Reduce Emission Levels Research Articles

Combustion and emission characteristics of a compression ignition engine operated on dual fuel mode using renewable and sustainable fuel combinations

The present experimental study aims to examine the combustion and emission characteristics of a single cylinder four stroke direct injection diesel engine operated in dual fuel mode using dairy scum oil methyl ester (DiSOME) and its blend (B20)—producer gas combination with and without addition of hydrogen. DiSOME/B20-producer gas combination without hydrogen addition exhibited inferior performance with increased hydrocarbon and carbon monoxide emissions owing to poor physic-chemical properties of both biodiesel and inducted low calorific value gas (producer gas) compared to the same fuel combination with hydrogen. Producer gas was inducted along with air, and hydrogen was allowed to mix with air-producer gas combination in the intake manifold. Experimental investigations were conducted at all load conditions and at constant flow rate of hydrogen (8 lpm). It was noticed that that B20-hydrogen enriched producer gas combination with optimum parameters resulted in amplified thermal efficiency with reduced emission levels compared to the operation with B20/DiSOME-producer gas combination. However, investigation showed that diesel-producer gas combination with hydrogen addition provided amplified brake thermal efficiency by 3.8%, 16.4% and 13.2% compared to the diesel/DiSOME/B20—producer gas combinations, respectively, at 80% load. Hydrogen addition provided enhanced cylinder pressure and heat release rate with reduced emission levels except nitric oxide emissions. It can be concluded that the deprived combustion associated with DiSOME/B20-producer gas combination can be improved with hydrogen addition. The combination of DiSOME-producer gas operation with hydrogen addition is uniqueness of this present work.

Evaluation of the performance and emission of diesel engine by using sterculia foetida biodiesel blend and DMC additive

The aim of the article is to determine the effects of Sterculia Foetida Biodiesel (SFB) blend and Di-Methyl Carbonate (DMC) blends in a Diesel engine. The selection of these SFB and DMC was taken into the consideration to reduce emission levels and improving the performance. The experimental study was carried out on a 4 S single cylinder diesel engine with standard best constant variables and under different load conditions of diesel engine with SFB20 mixture and various propagation of DMC (for example 5%, 10% and 15%). After that, the engine performance and emissions output were analyzed. The use of SFB20 fuel can improve the performance of the engine. In addition, it is found that by adding DMC with SFB20 fuel the better results of BTE and BSFC were obtained as compared to SFB20 fuel and diesel baseline fuel. It can also be seen that the amount of DMC additive mixed in the SFB20 fuel will reduce emission results such as HC, CO and smoke opacity. However, NOx increases with the addition of DMC additives. The main reason for these results is presence of more O2, low viscosity and high volatility in the additive, which helps to increase the temperature during the combustion process.

Hydrogen as the futuristic fuel for the aviation and aerospace industry – review

Purpose The rise in demand and high utilization of fuel causes severe environmental threat for the nations on the globe. Rapid burning potential of hydrogen produces enormous amount of thrust, and it is mainly owing to wide flame range and less onset of ignition. Design/methodology/approach The significant contribution of hydrogen as fuel has been explored by several researchers around the globe recently to use in aviation sector owing to its eco-friendly nature. Hydrogen is a safe and clean fuel, and it can be generated from several sources. The effects of addition on hydrogen on gas turbine on combustion characteristics and emission concentration level on atmosphere have been reviewed in this paper. Findings Incorporation of hydrogen is effective reducing nitrous oxide emission, high calorific value and flame less combustion. Addition of hydrogen to higher proportions enhances the combustion performance, minimizing the setbacks of conventional fuel and meets the specified standards on emission. Originality/value From the literature review, the comparative study on hydrogen with other fuel is explained. This paper concludes that addition of hydrogen in fuel enhances the performance of combustion on gas turbine engine along with significant reduction in emission levels.

Research on the Relationship between Economic Growth, Environmental Governance Investment and Carbon Emission--Based on the Time Series Data from 2000 to 2019

The study on the relationship between investment in environmental governance, carbon emission and economic growth is helpful for the relevant government departments to coordinate the influence among them when formulating the policies of reducing emission and conserving energy, so as to take the comparative advantages of various factors and promote the benign interaction between economic development and environmental governance. In this paper, the data of Per capita GDP, per capita investment in environmental governance and per capita CARBON dioxide emissions in China from 2000 to 2019 are selected as the research basis, and variables are studied by means of Granger causality and impulse response function. As shown in the results, there is a single Granger relationship between investment in environmental governance and carbon emissions, that is, the increase of investment in environmental governance leads to the reduction of carbon emissions. The influence of economic growth on environmental governance investment is small, but in the long term, it can restrain the growth of carbon emissions. Investment in environmental governance can promote economic growth and stimulate a reduction in the emissions in the short term; Economic growth was hindered by the emissions in the long term and fail to stimulate increased investment in environmental governance. Based on these findings, this paper proposes policy Suggestions for optimizing the structure of environmental governance investment, improving the carbon emission monitoring and response mechanism, and strengthening the technological level of energy conservation and emission reduction.

Integrating Price-Incentive and Trip-Selection Policies to Rebalance Shared Electric Vehicles

Because electric vehicle sharing (EVS) offers the advantages of high flexibility and convenience, it has been receiving increasing attention worldwide as an effective approach to easing traffic congestion and environmental pollution. However, unbalanced electric vehicle distribution is an obstacle in the development of EVS. In this paper, we propose an integrated strategy to mitigate the imbalance issue and enhance customers’ adoption of EVS. We construct an integrated strategy that combines the price-incentive approach with the trip-selection policy and models uncertain travel demand in a continuous trip-adopting process based on our integrated strategy. Aiming to improve EVS operating profits, we apply spatiotemporal nonlinear mixed-integer programming to formulate the travel pricing and rebalancing plan. Additionally, we approximate the model in a tractable form after analyzing the optimal service adoption and develop an efficient exact algorithm to handle the nonlinear items. The computational results of a real-world car2go Amsterdam case study demonstrate several economic and environmental benefits generated by our integrated policy, including (i) higher profits for EVS operators, (ii) improved service satisfaction for consumers, and (iii) a higher level of carbon emissions reduction, from 381 grams per mile to 225 grams per mile, beneficial for the social environment. Moreover, according to the case study, an appropriate initial fleet size, high rebalancing frequency, low labor cost, high potential travel demands, and short charging time also benefit EVS operation.

Life cycle assessment for enhanced Re-liquefaction systems applied to LNG carriers; effectiveness of partial Re-liquefaction system

The marine industry has been striving to seek for proper strategies to curb air emissions from global shipping activities. To support the transition to sustainable shipping, this paper was proposed to evaluate the holistic environmental benefits of the LNG partial re-liquefaction system applied to LNG carriers by comparing among five different combination/configuration of LNG re-liquefaction systems. The theory of life cycle assessment was employed with the help of a commercial software, Sphera GaBi version 2019 to quantify the magnitude of various emissions under different life stages of the proposed systems: manufacturing, installation, use and recycling. A case study was implemented with a 174,200 m3 LNG carrier and the input data for the analysis was collected from true-to-life sources provided by manufacturers and ship operators. The electric consumption of the five systems were calculated by means of Aspen HYSYS software. A range from 1.23 to 1.64 kWh/kg was estimated and was used as key parameters to confirm the onboard electricity demands at the use phase of the five systems. The results revealed that the partial re-liquefaction system had considerable effects on the reduction in emission levels across the following five impact categories: Global Warming Potential, Particulate Matter, Photochemical Ozone Creation Potential, Eutrophication Potential and Acidification Potential. An optimal option which adopted the partial re-liquefaction system was found to release 4.49 × 108 kg CO2 eq. 1.25 × 106 kg PM2.5 eq. 7.16 × 106 kg NMVOC eq. 2.46 × 106 kg N eq. and 1.13 × 107 kg SO2 eq. in its lifetime, which were roughly equivalent to 25% emission reductions compared to the rest of the candidates to which the partial re-liquefaction principle was not applied. Lastly, it clearly presents the effectiveness of life cycle assessment. This research, particularly, suggests that this holistic approach should not be underused for resolving innumerable maritime environmental issues that appear unsolvable with the current practices in the maritime industry.

Green Supply Chain Decisions Under Different Power Structures: Wholesale Price vs. Revenue Sharing Contract.

In the market, once consumers have a low-carbon preference, they will choose green low-carbon products. The market demand for green products is not only related to product price, but also consumers’ low-carbon preference. In this way, enterprise has to consider the cost of carbon emissions in the process of production and operation. In this paper, we consider a two-level supply chain system composed of a manufacturer and a retailer. The supply chain system can determine the price of products and the level of carbon emission reduction through different supply chain contracts: wholesale price contract and revenue sharing contract. However, the power control structure of a manufacturer and a retailer is different, which will further affect the decision-making strategy of the supply chain system. We set up four models (Wholesale Price—NM and NR, and Revenue-Sharing—SR and SM) of the supply chain with carbon emission reduction, and calculated and analyzed. The results show that firstly, regardless of whether the manufacturer’s power control structure or the retailer power structure is dominant, the manufacturer wholesale price with a contract on revenue-sharing is always higher than on wholesale price, and it is inversely proportional to the revenue-sharing proportion. Secondly, under the two power control structures, the carbon emission level of the manufacturer with a contract on revenue-sharing is always lower than on wholesale price, and it gradually decreases with the increase of the revenue-sharing proportion of the manufacturers. Thirdly, when the retailer dominates the supply chain, the retailer selling price with a contract on revenue-sharing is always higher than on wholesale price. Under the manufacturer’s power control structure, when the revenue-sharing ratio is small, the retailer selling price with a contract on revenue-sharing is higher than on wholesale price; when the revenue-sharing ratio is large, the retailer selling price with a contract on revenue-sharing is lower than on wholesale price. Finally, the validity of the model is verified by an example, and the sensitivity of the parameters is analyzed.

Omni-Channel Retailing With Consumer Preference and Carbon Emission Efforts

With the popularity of omni-channel retailing, many retailers have begun to offer customers choices to decide whether to shop online or in a physical store, considering customers preference for different channels. This paper has studied omni-channel retailing in which the retailers sell low-carbon products through online and physical channels. The research has been conducted under three different decision circumstances (i.e., physical store-leader Stackelberg model and online store-leader Stackelberg model under the decentralized decision and centralized decision). The results show that both the retailers' profit in a single channel and the total profit in two channels will decrease with the customers' preference and the effort level of emission reduction. In addition, under decentralized decision, online store-leader Stackelberg model is more beneficial to the retailers.

Impacts of partial-load service on energy, exergy, environmental and economic performances of low-temperature compressed air energy storage system

An energy analysis of the off-design operation of a low-temperature adiabatic compressed air energy storage system has recently been presented. However, it is still unknown how the partial-load operation of this system could affect its exergy parameters, economic feasibility, and environmental impacts. Therefore, this study investigates the effects of the partial-load service of a low-temperature adiabatic compressed air energy storage system on its technical (energy and exergy), economic and environmental performance. The findings of the study will be very useful for optimal energy management and bidding strategy determination of power plants using this technology as the storage unit. This will be primarily of more importance for an energy storage unit that is connected to a renewable power plant, and thus, is under higher risk of operating in off-design conditions. The results indicate that the energy and exergy efficiencies of the system at the nominal load can be as high as 65%, while at 30% load, neither of these can be higher than 45%. The economic analysis shows that in the Danish electricity system as the case study, the payback period can be as short as 12 years if the system continuously works at the nominal load while for 80% operation load, the payback period will be about 22 years. Similarly, the emission reduction level achievable by using the system significantly decreases if it works in off-design conditions.

Assessing transport emissions reduction while increasing electric vehicles and renewable generation levels

Electric Vehicles (EVs) appear as an environmental solution for transport sector since they emit zero emissions while driving. Nonetheless, the carbon intensity (CI) of the energy sources involved in the electricity generation system could seriously compromise this solution. Hence, this study proposes a methodology to verify the sustainability of the sector by the introduction of EVs. By means of the “Well-to-Wheel” tool, it compares emissions generated by two fleets: one based on internal combustion engine vehicles (ICEVs) and another one that also contemplates different EVs penetration levels. This methodology develops an iterative process on the contribution of renewable sources to the electricity generation system until a certain level of emissions reduction is achieved. The needed evolution of the CI for the electricity system is therefore deduced. The methodology has been applied to Spain by the mid-term future, given these country policies for both a high penetration of EVs and a progressive introduction of renewable sources in its electricity system. Results indicate that the current Spanish electricity mix allows for a reduction in CO2 emissions by the introduction of EVs, but a 100% renewable system will be needed for reductions up to 74 million tons per year. This research is a first-ever study to relate the forecasted Spanish environmental policies, in terms of urban transport and configuration of the power system, with a sustainable introduction of EVs in the urban fleet. Hence, this paper would be very helpful for policy makers on evaluation of the requirements for a transport fleet electrification.

Cleaner production of Pakistan’s chemical industry: Perspectives of energy conservation and emissions reduction

The chemical industry is one of the highest energy-consuming and CO2 (carbon dioxide) emitting sectors in Pakistan. It is important to understand and identify ways to improve the sustainability features of the input factors. This research has attempted to examine the potential of input factors (capital, labor and energy consumption), output elasticities, and substitution elasticities in Pakistan’s chemical sector by using a translog production function. The ridge regression technique was applied to investigate the parameters of the function during 1980–2018. The results show that the output elasticities between capital, labor and energy consumption are positive; the elasticities of substitution between capital-energy, capital-labor and labor-energy consumption are close to 1, stable, and positive, which shows that these indicators are substitutes for one another. Moreover, based on the analyzed methodology, we estimate the level of energy conservation and CO2 emission reduction in 2018. Policy suggestions related to the given outcomes are presented below.

The Game Analysis of Low Carbon Supply Chain Emission Reduction Considering Channel Power under the Concern of Fairness

The emission reduction strategies of different channel power structures is studied under the fair, neutral and fair concerns of manufacturers, and compares the emission reduction levels, wholesale and retail prices, and the changes and differences in the profits of supply chain members under various circumstances. The research shows that the increase of emission reduction cost factor is not conducive to the improvement of emission reduction level, price and profit. The profit level of manufacturer under the manufacturer-led structure is not conducive to the manufacturer-led structure due to other structures, but is conducive to the improvement of the profit level of manufacturer under other structures. Manufacturer’s equity concern behaviour is beneficial to the improvement of manufacturer’s utility, in which the equity concern factor should be kept at a certain level under Nash vertical structure. Equity concerns and emission reduction strategies under decentralized decision-making are not conducive to the improvement of the overall supply chain effectiveness.

How Behavioral Interventions Can Reduce the Climate Impact of Energy Use

Kristian S. Nielsen is a research associate in the Department of Zoology at University of Cambridge. He received a PhD from Copenhagen Business School in 2019 with a dissertation focused on the role of self-regulation in environmental behavior change. His current research focuses on bridging research in behavioral science and biodiversity conservation as part of an interdisciplinary project called Nudging for Nature. His other research interests revolve around behavior change as a climate change mitigation strategy, the dynamics of the behavior change process, self-regulation and self-control, and sustainable clothing consumption. Sander van der Linden is Reader in Social Psychology in Society and director of the Cambridge Social Decision-Making Lab in the Department of Psychology at the University of Cambridge. He is also a fellow in Psychological and Behavioral Sciences at Churchill College, Cambridge and the editor-in-chief of the Journal of Environmental Psychology. His research on the psychology of human judgment and decision-making, especially in the context of climate change, has received numerous awards including the Rising Star award from the Association for Psychological Science and the Sage Early Career Award from the Society for Personality and Social Psychology . Paul C. Stern is president of the Social and Environmental Research institute and was previously a principal staff officer at the US National Academy of Science, Engineering, and Medicine where he directed its Board on Environmental Change and Society. He is a fellow of the American Association for the Advancement of Science and the American Psychological Association. His research interests include the integration of social science into research and practice for governing environmental change and into risk assessment and management. Among his publications are Environmental Problems and Human Behavior (coauthor) and Understanding Risk: Informing Decisions in a Democratic Society (coeditor).

Exploring the growth-adjusted energy-emission efficiency of transportation industry in China

Abstract China's transportation industry has achieved significant progress but also proved one of China's primary energy- and carbon-intensive industries. Under this circumstance, it is necessary to assess the level of energy-saving and emission reduction (ESER) of China's transportation industry. Therefore, based on the panel data of China's 30 provinces during 2008–2017, this paper develops a new DEA model to evaluate the growth-adjusted energy-emission efficiency of transportation industry in China. The results show that, first of all, the growth-adjusted energy-emission efficiency of China's transportation industry is approximately 0.5543 during the sample period, and the provinces with high efficiency in their transportation industries are mainly concentrated in the central region and the Beijing-Tianjin-Hebei region; in particular, the central region takes the lead in low-carbon and energy-saving (LCES) technology of transportation industry. Second, during the sample period, the overall growth-adjusted energy-emission efficiency of China's transportation industry improves by 7.08% on average. The efficiency of the transportation industry in the eastern region improves the most, i.e., 28.99%. Finally, when evaluating the energy and/or environment-related efficiency of transportation industry, ignoring the transportation growth factors will underestimate the sustainability of transportation industry.

Occupant-based energy upgrades selection for Canadian residential buildings based on field energy data and calibrated simulations

Occupant behavior in residential buildings has a direct impact on the effectiveness of energy-saving measures. In order to realize a buildings’ carbon mitigation targets, the impact of individual occupancy profiles needs to be integrated with building simulation models. This paper introduces a decision support framework as a potential solution to make energy performance upgrade choices based on different occupancy profiles. This framework has been demonstrated through a case study of two single-family detached homes in Canada, which were highly instrumented with sensors for monitoring energy input and output. The case studies represented two common occupancy profiles-(1) a family of four (consisting of 2 working adults and 2 teenagers); and (2) a retired couple. Firstly, calibrated energy models were developed by using one-year energy use data collected through an intrusive load monitoring technique. Secondly, energy upgrade combinations were considered for each profile and tested for additional investment, payback period and greenhouse gas (GHG) emissions. Lastly, the most suitable combination of energy upgrade for each profile was ranked using a multi-criteria decision-making method (e.g., TOPSIS). Results indicated that the retired couple used more energy than the family of four and required energy upgrades with usually higher payback periods to achieve the same level of GHG emission reduction. The results of this research are timely for energy policymaking and developing best management practices, which need to be implemented along with the deployment of more stringent building standards and codes.

Collecting mode selection in a remanufacturing supply chain under cap-and-trade regulation

This paper investigates a remanufacturing closed-loop supply chain under the cap-and-trade regulation, where the collecting operations can be carried out by a manufacturer or a retailer or a third party. We construct models with and without remanufacturing to show the value of remanufacturing. The results indicate that remanufacturing can effectively improve the level of carbon emission reduction and the profits of the manufacturer and the retailer. For models with remanufacturing, we find that, interestingly, the result in the previous literature does not always hold. Specifically, the manufacturer will choose the third-party collecting mode when the unit carbon emissions in take-back process in the retailer collecting mode are much larger than those in the third-party collecting mode and the unit cost savings are relatively low, otherwise the manufacturer will choose the retailer collecting mode. As the numerical analysis shown, when the manufacturer subjects to a stringent emission control, total carbon emissions are always the lowest in the third-party collecting mode. The manufacturer's optimal collecting mode, whether is the retailer collecting mode or the third-party collecting mode, may result in the most carbon emissions when the carbon price is relatively low or the carbon intensity is high.

Strategies for Capital Constrained Timber and Carbon Sink Supply Chain under the Cap-and-Trade Scheme

We consider a capital constrained timber and carbon sink supply chain under the cap-and-trade scheme, where the forest company produces timber and carbon sink. We consider two subsidy modes: financing subsidy to the carbon sink forests and financing subsidy to the manufacturer’s emission reductions. We apply a Stackelberg model and mainly consider the impact of subsidies on the profits and the strategies of the supply chain members. The results show that when the government gives a financing subsidy to the carbon sink forests, it is conducive to promoting the expansion of carbon sink forests, as well as the enhancement of the forest company’s profit. However, a larger supply of carbon sinks generates a lower price, which leads to the manufacturer reducing the technical emission reduction level and purchasing more carbon emission rights instead. On the other hand, when the manufacturer receives a financing subsidy for the technical emission reduction costs, its production becomes cleaner than before, and the profits of the forest company and the manufacturer increase.

A Comprehensive Forecasting–Optimization Analysis Framework for Environmental-Oriented Power System Management—A Case Study of Harbin City, China

In this study, a comprehensive research framework coupled with electric power demand forecasting, a regional electric system planning model, and post-optimization analysis is proposed for electric power system management. For dealing with multiple forms of uncertainties and dynamics concerning energy utilization, capacity expansions, and environmental protection, the inexact two-stage stochastic robust programming optimization model was developed. The novel programming method, which integrates interval parameter programming (IPP), stochastic robust optimization (SRO), and two-stage stochastic programming (TSP), was applied to electric power system planning and management in Harbin, China. Furthermore, the Gray-Markov approach was employed for effective electricity consumption prediction, and the forecasted results can be described as interval values with corresponding occurrence probability, aiming to produce viable input parameters of the optimization model. Ten scenarios were analyzed with different emissions reduction levels and electricity power structure adjustment modes, and the technique for order of preference by similarity to ideal solution (TOPSIS) was selected to identify the most influential factors of planning decisions by selecting the optimal scheme. The results indicate that a diversified power structure that dominates by thermal power and is mainly supplemented by biomass power should be formed to ensure regional sustainable development and electricity power supply security in Harbin. In addition, power structure adjustment is more effective than the pollutants emission control for electricity power system management. The results are insightful for supporting supply-side energy reform, generating an electricity generation scheme, adjusting energy structures, and formulating energy consumption of local policies.

CO2 emission in transportation sector across 51 countries along the Belt and Road from 2000 to 2014

The transportation sector is a key economic sector and an important source of CO2 emissions. Due to these environmental implications and a desire to reduce emission levels, the number of empirical analyses on the transportation sector have increased significantly in recent times. Given this pretext, our study examines the heterogeneity and spatial autocorrelation CO2 emissions of the transportation sector for 51 belt and road economies from 2000 to 2014. As part of analysis, we examine the heterogeneity of CO2 emissions in the transportation sector through the use of the Theil index and semi-variogram analysis. Furthermore, our study also analyzed the global and local spatial autocorrelation of transport sector CO2 emissions using the Moran index for participating countries. From the analysis, this study found that the transportation CO2 emission intensity of Central and Western Asia and North Africa is significantly higher than that of other regions along the belt and road, and there is a strong spatial correlation in Southeast Asian countries. Our research provides a key reference point for governments by proposing carbon-reduction policies and the promotion of greener developmental initiatives within the transportation sector.

Introduction of Disruptive Gas Flow Via Fluidic Oscillation to Improve Solid Oxide Cell Performance

An increased focus on renewable technologies is necessary to meet the level of carbon emission reduction required to achieve the 2°C scenario (2DS). Carbon containing materials are at the root of most industrial value chains and currently 90% of organic chemicals are made from fossil fuels and 5-10% of global crude oil demand is for the manufacture of chemicals. By providing a process to convert waste CO2 into high value CO we can take steps towards the goal of reducing emissions and provide an important link between various sectors to turn waste materials into new products, improving resource efficiencies, and reducing negative environmental factors. This presents a significant opportunity to leverage CO2 as a feedstock while supporting global goals in green energy, manufacturing, etc.Solid oxide cells (SOCs) provide an effective mode of simultaneously reducing CO2 and separating O2, however, over 80% of the cost to co-electrolyse CO2 and H2O comes from electrical input necessary to drive a SOEC. While changes in cell geometry and composition have been used to improve performance, energy inputs need to be reduced to increase overall device efficiency for widespread commercialisation to be realised.In this work we focus on the use of oscillating the gas flow into an SOC to create a highly efficient energy conversion device to facilitate the reduction of CO2 to CO. Fluidic oscillation is known to cause disruptive flow which promotes turbulence in small flow fields, thereby increasing the overall efficiency – key to furthering their commercialisation.Fluidic oscillators are one of a variety of fluidic switching devices developed in the field of microfluidics. A single gas supply inlet guides an incoming gas flow into a destabilising microfluidic feature, generating the necessary disruption that results in jet diversion between two identical channels. This switching results in a pulsed flow in each of the outlet channels, alternating between full forward flow, and very slight backflow. The flow in the forward regime bears similarity to laminar flow, whereas the slight backflow regime more closely resembles turbulence. This effect can be observed even in extremely small channel diameters and causes a disruptive effect which interrupts the formation of a boundary layer of stagnant gas flow along flow field chamber walls. While conventional oscillators require high flow rates on the order of 50-80 L/min, for this particular work we are utilising a novel fluidic oscillator capable of producing an oscillatory flow at low onset flow rates of as low as 50 ml/min, which is necessary for operation with lab scale SOCs.Experimental results show improved performance with the addition of oscillating gas flow and no other changes to cell geometry, materials composition, or gas composition. The magnitude of improvement in polarization resistance was dependent on operating conditions, the reasons for which will be discussed in the paper.