Low Emission Levels Research Articles

Transient and altitude performance analysis of hydrogen fuelled internal combustion engines with different charging concepts

In the internal combustion engine industry, there is a significant shift towards alternative fuels to accomplish zero net carbon dioxide emissions as well as the legislation requirements. According to former studies, in addition to its advantages of being carbon-free and having appropriate combustion characteristics, low nitrogen oxide engine-out emission levels are achieved at lean burn combustion of hydrogen. Lean combustion leads to a turbocharging system requirement. Which is then utilized to generate the expected power output at high altitudes and during transient maneuvers.This study aims to determine the ideal air-charging vessel which can meet the objectives of high altitude. Which is 0 % torque derate and transient response time with respect to 0 %–90 % of maximum torque which is typically ∼3–4 s for diesel engines, while keeping the lean combustion to release ultra-low NOX emissions. Different charging concepts have been investigated by applying 1-D thermodynamic modeling on a H2ICE with a direct injection system which is for heavy-duty vehicles.

Inland waterway transport development: A Q-Method study on Tocantins River, Brazilian Amazon

In Brazil, increasing Inland Waterway Transport (IWT) figures among efforts for the Nationally Determined Contribution due to better energy efficiency and lower CO2 emission levels, when compared to highways and railways. Identifying barriers and drivers is useful to develop IWT as an alternative to terrestrial transportation modes, which are scarce in the Brazilian Amazon. As more than 50% of Brazilian electricity is generated in hydropower plants, the harmonic coexistence between multiple water uses is crucial. This paper aims to explore stakeholders' perceptions and priorities related to the development of inland waterway transport in the Tocantins River, Amazon, Brazil, where there are several hydropower plants. With an emphasis on sustainability issues, we used the Q-Method, a technique for assessing the relative importance of elements in various contexts. We identify and describe four perspectives (factors) using Q-method: (1) “critical shoals”; (2) “waterway, death project”; (3) “dams on waterways” and (4) “freedom for waterways”. Within these perspectives, economic incentives, with insights to cut down costs and increase freight are main concerns. We found disconnection between the reality of local communities and the lack of awareness on negative impacts by government officials and economic agents interested in waterway development. Mechanisms to guarantee social participation in IWT planning and implementing could foster socially acceptable solutions for technical, economic and governance issues.

Discrete Wavelet Transform and Ensemble Tree Algorithms for Air Pollutant Modeling: A Case Study

Air pollution is one of the greatest environmental problems of our time on a global and local scale. Elevated and even low but constant levels of harmful emissions in the air in urbanized areas pose serious risks to the health of the population. This paper develops a new approach for statistical modeling of time series of air pollutants, depending on meteorological factors. A new framework based on discrete wavelet transform (DWT) is proposed for decomposing pollutant's time series as a sum of components that represent trend, seasonality, and other specific characteristics. A key element in the applied DWT is an adaptive scheme for selecting the threshold value to control the reverse DWT's accuracy for achieving better prediction of the time series values. The resulting components are modeled with cutting-edge predictive ensemble tree algorithms, including bagging, boosting, and stacking techniques. This approach is tested with real data measured with a mobile automated station in the Plovdiv region, Bulgaria. All models are evaluated, analyzed, and cross-validated. The models are applied for short-term pollution forecasts.

Effect of Different Ratios of Gasoline-Ethanol Blend Fuels on Combustion Enhancement and Emission Reduction in Electronic Fuel Injection Engine.

The severity of engine emissions for the environment and human health cannot be ignored. This article optimizes the combustion and emission of gasoline-cassava bioethanol fuel blends in electronic fuel injection engines using response surface methodology to achieve the goal of reducing carbon and pollutant emissions. The experiment investigated the effects of different gasoline-cassava bioethanol mixing ratios (G100, G90E10, G80E20, and G70E30) on engine performance, including torque, brake specific fuel consumption, power, total hydrocarbons, nitrogen oxides, and carbon monoxide emissions. The results show that the gasoline-cassava bioethanol fuel blend is not as good as G100 in terms of braking power, torque, and brake specific fuel consumption, but better than G100 in terms of carbon monoxide emissions and total hydrocarbon emissions. Then, the optimization objective function was determined, and the combustion and emission characteristics were optimized using the response surface methodology method. The optimization results indicate that the response surface methodology method can determine the interaction between design variables such as brake specific fuel consumption, nitrogen oxides, and total hydrocarbon emissions and find the best solution. In this experiment, the independent variables of the best solution were 72.9 N·m torque, 30% G70E30 mixing rate, and 2000 rpm speed, corresponding to brake specific fuel consumption at 313 g/(kW·h), nitrogen oxide emissions at 2.85 × 103 ppm, and total hydrocarbon emissions at 166 ppm. The findings of this study indicate that by optimizing the gasoline-cassava bioethanol mixture ratio, lower emission levels can be achieved in electronic fuel injection engines, thereby promoting the sustainable development of renewable energy and reducing pollutant emissions.

Air Quality Implications of Using Ammonia as a Renewable Fuel: How Low Can NOx Emissions Go?

In addition to their lifecycle carbon emissions, another important issue with decarbonized energy pathways is their air quality, water, or land use implications. This paper considers the air quality issue for ammonia combustion. When directly combusting ammonia, reactions of its N atom with atmospheric oxygen lead to NOx emissions that are O(103) ppm, 2 orders of magnitude higher than EPA limits or the amount emitted by current natural-gas-fired technologies. In order to provide guidance to policymakers and technologists on what is fundamentally possible, this Perspective analyzes the fundamental minimum NOx emissions that can be produced from ammonia combustion. The analysis shows that it is possible to achieve quite low NOx emission levels of O(10) ppm, but these designs differ markedly from those used in today's lean, premixed combustion systems.

Entrainment effects on combustion and emission characteristics of turbulent non‐premixed ammonia/air and methane/air swirl flames through a developed perforated burner

AbstractA fuel/oxidizer mixture can be burned using a colourless distributed combustion (CDC) process to obtain low emissions and homogeneous combustion. As an alternative way, a perforated burner can be designed to achieve homogeneous combustion and low emissions without changing the combustion performance by having entrainment effects on the combustion chamber. In this study, computational fluid dynamics (CFD) 3D modelling was performed in a perforated burner for ammonia/methane fuels in order to obtain the distributed regime and focus on the entrainment effects. In numerical analysis, the eddy break‐up was used as combustion model, k‐Ɛ as turbulence model, and P‐1 as radiation model. In this study, 10% and 20% entrainment rates were provided from the flame holder wall of the perforated burner. The effects of entrainment rates on temperature, velocity, and NOX emission values were examined. According to the results, when the entrainment rate was increased from 10% to 20%, the overall temperature values of ammonia and methane combustion slightly increased by approximately 1.0%, while on the other hand the maximum temperature levels in the near burner zone decreased by about 5.0%. The findings demonstrated that temperature and velocity distributions got more uniform and the flame zones became thinner. This provided a more colourless and invisible flame appearance. In this way, an improvement in the thermal field has been achieved. In conclusion, when the effect of the distributed regime on NOX emission levels was examined, it has been noted that entrainment effects enable the achievement of low emission levels (approximately 9.0%).

New model for evaluating greenhouse gas emissions from sludge treatment based on fossil and biogenic carbon migration

The treatment and disposal of massive amounts of sewage sludge are potential emission sources of greenhouse gases (GHGs) which strongly depend on the migration of fossil and biogenic carbon into GHGs. Owing to the lack of fossil carbon data and suitable estimation models, CO2 emissions generated from sludge combustion and biodegradation are considered carbon-neutral according to the Intergovernmental Panel on Climate Change (IPCC), increasing the inaccuracy of GHG emissions accounting. Therefore, this study aimed to build a new comprehensive assessment model to accurately evaluate GHG emissions from four typical sludge treatment and disposal approaches. Notably, fossil and biogenic carbon migration were considered, rather than the emission factor method when measuring direct GHG emissions. The results of 14C analysis, which quantified the contributions of fossil and biogenic carbon to the sludge samples, showed significant differences in the average fossil carbon fractions among the four types of sludge: 84.11% for chemical sludge, 25.99% for tannery sludge, 79.19% for textile dyeing sludge, and 45.97% for municipal sludge. According to our model, the route of safely landfilling deep-dewatered sludge possessed the highest GHG emission factors of 1.18–3.75 tCO2eq/t dry sludge. The optimal sludge treatment option was anaerobic digestion followed by land application. This treatment maintained a low and stable level of GHG emissions (0.48–0.54 tCO2eq/t dry sludge) and exhibited low sensitivity to changes in fossil carbon fraction and carbon content according to the sensitivity analysis results. For sludge with a high calorific value and a low fossil carbon fraction, the route of dry incineration + utilization of ash and slag as building materials was carbon-negative and more suitable than anaerobic digestion to achieve carbon neutrality. This study complements the fossil carbon data gaps of sludge in the IPCC Guidelines and provides a more accurate GHG emissions accounting model, which will support the sludge treatment industry in developing effective strategies to reduce GHG emissions.

The effect of geopolitical risk on carbon emissions: influence mechanisms and heterogeneity analyzed using evidence from China.

To meet the goals of reducing adverse effects, continuing economic transformation, and achieving sustainable development, it is necessary to understand the impact mechanism and heterogeneous effects of geopolitical risk on carbon emissions. Using panel data from 30 provinces in China gathered between 2003 and 2019, we show that (1) geopolitical risk significantly contributes to the growth of carbon emissions, as does non-renewable energy consumption, trade, and economic growth, but that technological progress, industrial structure upgrading, and marketization inhibit the growth of carbon emissions; (2) geopolitical risk inhibits carbon emissions by suppressing non-renewable energy consumption and trade, and promoting technological progress; and (3) geopolitical risk has heterogeneous effects on carbon emissions in different quartiles. In the lower quartiles (i.e., groups with lower emission levels), geopolitical risk suppresses carbon emissions, while in higher quartiles (i.e., groups with higher emission levels), geopolitical risk promotes carbon emissions. As growing geopolitical risk and carbon emissions are now common problems for all countries, this study serves as a valuable reference not only for China, but for every member of the global community seeking to mitigate geopolitical risk shocks and achieve carbon emission reduction targets.

Numerical analysis of the effects of interconnector design and operating parameters on solid oxide fuel cell performance

Fuel cells can provide higher electrical conversion efficiency than traditional coal-fired power plants and electric generators based on internal combustion engines. In addition, high-efficiency solid oxide fuel cells (SOFC) have two specific advantages compared with other fuel cells as a result of their high-temperature operation. First, SOFCs are compatible with various fuels, ranging from hydrogen to CO and hydrocarbons. Second, SOFCs generate significant amounts of exhaust heat that can be used in combined heat and power systems. Furthermore, SOFCs have quiet and vibration-free operation, eliminating the noise typically associated with power generation systems. These fuel cells also produce no or very low levels of SO2 and NO emissions. In this study, we numerically investigated the performance of a planar SOFC with different interconnector designs at various operating temperatures. Multiple parameters were considered, such as interconnection geometries, anode and cathode materials, operating temperatures, and flow rates. As a result, the horizontal sinusoidal flow channel geometry, operating temperature of 600 °C, hydrogen gas flow rate of 86.5 SCCM/min, and oxygen gas flow rate of 28.75 SCCM/min, NiO anode material, and LSCF cathode material provided the greatest performance in terms of energy and current density.

A systematic literature review on machine learning applications at coal-fired thermal power plants for improved energy efficiency

ABSTRACT Power generation comprises high environmental and ecological impacts. The global power industry is under pressure to develop more efficient ways to operate and reduce the impacts of inherent process variability. With the rapid development of technologies within the energy sector, large volumes of data are available due to in-time operational measurements. With increased computer processing capabilities, machine learning is applied to explore these in-time operational measurements for improved process understanding. This research paper investigates machine learning algorithms for energy efficiency improvement at coal-fired thermal power plants by conducting a systematic literature review. This research is essential since it provides guidelines for applying machine learning towards sustainable energy supply and improved decision-making. Subsequently, efficient processes result in the reduction of fuel usage, which results in lower emission levels for equivalent power generation capacity. Furthermore, this study contributes towards future research by providing valuable insights from academic and industry-related studies.

Sector-Specific Pathways to Sustainability: Unravelling the Most Promising Renewable Energy Options

Energy consumption across industries accounts for more than seventy-five per cent of total greenhouse gas emissions in the European Union. Energy is a top priority for achieving climate goals and low greenhouse gas emission levels. The comparison of sustainable development patterns in renewable energy sources is carried out for all the different sectors analysed for the study, such as industry, services, agriculture, transport, and households. Specifically, researchers examined trends in each of these sectors. This study aims to create a model that combines qualitative and quantitative research approaches to obtain the most objective and descriptive data on RES technologies used in different sectors of the economy. According to the results, both solar energy and biomass have strong development potential overall, which is reflected in the higher average values of the overall results. This is also the case when looking at the impacts individually.

Reaction behaviors in pulverized coal MILD-oxy combustion affected by physical and chemical effects of diluents

In pulverized coal MILD-oxy combustion process, the oxidizer diluents are switched from N2 to CO2 and H2O. Hence, the remarkable discrepancies in combustion characteristics directly originate from the differences in physical and chemical properties of diluents, namely, the physical and chemical effects. This work utilizes the fictious materials, i.e., FCO2 and FH2O, which have the same physical properties with the real ones but are completely non-reactive, to isolate these two dilution effects. Their individual and combined impacts on the global reaction behaviors are numerically evaluated. Results reveal that the physical effect of CO2 and H2O plays an important role in enhancing the internal flue gas recirculation. Compared with H2O-dilution, CO2-dilution better inhibits the temperature rise and promotes the in-furnace thermal uniformity, which predominantly originates from its physical effect. Hence, the MILD reaction regime with high temperature and strong dilution levels occur in a wider region. The homogeneous diffusion/kinetics-controlled regime (0.2 < Dat < 2) is more susceptible to the chemical effect of CO2 and H2O. The kinetics-controlled regime of heterogeneous reaction is facilitated under CO2- and H2O-dilutions, where the physical effect is dominant in the former case while the physical and chemical effects act jointly in the latter case. The chemical effect of CO2 and H2O is responsible for greatly strengthening gasification reaction by direct participating in the reaction process, which in turn slows down the burnout of char. Importantly, H2O-dilution shows greater potential to lower NO emission level than CO2-dilution. The physical effect is revealed to play a dominant role in reducing the global NO formation rate, while the chemical effect enhances the reburning of NO in a wide lean-O2 reduction region. The findings of this work are expected to help gain a more comprehensive understanding in MILD-oxy combustion technology.

Fixed and mobile broadband penetration and CO2 emissions: evidence from OECD countries

The recent rapid increase in Internet data traffic and use of digital technologies—observed during the pandemic and forecasted as a consequence of the massive digital transition occurring in the world economies—are feeding concerns about the related possible negative environmental impacts, in terms of both energy consumption and Carbon Dioxide (CO2) emissions. We contribute to such debate by analysing the relation between two different digitalization dimensions, namely fixed and mobile broadband connections penetration, and CO2 emissions at the country level. Our paper provides empirical evidence, based on a panel of 35 OECD countries, that higher fixed and mobile broadband penetration levels are associated with lower levels of CO2 emissions, according to an Environmental Kuznets Curve-type relation. Moreover, we investigate whether the environmental effects of these two digitalization dimensions differ across high- and low-income OECD countries. By adopting fixed-effects models and fixed-effects two-stage least square estimators, the results, besides substantiating the Kuznet’s hypothesis in both groups of nations, confirm that higher fixed and mobile broadband penetration levels are associated to a reduction of CO2 emissions.

The global roots of pre-1900 legacy mercury

During the nineteenth century, a major change took place in the trade, production, and use of mercury that altered its nearly exclusive link to silver refining in the Hispanic New World. We track the global expansion of mercury markets in chronological detail from 1511 to 1900 using historical archives on production and trade, a detailed country-by-country accounting of the pool of anthropogenic mercury from which legacy mercury was ultimately generated. The nature and profile of pre-1900 legacy mercury extends beyond silver refining, mercury production, and gold extraction, and includes alternate sources (vermilion, felt, mercury fulminate) and new regions that were not major silver or gold producers (China, India, United Kingdom, France, among others), that accounted for approximately 50% of total mercury consumed in the nineteenth century. The nature of the pre-1900 mercury market requires a quantitative distinction between legacy mercury and historic anthropogenic mercury production and use, since the chemistry of its end-uses determines the pathways and timelines for its incorporation into the global biogeochemical cycle. We thus introduce the concept of a mercury source pool to account for total historic anthropogenic mercury within and outside this cycle. Together with a critical review of previous assumptions used to reconstruct the historical use and loss of mercury, a much lower level of emissions of pre-1900 legacy mercury is proposed. A coordinated effort across disciplines is needed, to complete a historically accurate scenario that can guide the multilateral policies adopted under the United Nations Minamata Convention to control mercury in the environment.

The role of resource rent in shaping CO2 emissions in BRICS countries: A panel data approach

This study investigates the impact of resource rent on CO2 emissions in the presence of GDP, renewable energy consumption, and research and development spending for BRICS nations from 1990 to 2020. Employing quantile regression approach, this study finds that resource rents are responsible for rising CO2 emissions in BRCIS countries. However, there exists a threshold level of resource rents beyond which the nature of the relationship between variables changes. Since, the extraction of natural resources requires a significant amount of energy, it may result in excessive levels of energy consumption as well as the reckless discharge of waste chemicals into the water, land, and air. We find that the impact of GDP on CO2 emissions is greater for nations with a low level of CO2 emissions and is lower for nations with relatively high CO2 emissions. The findings of the research paper highlight several policy implications for the BRICS nations to reduce their CO2 emissions. Policymakers should prioritize investment in renewable energy sources such as wind, solar, and hydroelectric power and encourage research and development spending in renewable energy technologies. The study encourages channelizing resources revenue for a sustainable environment and development.

Twin injector biogas diesel RCCI mode-an effective means to reduce NOx emissions without penalty in fuel consumption

The RCCI (Reactivity Controlled Charge Compression Ignition) mode of operation of an IC engine using biogas and diesel as fuels has the potential to offer high efficiencies and low NOx and soot emissions. One of the drawbacks while converting conventional diesel engines to run in this mode is the wall wetting of the diesel that has to be injected early in the compression stroke. This leads to high THC emissions and lubricating oil dilution. In this work a twin cylinder turbocharged, common rail diesel engine was modified to accommodate a newly developed Narrow angle Injector (NI) for early injection of diesel without wall wetting, along with the existing Wide angle Injector (WI). Biogas was also injected into the intake manifold and the engine was run in the RCCI mode. The effectiveness of this novel twin injector dual fuel RCCI concept has been experimentally assessed at different biogas energy shares under a BMEP of 3 bar and at a constant engine speed of 1500 rpm. The different biogas – diesel modes considered were the conventional dual fuel mode (CDF), RCCI with the WI alone, RCCI with the NI alone and finally RCCI with the combined NI-WI. In the biogas diesel RCCI mode the use of only the WI resulted in low efficiency, high THC and smoke emissions due to cylinder wall wetting of diesel. Though the use of only NI in this mode could eliminate cylinder wall wetting, the diesel directly hitting the piston bowl resulted in poor performance. However, the combination of NI and WI resulted in high BTE and extremely low levels of NOx emissions and lower THC as compared to the CDF mode. The range of injection timings for the NI was 90° to 45° bTDC while for the WI it was 42° to 4° bTDC when the energy share of biogas was changed. Thus the use of two injectors with wide and narrow injection spray angles for diesel gave enhanced flexibility in operating at widely different injection timings as required in biogas diesel RCCI operation.

CFD analysis of combustion and emission characteristics of biodiesel under conventional and late-injection based premixed combustion conditions

The simultaneous reduction in NOx and smoke emissions can be achieved with biodiesel under a late-injection based low temperature combustion (LTC) strategy. However, this occurs at the expense of a substantial increase in unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. It is worthwhile to understand the reasons behind the formation of these emissions, emphasizing comparison with conventional combustion, which is known to result in significantly low HC and CO emission levels, particularly with oxygenated biodiesel fuel. The present investigation attempts to examine the same with 3D CFD simulation. Experimental data were obtained from a light-duty diesel engine using biodiesel from non-edible Karanja oil. The unmodified engine with OEM low-pressure mechanical fuel injection system was utilized for conventional combustion operation. It is replaced with a modified common rail injection system for a late-injection-based LTC mode of operation. By combining retarded high-pressure injection with EGR, sufficient premixing was sustained to enable late injection-based premixed combustion (LI LTC). The combustion simulation was performed using CONVERGE CFD tool, utilizing a two-component surrogate of methyl butanoate (MB) and n-dodecane to represent biodiesel. A reduced chemical kinetic mechanism, developed and validated in an earlier investigation on biodiesel combustion, was utilized in the current study. The mechanism was solved using the SAGE Detailed CHEMKIN solver in CONVERGE. Validation was conducted at two engine operating conditions defining low and high loads for both combustion modes. The cylinder pressure and heat release rates were predicted with a maximum error of 1.5 and 13%, respectively. The validated CFD tool was employed to compare and analyze the equivalence ratio, in-cylinder gas temperatures, and HC and CO contours between conventional and LI LTC modes. Under LTC mode, the cylinder pressure and heat release rates were predicted with a maximum error of 10 and 15%, respectively. The comparison revealed fuel-rich regions concentrated near the bowl in conventional combustion, while the fuel was spread throughout the combustion chamber in LI LTC mode with over-rich and over-lean regions near the cylinder wall. The cylinder temperature is significantly higher for conventional combustion than LI LTC mode. The O and OH radical concentrations are higher for conventional combustion, corroborating with lower CO emissions, as they aid in CO oxidation. Fuel-rich regions contribute to increased CO emissions, whereas over-lean regions at a low-temperature result in high HC emissions, exhibited by the emission contours. Possible countermeasures to reduce high HC and CO emissions in LI LTC mode include maintaining higher coolant temperatures to enable HC and CO oxidation in the near-wall regions and fuel injection system modification to alter the air–fuel mixing.

Towards sustainable development goals: Does common prosperity contradict carbon reduction?

In the light of China’s synergistic need to achieve Sustainable Development Goals (SDG) 10 and 13, it is necessary to consider the potential nexus between common prosperity and carbon reduction. Therefore, this work proposes a new comprehensive measure to assess the degree of common prosperity in 30 Chinese provinces from 2006 to 2019. Furthermore, we examine the impact of common prosperity on carbon emissions applying the system-generalized method of moments (SYS-GMM) approach. All major conclusions are as follows: (1) the level of common prosperity has continued to increase between 2006 and 2019; (2) common prosperity and carbon reduction are compatible with each other, i.e., common prosperity significantly reduces carbon emissions; (3) common prosperity reduces carbon emissions indirectly by improving labor productivity and upgrading industrial structure; (4) carbon emissions are indirectly increased by common prosperity through the expansion of gross fixed capital formation and higher levels of urbanization, and (5) in provinces with higher levels of common prosperity and lower levels of carbon emissions, common prosperity has a considerably greater influence on carbon emissions. Finally, we suggest several policy implications for promoting China’s sustainable development.

Assessing light flex-fuel vehicle emissions with ethanol/gasoline blends along an urban corridor: A case of Fortaleza/Brazil

Brazil is the 9th largest producer of vehicles in the world, with 62.7% of the global fleet of Flex-Fuel Vehicles (FFVs). These vehicles used in Brazil operate with E27 (anhydrous ethanol used for gasohol blending) or E100 hydrous ethanol or any blend between these two. In recent years, Fortaleza city/Brazil has implemented Bus Rapid Transit (BRT) systems in two of the city’s most important avenues. Fortaleza BRT has two-way busways on the central verge of the roadway separated by two lanes from mixed traffic used by passenger cars, light commercial trucks, motorcycles, and heavy-duty vehicles. These systems have been regarded as a potential solution to improve some traffic factors, for only Buses, such as the average driving speed, thus benefiting both transportation and the environment. Thus, this research proposes a comprehensive impact evaluation of an FFV when traveling on BRT corridors, specifically on lanes from mixed traffic, and evaluate the emission factors, specifically on lanes from mixed traffic, composed of a wide variety of vehicle types. All tests in this study were performed at lanes from mixed traffic. Carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HCt) emissions were experimentally measured using a Portable Emission Measurement System (PEMS) under real-world traffic conditions in Fortaleza. FFV tailpipe emissions from E27, E85, and E100 fuels were highly sensitive to the power demand and traffic flow. Additionally, the VSP (Vehicle Specific Power) methodology was applied to characterize the driving modes. Overall, results showed the following: CO2 was, by far, the most highly emitted gas; the highest CO release occurred with E85 blend; NOx emission factors were similar for both E27 and E85, but much greater for E100; and HCt did not show a pattern, presenting both the highest and lowest emission levels with E100.

Large eddy simulation of a premixed dual-fuel combustion: Effects of inhomogeneity level on auto-ignition of micro-pilot fuel

In a premixed dual-fuel (DF) methane-diesel engine, the ignition of the lean premixed methane/air mixture starts with the assistance of a pilot diesel injection. Auto-ignition of pilot fuel is important as it triggers the subsequent combustion processes. A delay in the auto-ignition process may lead to misfiring, incomplete combustion, and thus higher greenhouse emissions due to methane slip. Hence, a better understanding of the auto-ignition process for the pilot fuel can help to improve the overall engine performance, combustion efficiency, and to lower exhaust emission levels. In the present study, large eddy simulation (LES) is used to investigate the auto-ignition process of micro-pilot diesel in premixed DF combustion in a constant volume combustion chamber (CVCC). The entire DF combustion processes including methane gas injection, methane/air mixing, pilot diesel injection, and ignition are simulated. The numerical model is validated against experimental data. The present numerical model is able to capture the ignition delay time (IDT) within a maximum relative difference of 7% to the measurements. A higher relative difference of 38% is obtained when methane gas injection and mixing are omitted in the simulation and the methane/air is assumed homogeneous. This demonstrates the importance of inhomogeneity pockets. To study the effects of temperature and methane inhomogeneities separately, different idealized inhomogeneities in temperature and methane distribution are considered inside the CVCC. The inhomogeneity in the temperature is observed to have a more profound influence on the IDT than the methane inhomogeneity. The inhomogeneity pockets of temperature advance the first-stage ignition and, subsequently, the second-stage ignition. A sensitivity analysis on the effect of inhomogeneity wavelength reveals that the larger wavelengths enhance the combustion due to the presence of pilot diesel jets in the desirable regions for a longer time duration.