Polyoxymethylene Dimethyl Ethers Research Articles

Optical engine investigation of ammonia combustion enhancement with polyoxymethylene dimethyl ethers (PODE₃) as pilot fuel

Ammonia, gaining attention as a carbon-free fuel amid declining fossil fuel reserves, faces challenges like combustion instability and misfiring in its application in internal combustion engines. In this study, polyoxymethylene dimethyl ethers (PODE3), a clean, renewable, and electrically synthesized fuel with high cetane number and oxygen content, is evaluated as a pilot fuel for ammonia in dual-fuel engines. The study, performed in a dual-fuel optical engine, investigates the use of PODE₃ compared to diesel as direct injection fuels for ammonia combustion, focusing on the impact of PODE3 injection timing and dwell (the interval between dual-stage injections) on the ignition characteristics of ammonia. The results demonstrate that, compared to diesel, using PODE3 enhances ammonia combustion in dual-fuel engines. This is evident from increased in-cylinder pressure, higher apparent heat release rate (AHRR), advanced combustion phases, and improved indicated mean effective pressure (IMEP), enhancing overall stability. PODE3 also effectively minimizes soot generation, evidenced by a 71.5 % reduction in spatially integrated natural luminosity (SINL), accompanied by a 16.9 % increase in peak flame area. Adjusting PODE3 injection timing is crucial; initial retardation improves combustion performance, marked by higher in-cylinder pressure and AHRR, as well as expanded flame area. However, over-delaying injection timing reduces these gains. The optimal performance is achieved under the SOI-25 condition, balancing combustion and flame development, though some areas remain unburnt. In a dual-stage injection strategy using PODE3, where the second injection timing remains fixed at −25 °CA ATDC, the critical adjustment of advancing the first injection timing to −35 °CA ATDC markedly enhances combustion performance compared to a single injection condition. This setting reduces ignition delays, increases peak in-cylinder pressures, and improves stability, which collectively contribute to a significant 20.4 % increase in the peak flame area, particularly between adjacent fuel jets. Expanding upon this, advancing the first injection timing further to −45 °CA ATDC leads to a decrease in peak in-cylinder pressure and AHRR, accompanied by a notable 40.3 % reduction in the peak flame area. This research affirms the advantages of PODE3 over diesel in ammonia-powered dual-fuel engines, markedly enhancing combustion performance and environmental sustainability, where the injection strategy of PODE3 emerges as a crucial element.

LES and RANS Spray Combustion Analysis of OME3-5 and n-Dodecane

Clean-burning oxygenated and synthetic fuels derived from renewable power, so-called e-fuels, are a promising pathway to decarbonize compression–ignition engines. Polyoxymethylene dimethyl ethers (PODEs or OMEs) are one candidate of such fuels with good prospects. Their lack of carbon-to-carbon bonds and high concentration of chemically bound oxygen effectively negate the emergence of polycyclic aromatic hydrocarbons (PAHs) and even their precursors like acetylene (C2H2), enabling soot-free combustion without the soot-NOx trade-off common for diesel engines. The differences in the spray combustion process for OMEs and diesel-like reference fuels like n-dodecane and their potential implications on engine applications include discrepancies in the observed ignition delay, the stabilized flame lift-off location, and significant deviations in high-temperature flame morphology. For CFD simulations, the accurate modeling and prediction of these differences between OMEs and n-dodecane proved challenging. This study investigates the spray combustion process of an OME3 − 5 mixture and n-dodecane with advanced optical diagnostics, Reynolds-Averaged Navier–Stokes (RANS), and Large-Eddy Simulations (LESs) within a constant-volume vessel. Cool-flame and high-temperature combustion were measured simultaneously via high-speed (50 kHz) imaging with formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) representing the former and line-of-sight OH* chemiluminescence the latter. Both RANS and LES simulations accurately describe the cool-flame development process with the formation of CH2O. However, CH2O consumption and the onset of high-temperature reactions, signaled by the rise of OH* levels, show significant deviations between RANS, LES, and experiments as well as between n-dodecane and OME. A focus is set on the quality of the simulated results compared to the experimentally observed spatial distribution of OH*, especially in OME fuel-rich regions. The influence of the turbulence modeling is investigated for the two distinct ambient temperatures of 900 K and 1200 K within the Engine Combustion Network Spray A setup. The capabilities and limitations of the RANS simulations are demonstrated with the initial cool-flame propagation and periodic oscillations of CH2O formation/consumption during the quasi-steady combustion period captured by the LES.

Combustion and emission of diesel/PODE/gasoline blended fuel in a diesel engine that meet the China VI emission standards

The present study examined the impact of blending polyoxymethylene dimethyl ethers (PODE) and gasoline with diesel on combustion and emission characteristics in an engine compliant with China VI emission standards. The effects on cylinder pressure, combustion duration, and emissions (CO, THC, PN, and NOx) by blending 20 % PODE into diesel and adjusting the gasoline content (0 %, 5 %, and 10 %) were analyzed. The results showed that the cylinder pressures and the combustion duration were reduced with the addition of PODE, compared to the cases of the pure diesel. Moreover, it was found that PODE contributed to reducing the emissions of CO, THC, and PN, and but increasing NOx emissions. Compared to the cases of PODE and diesel blended fuel, the effect of the addition of gasoline on the cylinder pressures and combustion duration presented a minor increasing tendency, and the lower proportion of gasoline blending was found to effectively curb NOx formation. Specifically, blending 5 % gasoline with a 20 % PODE and diesel mixtures resulted in a 4.01 % reduction in NOx emissions. Based on the results of the present study, it can be concluded that 5 % gasoline and 20 % PODE blend in diesel can enhance combustion efficiency and heat release rate and also can achieve a balanced reduction in NOx emissions. The present study provides valuable insights for the development of energy-saving and emission reduction technologies for diesel engines, highlighting the potential of optimized fuel blends to improve combustion and emissions control.

Potential Analysis of Defossilized Operation of a Heavy-Duty Dual-Fuel Engine Utilizing Dimethyl Carbonate/Methyl Formate as Primary and Poly Oxymethylene Dimethyl Ether as Pilot Fuel

Potential Analysis of Defossilized Operation of a Heavy-Duty Dual-Fuel Engine Utilizing Dimethyl Carbonate/Methyl Formate as Primary and Poly Oxymethylene Dimethyl Ether as Pilot Fuel

A Comparative Experimental Analysis of Natural Gas Dual Fuel Combustion Ignited by Diesel and Poly OxyMethylene Dimethyl Ether

A Comparative Experimental Analysis of Natural Gas Dual Fuel Combustion Ignited by Diesel and Poly OxyMethylene Dimethyl Ether

Combined experimental and kinetic modeling study on the low-temperature oxidation of OME3/n-heptane blends

Experimental and kinetic studies on the blending of ethers or diesters with larger alkanes at low temperatures are enormously scarce. In this paper, the low-temperature oxidation (LTO) kinetics model of polyoxymethylene dimethyl ether 3 (OME3)/n-heptane (500 K∼950 K) was established by using the jet-stirred reactor (JSR) to conduct the LTO experiments of OME3/n-heptane with different blending ratios. GC/MS was used to detect and quantify 17 kinds of stable products in the LTO process of OME3/n-heptane. The detailed OME3/n-heptane kinetic model was fully verified experimentally. The interaction mechanism of OME3/n-heptane was discussed based on the experiments and corresponding chemical kinetic analysis. Results show that the oxidative decomposition processes of OME3 and n-heptane were significantly different, the LTO and NTC process of OME3 were significantly weaker than those of n-heptane, but the high-temperature reactivity of OME3 was much stronger. In addition, n-heptane significantly promoted the intermediate species CH3OCHO and COCOC*O of OME3, mainly because n-heptane significantly prolonged the LTO of OME3 in the fuel blends. And the NTC process of the fuel blends was mainly dominated by OME3, while the LTO process was more influenced by n-heptane, which resulted in the weakened NTC of n-heptane and the significantly enhanced LTO process of OME3.

Effects of polyoxymethylene dimethyl ethers (PODEn) on soot characteristics in isooctane inverse diffusion flames

Polyoxymethylene dimethyl ethers (PODEn, n = 1–3) such as dimethoxymethane (DMM) and PODE3 are considered highly promising alternative fuels due to their lack of C–C bonds and significant oxygen contents. Particularly, PODE3-blends with diesel have been proven to substantially reduce soot emissions and fuel consumption rates under optimized engine conditions, although the impact on soot nanostructure properties remains unclear. This study explored the effects of DMM and PODE3 on soot characteristics in isooctane (i-octane) inverse diffusion flames, focusing on soot morphology, soot nanostructure, soot nanocrystallite, and soot spectral features. To compare soot particles behavior, DMM and PODE3 blended as the isooctane substitute (by 20% and 40% volumetric fractions) were examined with various diagnostic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).The results showed that DMM and PODE3 contributed to a reduction in sooting tendency from i-octane flames, whereas the average soot mass decreased significantly as the PODE3 ratio increased, consistent with a higher oxygen concentration. Therefore, 20% PODE3/i-octane exhibited growing disorganized arrangements of soot particles with shorter fringes, smaller crystallite sizes, and a relatively lower degree of graphitization than 20% and 40% DMM additions. However, XPS analysis indicated that soot produced from PODE3/i-octane mixtures had less oxygen atoms because PODE3 has multiple –CH2O- chain groups that can convert oxygen into carbon monoxide with little soot production. Moreover, HRTEM, XRD, and Raman spectra analyses of 40% PODE3-doped flames confirmed an exceptional correlation with turbostratic soot structure, as manifested by the shortest fringe length, longest fringe tortuosity, more amorphous soot with the smallest crystallite dimensions, and least degree of graphitization.

Numerical Study of Premixed PODE3-4/CH4 Flames at Engine-Relevant Conditions

Polyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a promising alternative fuel to diesel with higher reactivity and low soot formation tendency. In this study, PODE3-4 is used as a pilot ignition fuel for methane (CH4) and the combustion characteristics of PODE3-4/CH4 mixtures are investigated numerically using an updated PODE3-4 mechanism. The ignition delay time (IDT) and laminar burning velocity (LBV) of PODE3-4/CH4 blends were calculated at high temperature and high pressure relevant to engine conditions. It is discovered that addition of a small amount of PODE3-4 has a dramatic promotive effect on IDT and LBV of CH4, whereas such a promoting effect decays at higher PODE3-4 addition. Kinetic analysis was performed to gain more insight into the reaction process of PODE3-4/CH4 mixtures at different conditions. In general, the promoting effect originates from the high reactivity of PODE3-4 at low temperatures and it is further confirmed in simulations using a perfectly stirred reactor (PSR) model. The addition of PODE3-4 significantly extends the extinction limit of CH4 from a residence time of ~0.5 ms to that of ~0.08 ms, indicating that the flame stability is enhanced as well by PODE3-4 addition. It is also found that NO formation is reduced in lean or rich flames; moreover, NO formation is inhibited by too short a residence time.

CO2 solubility and absorption rate analysis of a mixed poly(oxymethylene) dimethyl ethers (PODE3–5) solution

Efficient and economical carbon capture is critical to counteract the diverse problems of global warming. In this work, the solubility of carbon dioxide (CO2) in different poly(oxymethylene) dimethyl ethers (PODE) solutions was experimentally investigated at temperatures from 278.15 to 308.15 K and pressures up to 1.2 MPa. The Henry's law constants of CO2 in the PODE system were determined and compared with other types of physical absorbents, which revealed PODE3–5 has great CO2 absorption ability in terms of molar and mass fraction. Meanwhile, the initial absorption rate of the physical absorption process of PODE3–5 was calculated and compared with commercially available absorbents using a gas absorption rate relationship. It was shown that the absorption rate of PODE3–5 in the CO2 absorption process is faster than that of other commercial absorbents. The CO2 solubility data of PODE3–5 were also correlated using the Jou-Mather model and the perturbed-chain statistical association fluid theory (PC-SAFT) equation of state model, and the recycling performance of the PODE3–5 absorbent was tested.

A conceptual model of polyoxymethylene dimethyl ether 3 (PODE3) spray combustion under compression ignition engine-like conditions

As one of the most popular synthetic fuels (E-fuels), Polyoxymethylene dimethyl ethers(PODEX) have garnered significant attention among researchers in the compression ignition engine field. This work aims to provide an exhaustive analysis of the combustion characteristics of PODE3, which typically constitutes the primary component of PODEX. This research seeks to deepen our understanding of the flame structure of PODE3, particularly in relation to ambient temperature variation, and unravel the underlying mechanisms driving the observed trends. To achieve this aim, a range of optical techniques was employed within a high-temperature high-pressure combustion vessel to quantify various general combustion parameters and assess OH* chemiluminescence, formaldehyde, and soot distribution. Two additional reference fuels, pure n-dodecane and a blend of 50 % vol n-dodecane and 50 % vol PODE3 were also tested. Additionally, some analysis from chemical kinetics and 1D spray model calculations were used to substantiate the experimental observations. The findings reveal that the flame structure of PODE3 differs significantly from traditional diffusion flames associated with diesel-like sprays. The flame lift-off length (LOL) of PODE3 aligns closely with that of n-dodecane, and maintains the two-lobe structure under high-temperature conditions. In contrast, under low ambient temperatures, the LOL of PODE3 significantly extends, accompanied by a concentration of OH* radicals at the spray center. The notable sensitivity of PODE3 flames to temperature variation is related to the chemical kinetics of formaldehyde and CO. As a result of the analysis, conceptual models of PODE3 flames under varying temperatures were proposed in the end.

Numerical study of novel OME1−6 combustion mechanism and spray combustion at changed ambient environments

AbstractFor a climate-neutral future mobility, the so-called e-fuels can play an essential part. Especially, oxygenated e-fuels containing oxygen in their chemical formula have the additional potential to burn with significantly lower soot levels. In particular, polyoxymethylene dimethyl ethers or oxymethylene ethers (PODEs or OMEs) do not contain carbon-carbon bonds, prohibiting the production of soot precursors like acetylene (C2H2). These properties make OMEs a highly interesting candidate for future climate-neutral compression-ignition engines. However, to fully leverage their potential, the auto-ignition process, flame propagation, and mixing regimes of the combustion need to be understood. To achieve this, efficient oxidation mechanisms suitable for computational fluid dynamics (CFD) calculations must be developed and validated. The present work aims to highlight the improvements made by developing an adapted oxidation mechanism for OME1−6 and introducing it into a validated spray combustion CFD model for OMEs. The simulations were conducted for single- and multi-injection patterns, changing ambient temperatures, and oxygen contents. The results were validated against high-pressure and high-temperature constant-pressure chamber experiments. OH*-chemiluminescence measurements accomplished the characterization of the auto-ignition process. Both experiments and simulations were conducted for two different injectors. Significant improvements concerning the prediction of the ignition delay time were accomplished while also retaining an excellent agreement for the flame lift-off length. The spatial zones of high-temperature reaction activity were also affected by the adaption of the reaction kinetics. They showed a greater tendency to form OH* radicals within the center of the spray in accordance with the experiments.

Direct Oxidation of Methanol to Polyoxymethylene Dimethyl Ethers over FeMo@HZSM-5 Core–Shell Catalyst

Direct Oxidation of Methanol to Polyoxymethylene Dimethyl Ethers over FeMo@HZSM-5 Core–Shell Catalyst

Correction: Numerical assessment of polyoxymethylene dimethyl ether (OME3) injection timing in compression ignition engine

Correction: Numerical assessment of polyoxymethylene dimethyl ether (OME3) injection timing in compression ignition engine

Investigation on formaldehyde generation characteristics and influencing factors of PODE/methanol dual-fuel combustion mode.

Polyoxymethylene dimethyl ether (PODE) and methanol are important low-carbon substitutable fuels for reducing carbon emissions in internal combustion engines. In the research, the impacts of methanol ratio, injection timing, and intake temperature on HCHO generation and emission were investigated using both engine tests and numerical simulations. Results suggest that an increase in methanol ratio suppresses auto-ignition tendency of PODE, leading to the increase of ignition delay period, pressure peak, and heat release rate peak inside the cylinder. The decrease in in-cylinder combustion temperature contributes to an increase in HCHO emission due to partial oxidation of methanol in the cylinder and exhaust pipe. While the injection timing is gradually postponed from -10 °CA ATDC to 2 °CA ATDC, in-cylinder high-temperature area decreases, the quantity of unburned methanol increases, but part of HCHO is converted to HCO due to H radical influence, resulting in 72% increased HCHO emission. With the increment of intake temperature, the oxidation and decomposition of in-cylinder methanol accelerate, leading to an improvement in combustion stability, more uniform temperature distribution, and a decrease in unburned methanol, which results in lower HCHO emission. When the intake temperature is rose from 30 to 60 °C, HCHO emission decreases by 11.2%.

Numerical assessment of polyoxymethylene dimethyl ether (OME3) injection timing in compression ignition engine

Numerical assessment of polyoxymethylene dimethyl ether (OME3) injection timing in compression ignition engine

Comparative analysis of PODE3 and PODE4 fuel additives for emission reduction and soot characteristics in compression ignition engines

Polyoxymethylene dimethyl ethers (PODEn) have been regarded as promising fuel additives in reducing engine emissions due to their extra oxygen content and absence of C–C bonds. This research compares the effectiveness of PODE3 and PODE4 as fuel additives (10 % oxygen content) in a compression ignition (CI) engine. The results show that PODE can retard the ignition delay and shorten the combustion duration. They can both reduce HC emissions, with PODE4 having the greatest reduction. Both additives comparably reduce NOx emissions while consuming similar oxygen amounts. PODE alters particle size distribution, favoring higher nucleation mode particles and reducing accumulation mode particles, especially for the case with Diesel/PODE3. Further, this study investigates the soot characteristics when with different fuel blends. Thermogravimetric analysis (TGA) reveals enhanced oxidative reactivity in soot when with Diesel/PODE3 and Diesel/PODE4 fuel blends. Raman spectroscopy shows reduced crystalline structure and increased crystalline width in soot when with PODE additives. Fourier transform infrared (FT-IR) spectroscopy indicates improved relative intensity of aliphatic C–H groups and intensified aromatic C–H groups with PODE addition. In summary, PODE3 and PODE4 are promising CI engine fuel additives, substantially reducing particulate matter (PM) emissions and enhancing soot reactivity. These findings hold significance for cleaner combustion technologies.

Influence of PODE1 additive into ethanol-gasoline blends (E10) on fuel properties and phase stability

Polyoxymethylene dimethyl ethers (PODEn, n = 1–8) as an oxygenated fuel are a promising alternative fuel with a high oxygen concentration, a low C:H ratio, and no C–C bonds in their chemical structure. This could lead to smoke-free combustion. In this study, we chose to focus on PODE1 because of its lower cetane number, which makes it more suitable for use in spark ignition (SI) engines. However, its lower boiling point and octane number remain challenges. A low boiling point may lead to high vapour pressure and require storage and handling comparable to gaseous fuels. We investigated the effect of adding PODE1 to gasoline-ethanol blends (E10) on fuel properties, including distillation curve, octane number, phase stability, C/O/H ratio, heat of combustion, kinematic viscosity, and density. Our results showed that the blended fuels of E10 and PODE1 are stable up to 10 % PODE1, and there was no phase separation. Additionally, up to 10 % PODE1 additive had no significant side effect on the fuel properties of E10, particularly boiling point and octane number. Thus, work offers creative points by proposing a new candidate for additive fuel to gasoline-ethanol blends, which contributes to reducing the soot emission of GDI engines.

Experimental investigation of performance and soot emissions of oxygenated fuel blends in a small aero engine

Recent studies show that mixing jet fuel with oxygenated fuels has an impact on exhaust gas soot formation. Soot particles are an environmental hazard with an impact on air quality around airports, and possibly influencing ice crystal nucleation, leading to contrail and ice cloud (cirrus) formation. These ice clouds significantly warm up the atmosphere by reflecting heat radiation back to Earth and, at the same time, being transparent to incoming sunlight. Many investigations concentrate on reducing aviation’s CO2 footprint, but only a few account for reducing soot emissions in aero engines. This study examines the potential of blending Jet A-1 with oxygenated fuels to decrease soot particle formation in aero engines. For this, blends with 5 vol% and 20 vol% of ethanol, and 5 vol% of a polyoxymethylene dimethyl ether 3–5 mix (OME3-5 mix) are investigated in an Allison 250-C20B turboshaft engine with the help of a condensation particle counter (CPC). The results show tendencies in soot particle reduction, which, in most cases, is larger than the volumetric percentage of the oxygenated fuel within the blend.

Polymer-based solid acids with adjustable textural and hydrophobic properties for polyoxymethylene dimethyl ethers synthesis from formaldehyde and methanol

Cation exchange resins are widely utilized in polyoxymethylene dimethyl ethers (PODEn) synthesis due to considerable catalytic performance. However, low specific surface area and strong hydrophilicity hinder the generation of long-chain PODEn and industrial applications. Herein, polymer-based solid acids with adjustable textural and hydrophobic properties were prepared by hydrothermal method. Results indicated that the use of tetrahydrofuran and water as solvents in the preparation process resulted in a significant increase in the specific surface area and pore size distribution of the catalysts. Meanwhile, hydrophobic catalysts prepared by copolymerization under optimal solvent exhibited superior performance over commercial resins. Moreover, two reaction pathways for the reaction of hemiformal (HF1, CH3OCH2OH) with formaldehyde and methanol were investigated by DFT calculations. The intermediate formed by combining sulfonic acid group with carbocation is favorable for embedding formaldehyde in HF1 to promote chain growth, while the direct attack of methanol on HF1 is conducive to chain termination.

Effects of intake conditions on a dual-fuel spark-assisted compression ignition engine with polyoxymethylene dimethyl ether and methanol as fuels

Dual-fuel spark-assisted compression ignition (DF-SACI) is an advanced engine combustion mode. The use of polyoxymethylene dimethyl ether (PODE) and methanol as fuel can reduce the carbon emissions of the DF-SACI engine. To improve the combustion continuity and minimize the knocking and emissions of DF-SACI engines, the effects of intake heating and boosting were investigated. The results showed that the combination of intake heating and delayed spark ignition promoted fuel diffusion and prevented multi-peak heat release. Intake boosting promoted the transformation of compression ignition into flame propagation ignition. Intake heating and boosting allowed engine combustion optimization. The brake thermal efficiency was 41.4 % and 44 % when the brake mean effective pressure was 0.6 and 0.8 MPa, respectively, and the maximum pressure rise rate, coefficient of cyclic variation in the indicated mean effective pressure, and emissions were within reasonable ranges. A high intake air temperature combined with delayed spark ignition reduced the enrichment of PODE, thereby reducing the self-ignition probability of the fuel mixture, which can reduce knocking. When intake boosting was applied, the adoption of an excess air coefficient (λ) of 1.8 eliminated knocking under most conditions. Intake heating improved fuel reactivity and increased the ratio of compression ignition, to allow for the simultaneous reduction of hydrocarbon (HC) and NOx emissions. The effects of intake boosting on NOx and HC emissions were related to the energy ratio of PODE. As the energy ratio of PODE is between 47 % and 68 %, the appropriate increase in λ reduced both HC and NOx emissions. The results are conducive to the development of low-carbon engines and can provide a new direction for engine research.