Combustion Of Alternative Fuels Research Articles

Strontium leaching from municipal waste subjected to incineration

The aim of the study was to determine the content and leachability of Sr in ashes obtained through combusting municipal waste in household furnaces. The waste had been collected as a mixed stream and as separate fractions (i.e. furniture, sponges, waste paper, PCV packaging, plastic-coated paper cartons, imitation leather, rubber, textiles and polystyrene). Using single-step chemical extractions, (HCl + HNO3, H2O, 0.01 M CaCl2, 0.1 M CH3COOH), we determined the total content of Sr (TC) and proportions of the following fractions: water-leachable, phytoavailable and easily soluble and bound to carbonates. We also analyzed the effect of reducing pH in the extraction solutions on St leachability from the study material. The study showed that Sr concentration in ash generated from the combustion of conventional fuels, alternative fuels and municipal waste ranged from 114 to 1006 mg/kg. The largest amounts of Sr were found in ash generated from the combustion of alternative fuels (coal pellets 488–1006 mg/kg), conventional fuels (hard coal 430–670 mg/kg) and mixed waste (237–825 mg/kg). The most mobile fraction of Sr (water-leachable) comprised from 1.3% to nearly 91% TC; the phytoavailable fraction and the ion-exchange and carbonate-bound fraction comprised 3–92% TC and 9–72% TC, respectively. We also found that the greatest pH reductions do not always entail the greatest amounts of extracted Sr. A much more significant factor in this respect is the mineral and chemical composition of primary materials, which can buffer changes in pH. The Risk Assessment Code (RAC) values pointed to a varied environmental risk and the highest RAC values (> 70) were found for coal pellets, wood pellets, straw, rubber and plastic containers for mixed oils.

Optical study on a heavy-duty natural gas dual-fuel engine applying POMDME as pilot fuel

In this study, a fully optically accessible single-cylinder research engine is the basis for the visualization and generation of extensive knowledge about the in-cylinder processes of mixture formation, ignition, and combustion of alternative fuels for the dual-fuel combustion process. POMDME substitutes the fossil pilot fuel as a drop-in, non-sooting alternative to widely eliminate the NOx-PM tradeoff. Furthermore, an optimized ignition behavior, increased degrees of freedom in combustion phasing, and the pilot’s energy content are expected. The flame luminosity transmitted via an optical piston was split in the optical path to record the natural flame luminosity simultaneously with an RGB high-speed camera. The second channel consisted of OH chemiluminescence recording, isolated by a bandpass filter via an intensified monochrome high-speed camera. To investigate the combustion process spectrally, spatially, and temporally resolved in more detail, selected operating points were re-recorded via a high-speed imaging spectrograph. POMDME is benchmarked against regular diesel oil, according to EN590. Synthetic natural gas is applied as the primary gaseous fuel. Experimental sweeps along the overall pilot’s energy content (2%, 5%, 10%), injection pressure (500–1600 bar), and start of energizing (5–55 CAD bFTDC) are carried out. The given conditions result in decreased liquid-penetration length between 25% and 30% for the oxygenate, larger for earlier SOE and higher dilution. The lift-off length is nearer the liquid penetration length, increasing for higher rail pressures. The light-based ignition delay for EN590 is enlarged by 0.8 CAD after adding methane, while the oxygenate is not visibly retarded. Without methane, the oxygenate preceded EN590 by 0.6 CAD. The temporal and spatial position and extent of premixed, diffusive, and OH*, change significantly. RCCI operation at practically relevant 18.4 bar IMEP is demonstrated, highlighting the influence of the start of energizing variation with 51% decreased burn duration in the first half of combustion.

Simulation of alternative fuel combustion process in internal combustion engines

BACKGROUND: The tasks of improving fuel efficiency and environmental performance of engines are interrelated with the technical, economic, resource performance and reliability of their operation. AIM: In this regard, the aim is simulation of the alternative fuels combustion process. METHODS: To achieve this aim, the method for preparing a water-fuel emulsion mixed with diesel fuel has been developed and experimental studies have been carried out with the measurement of toxic components of exhaust gases from diesel engines. RESULTS: As a result of the research, the most optimal droplet sizes of water-fuel emulsions were revealed after 4–6 processing cycles with the smokiness reduction by 3 to 5 times, the NOx reduction by 2 to 3 times, the CO reduction by 20–30%, depending on the operating modes. CONCLUSIONS: As a result of the research, it was found that the use of alternative fuels makes it possible to expand the fuel balance and to improve environmental performance.

Decarbonization of cement production by electrification

This study presents the techno-economic assessment of four electrified cement plants: i) using direct electrification and plasma technologies (eC-pK case); ii) consisting of indirect electrification via H2 combustion and oxy-combustion of alternative fuels (OC-HK); iii) combining direct electrification, alternative fuels combustion and post-combustion CO2 capture (eC-afK); iv) consisting in the electrification of the hydraulic Calcium Hydro Silicate production process (e-hCHS). Process modeling in Aspen Plus is used to estimate mass and energy balances and calculate techno-economic key performance indicators. The study finds that all the electrified alternatives achieve high levels of equivalent CO2 emissions avoidance (87.2%–101.8%), with a trade-off between the electricity demand (604–1341 kWh/tclk) and the amount of captured CO2 to be handled by the transport & storage infrastructure (357–834 kgCO2/tclk). With an electricity price of 50 €/MWh, the partially electrified alternatives (OC-HK, eC-afK) showed competitive additional cost of clinker (87 €/tclk) and cost of avoided CO2 (101 €/tCO2) against a benchmark case, though higher than the cost of the best CO2 capture technologies from the literature. The eC-pK case resulted in lower economic performance associated mainly to the higher price of electricity per unit of final energy supplied compared to alternative fuels.

Method for Converting the Energy Characteristics of Alternative Fuels

The article analyzes the reasons hindering the mass use of alternative fuels in the field of energy consumption of domestic transport, which for the most part have lower energy and kinetic indicators of combustion in comparison with traditional fuels. A new approach to solving the problem of improving the environmental and energy-saving indicators of combustion of alternative fuels based on their preliminary thermochemical processing - conversion on board a vehicle is presented. The results of a preliminary analytical study of the parameters of the on-board conversion process for a number of potentially acceptable types of alternative fuels are presented in order to assess the efficiency of this process. The possibility of practical implementation of the proposed process for improving the combustion indicators of alternative fuel with an assessment of its efficiency was tested based on the results of experimental approbation in the conditions of full-scale engine tests. According on the results of the study, the expediency of using this process in transport technologies is justified due to the technical simplicity of its implementation and efficiency. Thermocatalytic reactor is the simplest design of a heat exchanger, the mass and dimensional characteristics of which (in the volume of a conventional muffler) ensure the convenience of its installation in the engine exhaust system. The component composition of these products contains reactive compounds that contribute to the improvement of environmental and energy-saving indicators of the fuel combustion process, and an increase in the efficiency of the engine's operating cycle.

Combustion behavior and pollutant emission characteristics of polymers and biomass in a bubbling fluidized bed reactor

The paper presents the results of combustion of polymers and biomass in a bubbling fluidized bed reactor. It was determined that 850 °C is the minimum temperature at which the combustion process should be carried out. To simulate bubbles’ chemical composition in a hot fluidized bed, TG analysis coupled with FTIR analysis was performed under pyrolysis conditions. Recorded IR spectra were deconvoluted to determine the composition of fuel bubbles in the fluidized bed. It was shown that a uniform access to oxygen is necessary for the combustion of complex gas mixtures. The combustion processes were conducted in two ways. The materials were burned autothermally and in the process of co-combustion together with auxiliary fuel. Inorganic and organic substances were identified in the flue gases. The latter contained mainly short-chain aliphatic hydrocarbons. The detailed emission characteristics of gaseous products during the combustion of the polymeric materials in the bubbling fluidized bed was investigated. The increase of the combustion temperature intensifies the oxidation of the fuel-bound nitrogen and the NO conversion to N2 on the surface of the char. The obtained values of emission coefficients for different polymers will be useful in the choice of appropriate method of combustion of alternative fuels.

Impact of alcohol–diesel fuel blends on soot primary particle size in a compression ignition engine

The use of alternative fuels, such as bio-alcohols, in advanced propulsion systems could a feasible strategy to address several of the current issues associated to the use of internal combustion engines fuelled by carbonaceous fossil fuels. Particularly, soot particles, are one of the key pollutants emitted from compression ignition engines. Therefore, the development of soot formation prediction models providing new understanding on the impact of alternative fuels combustion in compression ignition engines become essential for soot mitigation purposes.This study proposes a new semi-empirical model that predicts in-cylinder soot primary particle growth from an engine fuelled with alcohol–diesel fuel blends. The model uses macroscopic experimental measurements of engine parameters such as instantaneous in-cylinder pressure. Furthermore, an empirical correlation is presented predicting the mean soot primary particle size as a function of alcohol–diesel fuel blend properties and fuel/air ratio. The experimental measurement of primary soot particle mean size are obtained from High Resolution Transmission Electron Microscope (HT-TEM) micrographs obtained from soot particles collected via thermophoresis. Overall, the research findings presented in this work contributes to propose environmentally friendly fuel candidates for transportation.

Recycling cement bypass dust and granulated blast furnace slag into hydraulic road binder

This paper is aimed at the possibility of recycling the cement bypass dust (BPD) and ground granulated blast furnace slag (GGBS) into a normal hardening hydraulic road binder in accordance with standard EN 13282-2. 10 wt.% addition of BPD as potentially hazardous waste formed during the clinker production by burning alternative fuels was used into cement mixtures. Binder mixtures’ composition was designed according to the recommended sheet of Slovak commercial product (DoroCem). The main constituents of the experimental hydraulic road binder mixture were Portland cement clinker, ground limestone and GGBS. Effect of additional component of BPD on behaviour of fresh mixtures and properties of mortar specimens after 56 days of hardening was studied. The results prove that only one of the tested mixtures (BM2) with the lowest SO3 content and clinker but with the highest amounts of GGBS, ground limestone and alkalis (Na2O + K2O) met the standard requirement for initial setting time for tested fresh mixtures. The higher values of compressive strength found for all hardened specimens are most likely related to the formation of the hydrated and geopolymer products in the binder system. Based on these conclusions, BM2 could be used as hydraulic road binder.

Oxy-Combustion of Solid Recovered Fuel in a Semi-Industrial CFB Reactor: On the Implications of Gas Atmosphere and Combustion Temperature.

Oxy-fuel combustion of refuse waste is gaining considerable attention as a viable CO2 negative technology that can enable the continued use of stationary combustion plants during the transition to renewable energy sources. Compared to fossil fuels, waste-derived fuels tend to be highly heterogeneous and to contain a greater amount of alkaline metals and chlorine. Therefore, experimental studies are mandatory to thoroughly elucidate refuse materials’ combustion and pollutant formation behavior. This paper presents an experimental investigation on the air and oxy-fuel combustion of solid recovered fuel at a 200 kWth circulating fluidized bed facility. In the course of two experimental campaigns, the effects of combustion atmosphere and temperature on pollutant formation (i.e., NOx, SO2, and HCl) and reactor hydrodynamics were systematically studied. In contrast to air-firing conditions, the experimental results showed that oxy-fuel combustion enhanced the volume concentration of NOx by about 50% while simultaneously decreasing the fuel-specific NOx emissions (by about 33%). The volume concentrations of SO2 and HCl were significantly influenced by the absorption capacity of calcium-containing ash particles, yielding corresponding values close to 10 and 200 ppmv at 871–880 °C under oxy-fuel combustion conditions. In addition, the analysis of hydrodynamic data revealed that smooth temperature profiles are indispensable to mitigate bed sintering and agglomeration risks during oxy-fuel operation. The results included in this study provide a valuable contribution to the database of experimental information on the oxy-fuel combustion of alternative fuels, which can be applied in future process model validations and scale-up studies.

The Effect of Inert Fuel Compounds on Flame Characteristics

To describe the effects of inert compounds in gaseous fuel, experiments on three different process burners (staged fuel burner, staged air burner, and low-calorific burner) were carried out. The tested burners are commercially available, but they were specially designed for experimental usage. Tests were carried out in the semi-industrial burner testing facility to investigate the influence of inert gases on the flame characteristics, emissions, and heat flux to the combustion chamber wall. Natural gas was used as a reference fuel, and, during all tests, thermal power of 500 kW was maintained. To simulate the combustion of alternative fuels with lower LHV, N2 and CO2 were used as diluents. The inert gas in the hydrocarbon fuel at certain conditions can lower NOx emissions (up to 80%) and increase heat flux (up to 5%). Once incombustible compounds are present in the fuel, the higher amount of fuel flowing through nozzles affects the flow in the combustion chamber by increasing the Reynolds number. This can change the flame pattern and temperature field, and it can be both positive and negative, depending on actual conditions.

Effect of Adding Emulsifier to Fuel on Work Efficiency and Gas Turbine Emissions

In an effort to reduce the emissivity of transport and energy, numerous studies are being carried out on the impact of the combustion of alternative fuels on the emission and operating parameters of propulsion and energy units. One of the observed trends is the use of emulsion fuels. The addition of an emulsifier to an emulsion fuel reduces the interfacial tension between two liquids, which allows obtaining an emulsion fuel with the expected stability. The research conducted on self-ignition engines and gas turbines (TG) does not give an unambiguous answer as to the influence of the use of fuel-water emulsion on CO emissions. One of the reasons for the discrepancy in the obtained results may be the type and amount of the emulsifier used in the emulsion fuel. Tests were carried out on the GTM-120 gas turbine to compare the operating parameters and emissions between the cases in which TG was supplied with three fuel mixtures—the standard fuel for TG (DF) and DF with 2% and 5% emulsifier addition. It was shown that the addition of 2% of the emulsifier to DF causes an increase in CO emission, with the remaining measured parameters unchanged. On the other hand, increasing the amount of emulsifier in DF to 5% reduces CO emissions to the level observed in the case in which DF was burned reduces NOx emissions and reduces the thermal efficiency of TG.

Sensitivity of pollutants abatement in oxidation catalysts to the use of alternative fuels

The aim to reduce well to wheel CO2 emissions incentives the utilisation of alternative fuels (low to zero carbon content and/or low well to tank CO2 emissions) as well as the enhancement of engine efficiency. In parallel, the reduction of engine tailpipe CO2 emissions brings new challenges such as the decrease of the exhaust gas temperature. This trend penalises the ability of the exhaust aftertreatment system to eliminate pollutant emissions. In addition, the combustion of alternative fuels and new combustion modes induce changes in the nature and concentration of the exhaust species, which is known to affect the pollutants abatement mechanisms. This investigation provides new understanding on the sensitivity of pollutants abatement in oxidation catalysts to the use of alternative fuels. The studied fuels are conventional diesel, alternative fuels (rapeseed methyl ester and gas to liquid) as well as propane using a dual-fuel combustion strategy. The research combines experimental conversion efficiency from genuine exhaust gases with modelling work useful to explain the reasons for the change in light-off temperature as a function of the fuel. In addition to the CO and NO impact, HC surrogates are proposed distinguishing species of different reactivity for each fuel based on the experimental HC speciation. The results highlight the role of the engine-out emissions on the pollutants conversion efficiency. Their fashion with different fuels contributes to evidence the interest for low engine-out emissions along with low light alkanes content in total HC, as promoted by alternative fuels, to reduce the oxidation light-off temperature.

Environmental levels and human health risks of metals and PCDD/Fs near cement plants co-processing alternative fuels in Catalonia, NE Spain: a mini-review

This paper was aimed at reviewing recent studies related with the impact on environment and human health of metals and PCDD/Fs near cement plants. It has been particularly focused on the impact of cement plants located in Catalonia, Spain, which have been monitored by our research for more than ten years. Environmental monitoring studies were performed under different cement plant conditions. While some of our studies examined temporal trends of the levels of the above indicated pollutants, the main goal of other surveys was to assess the impact of implementing alternative fuels in the facilities. Even one of the studies was performed before and after the cement plant temporally ceased its industrial activity. The impact of cement plants burning alternative fuels on the emissions of metals and PCDD/Fs elsewhere was also reviewed. Regarding the cement plants in Catalonia, no significant differences were found, neither in the long-term follow-up studies, nor when alternative fuels are used, nor when a cement plant temporally stopped its activity. These results are in agreement with those reported for several stack emissions of other cement plants working under different conditions. We conclude that emissions of metals and PCDD/Fs by cement plants working with the best available techniques (BAT), should not cause a significant negative impact neither on the surrounding environment, nor on the human health of the population living in the neighborhood.

COMPARATIVE ANALYSIS OF EMISSIONS OF HARMFUL SUBSTANCES IN USING ALTERNATIVE TO NATURAL GAS BIOFUELS

Feature of the topic and problem statement. The paper presents for the first time a comparative characteristic of emissions of harmful substances from the combustion of traditional fuels (natural gas) and biomass in fuel furnaces of boilers and recommended for the use the most environmentally efficient fuels. Comparative characteristics of emissions of harmful substances during the combustion of various types of fuel allows to determine the optimal type of fuel in the construction and commission of a new power plants, and also adds up-to-date information that will be useful in the scientific and scientific-popular discussions that are widespread today regarding the exhaustion and replacement of non-renewable energy sources, the safety of alternative fuels and their advantages in comparison with non-renewable ones. The purpose of the work is determining of the amount of emissions of harmful substsnces entering the environment during the combustion of natural gas and solid alternative fuels - wood waste, straw, flax straw and sunflower husk, their comparison, justification of calculation of the carbon content in the fuel of a given chemical composition. Findings. During the comparative analysis, high values for the carbon dioxide emissions for all the materials were considered. It is also noted that there are no emissions of suspended solid particles and sulfur diоxide during the combustion of natural gas and it is determined that at its combustion, methane emissions will be the smallest. In as-sessing the level of safety when using unrenewable and alternative fuels, the higher content of methane, dinitrogen oxide and unmethane volatile organic compounds and the lower content of nitrogen oxide, carbon dioxide in emissions from combustion of alternative fuels compared to emissions at combustion of unrenewable fuels were determined during the calculations. When burning natural gas there is mercury in small amounts in the emissions. Originality. The paper presents for the first time a comparative characteristic of emissions of harmful substances from the combustion of traditional fuels (natural gas and fuel oil) and biomass in fuel furnaces of boilers and recommended for the use the most environmentally efficient fuels. When making calculation works the following regularities are defined. In unrenewable and alternative fuels, a higher proportion of carbon passes into carbon dioxide emission and less to carbon oxide emission, while proportion of carbon in carbon dioxide emission is higher in unrenewable fuels. In addition, in unre-newable and alternative fuels, a large proportion of nitrogen is converted into nitrogen oxide emission, and less in emission of dinitrogen oxide, while the proportion of nitrogen in the emission of nitrogen oxide is also higher in unrenewable fuels. The paper defines a formula for calculating the carbon content in natural gas from the Central Asia-Center gas pipeline. The provided calculations and the introduction of simplified formulas serve as an example for the calculation of emis-sion factors and emissions in assessing the level of safety of existing equipment and can be used in the development of permit documents of enterprises that carry out emissions of harmful substances to the environment.

Characterization of emissions from a pilot-scale combustor operating on coal blended with woody biomass

Emissions generated from the combustion of coal have been a subject of regulation by the United States Environmental Protection Agency (U.S. EPA) and State agencies for years, as they have been associated with adverse effects on human health and the environment. Over the past several decades, regulations on these facility emissions have become more stringent and have therefore caused industry to look toward new pre- and post-combustion control technologies. In more recent years, there has been a “push” toward renewable and cleaner burning alternative fuels as replacements for traditional fossil fuels. Part of this “push” has been accomplished by States and Regions offering incentives and options for renewable portfolios, which over half of the states now have in some form.The current study investigates the potential changes in both gaseous and particulate emissions from the use of a variety of woody biomass materials as a drop-in replacement for coal as compared to use of 100% bituminous coal. Four different biomass materials are blended individually with coal at 20% and 40% by mass for testing on the U.S. EPA’s Multi-Pollutant Control Research Facility, a pilot-scale coal-fired facility located in Research Triangle Park, North Carolina. Emissions are calculated based on measurements from the flue gas to characterize gaseous species (CO, CO2, NOX, SO2, other acid gases, and several organic hazardous air pollutants) as well as fine and ultrafine particulate (mass, size distribution, number count, elemental carbon, organic carbon, and black carbon) and compared among each combination of fuels and 100% bituminous coal.

Comparison of fly ash from co-combustion of coal/solid recovered fuel (SRF) and coal/refuse derived fuel (RDF).

The formation of ashes originating from the combustion of alternative fuels causes a need to find ways for their practical application and demands the knowledge about their properties. Therefore, the present work is devoted to studying the co-combustion of slternative fuel SRF/coal and RDF/coal. The major objectives of this paper is to present the detail characteristics of ash by using the advanced instrumental techniques (XRF, XRD, SEM, BET, TGA).

Application of different numerical models capable to simulate combustion of alternative fuels in internal combustion engine

PurposeThe internal combustion engine operated on gaseous fuels shows great potential in terms of integration of the renewable and traditional sources for an effective solution for clean energy production challenge. Different fuel mixtures that can be used to power the engine are characterized by various combustion properties, which can affect its overall efficiency. The purpose of this paper is to provide reasonable answer, how the operation condition can change due to different fuel, without enormous cost of prototyping processes using physical models a digital model can be seen as promising technique.Design/methodology/approachPresented work discusses the application, and extensive description of two commercial codes Ansys Fluent and Forte for modeling stationary engine fueled by compressed natural gas (CNG) and biogas. To check the model accuracy, all carried out numerical results were compared against experimental data collected at in-house test rig of single cylinder four stroke engine. The impacts of tested gaseous fuel on the engine working conditions and emission levels were investigated.FindingsCarried out simulations showed good agreement with experimental data for investigated cases. Application on numerical models give possibility to visualize flame front propagation and pollutant formation for tested fuels. The biogas fuel has shown the impaired early flame phase, which led to longer combustion, lower efficiency, power output, repeatability and in some cases higher HC and carbon monoxide (CO) emissions as a result of combustion during the exhaust stroke. Looking at the CO formation it was observed that it instantly accrue with flame front propagation as a result of methane oxidation, while for NOx formation revers effect was seen.Originality/valueThe application of new approach for modeling combustion process in stationary engines fueled by CNG and alternative biogas fuel has been discussed. The cons and pros of the Forte code in terms of its application for engine prototaping process has been discussed.

Комплексное использование отходов деревообрабатывающей и сельскохозяйственной промышленности в энергетике Сибири

The article considers the methods of increasing technoeconomic and ecological indices of boilers of little and average power by the means of vertical-way combustion of alternative fuels (eg. husks, chips, wood waste). We analyzed the technology of combustion of solid fuels from plant biomass and revealed several issues in the combustion of light sailing particles. The article is dedicated to the investigation of the properties of alternative fuels, to the generation and refinement of furnace arrangements for combustion of low-grade fuels. The results of our work represent a new construction design of the furnace chamber for effective combustion of alternative fuels. The new construction design of the furnace chamber is obtained via the aerodynamic modelling with the use of the «SigmaFlame» software.

Image-Based Characterization of Alternative Fuel Combustion With Multifuel Burners

Many industrial high-temperature processes such as cement production employ multifuel burners in order to achieve the required energy input with low-cost alternative fuel. So far, a constant operation of multifuel burners with high fractions of alternative fuel (>70%) is not possible due to inherent fluctuating fuel properties. Energy input and product quality are directly affected by varying points of combustion time, different scattering of fuel, and insertion of unburned fuel or chemical substances into the product. We propose an image-processing system based on infrared images that detects the alternative fuel streakline and derives parameters for the characterization of the flight and burning behavior. Using these parameters, an adjustment of the burner settings depending on the fluctuating fuel properties can be carried out. This automatic monitoring and control of the combustion process allows an increased use of alternative fuels in constant operation. Experimental data from a rotary kiln for cement clinker production are used to validate the image-processing system.

Impact of alternative fuels on the operational and environmental performance of a small turbofan engine

A wide range of alternative jet fuels is studied in this work for use in a small two-spool turbofan engine. These embrace the five production pathways currently approved by the American Society for Testing and Materials. Both neat products and blends (within certified limits) have been considered. The present analysis is based on a 0-D thermodynamic modeling of the aero-engine for off-design and transient simulations. In addition, the selected approach incorporates fuel effects on combustion and the impact of fuel properties on the flame temperature, as well as on the droplet evaporation rate. Predicted performance and pollutant emission outputs for the alternative fuels are presented at different operating conditions, namely: take-off, top of climb, cruise, low power and ground idle. The results are discussed and comprehensively compared with data available in the literature. It was concluded that the combustion of alternative fuels generally leads to enhancements in engine performance with respect to the use of conventional kerosene. Reductions in pollutant emissions occur mostly in soot, but also in nitrogen oxides and carbon monoxide, depending on the fuel and operating conditions. In contrast, increased emissions of unburned hydrocarbons are generally observed. Concerns about the aero-engine dynamic response are raised only in very few cases, involving the use of neat products.