soot-NOx Trade-off Research Articles

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.

Combining Gasoline Compression Ignition and Powertrain Hybridization for Long-Haul Applications

Gasoline compression ignition (GCI) combustion was demonstrated to be an effective combustion concept to achieve high brake thermal efficiency with low-reactivity fuels while offering improved NOx–soot trade-off. Nevertheless, future greenhouse gas regulations still challenge the heavy-duty transportation sector on both engine and vehicle basis. Hybridization is a possible solution in this scenario, allowing the avoidance of low-efficiency conditions and energy recovery during regenerative braking, improving overall vehicle efficiency. In this sense, this investigation proposes a detailed analysis to understand the optimum hybridization strategy to be used together with GCI to simultaneously harness low pollutant and CO2 emissions. For that, different hybrid architectures were defined in GT Drive (Mild hybrid 48 V P0 and P2 and full Hybrid P2 500 V) and submitted to 15 different use cases, constituted by five normative and real-driving conditions from the US, China, India, and Europe and three different payloads. Results showed that all hybridization strategies could provide fuel savings benefits to some extent. Nonetheless, usage profile is a dominant factor to be accounted for, benefiting specific hybrid powertrains. For instance, P0 and P2 48 V could provide similar savings as P2 500 V, where regenerative braking is limited. Nonetheless, P2 500 V is a superior powertrain if more demanding cycles are considered, allowing it to drive and recuperate energy without exceeding the Crate limitations of the battery.

A numerical analysis of hydrotreated vegetable oil and dimethoxymethane (OME1) blends combustion and pollutant formation through the development of a reduced reaction mechanism

The solution to the dilemma of carbon footprint of internal combustion engines and pollutant emissions is necessary for the survival of this technology. In this context, alternative fuels have shown great potential in terms of achieving cleaner combustion and compliance with ever increasing pollutant emissions regulations. This work is focused on the study of two promising alternative fuels as Hydrotreated vegetable oil (HVO), which is a biofuel and Dimethoxymethane also termed as OME1, which is an e-fuel. A comprehensive numerical approach has been followed to study these fuels. Primarily a compact reaction mechanism having 121 species and 678 reactions has been developed which can be utilized to perform 3D CFD simulations of blends of these fuels. Secondly, a detailed numerical investigation including combustion and emissions analysis has been carried out. Results show that the developed mechanism is able to offer predictions, which match the experimental behavior observed in various combustion parameters and thus can be utilized for compression ignition engine applications involving these promising fuels. In addition, the numerical analysis also highlights that a reduction of 50% and 37% in terms soot and NOx emissions respectively can be achieved by addition of 30% OME1 in the blend containing HVO, suggesting that these blends can be utilized in unmodified CI engines to break the soot-NOx tradeoff without significantly penalizing the energy loss.

Understanding the ignition process and flame structure of conventional and oxygenated fuels under engine relevant conditions – An optical study

Renewably generated synthetic fuels such as poly-oxymethylene ethers (OME) have a significant potential to effectively break the soot-NOX trade-off in compression ignition engines by using exhaust gas recirculation (EGR) to maintain low nitrogen oxide (NOX) emissions while maintaining good efficiency and simultaneously contributing to circular carbon economy. However, owing to the fundamental differences in properties of OME when compared to fossil-based diesel fuels, it is critical to fully understand its ignition and combustion phenomenology to take advantage of this fuel to its utmost potential. In this context, this work outlines the results of a systematic experimental study performed in a heavy-duty, single-cylinder, optical engine probing the spatial and temporal progression of fuel decomposition and ignition behavior of OME when compared to n-dodecane, a diesel-fuel surrogate. Thermodynamic analysis and optical diagnostics techniques including simultaneous HCHO-PLIF and OH-PLIF complemented by high-speed OH* chemiluminescence were employed along with parametric sweeps of intake temperature and EGR dilution rates. OME does not exhibit any observable low temperature heat release irrespective of the ambient oxygen concentration. Differences in the observed diffusive flame structure such as longer flame lift-off length, less pronounced combustion recession, faster premixed burn at ignition (“volumetric” ignition), non-sooting behavior suggest that the inherent presence of fuel-bound oxygen in OME can skew the air-fuel ratio (AFR) distribution within the jet thereby reducing the reliance of combustion on mixing and air entrainment. This leads to rapid late-cycle oxidation leading to shorter combustion duration and favorable combustion phasing. Results also suggest that OME exhibits relatively weak negative temperature coefficient (NTC) behavior, however, the OME fuel-decomposition kinetic-pathways produce significant concentration of HCHO, which might be erroneously interpreted as a product of cool-flames.

Numerical study of effect of post injection coupled with EGR on combustion and emission performances of CRDI engine fueled with biodiesel-ethanol blends

Energy shortage and environmental pollution are becoming more serious, biodiesel is regarded as the most promising alternative fuel for diesel engines due to its environmentally friendly and renewable characteristics. In this study, the biodiesel-ethanol blends were used in a diesel engine, and the purpose of the study was to simultaneously control the NOx and soot emissions of the diesel engine by adjusting the injection strategy and EGR rate. A turbocharged, six-cylinder, common rail direct injection (CRDI) engine model was established using GT-Power. The effects of the main-post injection strategy and post injection coupled with exhaust gas recirculation (EGR) on combustion and emission characteristics were investigated at a maximum torque speed and a medium load. The results show that when the main-post injection strategy is employed, the combustion duration of the main injection is shortened with an increase in the main-post injection interval (MPI). When the MPI increased to more than 18 °CA, the heat release of post injection could be observed clearly from the curve of the heat release rate, NOx emissions decreased by 5.70% and 7.12%, respectively, and soot emissions decreased by 25.56% and 30.20%, respectively. Moreover, with the increasing post injection quantity, the combustion duration of the main injection shortened, and the peak heat release rate (PHRR) of the post injection increased. When the fuel quantity for the post injection increased from 2 to 6 mg, NOx emissions decreased from 2.33% to 9.80%, and soot emissions decreased from 16.10% to 34.97%. The effect of post injection quantity on emissions was more significant than that of the MPI. In addition, with increasing EGR rate, the ignition delay is prolonged, the peak cylinder pressure, PHRR, peak combustion temperature and NOx emissions decrease, whereas soot emissions increase gradually. Main-post injection can improve the NOx-soot trade-off, the optimal EGR rate is 22.86% under a post injection quantity of 4 mg and a MPI of 22 °CA.

CRDI Engine Emission Prediction Models with Injection Parameters Based on ANN and SVM to Improve the SOOT-NOx Trade-Off

Artificial Neural Network (ANN) and Support Vector Machine (SVM) have been widely used to solve non-linear problems. In the current study, based on 112 groups of experimental data, ANN and SVM models were established and compared to improve the trade-off relationship between SOOT and NOx emissions of a Common Rail Diesel Injection (CRDI) engine fueled with Fischer-Tropsch (F-T) diesel under different operating conditions and injection parameters. The model parameters for the different predictive targets were selected by evaluating the mean square error (MSE) and determination coefficient. Compared to the number of network iterations, the number of implied nodes had a greater effect on the MSE of the ANN model. Compared to the penalty parameter, the width coefficient had a weaker impact on the SVM performance. A comparative analysis showed that the SVM had better predictive accuracy and generalization ability than the ANN, with a maximum error not exceeding five percent and a determination coefficient of over 0.9. Subsequently, the optimal SVM model was combined with the NSGA-II algorithm to determine the optimal injection parameters for the CRDI engine, resulting in solutions to simultaneously decrease the SOOT and NOx emissions. The optimized injection parameters resulted in a 3.7–7.1% reduction in SOOT emission and a 1.2–2.6% reduction in NOx emissions compared to the original engine operating conditions. Based on limited experimental samples, SVM is inferred to be a useful tool for predicting the exhaust emissions of engines fueled with F-T diesel and can provide support for optimizing injection parameters.

The potential of dimethyl ether (DME) to meet current and future emissions standards in heavy-duty compression-ignition engines

Dimethyl Ether (DME, H3C-O-CH3) is regarded as a meaningful alternative fuel as it has a comparably high energy density, can easily be stored on vehicles, can be produced via different renewable pathways, has a high Cetane number and is therefore suitable for use in efficient and durable compression ignition engines. Moreover, the DME molecule lacks carbon bonds and due to the inbuilt oxygen atom enables low-sooting diffusion combustion. This study reports on the performance and emission characteristics of a state-of-the-art heavy-duty compression ignition engine with 11 L displacement which was optimized specifically for DME combustion. This includes the adaptation of the fuel supply and injection system as well as the combustion chamber geometry. In addition, the engine is equipped with an electrically driven volumetric pump in the exhaust gas recirculation (EGR) path which gives the freedom to set any desired EGR rate, independently from the pressure ratios across the turbocharger. The experimental results show that DME operation retains the performance on the base Diesel engine (338 kW peak power) while significantly reducing the engine out emissions. The NOx-soot tradeoff, typical of Diesel applications, basically does not exist anymore so that a desired NOx level can basically be set without the restrictions of sooting combustion. In addition, the combustion is very complete and very low levels of regulated and non-regulated pollutant emissions can be detected (e.g. for carbon monoxide, DME, methane, benzene, toluene, acetaldehyde, formaldehyde, formic acid). Transient operation is unproblematic and very low emissions can be achieved using the same exhaust gas treatment system as for diesel. Actually, total hydrocarbon, carbon monoxide and particle emission levels of the actual EuroVI and possibly even for the proposed EuroVII on-road legislation could be met without any exhaust gas purification. In terms of tailpipe CO2 emissions, a reduction of around 11% is possible compared with a diesel-fueled engine.

A Synergic Application of High-Oxygenated E-Fuels and New Bowl Designs for Low Soot Emissions: An Optical Analysis

Synthetic fuels significantly reduce pollutant emissions and the carbon footprint of ICE applications. Among these fuels, oxymethylene dimethyl ethers (OMEX) are an excellent candidate to entirely or partially replace conventional fuels in compression ignition (CI) engines due to their attractive properties. The very low soot particle formation tendency allows the decoupling of the soot-NOX trade-off in CI engines. In addition, innovative piston geometries have the potential to reduce soot formation inside the cylinder in the late combustion stage. This work aims to analyze the potential of combining OMEX with an innovative piston geometry to reduce soot formation inside the cylinder. In this way, several blends of OMEX-Diesel were tested using a radial-lips bowl geometry and a conventional reentrant bowl. Tests were conducted in an optically accessible engine under simulated EGR conditions, reducing the in-cylinder oxygen content. For this purpose, 2-colour pyrometry and high-speed excited state hydroxyl chemiluminescence techniques were applied to trace the in-cylinder soot formation and oxidation processes. The results confirm that increasing OMEX in Diesel improves the in-cylinder soot reduction under low oxygen conditions for both piston geometries. Moreover, using radial lips bowl geometry significantly improves the soot reduction, from 17% using neat Diesel to 70% less at the highest OMEX quantity studied in this paper.

Quantification of φ-operating range with impact of exhaust gas recirculation under low-temperature combustion mode with polyoxymethylene dimethyl ether: A perspective study

Low-Temperature Combustion (LTC) especially Homogeneous charge compression ignition (HCCI) mode of combustion is a capable substitute mode of combustion to conventional diesel combustion (CDC) to provide better soot-NOx trade-off and HC-CO trade-off characteristics. The current study mainly focuses on the Exhaust Gas Recirculation (EGR) effects and equivalence ratio optimization on W20P20 (64% diesel, 16% WCO biodiesel, and 20% PODE) fuel along with exergy analysis in the HCCI mode of operation. The reason for inculcating exergy analysis in this research is to depict that low-temperature combustion provides a better heat transfer rate inside the cylinder. EGR has been varied in terms of 10%, 20%, and 30% in volume proportions along with the inlet fuel-air mixtures since, the fuel was injected through a pilot fuel injector in the inlet manifold. A novel factor in this research is considering both soot-NOx and HC-CO trade-off characteristics in optimizing the equivalence ratio with the influence of EGR over W20P20 fuel. The performance parameters such as BTE and BSEC show a mere decrement of about 6.67% and 29% of maximum with the influence of EGR while better combustion was found in terms of avoiding misfiring at a low equivalence ratio of 0.29–0.35 and knocking at a high equivalence ratio of 0.61–0.71 for W20P20 fuel. The operating range extension of the equivalence ratio was found with W20P20 fuel which further increased again with the increase in EGR addition. The emission limits of soot, NOx, CO, and HC particles were analyzed, in which the highest NOx reduction of 53% was obtained with 30% EGR irrespective of the equivalence ratio. The highest soot reduction was 61.85% with 20% EGR at a higher equivalence ratio. The highest HC reduction was 18% with 20% EGR at a lower equivalence ratio. The CO emissions seemed to reduce by 12% at a lower equivalence ratio while they increased by 47% at a higher equivalence ratio. The comparative results were studied for EGR influence with W20P20 fuel in the HCCI mode of combustion.

Influence of the radial-lip concept design to achieve ultra-low soot emission reductions: An optical analysis

Nowadays, internal combustion engines must reduce pollutant emissions to achieve the upcoming strict regulations in the transport sector. In this context, new hardware designs have shown great potential to reduce pollutant emissions and comply with current and future regulations. This paper focuses on innovative bowl designs with radial lip protrusions, which are radially distributed inside the bowl. The potential of using these protrusions in order to reduce soot formation and improve soot oxidation has been demonstrated by different studies. For this reason, the present work addresses the impact of using two different radial-lip based geometries on soot formation and combustion behaviour in an optical single-cylinder compression ignition engine. High-speed OH* chemiluminescence imaging and 2-Colour pyrometry were applied simultaneously, in combination with a thermodynamic analysis of the in-cylinder pressure signal. The results show that more pronounced radial-lip geometry drive the flames closer to the bowl centre, where more oxygen is available to oxidize the soot, resulting in in-cylinder soot formation reduction. In addition, it has been observed that the improvement achieved by the more pronounced radial-lip geometry is more noticeable under high EGR conditions. This opens a path to reduce the soot-NOX trade-off in compression ignition engines.

Experimental and kinetic modeling studies on the interaction of DMM3-isooctane blends during the low-temperature oxidation

Reactivity controlled compression ignition (RCCI) engines have been extensively investigated in the past decade due to its good performance in balancing the NOx-soot trade off relationship and controlling the heat release rate. However, studies on the interaction between the reactive and inert fuels are scarce, which is critical for regulating the RCCI combustion process. In this study, the interaction mechanism between polyoxymethylene dimethyl ethers (DMM3) and isooctane during the low-temperature oxidation was investigated through experiments and simulations. The low-temperature oxidation experiments were conducted in a jet-stirred reactor (JSR) at near atmospheric pressure with different blending ratios. A detailed DMM3-isooctane mechanism containing 2896 species and 9676 reactions was developed and fully validated with the experimental results. In addition, an impact factor fw was proposed to quantitatively analyze the influence degree of interaction between fuel and intermediate species. The results indicate that the low-temperature oxidation of isooctane is triggered and significantly enhanced in the blending fuels. The OH radicals generated by DMM3 are crucial to trigger the low-temperature reaction of isooctane and always play a dominant role in the whole isooctane oxidation process. In addition, isooctane reveals an intense inhibition on the formation of two key intermediate species of DMM3, i.e., methyl formate and methoxymethyl formate. This inhibitory effect ranges from the beginning of low-temperature oxidation of DMM3 to the end of the NTC process (580 K ∼ 750 K). When the temperature is higher than 800 K, the inhibitory effect of isooctane on methyl formate and methoxymethyl formate is significantly weakened and negligible. In addition, the blending of inactive isooctane will result in an oxygen-rich environment for DMM3 during the low-temperature oxidation, which will accelerate the formation of methyl formate and methoxymethyl formate. However, this promoting effect is limited, compared with inhibiting effect of isooctane.

Potential of the Synthetic Fuel Oxymethylene Ether (OME) for the Usage in a Single-Cylinder Non-Road Diesel Engine: Thermodynamics and Emissions

Non-road sectors, such as agriculture and construction machinery, require high energy densities and flexibility in use, which is why diesel engines are mainly used. The use of climate-neutral fuels, produced from renewable energies, such as Oxymethylene Ether (OME) as a diesel substitute, can significantly reduce CO2 and pollutant emissions in these sectors. In addition to CO2 neutrality, OME also offers improved combustion characteristics compared to diesel fuel, eliminating the soot–NOx trade-off and thus enabling new opportunities in engine design and calibration. In this paper, the combustion of pure OME on a close-to-production, single-cylinder non-road diesel engine with a pump–line–nozzle injection system is analyzed. A variation of the center of combustion at constant power output was performed for diesel and OME at different operating points. Two injectors were investigated with OME. A study on ignition delay and a detailed thermodynamic analysis was carried out. In addition, the exhaust emissions CO, NOx, VOC, as well as particulate-matter, -number and -size distributions were measured. With OME, a significantly shorter ignition delay as well as a shortened combustion duration could be observed, despite a longer injection duration. In addition, the maximum injection pressure increases. VOC and CO emissions are reduced. Particulate matter was reduced by more than 99% and particle number (>10 nm) was reduced by multiple orders of magnitude. The median of the particle size distribution shifts from 60 to 85 nm (diesel) into a diameter range of sub 23 nm (OME). A significant reduction of NOx emissions with OME enables new degrees of freedom in engine calibration and an efficiency advantage without hardware adaption.

Experimental study on the combustion, emissions and fuel consumption of elliptical nozzle diesel engine

A series of experiments are carried out to investigate the combustion, emissions characteristics and fuel consumption of a diesel engine equipped with elliptical nozzle. The elliptical holes, which are made with an aspect ratio of 1.5, have a similar flow area as that of the references. In-cylinder pressure, exhaust emissions and fuel consumption are measured with varied fuel injection timing under a constant speed and different loads. The elliptical nozzles are characterized by shorter ignition delays, lower maximum rates of heat release and in-cylinder average temperature, and longer combustion durations. The NOx emission of the ICE with an elliptical nozzle is lower and while Soot emission higher. Under variable fuel injection timing, the NOx-Soot trade-off are affected by the nozzle shape. A substantial improvement in the fuel consumption-NOx emission trade-off is obtained for elliptic nozzles at three different loads. Employing moderate earlier injection couple with elliptical nozzle can reduce fuel consumption 2.5% while NOx and Soot emission remain unchanged at 25% load, and NOx emission reduce by 8.3% and 12.7%, and Soot emission reduce by 5.7% and 10.9%, and fuel consumption reduce by 2.4% and 1.7% at 50% and 75% load respectively.

A numerical investigation of the performance of oxymethylene ethers blended with fossil diesel to reduce soot emissions in compression ignition engines

The reduction of the carbon footprint of internal combustion engines and the pollutant emissions is mandatory for the survival of this technology. In this sense, e-fuels are considered as a potential pathway to achieve this reduction and even remarkable carbon footprint mitigation in compression ignition engines. Among numerous e-fuels, oxymethylene ethers stand out because of their low soot formation characteristics. However, the complexity of their physical and chemical properties makes it a challenge to be used in conventional engines. The aim of the current study is to investigate the effects of the stoichiometry of oxymethylene ether on the in-cylinder combustion behaviour and the pollutant formation when blended with fossil diesel. For this purpose, numerical simulations of a medium duty optical engine fuelled with these blends were carried out using CONVERGE CFD, which were validated with experimental data. Different reaction mechanisms that can be found in the literature were evaluated, using n-heptane as to the fossil diesel surrogate and OME3 as the oxymethylene ether surrogate. Results highlight the differences in terms of equivalence ratio fields achieved when varying the e-fuel content in the blend. As a consequence, the combustion process is faster and the soot formation is drastically reduced when the oxymethylene ethers content is above 30%. This makes these blends interesting to reduce the well-known soot-NOx trade off of compression ignition engines.

Mixing controlled compression ignition with methanol: An experimental study of injection and EGR strategy

Methanol is a fuel that can be produced using renewable electricity, green hydrogen, and a carbon-neutral carbon source. As a low-carbon liquid fuel, methanol is a leading candidate as a drop-in replacement fuel for rapid decarbonization of the transportation sector. In this work, methanol is tested experimentally in mixing-controlled compression ignition using a single-cylinder research engine. Specifically, the impact of a double injection strategy and high exhaust gas recirculation (EGR) dilution on performance and emissions parameters are studied. As a single-carbon, oxygenated fuel, methanol has a near-zero sooting potential, meaning there is no soot-NOx tradeoff as EGR dilution is increased. EGR dilution effectively reduces NOx emissions without a significant combustion efficiency or thermal efficiency penalty until the global equivalence ratio exceeds 0.9, at which point, a significant combustion efficiency penalty is incurred in the form of increased CO emissions. If stoichiometric operation with high EGR dilution is considered, engine-out NOx emissions are low, even at very high loads, and NOx aftertreatment is simplified through the use of a three-way catalyst. However, a relative decrease in the net fuel conversion efficiency of up to 8.5% was observed, demonstrating an emissions-efficiency tradeoff. Under lean and stoichiometric conditions, no appreciable agglomeration of particulate matter was observed.

Variable Valve Strategy Evaluation for Low-Load Operation in a Heavy-Duty Gasoline Compression Ignition Engine

By harnessing gasoline’s low reactivity for partially premixed combustion promotion, gasoline compression ignition (GCI) combustion shows the potential to produce markedly improved NOx-soot trade-off with high fuel efficiency compared to conventional diesel combustion. However, at low-load conditions, gasoline’s low reactivity poses challenges to attaining robust combustion with low unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. Increasing the in-cylinder charge temperature by using variable valve actuation (VVA) can be an effective means to address these challenges. In this numerical investigation, VVA strategies, including (1) early exhaust valve opening (EEVO), (2) positive valve overlap (PVO), and (3) exhaust rebreathe (ExReb), were investigated at 1375 RPM and 2 bar brake mean effective pressure in a heavy-duty GCI engine using a market-based gasoline with a research octane number (RON) of 93. The total residual gas level was kept over 50% to achieve an engine-out NOx target of below 1.5 g/kWh. For a complete engine system analysis, one-dimensional (1-D) system-level modeling and three-dimensional (3-D) computational fluid dynamics (CFD) analysis were close-coupled in this study. Performance of the VVA strategies was compared in terms of in-cylinder charge and exhaust gas temperatures increase versus brake-specific fuel consumption (BSFC). The EEVO strategy demonstrated in-cylinder charge and exhaust temperature increase up to 130 and 180 K, respectively. For similar in-cylinder charge temperature gains, the ExReb strategy demonstrated 11% to 18% lower BSFC compared to the EEVO strategy. This benefit primarily originated from a more efficient gas-exchange process. The PVO strategy, due to the valve–piston contact constraint, required excessive exhaust back-pressure valve (BPV) throttling for hot residuals trapping, thereby incurring higher BSFC compared to ExReb. In addition, the ExReb strategy demonstrated the highest potential for exhaust temperature increase (up to 673 K) among the three strategies. This was achieved by ExReb’s maximum air-fuel ratio reduction from high internal residuals mass and BPV throttling. Finally, the ExReb profile was optimized in terms of the peak lift, the duration, and the location for maximizing the fuel-efficiency potential of the strategy.

The energy analysis and performance of heavy-duty diesel engine with n-butanol addition and different coolant temperature

Energy flow assessment can grasp the distribution law of each energy balance term of engines and optimize the control parameters and related structures. In this study, the combustion and emission performance of a Euro-VI heavy-duty diesel engine were tested with different coolant temperature and addition of n-butanol. Research results shows that under idle and high-speed conditions, the position of maximum in-cylinder pressure (Pmax) moves backward with the increase of load. What’s more, and BSFC can only be effectively reduced when the coolant temperature is raised to 100 °C. About the exhaust energy flow, it can be concluded that the exhaust energy flow is not very sensitive to the coolant temperature, but the load and speed are. It is worth noting that coolant energy increased significantly as the ratio of butanol increased, and the proportion of the remaining loss is significantly reduced. Overall consideration, higher temperature of coolant has a positive effect on fuel consumption and Soot-NOx trade-off and coolant with a higher boiling point can improve engine performance and reduce energy loss. Moreover, the addition of a high proportion of n-butanol provides more room for energy recovery.

Numerical investigation on the impact of multiple injection strategies and spray included angles on combustion and emissions in a marine diesel engine

The computational fluid dynamical software AVL-FIRE code was used for investigating the impact of multiply injection strategies and spray included angles on combustion and emissions in a marine diesel engine. The fuel injection parameters of spray included angle and pilot injection timing with pilot-main injection, as well as post injection ratio and post injection duration angle with pilot-main-post injection, were all investigated and optimized. The results indicate that retarding pilot injection timing with pilot-main injection declines high temperature region, resulting in a notable reduction in NOx emissions. Since fuel evaporation and burn are hampered by long spray penetration due to low temperature and pressure with pilot injection, a suitable spray included angle are used to offer more efficient air-fuel mixing process. A wider spray included angle simultaneously reduces soot emission and indicated specific fuel consumption (ISFC). Post injection fuel exerts impact on combustion process by causing a great disturbance to flow field during post combustion. Increasing post injection ratio from 4% to 10% at a small post injection duration angle great emission performance is achieved by simultaneous reduction in NOx and soot emissions while only using a slight consumption of ISFC. To summarize, the defeat of traditional NOx-soot trade-off occurs as both NOx and soot emissions are decreased with optimized multiple injection strategy and spray included angle. Particularly, there are respectively four cases with pilot-main injection and two cases with pilot-main-post injection, that achieve simultaneous reduction in NOx emissions, soot emission, and ISFC, compared to the prototype.

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.

Hydrotreated vegetable oil as enabler for high-efficient and ultra-low emission vehicles in the view of 2030 targets

Studies consider the influence of biofuels on the decarbonization of the transport system not negligible. The employment of fossil fuels with an even higher degree of renewable biofuel content, produced with a mature technology process, such as the Hydrotreated Vegetable Oils (HVO), are expected to increase. The research community expects valuable research results to exploit the HVO characteristics in ultra-low emission vehicles equipped with internal combustion engines. In this context, new findings in setting combustion control parameters through proper experimental design are carried out on a modern internal combustion engine architecture. An advanced injection system capable of precise close-coupled multiple injections per cycle was utilized. Steady-state engine operating conditions were selected for this experimental study. Combustion, efficiency, and engine-out emissions indicators with HVO fuel are compared with standard diesel. For assessing the difference in combustion stages, a second derivative method data analysis was performed. It is found that in comparison to diesel fuel, HVO significantly reduces regulated engine-out emissions at the same efficiency and EU 6c NOx emissions targets. To this aim, a specific set of engine control parameters were adopted. The PM decreased up to 10 %, corresponding to 0.18 g/kWh, while the CO2 reduced by about 7–8% in the range of 0.2–0.5 g/kWh. The decrease of the total PN ranges between 10 and 55%, depending on the control strategy and test point, and the particle distribution shifts towards smaller particle sizes. Outstanding improvements of the NOx-soot trade-off are verified, which in turn demonstrates the capability to operate the engine at post-EU6 NOx conditions without performance and comfort penalties. Engine-out CO and HC emission reductions are confirmed.