Heptane Combustion Research Articles

Numerical simulation study on chemical ignition process of underground coal gasification

Underground coal gasification (UCG) is a process that produces combustible gas by the in-situ gasification of coal seams. For a steady and efficient gasification project, the ignition of coal seam is a prerequisite. The heating method and reacting process of coal seam play an essential role to the ignition. A coal seam ignition model coupled with heptane combustion was created to simulate the deep UCG ignition stage employing the chemical ignition method. A 1700 K heptane jet flame and a U-shaped pyrolysis gas flame formed the heat source. The flame temperature of pyrolysis gas was around 1300 K. The effective heating length of the flame increased with the heating time, which reached 600 mm at 400 s. The coal seam reaction process was divided into four stages: (1) heptane flame stabilization, (2) coal seam heating, (3) pyrolysis gas release, and (4) pyrolysis gas flame stabilization. It was the third stage when the coal seam ignited. The coal seam would ignite faster with a lower excess air coefficient, and the ignition time ranged from 225 to 275 s when the excess air coefficient was 1.39. The outlet carbon dioxide concentration increased by about 5 %–17 % when the coal seam ignited.

Experimental study of the characteristics of heptane combustion in a high-speed steam jet

This paper is devoted to the experimental study of the characteristics of heptane combustion in a high-speed superheated steam jet. The completeness of the combustion under steam gasification conditions and the gas composition of the heptane combustion products cooled to room temperature were determined. The averaged temperature of the flame was measured. It is shown that the presence of superheated steam ensures high combustion efficiency and reduces emissions of nitrogen oxides in comparison with a heated air combustion. It is also shown that the organization of liquid fuel combustion in a high-speed steam jet ensures effective burning of fuel in the absence of nozzles and swirlers.

Detonation Regime in Combustion of Heptane and Jet A-1 Propellant in a less than 0.5-m-Long Small-Size Combustor

Detonation Regime in Combustion of Heptane and Jet A-1 Propellant in a less than 0.5-m-Long Small-Size Combustor

Effects of n-Butanol Blends on the Formation of Hydrocarbons and PAHs from Fuel-Rich Heptane Combustion in a Micro Flow Reactor with a Controlled Temperature Profile

ABSTRACT The effects of the addition of n-butanol on the formation of hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) of n-heptane combustions were investigated using a micro flow reactor (MFR) with a controlled temperature profile. The concentrations of small and large hydrocarbons, as well as PAHs were measured at a maximum wall temperature of 1,100 K and atmospheric pressure. The values obtained from several mechanisms were compared to the measurement values at equivalence ratios of 2.0–5.0. The CRECK mechanism was in fair agreement with the measurements. The computational results confirmed that the concentration of the PAHs and soot precursors’ decreased, while that of CO and CO2 increased due to the addition of butanol. These trends were also shown by the measurement values. The reaction path and rate of production analyzes were carried out to identify the major reactions contributing toward species concentrations.

Numerical simulation of an experimental atrium fires in combined natural and forced ventilation by CFD

This study investigates the measurements data attained in Murcia Atrium fire tests (Gutiérrez-Montes, Sanmiguel-Rojas, Viedma, & Rein) using general CFD code, CFX-16.2 ( CFX-16.2, ANSYS, Inc.). Experiments were executed by burning heptane as a fuel for three different fires capacities, (1.32, 2.28 and 2.34 MW). Historically, CFX was validated with experimental data for compartment fires including natural ventilation only. In this paper validation was performed for developing fires during transient period in a large space, including the effect of combined natural and forced ventilation. Two different combustion models i.e. Non-combustion model and Eddy Dissipation Model (EDM) were used to represent the combustion of heptane. Four different approaches were employed to determine the predicted dynamic behavior of the smoke height and to evaluate the accuracy of CFX predictions. The results display CFX predictions have a reasonable concord with the experimental data. Therefore, CFX can be a valid tool for performance-based engineering to evaluate the smoke systems required for complex enclosed structures.

A computationally inexpensive CFD approach for small-scale biomass burners equipped with enhanced air staging

Computational Fluid Dynamics (CFD) is an upcoming technique for optimization and as a part of the design process of biomass combustion systems. An accurate simulation of biomass combustion can only be provided with high computational effort so far. This work presents an accurate, time efficient CFD approach for small-scale biomass combustion systems equipped with enhanced air staging. The model can handle the high amount of biomass tars in the primary combustion product at very low primary air ratios. Gas-phase combustion in the freeboard was performed by the Steady Flamelet Model (SFM) together with a detailed heptane combustion mechanism. The advantage of the SFM is that complex combustion chemistry can be taken into account at low computational effort because only two additional transport equations have to be solved to describe the chemistry in the reacting flow. Boundary conditions for primary combustion product composition were obtained from the fuel bed by experiments. The fuel bed data were used as fuel inlet boundary condition for the gas-phase combustion model. The numerical and experimental investigations were performed for different operating conditions and varying wood-chip moisture on a special designed real-scale reactor. The numerical predictions were validated with experimental results and a very good agreement was found. With the presented approach accurate results can be provided within 24h using a standard Central Processing Unit (CPU) consisting of six cores. Case studies e.g. for combustion geometry improvement can be realized effectively due to the short calculation time of the presented model. The current work provides a powerful tool for small-scale biomass boiler research and development with a perfect trade-off between quality in predicting physical trends and low computational running time.

Investigation of Auto-Ignition of Heptane-CNG Mixture in HCCI Engine

Homogeneous Charge Compression Ignition (HCCI) operating principals have been widely investigated yet the uncontrollable combustion of HCCI is the major obstacle in its development. This paper is trying to increase the understanding on the auto-ignition and combustion process of several fuels to be applied in HCCI combustion system. This paper investigates variation of fuel composition between heptane and compressed natural gas (CNG) with the composition ranges from 10-100% heptane/CNG. The investigation was done in a constant volume chamber with elevated temperature (800°C). Three lambdas were tested for each fuel, namely 0.8, 1, 1.2 and 2. From the results, it is found that the mixture composition highly affects the output of the combustion of dual fuel where CNG is able to suppress heptane combustion at CNG percentage more than 40%. Furthermore, homogeneity level highly determines the types of combustion produced by the mixture, distributed or propagation flame.

Lean heptane and propane combustion in a non-catalytic parallel-plate counter-flow reactor

Small scale lean combustors, in conjunction with mechanical and electrical conversion devices, have the potential to meet increasing portable power needs. This study examines the combustion of lean premixed fuels in a mesoscale, heat-recirculating parallel-plate counter-flow reactor. The reactor utilizes internal heat recirculation to produce temperatures in excess of the adiabatic flame temperature, known as superadiabatic combustion. As a result of these elevated temperatures, burning velocities above adiabatic values and extension of flammability limits, including stable operation at very lean equivalence ratios, may be attained. Combustor stability and emissions of carbon monoxide, nitrogen oxides, and unburned hydrocarbons have been previously studied for lean combustion of methane in the counter-flow reactor. This study examines lean combustion of two increasingly complex fuels, propane and heptane, due to the logistical importance of both gaseous and liquid fuels. Stability ranges and emissions measurements are presented for the counter-flow reactor operating on these fuels, and the results are compared to previously measured emissions for lean methane. Stability ranges of the counter-flow reactor operating on lean propane and heptane are also compared to those in the rich regime. Further analysis of the results for lean methane, propane and heptane combustion utilizes peak reactor wall temperatures as an indicator of favorable operating conditions, and highlights the importance of superadiabatic operation for achieving large turn-down ratios and low levels of emissions.

Experimental study of n-heptane/air combustion in meso-scale burners with porous media

The liquid fuel combustion in a meso-scale burner with porous media was experimentally investigated for n-heptane/air mixtures of varying equivalence ratios and flow speeds. Infrared thermography and appropriately placed thermocouples were to measure the surface temperature of the burner. A video camera recorded changes in the flame. Liquid heptane combustion in a meso-scale burner was demonstrated to be affected by many factors. First, heptanes droplets were formed at the capillary tip, and oscillating combustion occurred in the absence of a porous medium, resulting in an unstable flame, which could be easily blown out. Second, the addition of a porous medium stabilized the flame, but its position was affected by the airflow velocity and the position of the porous medium. Finally, the outer tube affected the flammable limits of the burner. The flame could easily be blown out in the absence of an outer tube. Furthermore, a double-layer vacuum tube insulated the burner more effectively and significantly reduced its heat loss.

Analysis of Flame and OH* Natural Emissions of n-Heptane Combustion in a Homogeneous Charge Compression Ignition (HCCI) Engine: Effect of Burnt Gas Dilution

The present study examines the global effect of a laboratory-simulated exhaust gas recirculation (EGR) on the homogeneous charge compression ignition (HCCI) combustion of n-heptane in a transparent monocylinder diesel engine. The investigations were carried out during the engine cycle for two EGR rates, 0 and 30%, at a constant 0.3 equivalence ratio. The analysis is focused on the relation between natural combustion emissions during the cold and main combustion phases and the OH* chemiluminescence and the processes involved inside the combustion chamber of a compression engine. By observing cool and main flame emissions, it was observed that the dilution by burnt gas delays and degrades the combustion phenomenon. For both cases, the natural flame emission is not uniformly distributed, because of the nonhomogeneity of the gas temperature. By coupling kinetic analysis, provided by a zero-dimensional model, it was shown that the natural emissions of combustion are sufficiently sensitive to yield combustion process analysis.

Effects of premixed n-heptane from the intake port on the combustion characteristics and emissions of biodiesel-fuelled engines

The combustion characteristics and emissions of biodiesel-fuelled direct-injection (DI) compression ignition engines with the addition of n-heptane from the intake port were investigated on a single-cylinder engine. The experimental results revealed that the homogeneous charge compression ignition (HCCI) combustion of the premixed n-heptane had important effects on the overall combustion characteristics and emission levels. The heat release curves exhibited a three-stage combustion mode, which includes the low-temperature reaction (LTR), high-temperature reaction (HTR) of n-heptane, and diffusion burn of biodiesel. On increase in the premixed ratio of the n-heptane, the peak values of both the LTR and the HTR increased linearly. When the overall equivalence ratio is kept constant, the HCCI combustion of premixed n-heptane had a moderate effect on the ignition timing of the biodiesel fuel, and the maximum heat release rate during the third-stage combustion decreased with increase in the premixed ratio. Regarding the regulated emissions, partial substitute of DI biodiesel by port injection of n-heptane caused the carbon monoxide and hydrocarbon emissions to deteriorate in comparison with those of the neat biodiesel engines. For low to medium equivalence ratios, the premixed combustion of heptane resulted in a decrease in the nitrogen oxide (NO x) emission, but had little effect on the smoke opacity. For a higher equivalence ratio, it was very interesting to find that both the NO x emissions and the smoke opacity were suppressed substantially by an n-heptane premixed ratio of 20—25 per cent.

Kinetic Modeling of Heptane Combustion and PAH Formation

A kinetic model for high-temperature oxidation and pyrolysis of heptane has been developed. This model is based on new results for heptane decomposition, decomposition and isomerization of heptyl radicals, and decomposition of olefins and olefinic radicals. It is combined with kinetic data from Grimech-3.0 model on the reactions of C 1 -C 2 species. The subset on C 3 -C 4 chemistry is based on the works of Marinov et al. (1998) and Laskin et al. (2000). The database for PAH formation is based on the results from kinetic models on heptane suitably modified from various soot formation models. The model was validated against experimental data on burning velocity, ignition delays, and OH time history during heptane ignition behind shock wave. The reactions determining burning velocity were established through sensitivity analysis. The main reactions determining burning velocity of heptane are similar to the reactions determining burning velocity of C 1 -C 4 hydrocarbons. The influence of product distribution of heptyl radical decomposition on PAH production was analyzed.

Laser-induced breakdown spectroscopy of gas mixtures of air, CO2, N2, and C3H8 for simultaneous C, H, O, and N measurement.

Laser-induced breakdown spectroscopy (LIBS) was applied for simultaneous measurement of the elements C, H, N, and O in CO2-air, C3H8-CO2, and C3H8-N2 gas mixtures at atmospheric pressure. A single 7-mm-diameter aperture at the sample chamber was used for 1064-nm Nd:YAG laser irradiation and plasma signal output to an echelle spectrometer. Double-pulse laser bursts of approximately 8-ns pulse width (FWHM) and 250-ns interpulse separation were applied to increase the plasma signal. Calibration curves of the LIBS signal versus the partial pressure or the atomic abundance ratios were taken by dilution series in intervals that are relevant in the combustion of heptane (C7H16) near an equivalence ratio of 1.

Implementation and Validation of a New Soot Model and Application to Aeroengine Combustors

The modeling of soot formation and oxidation under industrially relevant conditions has made significant progress in recent years. Simplified models introducing a small number of transport equations into a CFD code have been used with some success in research configurations simulating a reciprocating diesel engine. Soot formation and oxidation in the turbulent flow is calculated on the basis of a laminar flamelet library model. The gas phase reactions are modeled with a detailed mechanism for the combustion of heptane containing 89 species and 855 reactions developed by Frenklach and Warnatz and revised by Mauss. The soot model is divided into gas phase reactions, the growth of polycyclic aromatic hydrocarbons (PAH) and the processes of particle inception, heterogeneous surface growth, oxidation, and condensation. The first two are modeled within the laminar flamelet chemistry, while the soot model deals with the soot particle processes. The time scales of soot formation are assumed to be much larger than the turbulent time scales. Therefore rates of soot formation are tabulated in the flamelet libraries rather than the soot volume fraction itself. The different rates of soot formation, e.g., particle inception, surface growth, fragmentation, and oxidation, computed on the basis of a detailed soot model, are calculated in the mixture fraction/scalar dissipation rate space and further simplified by fitting them to simple analytical functions. A transport equation for the mean soot mass fraction is solved in the CFD code. The mean rate in this transport equation is closed with the help of presumed probability density functions for the mixture fraction and the scalar dissipation rate. Heat loss due to radiation can be taken into account by including a heat loss parameter in the flamelet calculations describing the change of enthalpy due to radiation, but was not used for the results reported here. The soot model was integrated into an existing commercial CFD code as a post-processing module to existing combustion CFD flow fields and is very robust with high convergence rates. The model is validated with laboratory flame data and using a realistic three-dimensional BMW Rolls-Royce combustor configuration, where test data at high pressure are available. Good agreement between experiment and simulation is achieved for laboratory flames, whereas soot is overpredicted for the aeroengine combustor configuration by 1–2 orders of magnitude.

Laser Attenuation Measurements of Soot Volume Fractions During Reduced-Gravity Combustion of Heptane and Heptane/Hexadecane Droplets

Abstract Results from reduced-gravity experiments on combustion of heptane/hexadecane mixture droplets and heptane droplets are presented. Initial droplet diameters were about 1 mm, and initial hexadecane mass fractions in the droplets were 0.6. The droplets were burned in air at 0.1 MPa. Attenuation of the beam from a diode laser was used to gain information on average soot volume fractions in the vicinities of the droplets. Results indicate that average soot volume fractions increased over the observation time for heptane droplets. For heptane/hexadecane mixture droplets, however, results indicate that average soot volume fractions increase after ignition, decrease when a flame contraction occurs, and then increase again after the flame contraction has been completed. Interpretation of the data indicates that peak soot volume fractions as high as about 50 ppm existed in these experiments. Simplified theory is developed to predict effects of droplet heating on quasisteady soot shell locations. The theory...

Estimates of Liquid Species Diffusivities from Experiments on Reduced-Gravity Combustion of Heptane–Hexadecane Droplets

Experiments on combustion of heptane/hexadecane mixture droplets were conducted in a reduced-gravity environment. Initial droplet diameters ranged from 0.47 to 1.5 mm, and initial hexadecane mass fractions ranged from 0.05 to 0.4. The ambient gas was O 2/He (with O 2 mole fractions of 0.3 and 0.5), or atmospheric air, and pressures were varied from 0.033 to 0.3 MPa (abs). A previous asymptotic theory was extended to allow data on flame contractions to be used to estimate liquid species diffusion coefficients. The liquid species diffusion coefficients were found to vary significantly with pressure; this is attributed to variations in droplet temperatures.

2-D Simulation of Turbulent Autoignition with Transient Laminar Flamelet Source Term Closure

Abstract The motivation for the present study is the attempt to enhance the understanding of the influence of inhomogeneous turbulence influence upon autoignition processes, which are of interest for practical applications such as the Diesel engine. Special attention is paid to the modelling of chemical source term closure and its coupling with inhomogeneous turbulence. Detailed two-dimensional simulations of turbulent autoignition with flamelet source term closure have been performed using a laminar flamelet presumed pdf model (pdf== probability density function). The transient autoignition calculations of the laminar flamelet are based on a reduced 4-step chemical kinetic mechanism of heptane combustion in air. New ways of modelling turbulent chemical source term closure are investigated. Specifically, an ignition time variable is introduced to characterize the aspect of transient chemical reaction during the turbulent autoignition process. The model successfully covers the period from early autoignition to flame propagation

On the identification of carbonaceous aerosols via 14C accelerator mass spectrometry, and laser muprobe mass spectrometry

Carbon isotopic measurements ( 12C, 14C), derived from chemical measurements of total carbon plus AMS measurements of 14C/ 12C have become an accepted means for estimating fossil and contemporary carbon source contributions to atmospheric carbon. Because of the limited sensitivity of these techniques, however, such measurements are restricted to “bulk” samples comprising at least 10–100 μg of carbon. Laser microprobe mass spectrometry (LMMS) offers an important complementary opportunity to investigate the chemical nature of individual particles as small as 0.1 μm in diameter. Although there is little hope to measure 14C/ 12C in such small samples, the compositional and structural information available with the laser microprobe is of interest for possible source discrimination. Also, the analysis of individual particles, which may reflect individual sources, yields significant potential increases in spatial, temporal and source resolution, in comparison to bulk sample analysis. Results of our exploratory investigation of known sources of carbonaceous particles, using LMMS, are presented. By applying multivariate techniques to laser mass spectra of soot from the combustion of heptane and wood, we found striking differences in the alkali metals (notably potassium) in the positive ion mass spectra. For ambient particles, 14C has proved to be a crucial adjunct for the development and validation of the LMMS approach to single particle source assignment via carbon cluster pattern recognition. The combined techniques offer great promise for objective modeling (number and types of carbon sources) and for extension of the dichotomous carbon apportionment (fossil, contemporary) to subclasses such as soot from wood and agricultural burning, and that from coal and petroleum combustion.

Dynamics of combustion processes of n.heptane, i.octane and their mixtures and knocking

Cool flames and multistage ignitions can be regarded as dynamic phenomena of hydrocarbon combustion processes. Any kinetic mechanism must also meet dynamic requirements in order to model the combustion process. Studies of the dynamics of combustion processes were rediscovered only recently, mainly with the help of the CSTR technique. Knocking is regaining interest among combustion researchers and consequently there should be a new interest in the auto ignition of hydrocarbons. Predictive models of the evolution of the end-gas are particularly needed. Knowledge of its dynamic behaviour places more constraints on the modeler. Dynamic behaviours of combustion processes of n .heptane, i .octane and their mixtures (0–100 O.N.) have been studied in a CSTR. Experiments were performed at atmospheric pressure and fuel-rich conditions. Behaviors of systems were studied for different temperatures (510–790 K) and residence time (8–21 s). The n .heptane combustion process exhibits unstable states at low temperatures, whereas i .octane evolves through unstable states at higher temperatures. Mixtures having O.N. less than 97 exhibit unstable states. Heat release rates were experimentally evaluated and compared. The overall results indicate that instability, and hence knocking, is thermokinetic in nature, with kinetics playing the major role.

Societies and Academies

PARIS Academy of Sciences, August 1.—M. Jamin in the chair.—The following papers were read:—On the formation of tails of comets (second note), by M. Faye. Herschel, Arago, Delaunay, and other astronomers did not thoroughly study the tails of comets, hut Newton had already given a quite sufficient explanation of the phenomena. The tail is nothing else—he maintained than the result of a continual emission of molecules from the head of the comet. It is very much like; the tail of smoke emitted by a running locomotive, its outer end being lost in space, and the inner one continually receiving a new supply of molecules. M. Roche, who has made the necessary calculations, taking account of the repulsive force M. Faye advocates, has worked out all those shapes of tails which we witness in reality.—On the equivalence of quadratic forms, by M. Jordan.—On a modification of the electric lamp, by M. Jamin, being the result of observations on the electric light in vacuum, and in closed vessels containing various gases.—On the perchloric acids, by M. Berthelot.—On the travels of Moncatch-Apé, by M. Quatrefages. This American Indian undertook a journey to the north-western coasts of America at the beginning of last century, in search of the origin of his race; whilst on this coast he learned and witnessed that it was visited every year by white men with long black beards, and M. Quatrefages proves that these men were originally from the Loo Choo islands.—On the first meteorological, topographical, and hydrographical observations at the future Panama canal, by M. de Lesseps. Several maps of the coast are prepared, and a meteorological station is opened at Colon.—On the application of electromotive power and of M. Planté's secondary piles to the direction of aërostats, by M. Tissandier. In an aërostat which has a volume of 2200 litres, 3·50m. long, with a diameter of 1·30m., and can raise a weight of 2 kilogrammes, having a Siemens machine which weighs 220 grammes, and a secondary couple of 1300 grammes, the propulsory helix makes six and a half revolutions per second, and the balloon acquires a speed of 1 metre per second for forty minutes. The small Siemens machine, with three elements, produces the work of 1 kilogrammetre.—The elements of comet c of 1881 (Schäberle), by M. Bigourdan, as deduced from observations at Vienna on July 18, and at Paris on July 23 and 28. Its brightness, which is still increasing, will be on August 23 seventeen times as much as it was on July 18.—Spectroscopical observations on the comets b and c, 1881, by MM. Thollon and Tacchini.—On the lengths of spectral bands given by compounds of carbon, by M. Thollon.—On the constitution of comets, by M. Prazmowski.—On the theory of trilinear forms, by M. Le Paige.—On the influence of pressure on dissociation, by M. Lemoine.—On the heat of formation of explosives, by MM. Sarrau and Vieille.—On oxycyanides of lead, cadmium, and mercury, by M. Joannis.—On the heat of combustion of heptane and of hexahydrotoluene, by M. Louguinine.—Third note on the magnesia industry, by M. Schlösing.—A contribution to the study of the transmission of tuberculosis, by M. Toussaint. The juices of animals which have had tuberculosis transmit the disease with very great ease, even when submitted to a high temperature, but especially when employed uncooked.—On the injection of the virus of rabies into the circulation, by M. Galtier. It seems to prevent infection.—On hemeralopia and on the functions of the visual purple, by H. Parinaud.—On the applications of electromotors, by M. Trouvé.