Ultra-low Emission Research Articles

The cavitation flow and spray characteristics of gasoline-diesel blends in the nozzle of a high-pressure common-rail injector

In compression-ignition engines, gasoline-diesel blends have been widely concerned for its potential to reach 50% thermal efficiency and ultra-low emissions. Due to physical property difference between the two fuels, the spray atomization characteristics of the blended fuels are different from that of a single fuel, and the cavitation flow characteristics of the blends in the high-pressure nozzle and their impact on the spray are not well understood. In this paper, the visualization of cavitation flow and spray characteristics of five different proportion blended fuels (D100G0, D80G20, D60G40, D40G60, D20G80) was carried out. The influence of fuel properties corresponding to the gasoline-diesel mixing ratio on the initial generation of vortex-induced cavitation, the development of transient cavitation flow process and the injection rate and spray characteristics were studied respectively. For the tapered orifice nozzle, string cavitation is captured mainly concentrating in the needle opening initial period and closing end period, which is the main factor of spray instability and fluctuations. At the injection starting, the addition of gasoline into the diesel fuel resulted in a significant increase in string cavitation strength and larger injection rate compared to the pure diesel, even if the percentage of gasoline added is small. However, the different gasoline addition ratios have little effect on the maximum intensity of string cavitation and the duration of string cavitation in the nozzle. Accordingly, the addition of gasoline increased the overall spray cone angle and spray fluctuations throughout the injection process. Meanwhile, as the injection volume increased, the injection rate curve in the initial process is flat at first and then become steep which was precisely related to the cavitation of the vortex line in the nozzle. The findings of this paper are important guidelines for the determination of fuel injection strategies and spray analysis of gasoline-diesel blends for compression-ignition engines.

Capture and migration of particulate matter in activated carbon sintering flue gas purification system based on ultra-low emission target

By using alkali metal K as the tracer component of sintered ash, the particulate matter (sintered ash and activated carbon powder) in the industrial two-stage moving bed purification project of sintered flue gas was studied. First, the distribution of K element in the gas phase and each link of the purification system was investigated. The material flowing direction as well as the trapping and releasing mechanism of sintered ash in the purification system were analyzed by BET, XRD, and SEM-EDS techniques. The migration and release rule of activated carbon (AC) powder from moving bed to gas phase was investigated, and the contribution of AC powder to flue gas particles and the key release link were clarified. The results showed that the sintered ash capture rate in the primary adsorption tower of AC was as high as 99.7%, while 65.92% of the sintered ash was captured in the middle chamber of the primary adsorption tower. Sintered ash is trapped by AC at 0–0.5 mm on the surface, which suggested the main trapping mechanisms are inertial collision and interception diffusion settling. The trapped sintered ash is recycled through the system with the AC, and eventually 99.9% ash is discharged with the sieved carbon powder from the desorption tower. The percentage of charcoal powder in the exit flue gas particulate matter is 55.45% and the release of activated charcoal powder to the gas phase in the secondary adsorption tower. Which is the key link affecting the exit flue gas particulate matter concentration. This study elucidates the capture and migration law of particulate matter in AC flue gas purification system, and provides a strong basis for the improvement of technology to achieve stable ultra-low emission of particulate matter from AC system.

A review of hydrogen chloride removal from calcium- and sodium-based sorbents.

With the steady progress of ultra-low emissions in various industries, the management of unconventional pollutants is gradually attracting attention. A such unconventional pollutant that negatively affects many different processes and pieces of equipment is hydrogen chloride (HCl). Although it has strong advantages and potential in the treatment of industrial waste gas and synthesis gas, the process technology of removing HCl by calcium- and sodium-based alkaline powder has not yet been thoroughly studied. The impact of reaction factors on the dechlorination of calcium- and sodium-based sorbents is reviewed, including temperature, particle size, and water form. The most recent developments in sodium- and calcium-based sorbents for capturing hydrogen chloride were presented, and the dechlorination capabilities of various sorbents were contrasted. In the low-temperature range, sodium-based sorbents had a stronger dechlorination impact than calcium-based sorbents. Surface chemical reactions and product layer diffusion between solid sorbents and gases are crucial mechanisms. Meanwhile, the effect of the competitive behavior of SO2 and CO2 with HCl on the dechlorination performance has been taken into account. The mechanism and necessity of selective hydrogen chloride removal are also provided and discussed, and future research directions are pointed out to provide the theoretical basis and technical reference for future industrial practical applications.

Experimental and numerical study of MILD combustion characteristics in the long-narrow confined space with different types of flue gas dilution

MILD combustion is extensively applied in wide confined spaces as a new ultralow NOx emission technology but is rarely reported in long-narrow confined spaces. To address this, as exemplified by a coke oven heat flue, a flue gas dual-dilution system in a long-narrow confined space was constructed to achieve MILD combustion, where combustion characteristics such as temperature distribution, flow field, flame morphology and NOx emission were assessed through experiments and numerical simulations. The results indicate that when the dilution rate reaches 25%, single-fuel dilution can achieve unstable MILD combustion, while single-air dilution is still in diffusion combustion, and the corresponding NOx emissions are reduced to 371 ppm and 325 ppm, respectively. When the fuel/air dilution ratio is 10/15 in flue gas dual-dilution, the flame front disappears completely, the flame volume ratio reaches 41.9%, and MILD combustion is established. The corresponding NOx emission is reduced to 58 ppm, which is 95.0% lower than conventional combustion and achieves ultralow NOx emission. An in-depth analysis proves that flue gas dual dilution is the key to achieving MILD combustion in a long-narrow confined space, which is irrelevant to the construction of the flue gas internal recirculation rate.

On the Stability and Characteristics of Biogas/Methane/Air Flames Fired by a Double Swirl Burner

CO2-diluted methane fuel is relevant to biogas combustion applications. Despite its poor heating value and low reactivity, which limit its practical applicability, biogas gains popularity as a renewable fuel. However, implementing it in combustion systems requires either modifying or replacing the existing burners. This study investigates the stability, temperature field, and pollutant emissions of CH4/CO2/air-premixed flames fired by a double-swirl burner. A CH4/air mixture of equivalence ratio, Φout, was used in the outer stream, while a CH4/CO2/air mixture was supplied to the inner stream. The CO2 mole fraction, $${x}_{{\mathrm{CO}}_{2}}$$ , in the inner fuel blend varied from 0 to 0.4 for various inner stream equivalence ratios, Φin. The stability diagram of these flames was mapped in terms of Φin verses $${x}_{{\mathrm{CO}}_{2}}$$ for a fixed Φout. Based on the stability map, the inflame temperature field was investigated for six flames. Increasing the %CO2 in the biogas modifies the stability map by increasing the inner stream lean blow-off limits. However, increasing Φout sustains the flame stability, while reducing the CO2 decreases the overall flame blow-off equivalence ratio. Flame size growth with increasing $${x}_{{\mathrm{CO}}_{2}}$$ requires a longer residence time for efficient combustion. The addition of CO2 physically and chemically affects the thermal flame structure, and hence the pollutant emissions. In this burner, ultra-low NOX emission was reported, while an increase in the CO and unburned hydrocarbons (UHC), with increasing $${x}_{{\mathrm{CO}}_{2}}$$ was observed. However, the results show that, for a given $${x}_{{\mathrm{CO}}_{2}}$$ , controlling Φin and Φout could reduce CO and UHC emissions.

A particle swarm optimization algorithm with novelty search for combustion systems with ultra-low emissions and minimum fuel consumption

The particle swarm optimization algorithm is primarily inspired by the natural behaviour of swarms and achieves important results in different applications. However, it is not exempt from stagnation in local optima and has a tendency to prematurely converge to them. Novelty Search is a concept that appeared recently in different fields of computational intelligence. It aims at exploring non-visited areas of the search space through solutions that bring novelty to already discovered solutions. The novelty of this work can be divided into two steps: on one side, this article proposes a variant of the particle swarm optimization algorithm which uses Novelty Search concepts to improve the algorithm’s performance. Our proposal is first checked and compared using the CEC 2005 benchmark suite and then, we apply it to solve a real-world optimization problem: the design of a combustion system targeting the reduction of pollutant emissions and fuel consumption. The combustion chamber design phase usually is a complex and time-consuming process even with advanced supercomputers, since it depends on several input variables which are highly non-linear and with crossed interaction. Then, the second contribution of this work is to develop a methodology that couples a computational fluid dynamics (CFD) simulation tool with the new optimization algorithm for minimizing the specific fuel consumption of a compression-ignited engine, while constraining the NOx and soot emissions. A 3D-CFD model of the combustion system was built to predict and analyse the performance of the combustion system and hence, select the parameters with a higher impact on the system. The method reduces the computational time and includes tools for the automatic preparation of the input parameters and geometry of the system. The input parameters correspond to geometrical variables that control the bowl shape, the number of holes in the injector, the injection pressure, the swirl number and the exhaust gas recirculation rate. Results show how the simulation tool and the new PSO with Novelty Search algorithm allow us to obtain a new combustion system that minimizes the fuel consumption by 3%, simultaneously reducing NOx and soot emissions.

Experimental Study on the Effect of Hydrogen Addition on the Laminar Burning Velocity of Methane/Ammonia–Air Flames

Variations in methane–ammonia blends with hydrogen enrichment can modify premixed flame behavior and play a crucial role in achieving ultra-low carbon emissions and sustainable energy consumption. Current combustion units may co-fire ammonia/methane/hydrogen, necessitating further investigation into flame characteristics to understand the behavior of multi-component fuels. This research aims to explore the potential of replacing natural gas with ammonia while making only minor adjustments to equipment and processes. The laminar burning velocity (LBV) of binary blends, such as ammonia–methane, ammonia–hydrogen, and hydrogen–methane–air mixtures, was investigated at an equivalence ratio of 0.8–1.2, within a constant volume combustion chamber at a pressure of 0.1 MPa and temperature of 298 K. Additionally, tertiary fuels were examined with varying hydrogen blending ratios ranging from 0% to 40%. The results show that the laminar burning velocity (LBV) increases as the hydrogen fraction increases for all mixtures, while methane increases the LBV during blending with ammonia. Hydrogen-ammonia blends are the most effective mixture for increasing LBV non-linearly. Enhancement parameters demonstrate the effect of ternary fuel, which behaves similarly to equivalent methane in terms of adiabatic flame temperature and LBV achieved at 40% hydrogen. Experimental data for neat and binary mixtures were validated by different kinetics models, which also showed good consistency. The ternary fuel mixtures were also validated with these models. The Li model may qualitatively predict well for ammonia-dominated fuel. The Shrestha model may overestimate results on the rich side due to the incomplete N2Hisub-mechanism, while lean and stoichiometric conditions have better predictions. The Okafor model is always overestimated.

Temperature Self-Adaptive Ultra-Thin Solar Absorber Based on Optimization Algorithm

In solar applications, the solar absorber is paramount to converting solar radiation to heat energy. We systematically examined the relationship between the efficiency of the solar absorber and operating temperature and other factors. By combining inverse designs with surface plasmonic and Fabry-Perot cavity solar absorption theories, we have developed several solar absorber devices with excellent performance at different temperatures. One of these devices displays a solar spectral absorption of 95.6%, an ultra-low emission rate of 5.7%, and optical-to-thermal conversion efficiency exceeding 90%, all within an ultra-thin depth of 0.45 μm under working temperatures of 600 K. The device has the potential to surpass the Shockley-Queisser limit (S-Q limit) in solar power generation systems. Our method is adaptable, enabling the design of optimal-performance devices to the greatest extent possible. The design was optimized using modern optimization algorithms to meet complex conditions and offers new insights for further study of the conversion from solar to thermal energy and the advancement of solar energy applications.

The effect of air pollution control devices in coal-fired power plants on the removal of condensable and filterable particulate matter.

Total particulate matter (TPM), including condensable and filterable particulate matter (CPM and FPM), is one of the pollutants that need to be controlled in the coal combustion process. In this study, CPM and FPM were sampled from sixteen coal-fired power units and two coal-fired industrial units. The removal effects of air pollution control devices equipped in the units on the migration and emission of particles were investigated by analyzing samples from inlets and outlets of apparatus. The average removal efficiency of TPM by dry-type dust removal equipment, wet flue gas desulfurization devices, and wet-type precipitators reached 98.57 ± 0.90%, 44.89 ± 15.01%, and 28.45 ± 7.78%, respectively. The removal efficiency of dry-type dust removal equipment and wet-type precipitators to TPM is mainly determined by the purification effect of FPM and CPM, respectively, and both types of particles contribute to the removal efficiency of desulfurization systems to total TPM. The concentrations of CPM (12.01 ± 5.64mg/Nm3) and FPM (1.95 ± 0.86mg/Nm3) emitted from ultra-low emission units were the lowest, and CPM is the dominant particle, especially the higher proportion of organic components in CPM.

Comparative analysis of energy efficiency of electrostatic precipitator before and after ultralow emission in coal‐fired power plants in China

AbstractElectrostatic precipitator (ESP) is the main equipment for flue dust control of coal‐fired power plants in China, accounting for about 70% of the total currently. In this paper, energy efficiency data of ESP, including 202 sets before ultra‐low emission and 45 sets after ultra‐low emission are systematically studied and analyzed by using the research method of field testing and technical investigation. The results showed that after ultra‐low emission, the energy consumption and converted CO2 emission of ESP in coal‐fired power plants increased significantly, and the specific power consumption and energy consumption corresponding to unit mass particulate matter (PM) removal increased by 49.61% and 139%, respectively, and the converted CO2 emission increased by 1.67 × 10−4 kg CO2/m3 and 31.12 kg CO2/t PM on average. The energy consumption of low‐low‐temperature ESP (LLT‐ESP) was positively correlated with its emission reduction range. Before and after the gas cooler operation, the power consumption, specific power consumption and energy consumption corresponding to unit mass PM removal increased by 8.06%–38.68%, 10.66%–60.14% and 7.23%–62.98%, respectively, and the CO2 emissions corresponded increased by 26.29–691.81 kg CO2/h, 0.46–2.18×10−4 kg CO2/m3, 1.10–23.62 kg CO2/t PM, respectively. LLT‐ESP had a great possibility to optimize the operation for energy‐saving and carbon‐reduction, because when the high voltage power supply operated on the maximum output mode and the energy‐saving mode, the drop of power consumption and specific power consumption was around 52.00%–58.23%, 52.02%–58.29%, respectively, and the CO2 emission reductions corresponded was 1,039.25–1,359.35 kg CO2/h, 2.71–3.58×10−4 kg CO2/m3, respectively. LLT‐ESP also had the great optimizing possibility for energy‐saving and carbon‐reduction during low load operation, as when the load reduced from 100% to 50%, the specific power consumption and energy consumption corresponding to unit mass PM removal increased by 5.05%–45.50%, 6.59%–63.90%, respectively, and the CO2 emissions corresponded increased by 0.38–2.44×10−4 kg CO2/m3, 6.76–45.98 kg CO2/h, respectively. The operation energy consumption can be effectively reduced by integrated use of multiple electric dust removal technologies, such as compared with LLT‐ESP technology, the power consumption, specific power consumption and energy consumption corresponding to unit mass PM removal of “low‐low‐temperature + moving electrode+ electrostatic agglomeration” decreased by 37.88%, 30.08% and 45.29% respectively, and the corresponding CO2 emission decreased by 697.22 kg CO2/h, 1.87×10−4 kg CO2/m3 and 32.98 kg CO2/t PM, respectively. The current national standard GB 37484‐2019 is no longer applicable to the energy efficiency evaluation of the ESP in ultra‐low emission units. This study can provide data support for the revision of national standard GB 37484‐2019 and the collaborative efficiency of coal power plant pollution reduction and carbon reduction. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Experimental research on effects of multi-layer injection of the high-temperature preheated pulverized coal on combustion characteristics and NOx emission

Under the background of carbon peak and carbon neutrality, cleanandefficientutilization ofcoal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broadprospectsforapplication, nevertheless, previous studies have mainly focused on limiting NOx generation by simply applying air staging method in the combustor, which made further NOx reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOx emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the self-preheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%∼15.48% and 600 mm ∼ 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 ∼ 0.99 s and 0.87 ∼ 1.11 s, respectively. What’s more, under the same reburning parameters, Alxa lignite coal had the largest NOx reduction rate (32.15%), with NOx emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOx reduction rate (5.34%) and the highest NOx emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOx emission (45.75 mg/m3, @6%O2) with the NOx reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.

Ultra-superhydrophobic MOFs coated on polydopamine-modified polyethylene terephthalate for efficient removal of particulate matter

To achieve ultra-low emissions in industrial flue gas, three different micro/nano metal–organic-framework (MOF) crystals (NH2-MIL-125, ZIF-8 and HKUST-1), as active purification units, were assembled on polydopamine (PoDA)-modified PET fibers (p-PET) by rapid, efficient, and supramolecular self-polymerization at room temperature to construct a novel superhydrophobic composite filter material (SH-Mp-PET(Ti, Zn, Cu)). The wrinkle structure and dielectric constant on the surface of SH-Mp-PET(Ti, Zn, Cu) filter fiber were improved by the synergistic effect of PoDA and MOF, and the charge effect on the surface of the three composite filter materials was improved, so that the electrostatic interaction between the fiber and the particles was improved. At the same time, the porous structure within the MOF did not result in significant pressure loss, and the purification quality factor (QF) of ultra-fine PM was significantly improved by the dual modification of RE and ΔP. The QF of three SH-Mp-PET(Ti, Zn, Cu) filter media were 22.9 %, 29.6 % and 28.1 % higher than PET, respectively. And SH-Mp-PET exhibited good thermal and mechanical stability. This approach can promote the development of industrials flue gas superhydrophobic filter materials and provides a new concept for developing MOF materials for flue gas treatment and reuse.

Numerical Investigation on the Characteristics of a Novel Multi-Swirl Lean Direct Injection Burner With Large Eddy Simulation-Flamelet Generated Manifold Method

Abstract The lean direct injection (LDI) concept can eventually replace the current combustion systems in aviation engines because of its low NOx emissions without compromising other parameters. A novel multiswirl LDI burner with distributed fuel injection surrounded by air- flow through multiple hexagonal swirlers of vane angle 45 deg was developed. In this study, large eddy simulation (LES), using the dynamic Smagorinsky-Lilly subgrid model together with the flamelet generated manifold (FGM) combustion model, has been used to analyze the correlation between aerodynamics, mixing, and combustion characteristics of the burner. The agreement between the experimental data and the LES simulation was good, and it can accurately predict the trend of variables like velocity, temperature, and mixture fraction at different Reynolds number and equivalence ratios. The LES-FGM results demonstrated the rapid formation of a homogeneous fuel-air mixture over a short distance, which results in excellent flame stability, and it has ultralow NOx emission due to low flame temperature and negligible internal recirculation. It was discovered that going from a global equivalence ratio of 0.7 to 0.9 increases the flame liftoff distance because the high fuel volume flowrate causes the mixing of swirling air and fuel jet to become more and more delayed. The research in this paper provides an insight into the ability of the LES-FGM method to capture the complex flow field structures and the flame behavior globally of a novel low NOx multiswirl burner that might be a competitor in the combustors of commercial gas turbine engines.

Reaction mechanism of NO and SO2 Co-removal by calcium hydroxide

Flue Gas simultaneous Desulfurization and Denitrification (FGDD) is expected to become a new generation of low-cost technology to achieve ultra-low emissions especially in smelting kilns and industrial boilers. The fixed bed system and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) were used to clarify the reaction mechanism of NO and SO2 co-removal by calcium hydroxide absorbent. The hydroxyl radical on the surface of calcium hydroxide was identified by Protium Nuclear Magnetic Resonance (1H NMR) and radical scavenger 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO). With synergistic effect of hydroxyl radical and oxygen, NO and SO2 are oxidized to NO2 and SO3 respectively, and then absorbed as nitrate and sulfate, according to the three-step chain reactions: SO2 +HO* →HOSO2 *, HOSO2 * +O2→SO3 +HO2 * and HO2 * +NO→HO* +NO2. The key point is the recycling of hydroxyl radical.

Emission Inventory of Building Material Industry in Henan Province Based on Multi-source Data Integration

The building materials industry is a typical resource and energy-consuming industry, as well as one of the major sources of air pollution. As the world's largest producer and consumer of building material products, China thus far has insufficient research on the emissions of the building materials industry, and the data sources are short of multiplicity. In this study, the building materials industry in Henan Province was chosen,and the control measures inventory for pollution emergency response (CMIPER) was applied to the development of the emission inventory for the first time. Through the integration of multi-source data such as CMIPER, a pollution discharge permit, and environmental statistics, the activity data of the building materials industry was refined, and a more accurate emission inventory of the building materials industry in Henan Province was established. The results showed that the SO2, NOx, primary PM2.5, and PM10 emissions of the building materials industry in Henan Province in 2020 were 21788, 51427, 10107, and 14471 t, respectively. Cement and bricks and tiles were the two categories with the highest contribution of emissions from the building materials industry in Henan Province, accounting for more than 50% in total. TheNOx emission of the cement industry was a key issue, and the overall emission control level of the brick and tile industry was relatively unadvanced. The central and northern parts of Henan Province contributed the most emissions in the building materials industry, accounting for more than 60%. It is recommended to further implement ultra-low emission retrofit in the cement industry, and for other industries such as the bricks and tiles, the improvement of local emission standards is encouraged to persistently promote the emission control of the building materials industry.

Dynamic prediction of SO2 emission based on hybrid modeling method for coal-fired circulating fluidized bed

Pollutant prediction for coal-fired circulating fluidized bed units is crucial for ultra-low emission optimization. Accurate prediction models can assist in the control optimization of the unit. Mechanism models are limited by the determination of parameters, coefficients, and fitting functions in the model and require a large amount of operational and unit design data in practical applications. With the development of deep learning, more and more deep learning models are used in parameter prediction. These models suffer from insufficient prediction accuracy when performing parameter prediction tasks due to the lack of a priori knowledge of the mechanism process. This paper analyzed the relationship between the differential equation model under the first-order Taylor expansion and the single-layer Gated Recurrent Unit neural network model. According to the analysis results, this paper proposed a mixed prediction model of SO2 concentration. The ablation study demonstrated the validity of the predictive model structure. The operation datasets of two actual units were used for verification. In terms of MAE indicators, the results of the proposed model on the two data sets are 124.5669 mg/Nm3 and 178.0473 mg/Nm3. In terms of MAPE indicators, the results of the proposed model on the two data sets are 5.85% and 14.07%.

Experimental study of emission characteristics and performance of SCR coated on DPF with different catalyst washcoat loadings

To improve the NOx conversion efficiency (CE) and inlet temperature of selective catalytic reduction (SCR) under low-temperature conditions, SCR coated on diesel particulate filter, so called SDPF, is one of the important technologies to meet the future Euro Ⅶ ultra-low emission regulations for diesel engines. In this study, the effects of different Cu-SSZ-13 catalyst washcoat loadings (60, 90, and 120 g/L) on the SDPF performance were investigated. The results showed that as the catalyst washcoat loading increased, the inlet temperature and pressure drop of the SDPF rose, the high-NOx-conversion-efficiency area expanded toward the low-speed and low-load directions of the engine, and the NOx CE first increased and then decreased. The number of active sites of the catalyst and the SDPF pressure drop together determine the NOx CE. When the catalyst washcoat loading was increased, the nucleation-mode (NM) particle factor decreased significantly, while the accumulation-mode (AM) particle factor decreased slightly. The filtration efficiency of the three types of particles was NM > total > AM from high to low. The higher the washcoat loading, the higher the particle filtration efficiency and the larger the geometric mean diameter. The reduction of NM particles was the result of a combination of the chemical reaction and the physical collection mechanism.

Additive manufacturing new piston design and injection strategies for highly efficient and ultra-low emissions combustion in view of 2030 targets

Internal combustion engines have been the most effective solution as the main mover for mobility. Despite the recent European regulations targeting zero tailpipe CO2 emissions for new passenger cars and light vans from 2035 onwards, the upcoming emission regulations still require further technology and fuel developments in the transport sectors. In recent years, studies on internal combustion engines have been increasingly shifting from performance and refinement through advanced fuel injection and air charging technologies to ultra-low emissions and efficiency. Particular attention has also been paid to carbon–neutral fuels. The problem merits further investigation since all are key factors for the powertrain competitiveness in the electrified automotive future, as the pollutants and the CO2 emissions will soon approach the Euro 7 regulation and the Fit to 55 standards, respectively. To this aim, the combustion system design is a crucial part of the internal combustion engine development in the view of exploiting renewable fuel characteristics. This study seeks to assess the effectiveness of a steel piston, realized through a specific design for additive manufacturing technologies, enabling an innovative bowl geometry. It features a highly re-entrant sharp-step and radial lips bowl profile enabling spray separation and radial mixing zone concept. A single-cylinder compression ignition engine has been employed to demonstrate the effectiveness of the innovative bowl shape to meet the challenging future ultra-low emission targets. The results confirm the additive manufacturing technology as a possible solution for innovative highly-stressed steel piston designs. The new bowl shape design, combined with optimised spray targeting and injection strategies, allows outstanding soot reductions, up to 80%, and ultra-low NOx emission levels compared to the conventional combustion system. Gains in fuel economy are also observed. Further emissions advantages are expected with renewable fuel applications.

Evaluation and extension of ignition delay correlations for dual-fuel operation with hydrogen or methanol in a medium speed single cylinder engine

Hydrogen (H2) and methanol (MeOH) are promising fuels for sustainable transport, owing to their ideal properties for use in internal combustion engines: CO2 neutral (when produced renewably), ultralow emissions, and high efficiencies. The dual-fuel (DF) technology where diesel is used as a pilot to ignite port fuel injected H2 or MeOH is of particular interest for retrofitting existing diesel engines (DE). Although some experimental work has been conducted on high-speed DE, there has been limited numerical investigation in this area. Therefore this work focuses on medium speed large bore engines and on the ignition delay (ID) timing of the diesel pilot, a crucial parameter to well predict numerically as it denotes the start of heat release. Experiments were carried out using H2 and MeOH in DF on the same single cylinder engine. The measured IDs are reported and visualize the difference of the effect of both fuels. Next, diesel ID correlations are evaluated on their predictive capabilities in DF. They fail however to predict the increasing ID from the inhibition effect of MeOH. Therefore, new ID correlations were developed for DF with H2 and MeOH, emphasizing the importance of additional terms such as the methanol equivalence ratio to describe this inhibition effect. Finally, the new correlations were compared with correlations for DF with natural gas to explore similarities and differences.

Distribution and bioavailability of mercury in size-fractioned atmospheric particles around an ultra-low emission power plant in Southwest China

Ultra-low emission (ULE) technology retrofits significantly impact the particulate-bound mercury (Hg) emissions from coal-fired power plants (CFPPs); however, the distribution and bioavailability of Hg in size-fractioned particulate matter (PM) around the ULE-retrofitted CFPPs are less understood. Here, total Hg and its chemical speciation in TSP (total suspended particles), PM10 (aerodynamic particle diameter ≤ 10 µm) and PM2.5 (aerodynamic particle diameter ≤ 2.5 µm) around a ULE-retrofitted CFPP in Guizhou Province were quantified. Atmospheric PM2.5 concentration was higher around this ULE-retrofitted CFPP than that in the intra-regional urban cities, and it had higher mass Hg concentration than other size-fractioned PM. Total Hg concentrations in PM had multifarious sources including CFPP, vehicle exhaust and biomass combustion, while they were significantly higher in autumn and winter than those in other seasons (P < 0.05). Regardless of particulate size, atmospheric PM-bound Hg had lower residual fractions (< 21%) while higher HCl-soluble fractions (> 40%). Mass concentrations of exchangeable, HCl-soluble, elemental, and residual Hg in PM2.5 were higher than those in other size-fractioned PM, and were markedly elevated in autumn and winter (P < 0.05). In PM2.5, HCl-soluble Hg presented a significantly positive relationship with elemental Hg (P < 0.05), while residual Hg showed the significantly positive relationships with HCl-soluble Hg and elemental Hg (P < 0.01). Overall, these results suggested that atmospheric PM-bound Hg around the ULE-retrofitted CFPP tends to accumulate in finer PM, and has higher bioavailable fractions, while has potential transformation between chemical speciation.