Jesper Schramm

Comparison of Diesel Spray Combustion in Different High-Temperature, High-Pressure Facilities

Diesel spray experiments at controlled high-temperature and high-pressure conditions offer the potential for an improved understanding of diesel combustion, and for the development of more accurate CFD models that will ultimately be used to improve engine design. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but uncertainties about their operation exist because of the uniqueness of each facility. For the IMEM meeting, we describe results from comparative studies using constant-volume vessels at Sandia National Laboratories and IFP. Targeting the same ambient gas conditions (900 K, 60 bar, 22.8 kg/m{sup 3}, 15% oxygen) and sharing the same injector (common rail, 1500 bar, KS1.5/86 nozzle, 0.090 mm orifice diameter, n-dodecane, 363 K), we describe detailed measurements of the temperature and pressure boundary conditions at each facility, followed by observations of spray penetration, ignition, and combustion using high-speed imaging. Performing experiments at the same high-temperature, high-pressure operating conditions is an objective of the Engine Combustion Network (http://www.ca.sandia.gov/ECN/), which seeks to leverage the research capabilities and advanced diagnostics of all participants in the ECN. We expect that this effort will generate a high-quality dataset to be used for advanced computational model development at engine conditions.

Physical and chemical characterization of particles in producer gas from wood chips.

Abstract Particles in the gas from a two-stage (separate pyrolysis and gasification) down-draft biomass gasifier were collected and characterized. Their concentration, geometries and chemical compositions were investigated. Special attention was given to features suspected to harm internal combustion (IC) engines fueled by the gas. The implications of the findings on engine wear are discussed. The majority (85%) of the total particulate matter (TPM) mass was identified, using scanning electron microscopy (SEM), as mono-sized spherical primary soot particles with diameters of 70 nm. Soot agglomerates, up to 30 μm were present. 77% of the TPM was determined, by thermogravimetric analysis (TGA) to be carbon structures. The dichloromethane (DCM)-soluble fraction (11% of the TPM) was extracted, separated into fractions of varying polarities using adsorption column chromatography and analyzed using gas chromatography with a flame ionization detector (GC-FID). More than 50% of the soluble mass was relatively non-polar. A well-separated fraction containing 10% of the DCM solubles had significantly higher polarities than the other solubles and/or contained relatively large molecules. Anisole extractions of the particles showed that a 3–7% of the DCM-insoluble TPM was dissolved using this solvent.

Solubility of gasoline components in different lubricants for combustion engines determined by gas—liquid partition chromatography

Abstract The solubility of typical gasoline fuel components in different lubricants for gasoline engines was determined at temperatures between 90 and 150°C. Solubility is an important parameter in combustion engine research, as the fuel during intake and compression dissolves in the lubricant film on the cylinder wall, thus escaping from the combustion processes. During the expansion and exhaust stroke the fuel is desorbed again and in this way contributes to the formation of unburned hydrocarbons in the exhaust gas. The solubility is characterized by Henrys constant. A gas—liquid partition chromatographic techniques was used for the determination of Henrys constants, and gave values in good agreement with the known values for selected reference components.

A model for hydrocarbon emissions from SI engines

A model which calculates the hydrocarbon emissions from an SI engine is presented. The model was developed in order to obtain a better understanding of experimental results from an engine operating on different fuels and lubricants. The model is based on the assumptions that fuel is stored in crevices and oil film during intake and compression followed by desorption during expansion and exhaust. The model also calculates the amount of desorbed material that undergoes in-cylinder oxidation and exhaust port oxidation. The model successfully predicts the trends followed by varying different engine parameters. The effect of changing the lubricant is of the same order of magnitude as found experimentally, but the effect of changing the fuel could not be predicted very well by the model. A possible explanation is that the lubricant film thickness varies due to viscosity variations of the oil film, when the fuel is dissolved in the film. (A) For the covering abstract see IRRD 851463.

Novel base metal-palladium catalytic diesel filter coating with NO2 reducing properties

A novel base metal-palladium catalytic coating was applied on commercial silicon carbide wall flow diesel filters and tested in an engine test bench. This catalytic coating limits the NO2 formation and even removes NO2 within a wide temperature range. Soot combustion, HC conversion and CO conversion properties are comparable to current platinum-based coatings, but at a lower cost. This paper compares the results from engine bench tests of present commercial solutions as regards NO2-, HC-, CO-removal and soot combustion with the novel coating. Furthermore, emission test results from base metal-palladium coated diesel particulate filters installed on operating taxis and related test cycle data are presented. A significant reduction in NO2 emission compared to present technology is measured.

Evaluation and optimisation of phenomenological multi-step soot model for spray combustion under diesel engine-like operating conditions

In this work, a two-dimensional computational fluid dynamics study is reported of an n-heptane combustion event and the associated soot formation process in a constant volume combustion chamber. The key interest here is to evaluate the sensitivity of the chemical kinetics and submodels of a semi-empirical soot model in predicting the associated events. Numerical computation is performed using an open-source code and a chemistry coordinate mapping approach is used to expedite the calculation. A library consisting of various phenomenological multi-step soot models is constructed and integrated with the spray combustion solver. Prior to the soot modelling, combustion simulations are carried out. Numerical results show that the ignition delay times and lift-off lengths exhibit good agreement with the experimental measurements across a wide range of operating conditions, apart from those in the cases with ambient temperature lower than 850 K. The variation of the soot precursor production with respect to the change of ambient oxygen levels qualitatively agrees with that of the conceptual models when the skeletal n-heptane mechanism is integrated with a reduced pyrene chemistry. Subsequently, a comprehensive sensitivity analysis is carried out to appraise the existing soot formation and oxidation submodels. It is revealed that the soot formation is captured when the surface growth rate is calculated using a square root function of the soot specific surface area and when a pressure-dependent model constant is considered. An optimised soot model is then proposed based on the knowledge gained through this exercise. With the implementation of optimised model, the simulated soot onset and transport phenomena before reaching quasi-steady state agree reasonably well with the experimental observation. Also, variation of spatial soot distribution and soot mass produced at oxygen molar fractions ranging from 10.0 to 21.0% for both low and high density conditions are reproduced.

Low-Temperature Miscibility of Ethanol-Gasoline-Water Blends in Flex Fuel Applications

Abstract The miscibility of blends of gasoline and hydrous ethanol was investigated experimentally at −25°C and −2°C. Furthermore, the maximum water content was found for ethanol in flex fuel blends. The results strongly indicate that blends containing ethanol with a water content above that of the ethanol/water azeotrope (4.4% water by mass) can be used as Flex Fuel blends together with gasoline at ambient temperatures of −25°C and −2°C, without phase separation occurring. Additionally, it was shown that the ethanol purity requirement of ethanol-rich flex fuel blends falls with increasing ethanol content in the gasoline-rich flex fuel blend.

Investigation of Chemical Kinetics on Soot Formation Event of n-Heptane Spray Combustion

In this reported work, 2-dimsensional computational fluid dynamics studies of n-heptane combustion and soot formation processes in the Sandia constant-volume vessel are carried out. The key interest here is to elucidate how the chemical kinetics affects the combustion and soot formation events. Numerical computation is performed using OpenFOAM and chemistry coordinate mapping (CCM) approach is used to expedite the calculation. Three n-heptane kinetic mechanisms with different chemistry sizes and comprehensiveness in oxidation pathways and soot precursor formation are adopted. The three examined chemical models use acetylene (C2H2), benzene ring (A1) and pyrene (A4) as soot precursor. They are henceforth addressed as nhepC2H2, nhepA1 and nhepA4, respectively for brevity. Here, a multistep soot model is coupled with the spray combustion solver to simulate the soot formation/oxidation processes. Comparison of the results shows that the simulated ignition delay times and liftoff lengths have good agreements with the experimental measurements across wide range of operating conditions when the nhepC2H2 model is implemented. The performance of this mechanism however drops in cases with low ambient temperatures. Besides, the overall soot precursor and particle distribution prediction is found to be improved with the use of A4 as soot precursor. The variation of the soot precursor production with respect to the change of ambient temperature and oxygen levels qualitatively agrees with that of the conceptual models. Also, the revised nhepC2H2 model replicates the experimental spatial soot distribution reasonably well, although the absolute soot volume fraction values are not reproduced with the default soot model constant values.

Effects of lubricating oil on hydrocarbon emissions in an Si engine

The effects of lubricant composition on hydrocarbon emissions from a SI engine have been experimentally investigated. In this paper results based on measurements of solubilities of different fuel components in different types of lubricants are presented. The results indicate that the lubricant plays a contributing, but not dominating role in hydrocarbon emissions from gasoline engines.

Soot Formation Modeling of n-dodecane and Diesel Sprays under Engine-Like Conditions

DTU Orbit (11/01/2019) Soot Formation Modeling of n-dodecane and Diesel Sprays under Engine-Like Conditions This work concerns the modelling of soot formation process in diesel spray combustion under engine-like conditions. The key aim is to investigate the soot formation characteristics at different ambient temperatures. Prior to simulating the diesel combustion, numerical models including a revised multi-step soot model is validated by comparing to the experimental data of n-dodecane fuel in which the associated chemistry is better understood. In the diesel spray simulations, a single component n-heptane mechanism and the multi-component Diesel Oil Surrogate (DOS) model are adopted. A newly developed C16-based model which comprises skeletal mechanisms of n-hexadecane, heptamethylnonane, cyclohexane and toluene is also implemented. Comparisons of the results show that the simulated liftoff lengths are reasonably wellmatched to the experimental measurement, where the relative differences are retained to below 18%. Only that predicted by the DOS model in the 900 K case is overestimated by approximately 28%. The experimental maximum soot volume fraction (SVF) rises by approximately 7.0 fold as the ambient temperature is raised from 900 K to 1000 K. The ratio calculated by chemical mechanisms without toluene chemistry is approximately two-fold. Improvement is observed when toluene chemistry is considered, producing ratios of greater than 3.7. This can be attributed to the higher amount of soot precursor and surface growth species formed through the toluene oxidation pathways in the 1000 K case. A surrogate model that considers the kinetics of aromatic compounds is hence more promising to improve the prediction of local SVF which is significant to soot radiation modelling.