hydrocarbons (HC), were analyzed. The results demonstrated that the incorporation of NP-doped biodiesel blends led to significant improvements in engine performance. A reduction in BSFC and an increase in BTE were observed, indicating enhanced fuel efficiency. Furthermore, the NP-doped blends contributed to a substantial decrease in smoke, NOx and other harmful emissions, suggesting a positive environmental impact. This research highlights the promising potential of green-synthesized NPs and biodiesel blends as a sustainable and efficient fuel alternative for CI engines.

Experimental investigation of the effect of CO2 dilution on the performance and hydrogen knock limit of a hydrogen–gasoline dual fuel spark ignition engine 1

This study investigates the effect of CO2 dilution on the performance and hydrogen knock limit of a spark ignition engine fueled with hydrogen–gasoline mixtures. The experimental runs were performed on a Ricardo single-cylinder engine with direct gasoline injection and hydrogen port induction. The hydrogen flow rate was increased at a step size of 2 L per minute (LPM) until the onset of knock, and the CO2 gas was introduced to the intake manifold with flow rates of 2, 4, and 6 LPM. The results revealed that CO2 dilution deteriorated the engine performance regarding the brake mean effective pressure and brake thermal efficiency. The hydrogen enrichment shortens the combustion duration, enhancing the performance and combustion characteristics. Increasing CO2 dilution levels decreased NOx emissions and increased CO emissions. Moreover, CO2 dilution extended the hydrogen knock limit to 10 and 16 LPM for spark timings of 12° and 4° crank angles before top dead center, respectively.

A comparative study on NH3/H2 and NH3/CH3OH combustion and emission in an optical SI engine

Ammonia is an attractive carbon-free fuel but suffers from poor combustion characteristics and heavy emissions. Green hydrogen and methanol are recognized as the most promising combustion promoters for enhancing ammonia reactivity in pursuit of a carbon–neutral solution. Nonetheless, a comparative study on ammonia combustion and emissions, incorporating hydrogen and methanol enrichment, is currently absent under actual engine conditions. In this work, the combustion performance, visualized flame characteristics, and pollution emissions of ammonia were investigated in an optical engine, allowing for low-level hydrogen and methanol enrichment, specifically at energy ratios of 5%, 10%, and 15%. We have identified the crucial role of hydrogen and methanol enrichment in enhancing various aspects of ammonia engine performance, including thermal efficiency, combustion stability, flame initiation and propagation, and nitrogen-based emissions. Specifically, hydrogen enrichment demonstrates a more pronounced effect on reducing cyclic variations, whereas methanol enrichment exhibits a greater influence on increasing thermal efficiency, manifesting improved controllability in combustion phasing. Combustion visualizations show the contribution of hydrogen enrichment to the formation process of the initial flame kernel, which is reflected as a lower cyclic variation from a macroscopic perspective, and meanwhile, methanol enrichment features a stronger acceleration effect during the turbulent flame propagation process. Furthermore, the quantification of flame response to turbulence is solved and observed much higher effects for NH3/CH3OH blends than for NH3/H2 blends, indicating a distinctly different mechanism of facilitation by methanol enrichment. Regarding nitrogen-based emissions, both hydrogen and methanol enrichment lead to a substantial reduction in NH3 slip and N2O emissions, consistent with observed variations in combustion stability. However, methanol enrichment induces noticeable decreases in NOx emissions, while hydrogen enrichment exhibits an opposing trend. The present study demonstrates the beneficial impacts of hydrogen and methanol enrichment on improving ammonia combustion and emissions, with the underlying reason correlated to flame dynamics and thermochemical interactions.

Numerical Investigations on the Effects of Dome Cooling Air Flow on Combustion Characteristics and Emission Behavior in a Can-Type Gas Turbine Combustor

To meet the requirements of achieving higher efficiency and lower NOx pollution, the flame temperature in gas turbine combustors increases continually; thus, the effusion-cooling technology has been used to ensure the combustor liner remains within the allowed temperature, by which the combustion characteristics and emission behavior are possibly influenced. In order to investigate the effects of dome cooling air flow on combustion characteristics and NOx emissions, three-dimensional combustion simulations for a swirl-stabilized can-type gas turbine combustor are carried out in this work by using the computational fluid dynamics (CFD) method. Through adjusting the ratio of the dome cooling air flow and the dilution cooling air flow, the characteristics of flow field, temperature distribution and NOx emissions under each work condition are analyzed. At different ratios of the dome-cooling air flow to the total air flow, the flow velocity field in the region near the center of the combustion chamber is not changed much, while the velocity field near the chamber wall shows a more significant difference. The temperature in the outer recirculation zone within the combustion chamber is effectively reduced as the dome cooling air flow increases. By analyzing the distribution characteristics of the concentration of OH*, it is demonstrated that the dome cooling air flow does not have a direct effect on the reaction of combustion. It is also found that as the ratio of the dome cooling air flow to the total air flow increases from 0 to 0.15, the value of the NOx emissions drops from 28.4 to 26.3 ppmv, about a 7.4% decrease. The distribution of the NOx generation rate in the combustion chamber does not vary significantly with the increasing dome cooling air flow. Furthermore, by calculating the residence time in different stages, when the the ratio of the dome cooling air flow to the total air flow varies from 0 to 0.15, the residence time in the pilot stage decreases obviously, from 42 ms to 18 ms. This means that reduction in residence time is the main factor in the decrease of NOx emissions when the dome cooling air flow increases.