Soot Reduction Research Articles

Experimental investigation of the impact of CeO2 nanoparticles in Jet-A and Jatropha-SPK blended fuel in an aircraft can-combustor at flight conditions

International consensus aimed at mitigating climate change, global perspective shift towards clean energy, uncertainties in conventional fuel supply, along with increasingly stringent emission norms for the aviation sector has prompted the ongoing research on low emissions aviation fuel technology. Consequently, aviation fuels blended with synthetic paraffinic kerosenes (SPKs) derived from Jatropha biomass have been tested extensively. The effect of nanoparticles (NPs) in the fuel blends towards emission reduction is not studied for aero-engines. This study aims to investigate the emissions impact of Jatropha SPK blended Jet-A aviation fuel along with CeO2 (Ceria) NPs, in an aircraft engine can-combustor operated at representative flight conditions. The base fuel blends used were Jet-A (ATF), 80% Jet-A with 20% Jatropha-SPK (A80J20), and 30% Jet-A with 70% Jatropha-SPK (A30J70). NPs at 0.5% and 1% weight concentration were added to the base fuel blends, which resulted in nine different fuel types. NOx reduction is observed with increasing CeO2 NP concentration. CO, UHC and soot reduction occurs with increasing Jatropha and CeO2 content. CeO2 NPs reduce all the emissions of concern, and could be an important additive for aviation fuel.

Effects of Injection Rate Shape on Performance and Emissions of a Diesel Engine Fuelled by Diesel and Biodiesel B20

The combustion process in diesel engines is controlled by the injection rate shape. The stricter emission regulations requiring simultaneous reduction of nitrogen oxides and particulate matter imposes intense research and development activity for achieving clean and robust combustion. This work describes the experimental investigation made for calibration of an engine model and the numerical investigation performed to assess the influences of different injection rate shapes on performances of a diesel engine fuelled with diesel and rapeseed biodiesel B20. The engine model was developed with the AVL-BOOST code using the AVL-MCC combustion mode. The model was calibrated for the reference Top-Hat injection rate shape using experimental data registered for maximum brake torque and maximum brake power speed conditions. Other injection rate shapes such as triangular, trapezoidal, and boot having the same area, start, and duration of injection were investigated in terms of combustion characteristics, performance, and pollutant emissions. The link existing between the injection characteristics and the NOx and Soot emissions highlights that, for the optimal rate of injection shape, a simultaneous reduction of NOx and Soot by 11%, respectively 4% for maximum brake torque and by 22%, respectively 7% for maximum brake power, can be obtained using biodiesel B20.

Optical study on the spray and combustion of diesel cyclopentanol blend fuels on a constant volume chamber

Among the biofuels produced from lignocelluloses, cyclopentanol is a promising candidate. In this study, a constant volume chamber (CVC) is employed to investigate the effects of adding cyclopentanol in diesel with different proportions (0%, 10%, and 20% in volume) on the spray and combustion characteristics. Tests are performed under three injection pressures (100, 120 and 140 MPa). The experimental results in the CVC show that the atomization characteristics of cyclopentanol-diesel blends are better in the early stage of spray and slightly worse in the later stage than those of diesel. As the injection pressure increases, the diesel cyclopentanol blend fuels improve the air fuel mixing. The addition of cyclopentanol has risen the temperature of the flames and cut the soot formation of diesel by 12.7–89.2% under all injection pressure conditions. The addition of cyclopentanol is found to reduce the natural flame luminosity and combustion duration significantly due to the effective combustion process acceleration and is helpful for improving the combustion, especially for CP10. Overall, blending cyclopentanol into diesel has a great soot reduction potential with a low cetane number and improved mixing, and CP10 can be seen as a future alternative fuel, especially under an injection pressure of 140 MPa.

Experimental investigation on combustion and particulate emissions of the high compressed natural gas reactivity controlled compression ignition over wide ranges of intake conditions in a multi-cylinder engine using a two-stage intake boost system

Compressed natural gas (CNG)/diesel reactivity-controlled compression ignition was investigated to understand the combustion and emission characteristics over wide ranges of intake pressure and exhaust gas recirculation (EGR) rate at high load condition. Reactivity-controlled compression ignition is a dual fuel engine combustion strategy that employs in-cylinder fuel blending with two different reactivity fuels, and multiple injections for the in-cylinder fuel reactivity control to optimize the combustion phasing, duration, and magnitude as well as NOx and soot reduction. High CNG substitution was of interest since it could lead to greater CO2 and particulate matter reductions. The present 80% CNG substitution required substantial intake boosting due to the charge air displaced by CNG. The experimental engine is commissioned for the reactivity-controlled compression ignition regime using natural gas and diesel fuel with a two-stage turbocharging system. The intake boosting system achieved the intake pressure and EGR rate of 210 kPa and 25%, respectively, when the EGR valve was fully open. The intake pressure and EGR levels varied in the ranges of 150 to 210 kPa and 0 to 25%, respectively. The corresponding equivalence ratio ranged from 0.85 to 0.5. The intake system achieved the highest turbocharger efficiency of 56% at the maximum boosting operation. The highest CO2 reduction was 23.4% at the maximum boosting condition. The improvements under the enhanced intake condition were significant from the standpoints of both efficiency and emissions, including in terms of the particle concentrations.

Experimental investigation of the impact ethanol-biodiesel-diesel blended fuels on combustion, emission, and performance of compression ignition diesel engine

This research was directed to reduce the global diesel engine emissions and dependency on finite fossil fuel reserves. The ethanol was blended by weight ratio with commercial “B20” fuel (20% palm oil’s biodiesel and 80% diesel) as B20E5 (95% B20 with 5% ethanol), B20E10 (90% B20 with 10% ethanol) and B20E20 (80% B20 with 20% ethanol). The results of the engine’s performance, combustion, emission, and agglomerate particles size using blended fuels were compared with the results of based commercial B20 fuel. All fuel samples were tested on a four-cylinder direct injection diesel engine at a constant load of 140Nm with engine speeds of 1000RPM, 1500RPM and 2000RPM. When the engine speed increased, the brake-specific fuel consumption decreased, and the brake thermal efficiency increased. The B20E20 shows the highest brake-specific fuel consumption because of the low energy content of the fuel blend and the highest thermal efficiency because of a better combustion process. The ethanol-blended fuels show higher peaks of in-cylinder pressure and heat release rate than the base B20 fuel, with B20E20 as the highest. Ethanol blended fuels have significant advantages in particulate matters reduction, especially in idle engine speed. The blended fuels decreased soot and CO2 emissions and increased NOx emission. The agglomerate particles size distribution was analysed with 100 samples for each fuel by using Scanning Electron Microscopy (SEM) and Image J tools. The average agglomerate particle size of B20, B20E5, B20E10 and B20E20 are 0.253 µm, 0.245 µm, 0.225 µm and 0.187 µm, respectively. As conclusion, adding ethanol to diesel fuel provide strong advantages on soot reduction and higher engine efficiency due to the enrich of fuel oxygen.

Machine learning and deep learning enabled fuel sooting tendency prediction from molecular structure

Soot formation models become increasingly important in advanced renewable fuels formulation for soot reduction benefit. This work evaluates performance of machine learning (ML) and deep learning (DL) to predict yield sooting index (YSI) from chemical structure and proposes a tailor-made convolution neural network (CNN)-SDSeries38 for regression problem. In ML, a novel quantitative structure-property relationship (QSPR) is developed for feature extraction and the relationship between molecular structure and YSI is built by ML algorithm. In DL, SDSeries38 contains 9 feature learning modules, 1 regression module for automated feature learning and regression. It adopts standard series network architecture and modular structure, each feature learning module is a stack of convolution, batch normalization, activation, pooling layers. ML-QSPR model outperforms SDSeries38 in accuracy (RMSE = 7.563 vs 19.58), computational speed and the former applies to fuel mixtures. In DL, SDSeries38 network exceeds 10 classical CNN and provides a generic architecture enabling transfer application to other regression problem. DL application to regression is still in its infancy and there is no complete guide on how to develop specific CNN architectures for regression. Some gaps need to be filled: (1) Specially developed CNN architectures for regression are required; (2) The performances of direct transfer learning the classical CNN architectures from classification to regression are modest. A modular structure with typical function modules may provide an ideal solution; (3) Going deeper into the sequence of convolution layers improves predictive accuracy, but bears in mind to keep the number of layers below the threshold to avoid vanishing gradient.

Leveraging hydrogen as the low reactive component in the optimization of the PPCI-RCCI transition regimes in an existing diesel engine under varying injection phasing and reactivity stratification strategies

This research illustrates the novel interposed zone of partially premixed and reactivity-controlled combustion in conjunction with injection phasing and reactivity phasing strategies to understand the performance emission and stability characteristics of a single-cylinder common rail direct injection diesel engine. However, this study determined the optimum interposed zone of operation using Response Surface Methodology (RSM). The findings indicate that raising the rate of hydrogen induction enhances the stability of interposed zone of combustion. The interposed optimum regime has a 31.58% exergy efficiency and 99.1% desirability. Compared to the similar trial run, the optimization study revealed a 45.09% reduction in Soot, a 14.29% reduction in total unburnt hydrocarbon (TUHC), and a 39.83% reduction in NOx emission levels. Thus, experimental and predicted values have been compared. Hence, this variable injection and reactivity phasing under hydrogen enrichment strategies are feasible enough to achieve the goals of advanced low-temperature combustion (LTC) concepts in an existing diesel engine without making significant design modifications.

A phenomenological model for near-nozzle fluid processes: Identification and qualitative characterisations

It is well established that emissions and inefficiencies primarily arise from localised fuel rich regions, which do not undergo complete combustion. In order to achieve significant reductions in NOx and soot, modern engines employ multiple injection and flow rate profiling strategies. However, during the end of each injection event, the needle restricts the internal flow of fuel, rapidly reducing the inertia of the emerging spray. Atomisation is inhibited and large fluid structures are released into the cylinder. Once the flow subsides, fuel films remain on the nozzle surface well into the cycle. Fuel residing in the nozzle cavities emerges as the cycles progresses, amalgamating with the spray deposited films. The surface-bound fuel presents an ideal environment for deposit forming reactions and a medium for precursors to adhere onto. In order to better understand these processes we performed measurements of injection transients inside an optical reciprocating rapid compression machine, using high-speed long-distance microscopy to obtain detailed characterisations of fuel films on the surface of an injector. We summarise our observations into a new phenomenological model which describes the uncontrolled release of fuel over an entire engine cycle. This model identifies the micro-scale processes that lead to the ejection, accumulation and vaporisation of fuel in-between injection events. Characterisation of these critical, transient processes can support mitigation strategies that inhibit pollutants and the formation of injector deposits.

Numerical investigation of glycerol/diesel emulsion combustion in compression ignition conditions using Stochastic Reactor Model

In this work, we numerically investigate the potential of glycerol as a diesel fuel additive to reduce soot emissions. Many different fuel additives offer environmental benefits, since there is a surplus supply of glycerol as a by-product of biodiesel production, it is considered as a promising available candidate. The combustion process of glycerol in a direct injection compression ignition engine has been previously investigated experimentally for a 10 % (vol) glycerol emulsion. Based on the experimental set-up, a zero-dimensional Stochastic Reactor Model (SRM) is constructed to conduct numerical analysis with a detailed chemical mechanism for the combustion of hydrocarbon and oxygenated fuels. Applied models are presented and discussed with a focus on the characteristic mixing time scale of micromixing closure which is calculated using a 0D k-ε. The model constants are optimized to the analysed engine with the aid of a genetic algorithm and the sensitivity analysis is presented. For both fuels, emissions of major species are reproduced well but NOx results are slightly overestimated. Emissions of carbon monoxide are predicted well for the reference diesel fuel, but the SRM does not capture the trend of increased CO with glycerol emulsion. The stochastic nature of the model is used to represent the mixture inhomogeneity, and the results are analysed using equivalence ratio–temperature plots to identify soot promoting conditions. The evolution of selected soot precursor and oxidizers is analysed, showing the capability of glycerol to reduce the former and increase the latter with a moderate effect. Soot formation and decomposition rates are presented, with very similar behaviour for both fuels. A shorter combustion phasing for the glycerol emulsion was observed and identified as the main contributory factor that led to the soot reduction while the chemical effect i.e oxygen content of the glycerol was present but not the dominant factor. The soot model results do not provide any evidence for the origin of experimentally observed small-sized particles, but it is discussed that the emissions results indicate the presence of low volatile compounds that could condense in the exhaust system.

Potential improvement in conventional diesel combustion mode on a common rail direct injection diesel engine with PODE/WCO blend as a high reactive fuel to achieve effective Soot-NOx trade-off

Many countries in and around the world have conducted various studies on biodiesel usage over common rail direct injection (CRDI) diesel engines, among which waste cooking oil (WCO) biodiesel has made a major impact on diesel engine research because of its cost-efficient nature and elimination of waste disposal. The deposits of carbon and very high viscosity are some of the key factors which deteriorate the usage of raw WCO biodiesel. Lower volume proportionate blends of WCO biodiesel produce excellent combustion characteristics reducing hydrocarbon (HC), carbon mono oxide (CO), and soot emissions, but they seem to promote the formation of nitrous oxides (NOx). As a solution to overcome this problem, polyoxymethylene dimethyl ether (PODE) with lower viscosity, higher oxygen content, high cetane number, showing better combustion characteristics with a good soot-NOx trade-off is selected for the present research work. The novelty of the current research work shows the reduction of soot and NOx emissions using PODE/WCO/Diesel blends by varying the proportions in a conventional combustion mode of a CRDI diesel engine without any modifications which was lagging by the previous researches. A trans-esterified WCO biodiesel is blended with diesel in varying volumes as 10, 20, and 30%. The chemical properties of the blend fuels were determined using ASTM standards. The investigation was carried out and it was found that W20 blend fuel showed a highest reduction of 21.11%, 23.51%, and 22.45% of CO, HC, and soot emissions respectively with a rise of 6.39% of NOx emissions. W20 blend with a good soot-NOx trade-off was selected in which PODE was blended in varying proportions such as 10, 20, and 30% respectively. The properties of the test fuels were determined and the further investigation was carried out. This second stage of reduction was done in determining the fuel with excellent soot-NOx trade-off without compromising the performance of the engine. It was found that W20P20 blend fuel showed the highest reduction of 33.86%, 50.78%, and 80.86% of HC, CO, and Soot emissions with a slight increase of 0.78% of NOx emissions. Brake Thermal Efficiency was found better for W20P20 fuel in comparison with W20 fuel. Thus, two stages of reduction in emissions were carried out with the aim of meeting the stringent emissions norms in the conventional diesel combustion technique.

Effect of direct water injection temperature on combustion process and thermal efficiency within compression ignition internal combustion Rankine engine

Compression ignition-internal combustion Rankine cycle (CI-ICRC) concept implement oxy-fuel combustion, direct water injection (DWI) and waster heat recovery into traditional diesel cycle to realize ultra-high thermal efficiency and low emission powertrain. As indicated by ICRC concept, the DWI process show critical impact on its combustion process and thermal efficiency. This paper dedicated in investigating the effect of different DWI temperature on cycle performance and thermal efficiency within prototype CI-ICRC engine, in order to do so, independent DWI system, O2/CO2 intake system and reconfigurable electronic controller is established. Combustion characteristics including in-cylinder pressure, heat release rate, combustion stability, brake thermal efficiency are experimentally investigated. The cycle performance and thermal efficiency are proved to be optimized under elevated DWI temperature, an optimum 46.6% brake thermal efficiency is achieved, while the coefficient of variation remains around 1%. The NOX and soot emissions are both reduced under DWI utilization, the mechanism of soot reduction is highly related to thermolysis of water or carbon-water reactions which further chemical kinetic analysis is needed. The result of this study provides fundamental information for future CI-ICRC engine optimization, and can also be utilized in providing reference guidance for DWI implementation within modern internal combustion engines.

Mixture formation and combustion process analysis of an innovative diesel piston bowl design through the synergetic application of numerical and optical techniques

The optimization of diesel engine piston bowl geometries has a crucial role in improving the near-wall flame evolution for better air/fuel mixing and soot reduction. With these aims, an innovative piston bowl for a light-duty diesel engine was designed, coupling both a sharp-stepped lip and radial bumps in the inner bowl rim. The impact of the proposed design was investigated through both 3D-CFD and single-cylinder optical engine. The numerical model, featuring a calibrated spray model and a detailed combustion mechanism, was used to analyse the non-reactive air/fuel mixing and the combustion processes. Results highlighted a reduced jet-to-jet interaction and better air/fuel mixing for the innovative bowl with respect to a conventional re-entrant design, thus enabling faster combustion process after the end of main injection. Numerical results in terms of flame’s kinematic and oxidation process were compared with the combustion image velocimetry (CIV) and OH* chemiluminescence from the optical engine, showing higher velocity near the radial bumps, and faster flame recirculation towards the piston center. Moreover, both experiments and simulations showed a more intense OH distribution in the radial-bumps region and above the step during the first stage of the combustion process, thanks to the enhanced air/fuel mixing.

Emission and performance characteristics of CRDI diesel engine using Quadruple injection strategy with different pilots and post injection timing

Multiple injections in association with suitable (High/heavy) exhaust gas recirculation (EGR) is a promising technique to achieve low temperature combustion (LTC) regime in modern CRDI (common rail direct injection) diesel engine. This helps for simultaneous reduction of NOx and Soot to meet the stringent emission norms without penalizing the fuel efficiency and overcome the drawbacks of EGR-LTC. There are limited insights available which discuss about the potentiality of latest Quadruple injection (early-pilot-main-post/after; epMa) strategy in combination with high EGR and different injection timing over triple injections (pilot-main-after; pMa) at wide operating conditions. This paper deals with the study on the effect of Quadruple injection (epMa) startegy on performance, emissions and noise with different Pilot injection timing and post injection dwell combinations (8 Nos) on a CRDI diesel engine with high EGR and fixed main injection schedule at 4 operating loads and 5 speeds. The study shows that Quadruple injection strategy with retarded early and advanced pilot (early 35° and pilot 19°CA BTDC) and advanced post injection dwell timing 1100 ms is superior in providing optimum results in emissions (NOx, PM, THC, CO) and combustion noise (CN)[1.55–2 dBA @Rig level and 0.7 dBA @ Vehicle level Pass by Noise (PBN)]. This gives the best results in brake specific fuel consumption (BSFC)[0.2 to 1.31%], Torque and brake thermal efficiency (BTE) performance w.r.t other combinations and base triple injections (pMa). In contrary, the quadruple injection strategy having advanced double pilots with delayed post injection dwell (early-39°, Pilot-19°CA BTDC and DtA 1300 ms); shows the best CN reduction. Best smoke results found with the combination of retarded pilots and advanced post injection dwell. This study shows the importance of injection timing specially the twin pilots (early, pilot) along with post injection dwell. Furthermore, it indicates the potentiality of newest Quadruple injection strategy over triple injection.

Experimental study on correlation between PAHs and soot in laminar co-flow diffusion flames of n-heptane at elevated pressure

As Polycyclic Aromatic Hydrocarbons (PAHs) are the main precursors of soot formation, the investigation of PAHs formation and PAHs transforming to soot is essential for understanding the soot formation and soot reduction in combustion. This study investigated PAHs and soot formation in laminar co-flow diffusion flames fueled by n-heptane at elevated pressures. By using the combination of Laser-induced Incandescence (LII) and Laser-induced Fluorescence (LIF) techniques, the distributions of PAHs and soot concentration in flames were obtained with the energy of 6 and 48 mJ at various detection times. The flame stability at different pressures was analyzed, and the relationship between the integrated signal intensities of Soot-LII and PAHs-LIF in the region near the flame centerline was discussed. The results revealed that, with the increase of pressure, the flame stability becomes worse and both the soot and PAHs concentrations are increased. The integrated intensities of Soot-LII and PAHs-LIF in the region near the centerline of the flame scale with pn. In addition, the integrated signal intensity of Soot-LII has a good linear correlation with that of the PAHs-LIF, and the slopes of correlations are 0.33 and 1.81 at the laser energy of 6 and 48 mJ respectively.

Assessment of performance, combustion and emissions characteristics of methanol-diesel dual-fuel compression ignition engine: A review

The energy security concern and rapidly diminishing fossil fuel resources demand the development of renewable and economically attractive fuel for reciprocating engines. Methanol is a promising renewable alternative fuel. Numerous studies have been carried out to explore the various aspects of the utilization of methanol in compression ignition (CI) engine. This review paper presents a detailed analysis of the effect of methanol on performance, combustion, and emission (NOx, CO, HC, and soot) characteristics of conventional CI-engine along with dual-fuel combustion mode. This study focuses on methanol utilization in dual-fuel mode, which is an advanced engine combustion mode. First, methanol production and solubility issues of methanol in diesel are briefly discussed. This study discusses the soot and nano-particle emission from the methanol fueled CI-engine, which is one of the main concerns in the current emission legislation. It was found that the utilization of methanol in CI-engine has the potential to improve the performance and simultaneously with a significant reduction in NOx, CO, soot, and nano-particle emissions in comparison to neat diesel operation. However, unburnt HC emission reduces for methanol-diesel blended fuel operation whereas HC emissions are higher for methanol-diesel dual-fuel operation.

Artificial intelligence assisted MOPSO strategy for discerning the exergy efficiency potential of a methanol induced RCCI endeavour through GA coupled multi-attribute decision making approach

The present study undertakes a comprehensive effort to explore the exergy efficiency-emissions-stability-combustion quality characteristics of premixed methanol with diesel reactivity controlled operation. The combustion phasing of the dual fuel operation primarily depends on the methanol participation rate, wherein the peak in-cylinder pressure and heat release rate decreases with increased methanol injection duration. Though simultaneous reductions of NOx and soot were observed in this study, the stability of the operations deteriorates along with unburned hydrocarbon (UHC) and carbon monoxide (CO) with increasing methanol participations resulting in a trade-off situation. Besides, the severe instability of the operation at 50% load causes misfire due to excessive dilution of the charge at higher methanol participation. The study further explores the potential of Gene Expression Programming assisted meta-model coupled Multi-objective Particle Swarm optimization (MOPSO) algorithm based multi-objective optimization endeavour to explore the optimal operational design space considering the multiple responses of exergy efficiency, NOx, PM, UHC, CO, Coefficient of Variance of indicated mean effective pressure (COVIMEP), lowest normalized value (LNV) of indicated mean effective pressure. In this present case of study, the optimization endeavor has yielded 350 numbers of Pareto solutions, while only 26 numbers of Pareto solutions were observed in the experimental counterpart. Moreover, the experimental domain of the present study has produced only single set of experiment which can satisfy the respective emission limits of NHC and PM altogether, whereas 13 sets were evident in the optimization study to maintain the NHC and PM footprint under the emission constraints simultaneously. The overall analysis of the Pareto solutions evolved in the optimization study has revealed that to attain the minimum NHC and PM footprints, the penalty of exergy efficiency and CO emissions must be incurred. The overall minimum of NHC footprint in the optimization study was recorded as 4.19 g/kWhr, compared to 6.58 g/kWhr as observed in the experimental endeavor. Similarly, the footprint of minimum PM was discovered as 0.13 g/kWhr in the optimization regime, which was 27% lower than the experimental counterpart. However, an imperceptible penalty of 1% was incurred in exergy efficiency, despite of significant lowering of overall minimum CO emissions by 84% in the optimization endeavor compared to the experimental counterpart.

Numerical Investigation on the Effect of the Oxymethylene Ether-3 (OME3) Blending Ratio in Premixed Sooting Ethylene Flames

Synthetic fuels, especially oxygenated fuels, which can be used as blending components, make it possible to modify the emission properties of conventional fossil fuels. Among oxygenated fuels, one promising candidate is oxymethylene ether-3 (OME3). In this work, the sooting propensity of ethylene (C2H4) blended with OME3 is numerically investigated on a series of laminar burner-stabilized premixed flames with increasing amounts of OME3, from pure ethylene to pure OME3. The numerical analysis is performed using the Conditional Quadrature Method of Moments combined with a detailed physico-chemical soot model. Two different equivalence ratios corresponding to a lightly and a highly sooting flame condition have been investigated. The study examines how different blending ratios of the two fuels affect soot particle formation and a correlation between OME3 blending ratio and corresponding soot reduction is established. The soot precursor species in the gas-phase are analyzed along with the soot volume fraction of small nanoparticles and large aggregates. Furthermore, the influence of the OME3 blending on the particle size distribution is studied applying the entropy maximization concept. The effect of increasing amounts of OME3 is found to be different for soot nanoparticles and larger aggregates. While OME3 blending significantly reduces the amount of larger aggregates, only large amounts of OME3, close to pure OME3, lead to a considerable suppression of nanoparticles formed throughout the flame. A linear correlation is identified between the OME3 content in the fuel and the reduction in the soot volume fraction of larger aggregates, while smaller blending ratios may lead to an increased number of nanoparticles for some positions in the flame for the richer flame condition.

Combustion Study of Polyoxymethylene Dimethyl Ethers and Diesel Blend Fuels on an Optical Engine

Polyoxymethylene dimethyl ethers (PODE) are a newly appeared promising oxygenated alternative that can greatly reduce soot emissions of diesel engines. The combustion characteristics of the PODE and diesel blends (the blending ratios of PODE are 0%, 20%, 50% and 100% by volume, respectively) are investigated based on an optical engine under the injection timings of 6, 9, 12 and 15-degree crank angles before top dead center and injection pressures of 100 MPa, 120 MPa and 140 MPa in this study. The results show that both the ignition delay and combustion duration of the fuels decrease with the increasing of PODE ratio in the blends. However, in the case of the fuel supply of the optical engine being fixed, the heat release rate, cylinder pressure and temperature of the blend fuels decrease with the PODE addition due to the low lower heating value of PODE. The addition of PODE in diesel can significantly reduce the integrated natural flame luminosity and the soot formation under all injection conditions. When the proportion of the PODE addition is 50% and 100%, the chemical properties of the blends play a leading role in soot formation, while the change of the injection conditions have an inconspicuous effect on it. When the proportion of the PODE addition is 20%, the blend shows excellent characteristics in a comprehensive evaluation of combustion and soot reduction.

Performance and emissions of renewable blends with OME3-5 and HVO in heavy duty and light duty compression ignition engines

Interest in poly(oxymethylene)dimethyl ether (OME3-5) as an alternative to fossil fuels in compression ignition engines has increased owing to its potential for soot reduction. The high oxygen content of the polymer and lack of carbon–carbon bonds and aromatic structures can help to reduce engine out soot emissions. However, OME3-5 is potentially damaging to engine components, and thus engine modifications are required when using neat OME3-5.In the present study, OME3-5 was blended with hydrotreated vegetable oil (HVO), rapeseed methyl ester and the C8-alcohol 2-ethylhexanol (an isomer of n-octanol) to ensure miscibility. Three blends were designed with an oxygen content of 6.4, 12.8 and 17.8% by mass. Performance and emissions were compared to the reference fuels fossil diesel and HVO in a single cylinder light duty and heavy duty compression ignition engine at different loads.Evaluation of the combustion in both engines showed similar trends: The indicated thermal efficiency was slightly higher for the oxygenated fuel and the combustion duration shorter compared to diesel. Due to the lower heating value of the blends, the indicated specific fuel combustion increased with increasing share of OME3-5 in the blend.For both engines, engine out soot emissions were decreased strongly, whereas NOx emissions were slightly increased. Analysis of the particle size distribution showed a decrease in the particle number of agglomerated particles (>30 nm) for the blends. For the heavy duty engine, an increase in nucleation mode particles (<30 nm) was measured.

Cleaner burning aviation fuels can reduce contrail cloudiness

Contrail cirrus account for the major share of aviation’s climate impact. Yet, the links between jet fuel composition, contrail microphysics and climate impact remain unresolved. Here we present unique observations from two DLR-NASA aircraft campaigns that measured exhaust and contrail characteristics of an Airbus A320 burning either standard jet fuels or low aromatic sustainable aviation fuel blends. Our results show that soot particles can regulate the number of contrail cirrus ice crystals for current emission levels. We provide experimental evidence that burning low aromatic sustainable aviation fuel can result in a 50 to 70% reduction in soot and ice number concentrations and an increase in ice crystal size. Reduced contrail ice numbers cause less energy deposition in the atmosphere and less warming. Meaningful reductions in aviation’s climate impact could therefore be obtained from the widespread adoptation of low aromatic fuels, and from regulations to lower the maximum aromatic fuel content.