Reduce Soot Emissions Research Articles

Effects of various split injection strategies on combustion and emissions characteristics in a single-cylinder diesel engine

The purpose of this study is to investigate combustion and exhaust emissions characteristics by applying various split-injection strategies in order to determine the optimal injection that improves fuel efficiency and reduces exhaust emissions, compared with single-injection combustion. The split-injection strategies, such as the change of injection pressure, injection timing, and injection interval, were applied to single-cylinder diesel engine.From the analysis of the experimental results, it was revealed that, when the injection pressure was increased without changing the injection timing in split injection, indicated mean effective pressure (IMEP) and brake mean effective pressure (BMEP) decreased and brake specific fuel consumption (BSFC) deteriorated, owing to the increase of dwell duration. The increase of injection interval induced deterioration of BSFC and caused an increase in NOx and HC emissions with significant reduction in CO and soot emissions. On the other hand, the retardation of injection timing with a fixed injection interval caused an improvement of the BSFC, and a decrease in NOx, CO, and HC emissions. However, soot emission increased. According to the analysis, a short injection interval and injection timing around top dead center (TDC), with not too high injection pressure, improve the BSFC and emission characteristics in split-injection diesel combustion.

Computational Study to Identify Feasible Operating Space for a Mixed Mode Combustion Strategy—A Pathway for Premixed Compression Ignition High Load Operation

A mixed mode combustion strategy with a premixed compression ignition (PCI) combustion event and a mixing controlled load extension injection was investigated in the current study. Computational fluid dynamics (CFD) modeling was used to perform a full factorial design of experiments (DOE) to study the effects of premixed fuel fraction, load extension injection timing, and exhaust gas recirculation (EGR). The goal of the study was to identify a feasible operating space and demonstrate a pathway to enable high-load operation with the mixed mode combustion strategy. The gross-indicated efficiency (GIE) increased with premix fraction, but the maximum premix fraction was constrained by pressure rise rate which confined the feasible operating space to a premix fuel mass range of 70–80%. Injecting part of the premixed fuel as a stratified injection relieved the pressure rise rate constraint considerably through in-cylinder equivalence ratio stratification. This allowed operation with premix fuel mass of 70% and higher and EGR rates less than 40% which resulted in improved GIE of the late cycle injection cases. It was also identified that by targeting the fuel from the stratified injection into the squish region, there is improved oxygen availability in the bowl for the load extension injection, which resulted in reduced soot emissions. This allowed the load extension injection to be brought closer to top dead center while meeting the soot constraint, which further improved the GIE. Finally, the results from the study were used to demonstrate high-load operation at 20 bar and 1300 rev/min.

Effect of Alcohol Addition to Gasoline on Soot Distribution Characteristics in Laminar Diffusion Flames

AbstractAlcohols are widely used as alternative fuel for spark ignition engines to reduce soot emission. 2D soot distributions of alcohols‐gasoline blends were studied in laminar diffusion flames by two‐color laser‐induced incandescence technique. The soot volume fraction decreases significantly with the alcohol blending ratio. At the same blending ratio, the soot‐reducing ability declined with the carbon length of the alcohol, but the reducing effect for short‐chain alcohols, i.e., methanol and ethanol, deteriorated at high blending ratio while it remained constant for the long‐chain alcohol n‐butanol. At fixed oxygen content, the soot‐reducing ability of a short‐chain alcohol is still higher than that of a long‐chain alcohol, i.e., not only the oxygen content but also the molecular structure dominates the soot‐reducing ability.

Effect of after injections on late cycle soot oxidation in a small-bore diesel engine

After injection, for which a short fuel injection follows the main injection, is proved to be effective in reducing soot emissions in diesel engines. The present study aims to better understand this in-cylinder soot reduction mechanism of after injection with a particular emphasis on its efficacy in a small-bore diesel engine in which more significant flame-wall interactions could cause different behaviour compared with extensively studied heavy-duty diesel engines in the literature. With the main injection only case as a baseline, two after-injection cases of close-coupled and long-dwell timings have been investigated in a single-cylinder common-rail optical engine. Various optical/laser-based imaging diagnostics have been performed including line-of-sight integrated chemiluminescence imaging of OH*, planar laser-induced florescence of hydroxyl (OH-PLIF), planar laser-induced incandescence of soot (PLII) and transmission electron microscope (TEM) imaging of thermophoretically sampled in-flame soot particles to visualise the spatial and temporal evolution of high temperature reaction and soot as well as particle structure. The results indicate that both after-injection strategies introduce a secondary heat release that leads to additional bulk gas temperature rise and thereby promoting the late-cycle soot oxidation. However, the efficacy is found to be dependent upon the after-injection timing. The OH-PLIF and PLII images show that the close-coupled after-injection induces additional high-temperature reaction and soot formation due to high ambient gas temperature. The new reaction occurs near the jet–wall impingement point, which is well separated from the main combustion zone as the main fuel jet travelled along the bowl wall due to significant jet–wall interactions. Although the main and after-injection soot are decoupled, soot morphology analysis based on TEM images suggests that the close-coupled after-injection does enhance the oxidation of main combustion-generated soot particles through the breakdown of large soot aggregates at elevated temperatures and with increased OH radicals. In comparison, both OH-PLIF and PLII images show no visual evidences of decoupled after-injection combustion for the long-dwell case due to insufficient temperature as the additional reaction occurs later in the expansion stroke. However, the increased OH radicals and breakdown of soot aggregates in the main combustion region are evident in OH-PLIF and TEM images. Overall, the close-coupled after-injection adds more soot but induces a higher degree of oxidation for the main combustion-generated soot particles. By contrast, the promotion of soot oxidation is less significant for the long-dwell after-injection but it produces no extra soot.

Miller cycle for improved efficiency, load range and emissions in a heavy-duty engine running under reactivity controlled compression ignition combustion

The low temperature, premixed combustion strategies are being investigated in the recent years as a mean to break the NOx-soot trade-off appearing during the diffusive conventional diesel combustion. This approach relies on promoting premixed combustion events with shortened duration, which reduces the heat transfer losses, improves the thermal efficiency, and allows a simultaneous reduction of engine-out NOx and soot emissions. However, since the combustion onset only depends on chemical kinetics, most of these strategies cannot be implemented at medium and high loads due to excessive pressure gradients, which lead to unacceptable noise levels and reliability issues.This experimental work investigates the potential of the Miller cycle as a strategy to minimize the aforementioned challenges when operating under reactivity controlled compression ignition combustion. Moreover, the coupled effect of the Miller cycle with the fuel reactivity modulation is also explored as a way for improving the combustion control. For this purpose, parametric studies varying the effective compression ratio and gasoline fraction have been done in a single-cylinder heavy-duty engine operating at 14 bar indicated mean effective pressure and 1200 rev/min as a baseline condition. The results show that this strategy allows better control of the in-cylinder thermodynamic conditions, enabling a simultaneous reduction of nitrogen oxides and soot emissions down to the EURO VI limits, while keeping a reduced fuel consumption and suitable in-cylinder maximum pressure gradients.

An experimental investigation of the effects of fuel injection strategy on the efficiency and emissions of a heavy-duty engine at high load with gasoline compression ignition

Based on a single-cylinder engine modified from a heavy-duty compression ignition engine with gasoline compression ignition (GCI), the influences of (i) delaying the intake valve closing timing (IVCT), (ii) a two-pulse fuel injection strategy and (iii) the injection pressure on combustion and emissions under high-load conditions are studied. By delaying the IVCT, the effective compression ratio and cylinder temperature during the compression stroke can be reduced, which can increase the fuel ignition delay and reduce soot emission and the heat-transfer loss rate, contributing to expand the engine’s high-load limit for high efficiency and clean combustion. With IVCT delay at an inlet pressure of 3.0 bar and a gross indicated mean effective pressure (IMEPg) of 16.5 bar, the gross indicated thermal efficiency (ITEg) is 52.3%, which increases by 2.4% compared to the case without IVCT delay. Combining IVCT delay, two-pulse injection, and an appropriate injection pressure can reduce the fuel mixing time, which can decrease the ringing intensity (RI) and achieve clean combustion at high engine load. Using IVCT delay, an intake pressure of 3.4 bar, an exhaust-gas recirculation (EGR) rate of 47%, a pilot injection of 10% at (−70, −7), an injection pressure of 80 MPa, and an IMEPg of 15 bar, the ITEg is 53.1% and the emissions of soot and NOx are 0.0068 g/kWh and 0.21 g/kWh, respectively.

Heterogeneously catalyzed synthesis of oxymethylene dimethyl ethers (OME) from dimethyl ether and trioxane

Oligomeric oxymethylene ethers (OMEs) are promising fuels for internal combustion engines with self-ignition. A tremendous reduction of soot, nitrogen oxide and hydrocarbon emissions can be realized by employing OMEs. This work describes the synthesis of OMEs from dimethyl ether (DME) and trioxane. Zeolite H-BEA 25 was found to be a suitable catalyst for this reaction and a study on reaction parameters (e.g. temperature, reactant feed ratio and reaction time) has been carried out. A maximum DME conversion of 13.9 wt% could be obtained and the maximum reactant-related product yield for OME3–5 was 8.2 wt%. An OME formation mechanism is proposed which explains the observed product spectrum.

Effects of injection timing and injection pressure on performance and exhaust emissions of a common rail diesel engine fueled by various concentrations of fish-oil biodiesel blends

To evaluate the performance and emissions of a test engine fueled by biodiesel blends produced from fish processing by-products, the experimental and simulation methods were used to investigate the effects of injection pressure and timing on engine operation and correlation of these effects with varying fish-oil concentrations in the biodiesel blends. Consequently, commercial diesel fuel blended with different concentrations of fish-oil biodiesel including B0, B10, B20, B30, B40 and B50 (corresponding to 0%, 10%, 20%, 30%, 40%, and 50% of biodiesel in blend) were used for the test engine. Compared to B0, the average reduction in brake power of the biodiesel fuels was reduced proportionally with the biodiesel ratio in the fuel blends. The brake specific fuel consumption (BSFC) and NOx emissions increased together with a reduction in soot, HC and CO emissions as the percentage of biodiesel increases. Moreover, the engine characteristics depend on operating parameters such as injection timing and injection pressure as also mentioned in many previous studies. When increasing injection timing, the brake power initially increases until reaching a maximum value and then decreases slightly for all types of fuels tested. Meanwhile, the effect of injection pressure differs depending on the pressure range and biodiesel blends.

Effects of changing nozzle holes-diameter in double-injection strategies using numerical modeling

Fuel–air mixture in diesel engines could be controlled by various methods such as split-injection strategies and nozzle-holes configurations. For the first time and in this paper, a numerical study has been conducted to examine the effects of changing nozzle holes-diameter in double-injection strategies on pollutant emissions. Results showed that heat release rate in double-injection strategies has two peaks due to the two-stage injections. Furthermore, decreasing the nozzle holes-diameter could cause better fuel atomization that increases the heat release rate peak. Changing nozzle holes-diameter could strongly affect pollutant emissions, in which decreasing the diameter could reduce soot emission and increasing the nozzle holes-diameter could reduce NOx emission formation.

Soot reduction by addition of dimethyl carbonate in normal and inverse ethylene diffusion flames: Nanostructural evidence

Oxygenated fuel represents an attractive alternative as an additive for reducing soot emissions. Dimethyl carbonate (DMC) is an oxygenated compound which is a good option to reduce soot, but the detailed characteristics of soot produced from combustion of hydrocarbon fuels blended with DMC are still lacking. The present research studied the nanostructure and reactivity of soot particles in ethylene/DMC normal and inverse diffusion flames. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to analyze the nanostructure and reactivity of soot. It was found that DMC addition was effective in decreasing the average weights of soot formed in flames. The results of HRTEM images showed that soot particles obtained with DMC addition showed liquid-like material and tight bonding, and exhibited more highly disorganized layers, which give it higher reactivity than soot obtained without DMC addition. Furthermore, HRTEM was used to analyze soot fringe characteristics consisting of fringe tortuosity, fringe length, and fringe separation. XRD was used to crosscheck the results for fringe separation, and was consistent with HRTEM results. In addition, the mass loss curve of TGA experiments showed that DMC addition could enhance the reactivity of soot particles.

Model based Diesel Injection Profile Optimization to Reduce Transient Soot Peaks

To meet current legislation limits, modern Diesel engines achieve low raw emission levels and utilize complex aftertreatment systems. Still, during fast transients undesired emission peaks may occur for both soot and NOx. These are caused by deviations in the in-cylinder conditions between the quasi steady engine calibration and the transient operation, e.g. during tip-ins. In this work a case study is performed to analyze the potential reduction of transient soot emissions during a specified engine maneuver. An additional target is to investigate potential benefits of a novel in-situ soot sensor based on the Laser Induced Incandescence (LII) principle which offers a high temporal resolution. Measurement data from a Diesel engine is used to develop time varying setpoint deviation models which will be utilized in a numerical optimization problem to determine an optimized injection profile. The modeling and optimization is carried out in parallel for both sensors and results are compared against each other. In the experimental validation the optimized injection profiles were capable of reducing undesired overshoots during transients with minimal impact on the torque response. Furthermore, the novel sensor allows to gain additional insights in the relation between input parameters and soot response, which is reflected by the obtained models and control action.

Investigation of Sectional-Stage Loading Strategies on a Two-Stage Turbocharged Heavy-Duty Diesel Engine under Transient Operation with EGR

The influence of loading strategies on combustion and emissions parameters is experimentally and numerically studied under typical 5 s transient conditions of constant speed and increasing torque. The experiment is conducted on a two-stage turbocharged heavy-duty diesel engine with a constant opening valve high-pressure exhaust gas recirculation (EGR) system. The test results show that: compared with the full-stage loading (FSL) strategy (constant loading rate during the entire transient process), the sectional-stage loading (SSL) strategies (holding a certain time at 50% load) can significantly reduce soot emissions (by 41.3%); the greater the first-stage loading rate, the better the torque response performance, which maximally increases by 56.7%. Besides, longer loading holding time can effectively restrain the overshoot of EGR rate and advance the combustion phase (CA10, CA50) at medium and large loads. However, the larger second-stage loading rate slightly deteriorates the combustion and emission performance. This deterioration situation can be markedly suppressed by adopting a suitable loading hold time.

Experimental and kinetic studies of soot formation in methanol-gasoline coflow diffusion flames

Methanol has been considered to be a potential alternative fuel to reduce soot emissions from GDI engine. In order to fully understand the effect of methanol addition on soot formation, the 2-D distribution of soot volume fraction in methanol/gasoline laminar diffusion flames was measured quantitatively with two-color laser induced incandescence (TC-LII) technique. In addition, the Methanol-TRF-PAH mechanism is constructed and used to analyze the formation pathways of soot precursors based on the CHEMKIN PRO 0-D constant pressure reactor. In this experiment, the blending ratio of methanol/gasoline was set as M0/20/40/60/80. Considering the carbon content decreasing due to methanol addition, carbon mass flow rate was remained constant. The experimental results showed that methanol is able to decrease the soot significantly, while the effect of methanol on soot reduction is weakened with the increasing methanol ratio. Compared with pure gasoline, the average soot volume fraction in the M20, M40, M60, and M80 flames decrease by 48.2%, 70.4%, 83.8%, and 97.7%, and the peak soot volume fraction decrease by 41.5%, 64.1%, 75.8% and 91.8% respectively. There is little soot formation in the M80 flame, inferring the pure methanol hardly forms soot. The kinetic analysis showed that mole fraction of A1-A4 decrease with the increasing methanol ratio. For the toluene-containing fuel M0-M80, A1 is mainly formed by C6H5CH3 + H = A1 + CH3 and oxidized by A1 + OH = A1- + H2O. A4 is mainly produced by C6H5CH2 + C9H7 = A4 + 2H2 and oxidized by H-abstraction reaction with H or OH radical. The major reaction pathways of A1 and A4 formation are consistent under different methanol blending ratios. The soot reduction as methanol added mainly attributes to aromatics dilution effect. In addition, the formation process of soot precursors is largely affected by chemical processes of OH, CH3, HO2 radicals.

Fluid properties at high pressures and temperatures: Experimental and modelling challenges

Thermophysical properties impact many aspects of the chemical process industries. Here three example areas, primarily in the energy sector, are highlighted to provide context for the experimental and modelling challenges associated with obtaining fluid property data at high pressures and temperatures (HPHT). These three areas include the recovery of petroleum reserves in ultra-deep reservoirs, the use of lubricants to reduce frictional losses in the automotive industries, and the use of high-pressure, common rail diesel fuel delivery to reduce soot emissions for greener environments. The accurate knowledge of thermodynamic and transport properties in these three focused areas minimizes associated operating uncertainties and accelerates safe, reliable, and robust process and product development.

Spray Combustion Characteristics and Soot Emission Reduction of Hydrous Ethanol Diesel Emulsion Fuel Using Color-Ratio Pyrometry

To elucidate the relationship between physicochemical properties, spray characteristics, and combustion performance, a series of experiments have been conducted in a constant volume vessel with injection of hydrous ethanol diesel emulsion and regular diesel. HE30 (emulsion with 30% volume fraction of 20% water-containing ethanol and 70% volume fraction of 0# diesel) is developed using Shah’s technique and regular diesel is also employed for comparison. Firstly, the physicochemical properties of two kinds of fuels are investigated. Then, the non-evaporating and evaporating spray characteristics are examined through the high-speed shadowgraphs. Finally, spray combustion experiments under different ambient oxygen concentrations are carried out, and color-ratio pyrometry (CRP) is applied to measure the flame temperature and soot concentration (KL) distributions. The results indicate that the physicochemical properties, such as density, surface tension, kinematic viscosity, cetane number, and oxygen content, have significant impact on the spray mixture formation and combustion performance. HE30 exhibits lower soot emissions than that of regular diesel. Further analysis supports the standpoint that the hydrous ethanol diesel emulsion can suppress the soot and NOx simultaneously. Therefore, the hydrous ethanol diesel emulsion has great potential to be an alternative clean energy resource.

Influence of ethanol/diesel fuel and propanol/diesel fuel blends over exhaust and noise emissions

Nowadays, alternative fuels to fossil-based ones are emerging, one of them consisting in the use of oxygenated fuels, i.e. short-chain alcohols. Their main advantage is that alcohols may be produced by renewable processes. In the present work, diesel engine exhaust and acoustic emissions using different short-chain alcohols (ethanol and 1-propanol)/diesel fuel blends have been analyzed. For this purpose, nine engine steady-state operating conditions at moderate loads, covering the most used quarter of the engine map, have been selected. The effect of the increase of alcohol in the blend provided a reduction of nitrogen oxides (NOx) and soot emissions, while soluble organic fraction (SOF), total hydrocarbons (THC) and carbon monoxide (CO) emissions increased. Moreover, a rise of noise was observed with the increase of the amount of alcohol in the blend. It may be concluded, from this field trial, that at similar concentration of alcohol blended with diesel fuel (10% v/v), propanol showed better behavior in terms of global exhaust and noise emissions than ethanol.

Optimization of Diesel Engine Fuel Injection System Parameters Based on Simulations

This paper simulated a six-cylinder diesel engine with 3d model, and optimized combustion and emission through modify project distance of injector and nozzle angle. Simulation result shows that appropriate project distance will enhance entraining power of vortices and reduce soot generation without increasing NOx generation; yet inappropriate nozzle angle will deteriorate combustion in either clearance volume or combustion chamber bowl. Variation in either project distance or nozzle angle has greater influence on soot generation than NOx generation, and both can be optimized to reduce soot emission without affect NOx emission significantly.

Development and testing of a soot particle concentration estimator using Lagrangian post-processing

ABSTRACTSoot emissions from combustion devices are known to have harmful effects on the environment and human health. As the transportation industry continues to expand, the development of techniques to reduce soot emissions remains a significant goal of researchers and industry. In order for current soot modeling techniques to be reliably accurate, they must incur an intractably high computational cost. This project leverages existing knowledge in soot modeling and soot formation fundamentals to develop a stand-alone, computationally inexpensive soot concentration estimator to be linked to Computational Fluid Dynamics simulations as a post-processor. Preliminary development and testing of the estimator is presented here for laminar flames. As soot properties cannot be determined by local conditions, the estimator consists of a library generated using the hystereses of soot-containing fluid parcels, which relates soot concentration to the aggregated gas-phase environment histories to which a fluid parcel has been exposed. The estimator can be used to relate soot concentration to computed parcel hystereses through interpolation techniques. The estimator shows the potential ability to produce accurate results with very low computational cost in laminar coflow diffusion flames. Results also show that as flame data representing a broader set of conditions (temperature, mixture fraction, residence time, etc.) are added to the library, the estimator becomes applicable to a wider range of flames.

Synoptic Control of Contrail Cirrus Life Cycles and Their Modification Due to Reduced Soot Number Emissions

AbstractThe atmospheric state, aircraft emissions, and engine properties determine formation and initial properties of contrails. The synoptic situation controls microphysical and dynamical processes and causes a wide variability of contrail cirrus life cycles. A reduction of soot particle number emissions, resulting, for example, from the use of alternative fuels, strongly impacts initial ice crystal numbers and microphysical process rates of contrail cirrus. We use the European Centre/Hamburg (ECHAM) climate model version 5 including a contrail cirrus modul, studying process rates, properties, and life cycles of contrail cirrus clusters within different synoptic situations. The impact of reduced soot number emissions is approximated by a reduction in the initial ice crystal number, exemplarily studied for 80%. Contrail cirrus microphysical and macrophysical properties can depend much more strongly on the synoptic situation than on the initial ice crystal number. They can attain a large cover, optical depth, and ice water content in long‐lived and large‐scale ice‐supersaturated areas, making them particularly climate‐relevant. In those synoptic situations, the accumulated ice crystal loss due to sedimentation is increased by around 15% and the volume of contrail cirrus, exceeding an optical depth of 0.02, and their short‐wave radiative impact are strongly decreased due to reduced soot emissions. These reductions are of little consequence in short‐lived and small‐scale ice‐supersaturated areas, where contrail cirrus stay optically very thin and attain a low cover. The synoptic situations in which long‐lived and climate‐relevant contrail cirrus clusters can be found over the eastern U.S. occur in around 25% of cases.

Production of oxymethylene dimethyl ether (OME)-hydrocarbon fuel blends in a one-step synthesis/extraction procedure

Oligomeric oxymethylene dimethyl ethers (OMEs) of the type CH3O-(CH2O)n-CH3 are promising diesel fuels with an enormous potential for the reduction of soot and NOx emissions. Oligomers with n = 3–5 are particularly advantageous, since their physicochemical and combustion properties are similar to conventional diesel. OMEs can be produced from methanol and formaldehyde but a series of byproducts, especially hemiformals, glycols, water and minor amounts of cyclic ethers, are also formed. These need to be separated from the product mixtures, which affects efficiency of this synthesis pathway. To isolate the desired OMEs, a one-step synthesis/extraction procedure is described. It implies highly selective extraction of OMEs from aqueous reaction solutions employing hydrocarbons as extraction agents. If fuel-type hydrocarbons are used, the resulting OME-hydrocarbon blends can be directly used in fuel applications. The corresponding oxymethylene diethyl ethers (OMDEEs) have also been investigated. Compared to OMEs, OMDEEs exhibit an increased solubility in nonpolar media but, as a result, solubility of educts and byproducts also increases. OME blends with hydrogenated vegetable oil and diesel have been prepared containing 10% of OMEs. It could be shown that such blends meet current diesel standards to a large extent.