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  • 1.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Numerical Studies of Wall Effects of Laminar Flames2001Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Numerical simulations have been done with the CHEMKINsoftware to study different aspects of wall effects in thecombustion of lean, laminar and premixed flames in anaxisymmetric boundary-layer flow.

    The importance of the chemical wall effects compared to thethermal wall effects caused by the development of the thermaland velocity boundary layer has been investigated in thereaction zone by using different wall boundary conditions, walltemperatures and fuel/air ratios. Surface mechanisms include acatalytic surface (Platinum), a surface that promotesrecombination of active intermediates and a completely inertwall with no species and reactions as the simplest possibleboundary condition.

    When hydrogen is the model fuel, the analysis of the resultsshow that for atmospheric pressure and a wall temperature of600 K, the surface chemistry gives significant wall effects atthe richer combustion case (f=0.5), while the thermal andvelocity boundary layer gives rather small effects. For theleaner combustion case (f=0.1) the thermal and velocityboundary layer gives more significant wall effects, whilesurface chemistry gives less significant wall effects comparedto the other case.

    For methane as model fuel, the thermal and velocity boundarylayer gives significant wall effects at the lower walltemperature (600 K), while surface chemistry gives rather smalleffects. The wall can then be modelled as chemically inert forthe lean mixtures used (f=0.2 and 0.4). For the higher walltemperature (1200 K) the surface chemistry gives significantwall effects.

    For both model fuels, the catalytic wall unexpectedlyretards homogeneous combustion of the fuel more than the wallthat acts like a sink for active intermediates. This is due toproduct inhibition by catalytic combustion. For hydrogen thisoccurs at atmospheric pressure, but for methane only at thehigher wall temperature (1200 K) and the higher pressure (10atm).

    As expected, the overall wall effects (i.e. a lowerconversion) were more pronounced for the leaner fuel-air ratiosand at the lower wall temperatures.

    To estimate a possible discrepancy in flame position as aresult of neglecting the axial diffusion in the boundary layerassumption, calculations have been performed with PREMIX, alsoa part of the CHEMKIN software. With PREMIX, where axialdiffusion is considered, steady, laminar, one-dimensionalpremixed flames can be modelled. Results obtained with the sameinitial conditions as in the boundary layer calculations showthat for the richer mixtures at atmospheric pressure the axialdiffusion generally has a strong impact on the flame position,but in the other cases the axial diffusion may beneglected.

    Keywords:wall effects, laminar premixed flames,platinum surfaces, boundary layer flow

  • 2.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wall Related Lean Premixed Combustion Modeled with Complex Chemistry2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Increased knowledge into the physics and chemistrycontrolling emissions from flame-surface interactions shouldhelp in the design of combustion engines featuring improvedfuel economy and reduced emissions.

    The overall aim of this work has been to obtain afundamental understanding of wall-related, premixed combustionusing numerical modeling with detailed chemical kinetics. Thiswork has utilized CHEMKIN®, one of the leading softwarepackages for modeling combustion kinetics.

    The simple fuels hydrogen and methane as well as the morecomplex fuels propane and gasified biomass have been used inthe model. The main emphasis has been on lean combustion, andthe principal flow field studied is a laminar boundary layerflow in two-dimensional channels. The assumption has been madethat the wall effects may at least in principle be the same forlaminar and turbulent flames.

    Different flame geometries have been investigated, includingfor example autoignition flames (Papers I and II) and premixedflame fronts propagating toward a wall (Papers III and IV).Analysis of the results has shown that the wall effects arisingdue to the surface chemistry are strongly affected by changesin flame geometry. When a wall material promoting catalyticcombustion (Pt) is used, the homogeneous reactions in theboundary layer are inhibited (Papers I, II and IV). This isexplained by a process whereby water produced by catalyticcombustion increases the rate of the third-body recombinationreaction: H+O2+M ⇔ HO2+M. In addition, the water produced at higherpressures increases the rate of the 2CH3(+M) ⇔ C2H6(+M) reaction, giving rise to increased unburnedhydrocarbon emissions (Paper IV).

    The thermal coupling between the flame and the wall (theheat transfer and development of the boundary layers) issignificant in lean combustion. This leads to a sloweroxidation rate of the fuel than of the intermediatehydrocarbons (Paper III).

    Finally in Paper V, a well-known problem in the combustionof gasified biomass has been addressed, being the formation offuel-NOx due to the presence of NH3 in the biogas. A hybridcatalytic gas-turbine combustor has been designed, which cansignificantly reduce fuel-NOx formation.

    Keywords:wall effects, premixed flames, flamequenching, numerical modeling, CHEMKIN, boundarylayerapproximation, gasified biomass, fuel-NOx, hybrid catalytic combustor.

  • 3.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wall Effects of Laminar Hydrogen Flames over Platinum and Inert Surfaces2000In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 46, no 7, p. 1454-1460Article in journal (Refereed)
    Abstract [en]

    Different aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary-layer flow were studied using numerical simulations with the program CRESLAF. The importance of the chemical wall effects compared to thermal wall effects caused by heat transfer to a cold wall was investigated in the reaction zone by using different combustion systems at atmospheric pressure. Surface mechanisms include a catalytic surface, an inert surface that promotes radical recombinations, and a completely inert wall used as reference was the simplest possible boundary condition. The analysis of the results show that for the richer combustion case ( = 0.5) the surface chemistry gives significant wall effects, while the thermal and velocity boundary layer gives rather small effects. But for the leaner combustion case ( = 0.1) the thermal and velocity boundary layer gives more significant wall effects, while surface chemistry gives less significant wall effects compared to the other case. As expected, the overall wall effects were more pronounced for the leaner combustion case.

  • 4.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical studies of wall effects with laminar methane flames2002In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 128, no 1-2, p. 165-180Article in journal (Refereed)
    Abstract [en]

    Wall effects in the combustion of lean methane mixtures have been studied numerically using the CHEMKIN software. To gain a deeper understanding of the flame-wall interaction in lean burn combustion, and in particular the kinetic and thermal effects, we have simulated lean and steady methane/air flames in a boundary layer flow. The gas-phase chemistry is modeled with the GRI mechanism version 1.2. Boundary conditions include an inert wall, a recombination wall and catalytic combustion of methane. Different pressures, wall temperatures and fuel-air ratios are used to address questions such as which part of the wall effects is most important at a given set of conditions. As the results are analyzed it can be seen that the thermal wall effects are more significant at the lower wall temperature (600 K) and the wall can essentially be modeled as chemical inert for the lean mixtures used. At the higher wall temperature (1,200 K), the chemical wall effects become more significant and at the higher pressure (10 atm) the catalytic surface retards homogeneous combustion of methane more than the recombination wall because of product inhibition. This may explain the increased emissions of unburned fuel observed in engine studies, when using catalytic coatings on the cylinder walls. The overall wall effects were more pronounced for the leaner combustion case (phi = 0.2). When the position of the reaction zone obtained from the boundary layer calculations is compared with the results from a one-dimensional premixed flame model, there is a small but significant difference except at the richer combustion case (phi = 0.4) at atmospheric pressure, where the boundary layer model may not predict the flame position for the given initial conditions.

  • 5.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Eriksson, L-E
    Volvo Aero Corporation.
    A Numerical Study of Sidewall Quenching with Propane/Air Flames2002In: Proceedings of the Combustion Institute, ISSN 0082-0784, E-ISSN 1878-027X, Vol. 29, p. 789-795Article in journal (Refereed)
    Abstract [en]

    The head-on (i.e., stagnation) configuration has generally been used to numerically and experimentally characterize the flame-wall interaction with complex chemistry and multicomponent transport. Other studies have treated the transient case of a flame propagating toward a wall, and combustion in a boundary layer has also been dealt with. In this paper, a two-dimensional stationary model has been used to study the sidewall quenching,of laminar propane/air flames in a boundary-layer flow. This geometry may be described as a flame parallel to the wall that is swept away with a laminar boundary-layer flow while propagating toward and interacting with the wall. The main purpose has been to examine the extent to which the flame can propagate toward the cooled wall for lean flames compared to stoichiometric flames. A detailed kinetic model is used to examine the oxidation of both the fuel and the intermediate hydrocarbons (IHCs). For stoichiometric and near stoichiometric mixtures, the thermal coupling between the flame and the wall is small but significant. However, for very lean flames, the thermal coupling between the flame and the wall is found to be very significant. The intermediate hydrocarbons are the dominant emissions for stoichiometric and near-stoichiometric flames in contrast to the leaner flames in which the fuel becomes more significant. This implies that the IHCs are very important for the overall hydrocarbon emissions from flame quenching; as a result detailed kinetics of complex fuels should be used when determining the unburned hydrocarbon emissions.

  • 6.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    Eriksson, L-E
    Kinetic and Transport Effects of Pressurized Methane Flames in a Boundary Layer2003In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 133, no 4, p. 503-506Article in journal (Refereed)
    Abstract [en]

    We have recently modeled combustion of lean methane-air [1] mixtures in a boundary layer flow using the program CRESLAF [2, 3 and 4]. A uniform fuel-air mixture above the auto-ignition temperature was introduced at the inlet edge of the wall, which gave an arrested flame zone, propagating in the upstream direction with a local flame speed that is equal and opposite to the local flow velocity. We compared the interaction of this flame with three model wall materials representing three idealized cases from a chemical point of view, a completely inert wall, a radical recombining wall, and a wall supporting catalytic combustion.

    Here we report on an analogous study of a flame geometry that may be considered a combination of a one-dimensional flame propagating towards a wall and the combustion of a uniform fuel-air mixture in a boundary layer flow. In contrast to our previous work [1] where we had a uniform inlet flow composition consisting of unburnt gas, here there is only unburnt gas close to the walls while there is burnt gas in the center of the channel. The present study concerns lean pressurized methane flames propagating toward hot isothermal walls where chemistry on the wall is considered important.

    The main purpose is to compare the results with those obtained in Ref. [1], which enables us, for the same flow field (boundary layer flow), to compare the effect of flame geometry on the wall effects. We have found and have been able to explain theoretically that such subtle changes of the flame geometry, which would be rather difficult to study experimentally, may have surprisingly significant effects on the combustion process.

  • 7.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Glarborg, P
    A Design Concept to Reduce Fuel NOx in Catalytic Combustion of Gasified Biomass2003In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 49, no 8, p. 2149-2157Article in journal (Refereed)
    Abstract [en]

    A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air-fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H-2.

  • 8.
    Andrae, Johan C. G.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Head, R. A.
    HCCl experiments with gasoline surrogate fuels modeled by a semidetailed chemical kinetic model2009In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 156, no 4, p. 842-851Article in journal (Refereed)
    Abstract [en]

    Experiments in a homogeneous charge compression ignition (HCCI) engine have been conducted with four gasoline surrogate fuel blends. The pure components in the Surrogate fuels consisted of n-heptane, isooctane, toluene, ethanol and diisobutylene and fuel sensitivities (RON-MON) in the fuel blends ranged from two to nine. The operating conditions for the engine were p(in) = 0.1 and 0.2 MPa, T-in = 80 and 250 degrees C, phi = 0.25 in air and engine speed 1200 rpm. A semidetailed chemical kinetic model (142 species and 672 reactions) for gasoline surrogate fuels, validated against ignition data from experiments conducted in shock tubes for gasoline Surrogate fuel blends at 1.0 <= p <= 5.0 MPa, 700 <= T <= 1200 K and 0 = 1.0, was successfully used to qualitatively predict the HCCI experiments using a single zone modeling approach. The fuel blends that had higher fuel sensitivity were more resistant to autoignition for low intake temperature and high intake pressure and less resistant to autoignition for high intake temperature and low intake pressure. A sensitivity analysis shows that at high intake temperature the chemistry of the fuels ethanol, toluene and diisobutylene helps to advance ignition. This is consistent with the trend that fuels with the least Negative Temperature Coefficient (NTC) behavior show the highest octane sensitivity, and become less resistant to autoignition at high intake temperatures. For high intake pressure the sensitivity analysis shows that fuels in the fuel blend with no NTC behavior consume OH radicals and acts as a radical scavenger for the fuels with NTC behavior. This is consistent with the observed trend of an increase in RON and fuel sensitivity. With data from shock tube experiments in the literature and HCCI modeling in this work, a correlation between the reciprocal pressure exponent oil the ignition delay to the fuel sensitivity and volume percentage of single-stage ignition fuel in the fuel blend was found. Higher fuel sensitivity and single-stage fuel content generally gives a lower value of the pressure exponent. This helps to explain the results obtained while boosting the intake pressure in the HCCI engine.

  • 9.
    Andrae, Johan C. G.
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Johansson, A.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rosen, A.
    OH desorption energies for a palladium catalyst characterised by kinetic modelling and laser-induced fluorescence2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 563, no 03-jan, p. 145-158Article in journal (Refereed)
    Abstract [en]

    A kinetic model for the H-2/O-2 reaction on a polycrystalline palladium catalyst has been constructed using CHEMKIN in order to understand the coverage-dependent OH desorption energy. Each adsorbed oxygen atom was modelled to cover four I'd surface sites. The yield of OH and the water production were measured with laser-induced fluorescence (LIF) and microcalorimetry respectively as a function of the relative hydrogen concentration, alpha(H2). The temperature of the catalyst was 1300 K, the total pressure was 13 Pa and the flow was set to 100 SCCM. In fitting the model to the experimental data, the OH desorption energy E-OH(d) was found to have a first-order coverage dependence according to: E-OH(d)(theta) = E-OH(d)(0) - Btheta, where B is a constant set to 92 kJ/mol. The desorption energy at zero coverage E-OH(d)(0) was determined to be 226 kJ/mol. The model could also qualitatively and quantitatively reproduce the apparent desorption energy as a function of alpha(H2); therefore it is believed that the coverage could be predicted by the model. The values for E-OH(d)(theta) were calculated as a function of alpha(H2). From the results of a sensitivity analysis and rate of production calculations' there are strong reasons to believe that the main water-forming reaction on Pd at 1300 K is the hydrogen addition reaction, H + OH reversible arrow H2O. Enthalpy diagrams for the water-forming reactions are also presented.

  • 10.
    Andrae, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Risberg, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Kalghatgi, Gautam
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Cooxidation in the auto-ignition of primary reference fuels and n-heptane/toluene blends2005In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 140, no 4, p. 267-286Article in journal (Refereed)
    Abstract [en]

    Auto-ignition of fuel mixtures was investigated both theoretically and experimentally to gain further understanding of the fuel chemistry. A homogeneous charge compression ignition (HCCI) engine was run under different operating conditions with fuels of different RON and MON and different chemistries. Fuels considered were primary reference fuels and toluene/n-heptane blends. The experiments were modeled with a single-zone adiabatic model together with detailed chemical kinetic models. In the model validation, co-oxidation reactions between the individual fuel components were found to be important in order to predict HCCI experiments, shock-tube ignition delay time data, and ignition delay times in rapid compression machines. The kinetic models with added co-oxidation reactions further predicted that an n-heptane/toluene fuel with the same RON as the corresponding primary reference fuel had higher resistance to auto-ignition in HCCI combustion for lower intake temperatures and higher intake pressures. However, for higher intake temperatures and lower intake pressures the n-heptane/toluene fuel and the PRF fuel had similar combustion phasing.

  • 11.
    Andrae, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Bursell, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Fakhrai, Reza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Jayasuriya, Jeevan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Manrique Carrera, Arturo
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    High-pressure catalytic combustion of gasified biomass in a hybrid combustor2005In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 293, no 1-2, p. 129-136Article in journal (Refereed)
    Abstract [en]

    Catalytic combustion of synthetic gasified biomass was conducted in a high-pressure facility at pressures ranging from 5 to 16 bars. The catalytic combustor design considered was a hybrid monolith (400 cpsi, diameter 3.5 cm, length 3.6 cm and every other channel coated). The active phase consisted of 1 wt.% Pt/gamma-Al2O3 With wash coat loading of total monolith 15 wt.%. In the interpretation of the experiments, a twodimensional boundary layer model was applied successfully to model a single channel of the monolith. At constant inlet velocity to the monolith the combustion efficiency decreased with increasing pressure. A multi-step surface mechanism predicted that the flux of carbon dioxide and water from the surface increased with pressure. However, as the pressure (i.e. the Reynolds number) was increased, unreacted gas near the center of the channel penetrated significantly longer into the channel compared to lower pressures. For the conditions studied (lambda = 46, T-in = 218-257 degrees C and residence time similar to 5 ms), conversion of hydrogen and carbon monoxide were diffusion limited after ignition, while methane never ignited and was kinetically controlled. According to the kinetic model surface coverage of major species changed from CO, H and CO2 before ignition to O, OH, CO2 and free surface sites after ignition. The model predicted further that for constant mass flow combustion efficiency increased with pressure, and was more pronounced at lower pressures (2.5-10 bar) than at higher pressures (> 10 bar).

  • 12. Cracknell, R. F.
    et al.
    Andrae, Johan C. G.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    McAllister, L. J.
    Norton, M.
    Walmsley, H. L.
    The chemical origin of octane sensitivity in gasoline fuels containing nitroalkanes2009In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 156, no 5, p. 1046-1052Article in journal (Refereed)
    Abstract [en]

    Experimental octane measurements are presented for a standard gasoline to which has been added various quantities of nitromethane, nitroethane and 1-nitropropane. The addition of nitroalkanes was found to suppress the Motor Octane Number to a much greater extent than the Research Octane Number. in other words addition of nitroalkanes increases the octane sensitivity of gasoline. Density Functional Theory was used to model the equilibrium thermodynamics and the barrier heights for reactions leading to the break-up of nitroethane. These results were used to develop a chemical kinetic scheme for nitroalkanes combined with a surrogate gasoline (for which a mechanism has been developed previously). Finally the chemical kinetic simulations were combined with a quasi-dimensional engine model in order to predict autoignition in octane rating tests. Our results suggest that the chemical origin of octane sensitivity in gasoline/nitroalkane blends cannot be fully explained on the conventional basis of the extent to which NTC behaviour is absent. Instead we have shown that the contribution of the two pathways leading to autoignition in gasoline containing nitroalkanes becomes much more significant under the more severe conditions of the Motor Octane method than the Research Octane method.

  • 13. Cracknell, R. F.
    et al.
    Head, R. A.
    McAllister, L. J.
    Andrae, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Octane sensitivity in gasoline fuels containing nitro-alkanes: A possible means of controlling combustion phasing for HCCI2009In: SAE technical paper series, ISSN 0148-7191Article in journal (Refereed)
    Abstract [en]

    Addition of nitroalkanes to gasoline is shown to reduce the octane quality. The reduction in the Motor Octane Number (MON) is greater than the reduction in the Research Octane Number (RON). In other words addition of nitroalkanes causes an increase in octane sensitivity. The temperature of the compressed air/fuel mixture in the MON test is higher then in the RON test. Through chemical kinetic modelling, we are able to show how the temperature dependence of the reactions responsible for break-up of the nitroalkane molecule can lead to an increase in octane sensitivity. Results are presented from an Homogenous Charge Compression Ignition (HCCI) engine with a homogeneous charge in which the air intake temperature was varied. When the engine was operated on gasoline-like fuels containing nitroalkanes, it was observed that the combustion phasing was much more sensitive to the air intake temperature. This suggests a possible means of controlling combustion phasing for HCCI.

  • 14.
    Johansson, David
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Coupling of CHEMKIN and MATLAB for HCCI combustion application2004In: International Symposium on Combustion, Abstracts of Works-in-Progress Posters, 2004Conference paper (Refereed)
    Abstract [en]

    In Homogeneous Charge Compression Ignition (HCCI) engine applications a mixture of fuel and oxidizer is compressed in an engine cylinder until self-ignition occurs. Since no flame propagation or fuel-rich regions exists no soot will form and in-cylinder temperatures will be rather low leading to very low NOx emissions. Another benefit is a high, diesel like, efficiency. The problems will HCCI combustion are mainly high hydrocarbon and CO emissions, high peak pressures, control difficulties, etc. A possible way to utilize the benefits is to use a dual mode engine that works in HCCI mode at low and medium loads and in diesel mode at high loads. A way to link CHEMKIN III to the MATLAB environment is presented. The coupling between the programs gives MATLAB access to rate of production, enthalpy and specific heat producing subroutines from the CHEMKIN III package. All modeling is done in MATLAB after the link has been established. The coupling is then used to make a HCCI engine model, consisting of three zones, each of uniform temperatures and composition, of each zone, and the inputs are temperatures of the different zones, pressure and composition of the initial fuel/ox load and engine data. Analysis of a mixture of 84% iso-octane and 16% and n-heptane/air HCCI combustion was presented and compared to experimental results. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).

  • 15. Kalghatgi, G. T.
    et al.
    Bradley, D.
    Andrae, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Harrison, A. J.
    The nature of "superknock" and its origins in SI engines2009In: Internal combustion engines: performance, fuel economy and emissions, Institution of Mechanical Engineers, 2009, p. 259-269Conference paper (Refereed)
    Abstract [en]

    Extremely high knock intensities are observed occasionally in turbo charged spark ignition (SI) engines. Such events have been informally described as "Super knock" and are often associated with pre-ignition. Knock is initiated by auto ignition at one or more "hot spots". The mode of propagation of the resulting pressure wave depends on the propagation velocity of the auto ignitive front. When this becomes coupled with the acoustic wave, a localised detonation begins to develop, resulting in a very high rate of pressure rise. It is shown, through semi quantitative analysis including chemical kinetic calculations, that developing detonation becomes more likely when end-gas pressures and temperatures increase and might be the reason for "Super knock".

  • 16.
    Risberg, Per
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Andrae, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Kalghatgi, Gautam
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    The Influence of NO on the Combustion Phasing in an HCCI Engine2006In: SAE 2006 World Congress & Exhibition Technical Papers, 2006, no 2006-01-0416Conference paper (Refereed)
    Abstract [en]

    In this work the influence of NO on combustion phasing has been studied experimentally in a single cylinder HCCI engine. A isooctane/n-heptane blend (PRF), a toluene/n-heptane mixture (TRF) and a full boiling range gasoline were tested at two different operating conditions with NO concentrations ranging from 4 up to 476 ppm in the fresh intake air. All three fuels had the same RON of 84. The first operating condition had a high intake pressure (2 bar absolute) and low intake temperature (40 °C), where low temperature chemistry is relatively prominent. The other operating condition had a high intake temperature (100 °C) and atmospheric intake pressure with significantly lower cool flame reactivity. Additionally the effect of NO at two different engine speeds, 900 and 1200 rpm were studied.

    The combustion phasing, represented by CA50 was advanced up to 12.5 CAD by the influence of NO. In the cases with the TRF and the full boiling range gasoline the combustion phasing advanced with an increasing NO concentration. The combustion phasing in the PRF case also advanced at low concentrations of NO, but retarded beyond the baseline case at high concentrations in the high-pressure case. Such effects on combustion phasing are explained in terms of reaction kinetic theory from the literature. At low concentrations NO provides extra branching pathways, but as NO concentration increases termination reactions take over. The interaction of NO and aromatic fuels has not been theoretically examined to the same extent in the literature and more work in this area is needed.

  • 17. Soyhan, H. S.
    et al.
    Andrae, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Evaluation of kinetic models for autoignition of automotive reference fuels in HCCl applications2007In: Turkish Journal of Engineering and Environmental Sciences, ISSN 1300-0160, E-ISSN 1303-6157, Vol. 31, no 6, p. 383-390Article in journal (Refereed)
    Abstract [en]

    Clean and efficient engine research and development work needs reliable models where autoignition for automotive reference fuels are described well. These models have to include chemistry containing numbers of reactions. The predictive capability depends more on the quality of reactions describing the chemical phenomena in the mechanism than on the number of the reactions. In this work three chemical mechanisms containing 1034, 74 and 63 species for primary reference fuels (PRFs) are compared with respect to the prediction of autoignition at conditions relevant for HCCI Engines and kaock in SI Engines. After validation to experimental data for iso-octane, n-heptane and mixtures of the two fuels obtained from shock tube experiments over the temperature range 700 < T < 1200K at pressures 15-60 bars, a single zone engine model is used to simulate the point of autoignition and compared against experimental results obtained from an HCCI engine in KTH labs in Stockholm. The work shows the performance of the chemical mechanisms in prediction of autoignition delay time in HCCI engines.

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