Particulate Matter Emissions from Partially Premixed Combustion with Diesel, Gasoline and Ethanol

To achieve cleaner combustion and higher efficiency in compression ignition (CI) engines, many new combustion strategies have been developed. Among these new concepts, partially premixed combustion (PPC) attracts a lot of attention, because of its possibility to achieve simultaneously low soot and NOx. Compared to homogeneous charge compression ignition (HCCI) combustion, charge stratification in PPC can lead to increased soot emissions. This thesis deals with questions related to soot emissions in PPC. The main focus is to gain information and better understanding of soot particle characteristics with diesel, gasoline and ethanol fuels with varied in-cylinder emission control parameters.By means of injection timing, it is possible to have combustion from HCCI into PPC mode with the assistance of intake temperature. PPC shows benefits of higher engine efficiency and lower UHC and CO emissions over HCCI. However, it can also face the challenges of higher soot emissions. The study carried out with altered dilutions and different kinds of fuels illustrates that NOx emissions can be suppressed by increasing exhaust gas recirculation (EGR) or reducing intake pressure, but at the expense of an increase in soot emissions with diesel and gasoline fuels. The significant soot increase and largely reduced engine efficiency in stoichiometric operations also indicated low possibility for clean PPC with simple three-way catalyst with these fuels. On the contrary, ethanol emitted close to zero level soot emissions regardless of variations in engine operating parameters. This has made it an attractive fuel for PPC study.To be compliant with future stringent exhaust gas legislations for CI engines, soot exhaust after-treatment system may need together with new fuel strategies in PPC operations. Hence, information of the corresponding soot particle characteristics, including particle number and size, is necessary. Ethanol, high-octane and low-octane gasoline were used to perform PPC soot emissions investigations, with diesel fuel as a comparison. In-cylinder emission control parameters, such as injection timing, intake temperature, EGR and injection pressure were selected and tested to find their effects on soot emissions. Retarding injection timing can increase fuel stratification, which resulted in increased soot emissions of larger particle size and higher number density. Other engine parameters showed two quite different trends for fossil fuels and ethanol fuel respectively. When EGR increased, first soot mass emissions increased with higher particle number and larger size. Upon higher EGR, soot mass decreased with smaller particles and lower particle number concentration. Increasing intake temperature or reducing injection pressure can promote soot production with larger particle size and higher particle number concentration. Compared to diesel, gasoline showed great improvements in emission levels due to lower particle number emissions and smaller particle sizes, particularly with high octane gasoline fuel. On the other hand, ethanol produced ultra-low soot mass emissions and number emissions in all condition. Consequently it requires less engine efficiency compromises to comply with the legislation standards.In the meantime, the exhaust after-treatment system can be simplified. Very slight soot emission change in response to variations in engine conditions also increases the robustness. In addition to the findings in the exhaust, an in-cylinder soot particle analysis was done via in-cylinder gas fast sampling technique and on-line aerosol instruments. It has revealed that during combustion, EGR reduced both soot formation and soot oxidation, but the more reduced soot oxidation was the main reason for increased soot mass emissions in diesel PPC. Comparison of soot processes with gasoline and diesel indicated that, very low soot formation was the main reason for lower exhaust soot emissions in gasoline PPC. Much larger particles were formed in diesel PPC

Evolution of In-Cylinder Diesel Engine Soot and Emission Characteristics Investigated with Online Aerosol Mass Spectrometry

To design diesel engines with low environmental impact, it is important to link health and climate-relevant soot (black carbon) emission characteristics to specific combustion conditions. The in-cylinder evolution of soot properties over the combustion cycle and as a function of exhaust gas recirculation (EGR) was investigated in a modern heavy-duty diesel engine. A novel combination of a fast gas-sampling valve and a soot particle aerosol mass spectrometer (SP-AMS) enabled online measurements of the in-cylinder soot chemistry. The results show that EGR reduced the soot formation rate. However, the late cycle soot oxidation rate (soot removal) was reduced even more, and the net effect was increased soot emissions. EGR resulted in an accumulation of polycyclic aromatic hydrocarbons (PAHs) during combustion, and led to increased PAH emissions. We show that mass spectral and optical signatures of the in-cylinder soot and associated low volatility organics change dramatically from the soot formation dominated phase to the soot oxidation dominated phase. These signatures include a class of fullerene carbon clusters that we hypothesize represent less graphitized, C5-containing fullerenic (high tortuosity or curved) soot nanostructures arising from decreased combustion temperatures and increased premixing of air and fuel with EGR. Altered soot properties are of key importance when designing emission control strategies such as diesel particulate filters and when introducing novel biofuels

Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines

[EN] This study focuses on the relative importance of O-2 and OH as oxidizers of soot during the late cycle in diesel engines, where the soot oxidation is characterized in an optically accessible engine using laser extinction measurements. These are combined with in-cylinder gas sampling data from a single cylinder engine fitted with a fast gas-sampling valve. Both measurements confirm that the in-cylinder soot oxidation slows down when the inlet concentration of O-2 is reduced. A 38% decrease in intake O-2 concentration reduces the soot oxidation rate by 83%, a non-linearity suggesting that O-2 in itself is not the main soot oxidizing species. Chemical kinetics simulations of OH concentrations in the oxidation zone and estimates of the OH-soot oxidation rates point towards OH being the dominant oxidizer.The authors gratefully acknowledge the Swedish Energy Agency, the Competence Center for Combustion Processes KCFP (Project number 22485-3), and the competence center METALUND funded by FORTE for financially supporting this research. The authors acknowledge Volvo AB for providing the gas-sampling valve and personally Jan Eismark (Volvo AB) and Mats Bengtsson (Lund University) for their technical support.Gallo, Y.; Malmborg, VB.; Simonsson, J.; Svensson, E.; Shen, M.; Bengtsson, P.; Pagels, J.... (2017). Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines. Fuel. 193:308-314. https://doi.org/10.1016/j.fuel.2016.12.013S30831419

Prognostic values of ALDOB expression and 18F-FDG PET/CT in hepatocellular carcinoma

PurposeThe glycolytic enzyme fructose 1,6-bisphosphate aldolase B (ALDOB) is aberrantly expressed and impacts the prognosis in hepatocellular carcinoma (HCC). Hepatic ALDOB loss leads to paradoxical upregulation of glucose metabolism, favoring hepatocellular carcinogenesis. Nevertheless, the relationship between ALDOB expression and 18F-fluorodeoxyglucose (18F-FDG) uptake, and their effects on HCC prognosis remain unclear. We evaluated whether ALDOB expression is associated with 18F-FDG uptake and their impacts on HCC prognosis prediction.MethodsChanges in ALDOB expression levels and the prognostic values in HCC were analyzed using data from The Cancer Genome Atlas (TCGA) database. Ultimately, 34 patients with HCC who underwent 18F-FDG positron emission tomography/computed tomography (PET/CT) preoperatively were enrolled in this retrospective study. ALDOB expression was determined using immunohistochemistry (IHC) staining, and the maximum standardized uptake value (SUVmax) of HCC was calculated from the 18F-FDG PET/CT scans. The relationship between ALDOB expression and SUVmax was examined, and their impacts on overall survival were evaluated using Cox proportional hazards models and Kaplan–Meier survival analysis. ALDOB overexpression in HUH7 and 7721 cells was used to analyze its role in tumor metabolism.ResultsAccording to TCGA database, the ALDOB mRNA level was downregulated in HCC compared to normal tissue, and significantly shortened overall survival in HCC patients. ALDOB protein expression was similarly decreased in IHC findings in HCC than that in adjacent normal tissues (P<0.05) and was significantly associated with tumor size (P<0.001), high tumor-node-metastasis stage (P=0.022), and elevated SUVmax (P=0.009). ALDOB expression in HCC was inversely correlated with SUVmax (r=-0.454; P=0.012), and the optimal SUVmax cutoff value for predicting its expression was 4.15. Prognostically, low ALDOB expression or SUVmax ≥3.9 indicated shorter overall survival time in HCC. Moreover, COX regression analysis suggested high SUVmax as an independent prognostic risk factor for HCC (P=0.036). HCC patients with negative ALDOB expression and positive SUVmax (≥3.9) were correlated with worse prognosis. ALDOB overexpression in HCC cells significantly decreases 18F-FDG uptake and lactate production.ConclusionSUVmax in HCC patients is inversely correlated with ALDOB expression, and 18F-FDG PET/CT may be useful for ALDOB status prediction. The combined use of ALDOB expression and 18F-FDG PET/CT data can provide additional information on disease prognosis in HCC patients

Cannabinoid Receptor Subtype 2 (Cb2R) Agonist Gw405833 Reduces Agonist-Induced Ca2+ Oscillations In Mouse Pancreatic Acinar Cells

Emerging evidence demonstrates that the blockade of intracellular Ca 2+ signals may protect pancreatic acinar cells against Ca 2+ overload, intracellular protease activation, and necrosis. The activation of cannabinoid receptor subtype 2 (CB 2 R) prevents acinar cell pathogenesis in animal models of acute pancreatitis. However, whether CB 2 Rs modulate intracellular Ca 2+ signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB 2 R agonist, GW405833 (GW) in agonist-induced Ca 2+ oscillations in pancreatic acinar cells using multiple experimental approaches with acute dissociated pancreatic acinar cells prepared from wild type, CB 1 R-knockout (KO), and CB 2 R-KO mice. Immunohistochemical labeling revealed that CB 2 R protein was expressed in mouse pancreatic acinar cells. Electrophysiological experiments showed that activation of CB 2 Rs by GW reduced acetylcholine (ACh)-, but not cholecystokinin (CCK)-induced Ca 2+ oscillations in a concentration-dependent manner; this inhibition was prevented by a selective CB 2 R antagonist, AM630, or was absent in CB 2 R-KO but not CB 1 R-KO mice. In addition, GW eliminated L-arginine-induced enhancement of Ca 2+ oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB 2 Rs eliminates ACh-induced Ca 2+ oscillations and L-arginine-induced enhancement of Ca 2+ signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB 2 R-mediated protection in acute pancreatitis

Effect of Shot Blasting on Fatigue Strength of Q345B Steel Plate with a Central Hole

The fatigue strength of Q345B steel plate with a central hole after shot blasting is studied herein. The improvement of fatigue strength related to the failure behavior is highlighted with due analysis of fatigue cracks initiation at the defect below the condensed surface induced by shot blasting. The effect of stress concentration is shown to be non-ignorable in the fatigue strength analysis. Codified fatigue categories in accordance with EN 1993-1-9 are used in drawing a comparison of studied fatigue behavior. Finally, an analytical model based on a modified reference model is proposed for the evaluation of the test fatigue strength results. It is demonstrated that the predicted results agree well with test data, since the stress ratio and the size of the defect as well as the stress concentration are appropriately considered

Measurement of gasoline exhaust particulate matter emissions with a wide-range EGR in a heavy-duty diesel engine

A large number of measurement techniques have been developed or adapted from other fields to measure various parameters of engine particulates. With the strict limits given by regulations on pollutant emissions, many advanced combustion strategies have been developed towards cleaner combustion. Exhaust gas recirculation (EGR) is widely applied to suppress nitrogen oxide (NOx) and reduce soot emissions. On the other hand, gasoline starts to be utilized in compression ignition engines due to great potential in soot reduction and high engine efficiency. New engine trends raise the need for good sensitivity and suitable accuracy of the PM measurement techniques to detect particulates with smaller size and low particulate mass emissions. In this work, we present a comparison between different measurement techniques for particulate matter (PM) emissions in a compression ignition engine running on gasoline fuel. A wide-range of EGR was used with lambda varied from 3 down to 1. The compared equipment includes AVL smoke meter, AVL Micro Soot Sensor, Pegasor and Cambustion Differential Mobility Spectrometer (DMS). The goal of this paper is to compare the recorded values and show the sensitivity of the instruments to soot properties altering, in both lean and stoichiometric combustion situations

Influence of Injection Timing on Exhaust Particulate Matter Emissions of Gasoline in HCCI and PPC

In order to reduce nitrogen oxides (NOx) and soot emissions while maintaining high thermal efficiency, more advanced combustion concepts have been developed over the years, such as Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC), as possible combustion processes in commercial engines. Compared to HCCI, PPC has advantages of lower unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions; however, due to increased fuel stratifications, soot emissions can be a challenge when adding Exhaust-Gas Recirculation (EGR) gas. The current work presents particle size distribution measurements performed from HCCI-like combustion with very early (120 CAD BTDC) to PPC combustion with late injection timing (11 CAD BTDC) at two intake oxygen rates, 21% and 15% respectively. Particle size distributions were measured using a differential mobility spectrometer DMS500. Additionally, to get knowledge of the effect of injection timing on particle size distributions in PPC mode, measurements were performed in injection timing sweeps at engine speeds 800 rpm and 1600 rpm. Results show that, without EGR, throughout the injection timing from very early to late injection, a unimodal particle size distribution dominated by nucleation mode particles can be observed. Adding EGR, similar unimodal particle size distributions are obtained for early injection timings whereas bimodal size distributions appear for late injection timings when injecting goes into the bowl. The corresponding accumulation mode particle number rapidly increases and results in a high engine-out soot output. In PPC mode with high fuel stratification, a similar trend is found at engine speeds 800 rpm and 1600 rpm during injection timing sweeps. Retarding injection is generally found to reduce particle numbers in nucleation mode and increase numbers in accumulation mode, which leads to a higher soot mass output despite of a reduction in total particle numbers. It can be concluded that charge stratification and fuel impingement influence particle size distributions during injection timing variations

Waste Heat Recovery from Multiple Heat Sources in a HD Truck Diesel Engine Using a Rankine Cycle - A Theoretical Evaluation

Few previous publications investigate the possibility of combining multiple waste heat sources in a combustion engine waste heat recovery system. A waste heat recovery system for a HD truck diesel engine is evaluated for utilizing multiple heat sources found in a conventional HD diesel engine. In this type of engine more than 50% of heat energy goes futile. The majority of the heat energy is lost through engine exhaust and cooling devices such as EGRC (Exhaust gas recirculation cooler), CAC (Charge air cooler) and engine cooling. In this paper, the potential of usable heat recuperation from these devices using thermodynamic analysis was studied, and also an effort is made to recuperate most of the available heat energy that would otherwise be lost. A well-known way of recuperating this heat energy is by employing a Rankine cycle circuit with these devices as heat sources (single loop or dual loop), and thus this study is focused on using a Rankine cycle for the heat recovery system. Furthermore, this paper investigates the possibilities and challenges involved in coupling these different sources in a single Rankine cycle and the selection of suitable working fluid for this Rankine cycle. The study shows that with recuperation from these multiple sources it is possible to recover 5-10% of the otherwise wasted heat energy, which results in ~5% power increase. REFPROP was used for studying fluid properties, and the commercial software IPSEpro is used to build and simulate the Rankine cycle

Exhaust PM Emissions Analysis of Alcohol Fueled Heavy-Duty Engine Utilizing PPC

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well. Regarding soot mass concentration measurements; methanol never exceeded 1.6 mg/m3 while when operating on gasoline this value never descended below 1.6 mg/m3. From this result it can be concluded that the main contributor to PM mass emissions is mainly increasing CMD (Count Mean Diameter) in the accumulation mode size range, but can in diffusion combustion also be caused by a high amount of nucleation mode particles. A probable cause of higher particle number emissions, when running the engine on methanol compared to ethanol, is the corrosiveness of the fuel itself. Except for the ultra-low PM mass emitted from alcohol combustion, it is also possible to alter the EGR concentration with a higher level of freedom without having to consider the NOX - soot tradeoff