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Unburned methane entrained in exhaust from natural gas-fired compressor engines ("combustion slip") can account for a substantial portion of station-level methane emissions. A novel in-stack, tracer gas method was coupled with Fourier transform infrared (FTIR) species measurements to quantify combustion slip from natural gas compressor engines at 67 gathering and boosting stations owned or managed by nine "study partner" operators in 11 U.S. states. The mean methane emission rate from 63 four-stroke, lean-burn (4SLB) compressor engines was 5.62 kg/h (95% CI = 5.15-6.17 kg/h) and ranged from 0.3 to 12.6 kg/h. The mean methane emission rate from 39 four-stroke, rich-burn (4SRB) compressor engines was 0.40 kg/h (95% CI = 0.37-0.42 kg/h) and ranged from 0.01 to 4.5 kg/h. Study results for 4SLB engines were lower than both the U.S. EPA compilation of air pollutant emission factors (AP-42) and Inventory of U.S. Greenhouse Gas Emissions and Sinks (GHGI) by 8 and 9%, respectively. Study results for 4SRB engines were 43% of the AP-42 emission factor and 8% of the GHGI emission factor, the latter of which does not distinguish between engine types. Total annual combustion slip from the U.S. natural gas gathering and boosting sector was modeled using measured emission rates and compressor unit counts from the U.S. EPA Greenhouse Gas Reporting Program. Modeled results [328 Gg/y (95% CI = 235-436 Gg/y) of unburned methane] would account for 24% (95% CI = 17-31%) of the 1391 Gg of methane emissions for "Gathering and Boosting Stations", or 6% of the net emissions for "Natural Gas Systems" (5598 Gg) as reported in the 2020 U.S. EPA GHGI. Gathering and boosting combustion slip emissions reported in the 2020 GHGI (374 Gg) fall within the uncertainty of this model.

Engine knock and misfire are barriers to pathways leading to high-efficiency Spark-Ignited (SI) Natural Gas engines. The general tendency to knock is highly dependent on engine operating conditions and the fuel reactivity. The problem is further complicated by low emission limits and the wide range of chemical reactivity in pipeline quality natural gas. Depending on the region and the source of the natural gas, its reactivity, described by its methane number (analogous to the octane number for liquid SI fuels) can span from 65–95. In order to realize diesel-like efficiencies, SI natural gas engines must be designed to operate at high BMEP near knock limits over a wide range of fuel reactivity. This requires a deep understanding regarding the combustion-engine interactions pertaining to flame propagation and end-gas autoignition (EGAI). However, EGAI, if controlled, provides an opportunity to increase SI natural gas engine efficiency by increasing combustion rate and the total burned fuel, mitigating the effects of the slow flame speeds of natural gas fuels which generally reduce BMEP and increase unburned hydrocarbon emissions. For this reason, in order to study EGAI phenomenon, the present work highlights multi-dimensional computational fluid dynamics (CFD) models of the Cooperative Fuel Research (CFR) engine. The CFR engine models are used to investigate fuel-engine interactions that lead to EGAI with natural gas, including effects of fuel reactivity, engine operating parameters, and exhaust gas recirculation (EGR). A Three-Pressure Analysis, performed with GT-Power, was used to estimate initial and boundary conditions for the three-dimensional CFD model. CONVERGE CFD v2.4 was used for the three-dimensional CFD modeling where the level set G-Equation model and SAGE detailed chemical kinetics solver were used. An assessment of the different modeling approaches is also provided to evaluate their limitations, advantages and disadvantages, and for which situations they are most applicable. Model validation was performed with experimental data taken with a CFR engine over varying compression ratio, CA50, EGR fraction, and IMEP and shows good agreement in Peak Cylinder Pressure (PCP), PCP crank angle, and the location of the 10%, 50%, and 90% mass fraction burned (CA10, CA50, and CA90, respectively). The models can predict the onset crank angle and pressure rise rate for light, medium, and heavy EGAI under a variety of fuel reactivities and engine operating conditions.

Waste management cost for Australia is increasing every year, and thus, it is important to find alternative ways to use the waste. For example, essential oil has a significant waste stream that can be utilized in vehicles of their producers. However, some of the essential oils contain oxygen which considerably affects engine performance, emission, and combustion characteristics of diesel engines. Thus, this research paper will try to evaluate the essential oils as a replacement of diesel fuel to operate a multicylider diesel engine. For this study, two essential oils are selected which contain different oxygenated functional groups, tea tree oil (5.4% oxygen) and eucalyptus oil (8.4% oxygen), with an aim to evaluate the effect of these functional groups on engine performance and emission parameters. These oils were blended with neat diesel (0% oxygen) to obtain a blend cotaining 2.2% oxygen by weight. The blends produced similar brake power; however, brake-specific fuel consumption (BSFC) increased for eucalyptus oil blends (2.4–3.7%) and tea tree oil blends (3.9–5.3%). Essential oil–diesel blends resulted in less CO and increased NOX emission, produced similar peak pressure, and indicated mean effective pressure. The results then lead to the conclusion that oxygenated essential oils can have a role to reduce dependency of agricultural sector on diesel in the near future.

A reduced chemical kinetic mechanism consisting of 141 species and 709 reactions has been constructed to simulate the combustion of both natural gas and diesel fuels in a dual-fuel engine. Natural gas is modeled as a mixture of methane, ethane, and propane, while the diesel fuel is modeled as n-heptane. The new reduced mechanism combines reduced versions of a detailed n-heptane mechanism and a detailed methane through n-pentane mechanism, each of which was reduced using a direct relation graph method. The reduced dual-fuel mechanism is validated against ignition delay computations with full detailed mechanisms, adiabatic homogeneous charge compression ignition simulations with full detailed mechanisms, experimental premixed laminar flame speeds of CH4/O2/He mixtures at 40 and 60 atm, ignition delay and lift-off length from a diesel spray experiment in a constant-volume chamber, and finally against dual-fuel engine experiments using multidimensional computational fluid dynamics simulations. The engine simu...

Essential oils are derived from not-fatty parts of plants and are mostly used in aromatherapy, as well as cosmetics and perfume production. The essential oils market is growing rapidly due to their claimed health benefits. However, because only therapeutic grade oil is required in the medicinal sector, there is a substantial low-value waste stream of essential oils that can be used in the transportation and agricultural sectors. This study investigated the influence of orange, eucalyptus, and tea tree oil on engine performance and combustion characteristics of a multi-cylinder compression ignition engine. Orange, eucalyptus, and tea tree oil were blended with diesel at 10% by volume. For benchmarking, neat diesel and 10% waste cooking biodiesel-diesel blend were also tested. The selected fuels were used to conduct engine test runs with a constant engine speed (1500 RPM (revolutions per minute)) at four loads. As the load increased, frictional power losses decreased for all of the fuel samples and thus mechanical efficiency increased. At higher loads (75% and 100%), only orange oil-diesel blends produced comparable power to diesel and waste cooking biodiesel-diesel blends. Fuel consumption (brake and indicated) for the essential oil-diesel blends was higher when compared to base diesel and waste cooking biodiesel-diesel blends. Thermal efficiency for the essential oil-diesel blends was comparable to base diesel and waste cooking biodiesel-diesel blends. At higher loads, blow-by was lower for essential oil blends as compared to base diesel and waste cooking biodiesel-diesel blends. At 50% and 100% load, peak pressure was lower for all of the essential oil-diesel blends when compared to base diesel and waste cooking biodiesel-diesel blends. From the heat release rate curve, the essential oil-diesel blends ignition delay times were longer because the oils have lower cetane values. Overall, the low-value streams of these essential oils were found to be suitable for use in diesel engines at 10% blends by agricultural producers of these oils.

Processes such as fast pyrolysis of whole biomass or base-catalyzed depolymerization of lignin produce complex mixtures of oxygenated compounds that must be upgraded to be suitable for blending with petroleum and processing in a refinery. Complete removal of these oxygenated compounds is exceedingly energy intensive, and it is likely that upgraded pyrolysis oils will contain up to 2% oxygen content to be economically viable. The purpose of this study was to evaluate the effect of the presence of oxygenated chemical components representative of those present in upgraded pyrolysis oil on diesel engine performance and emissions. Engine testing was performed by blending seven different oxygenated components and one multicomponent blend with certification ultralow sulfur diesel fuel and quantifying the performance and emissions from the combustion of these fuels in a four-cylinder, turbocharged, 4.5 L John Deere PowerTech Plus common rail, direct injection diesel engine that meets Tier 3 off-highway emissions ...

Methane emissions from the U.S. oil and natural gas supply chain were estimated by using ground-based, facility-scale measurements and validated with aircraft observations in areas accounting for ~30% of U.S. gas production. When scaled up nationally, our facility-based estimate of 2015 supply chain emissions is 13 ± 2 teragrams per year, equivalent to 2.3% of gross U.S. gas production. This value is ~60% higher than the U.S. Environmental Protection Agency inventory estimate, likely because existing inventory methods miss emissions released during abnormal operating conditions. Methane emissions of this magnitude, per unit of natural gas consumed, produce radiative forcing over a 20-year time horizon comparable to the CO2 from natural gas combustion. Substantial emission reductions are feasible through rapid detection of the root causes of high emissions and deployment of less failure-prone systems.

This work examines whether a chimney has influence over the combustion characteristics of biomass within a stove. Experimental work as well as a simplified chemical kinetic model suggests that a chimney plays an active role in the performance of a stove by influencing the overall air-to-fuel ratio and subsequently the production of carbon monoxide. Two different stoves, operated at multiple wood consumption rates, were shown to run with steady state excess air of 300 % − 1250 %. The wood consumption rate was found to be independent of the chimney draft for both stoves. Increasing draft was shown to increase excess air. Draft served to cool combustion gases through dilution with makeup air. Increasing excess air decreased modified combustion efficiency in experiments and kinetic modeling. Increasing the frictional loss coefficient of a chimney by decreasing the diameter was shown to reduce CO production through a reduction of excess air.

In this study, the autoignition behavior of primary reference fuels (PRF) and blends of n-heptane/n-butanol were examined in a Waukesha Fuel Ignition Tester (FIT) and a Homogeneous Charge Compression Engine (HCCI). Fourteen different blends of iso-octane, n-heptane, and n-butanol were tested in the FIT—28 test runs with 25 ignition measurements for each test run, totaling 350 individual tests in all. These experimental results supported previous findings that fuel blends with high alcohol content can exhibit very different ignition delay periods than similarly blended reference fuels. The experiments further showed that n-butanol blends behaved unlike PRF blends when comparing the autoignition behavior as a function of the percentage of low reactivity component. The HCCI and FIT experimental results favorably compared against single and multizone models with detailed chemical kinetic mechanisms—both an existing mechanism as well as one developed during this study were used. The experimental and modeling r...

Recent optical engine studies have linked increases in NO x emissions from fatty acid methyl ester combustion to differences in the premixed autoignition zone of the diesel fuel jet. In this study, ignition of single, isolated liquid droplets in quiescent, high temperature air was considered as a means of gaining insight into the transient, partially premixed ignition conditions that exist in the autoignition zone of a fatty acid methyl ester fuel jet. Normal gravity and microgravity (10 −4 m/s 2 ) droplet ignition delay experiments were conducted by use of a variety of neat methyl esters and commercial soy methyl ester. Droplet ignition experiments were chosen because spherically symmetric droplet combustion represents the simplest two-phase, time-dependent chemically reacting flow system permitting a numerical solution with complex physical submodels. To create spherically symmetric conditions for direct comparison with a detailed numerical model, experiments were conducted in microgravity by use of a 1.1 s drop tower. In the experiments, droplets were grown and deployed onto 14 μm silicon carbide fibers and injected into a tube furnace containing atmospheric pressure air at temperatures up to 1300 K. The ignition event was characterized by measurement of UV emission from hydroxyl radical (OH*) chemiluminescence. The experimental results were compared against predictions from a time-dependent, spherically symmetric droplet combustion simulation with detailed gas phase chemical kinetics, spectrally resolved radiative heat transfer and multi-component transport. By use of a skeletal chemical kinetic mechanism (125 species, 713 reactions), the computed ignition delay period for methyl decanoate (C 11 H 22 O 2 ) showed excellent agreement with experimental results at furnace temperatures greater than 1200 K.

Flame propagation through non-uniformly premixed gases occurs in several common combustion situations. Compared with the more usual limiting cases of diffusion or uniformly premixed flames, the practical concern of non-uniform premixed gas flame spread has received scant attention, especially regarding the potential role of gravity. This research examines a system in which a fuel concentration gradient exists normal to the direction of flame propagation and parallel with the gravitational vector. This paper presents experimental and numerical results for flame spread through alcohol/air layers formed by diffusive evaporation of liquid fuel at temperatures between the flash-point temperature and the stoichiometric temperature. A gallery, which had either the top and/or one end open to maintain constant pressure, surrounded the test section. The numerical simulations and experiments conducted include normal and microgravity cases. An interferometer was used, in normal gravity only, to determine the initial fuel layer thickness and fuel concentration distribution before and during flame spread. Both the model and experimental results show that the absence of gravity results in a faster spreading flame, by as much as 80% depending on conditions. This is the opposite effect to that predicted by an independent model reported earlier in this symposium series. Determination of the flame height showed that the flame was taller in microgravity, an effect also seen in the results of the numerical model reported here. Having a gallery lid results in faster flame spread, an effect more pronounced at normal gravity, demonstrating the importance of enclosure geometry. The interferometry and numerical model both indicated a redistribution of fuel vapor ahead of the flame. Numerical simulations show that, despite the rapid flame spread in these systems, the presence of gravity strongly affects the overall flow field in the gallery.

Previous attempts to model natural gas/diesel reactivity controlled compression ignition (RCCI) engines using single fuel component chemical kinetics have demonstrated difficulties with reproducing the gradual increase in combustion rate observed experimentally. This study investigates whether employing a multi-component vaporisation and chemical kinetics model for diesel fuel can yield closer agreement with experimental combustion rates. Multi-dimensional CFD simulations are compared against an injection timing sweep from a GM 1.9 L diesel engine modified with port injected natural gas. Using the multi-component model for both diesel vaporisation and diesel chemical kinetics resulted in a closer match with experimental heat release rate than using single component diesel chemical kinetics. However, the overly fast combustion rates at ignition could not be completely eliminated. In addition, a parameter study revealed that the simulation results are strongly sensitive to the ratio of components in the diesel fuel surrogate, the injected mass, and the injection velocity.

Transient, spherically symmetric, combustion of single and multi-component liquid n-alkane droplets is numerically simulated with a model that includes gas phase detailed, multi-component molecular transport and complex chemical kinetics. A compact semi-detailed kinetic mechanism for n-heptane and n-hexadecane oxidation consisting of 51 species (including He, Ar, and N2) and 282 reactions is used to describe the gas phase. Non-luminous, gas phase radiative heat transfer and conservation of energy and species within the liquid droplet interior are also considered. Computed quasi-steady flame structure for pure n-heptane droplets is compared with that produced using the kinetic mechanism of Warnatz (frequently used in the past for modeling both premixed and diffusion flame properties). Transient calculations are also compared with the numerical results of King, which consider infinite rate chemical kinetics, but temperature dependent molecular diffusion. Modeling results are in reasonable agreement with small-diameter, drop tower experiments, though slow convective effects and droplet sooting effects exist in the experimental data. Comparisons with isolated large-diameter free droplet data (1 atm, He/O2 mixtures and air) from recent space experiments are reasonable for droplet gasification rate, flame position, and flame extinction. Very small extinction diameters are predicted for small initial diameter droplets (

Results are presented from experiments on the combustion of freely floated n-heptane droplets in helium-oxygen environments conducted in Spacelab onboard the Space Shuttle Columbia during the first launch (STS-83) of the Microgravity Science Laboratory mission in April 1997. During this shortened flight, a total of eight droplets were burned successfully in nominally 300 K oxygen-helium atmospheres having oxygen mole fractions of 25, 30, and 35% at a total pressure of 1 atm. Initial droplet sizes ranged from about 2 to 4 mm. The results demonstrated both radiative and diffusive flame extinction during burning, whereas droplet surface regression followed the d-square law. The full range of possible droplet-burning behaviors was thus observed. The results provide information for testing future theoretical and computational predictions of burning rates, soot and flame characteristics, and extinction conditions.

The results from methanol/water droplet combustion experiments conducted on two separate spacebased investigations are analyzed and compared against the predictions of a detailed numerical model. These two investigations (Fiber Supported Droplet Combustion Investigations 1 and 2) were conducted aboard Space Shuttle Columbia missions STS-73 and STS-94 in November 1995 and July 1997, respectively. In these experiments, pure methanol droplets and methanol/water droplets of 2–7 mm were suspended on a silicon carbide fiber and ignited with a hot wire. In some cases, droplets burned for over 40 s, and flame extinction was observed at small but finite droplet diameters. In other cases, droplets ignited but the flames rapidly extinguished. Each of the experiments is compared against the results of a detailed numerical model that simulates the time-dependent, spherically symmetric combustion of a multicomponent liquid droplet in an infinite oxidizing environemnt. The model includes detailed chemistry, multicomponent molecular diffusion and radiative heat transfer. The model quantitatively reproduces (without modifications or adjustments) measured burning rate, flame position, and extinction diameter for a wide range of initial diameters and initial water content. The results show that the effect of radiative heat loss is significant in experiments with initial diameters greater than 3 mm. Specifically, decreased burning rate and a nonlinear increase in extinction diameter are observed with increasing initial diameter. Moreover, a critical radiative extinction diameter of 6 mm, predicted in a previous study for methanol droplet combustion in 1-atm air, is verified experimentally.

The effect or radiative heat loss from isolated droplet flames is usually assumed to be negligible. For the small droplet sizes studied in most isolated droplet combustion experiments conducted to dale (< 1.0 mm), this assumption has been shown to be reasonable. For example, by neglecting radiation, a detailed numerical model accurately predicts the burning rate, flame position and extinction diameter for 1 millimeter-sized methanol/waler droplets. However, recent space-based 3 to 5 millimeter methanol/water droplet combustion data show an increase in extinction diameter and a decrease in burning rate with increasing initial diameter. These results suggest that, at larger initial droplet diameters, the effect of radiative heat loss cannot be neglected. By including a radiation sub-model, the modified numerical model predicts that at droplet diameters greater than about 1 mm the effect of radiation results in a decrease in burning rate and a non-linear increase in extinction diameter with increasing initia...

A new semi-empirical mechanism for n-heptane oxidation and pyrolysis has been developed and validated against several independent data sets, including new flow reactor experiments. Previous semi-empirical chemical kinetic mechanisms assumed that a generic n-alkyl radical, formed by abstraction of an H-atom from the parent fuel, thermally decomposes into a fixed ratio of methyl and propene. While such an approach has been reasonably successful in predicting premixed, laminar flame speeds, the mechanism lacks sufficient detail to quantitatively capture transient phenomena and intermediate species distributions. The new chemical kinetic mechanism retains significantly more detail, yet is sufficiently compact to be used in combined fluid-mechanical/chemical kinetic computational studies. The mechanistic approach is sufficiently general to be extended to a wide variety of large linear and branched alkane fuels.

The time-dependent combustion of isolated, bicomponent liquid droplets of methanol and water is simulated using a spherosymmetric, finite-element, chemically reacting flow model. The computations consider multi-component molecular transport and detailed chemical kinetics (19 species, 89 forward reactions) in the gas phase; semiempirically formulated vapor-liquid equilibrium with water vaporization/condensation at the liquid surface; and liquid species mass transfer and energy conservation in the liquid phase. The results are compared with previously reported data from microgravity drop tower, freely falling isolated droplet, and suspended droplet combustion experiments, all of which show significant departure from d2-law burning behavior and/or substantial water accumulation in the liquid phase. The liquid mass Peclet number (defined as the ratio of the droplet surface regression velocity to the effective diffusion velocity of water within the liquid droplet) is greater than 20 for methanol burning in air. The numerical model predicts little or no water accumulation for such circumstances. However, numerical results are consistent with experiments when it is speculated that sufficient internal liquid phase motion is present to reduce the effective liquid mass Peclet number to the order of one. Such internal motion has been noted in droplet combustion experiments and most likely arises from droplet generation/deployment techniques and/or surface tension gradients. Calculations show that the droplet combustion characteristics of methanol/water mixtures of 0%–50% initial water content are extremely sensitive to the liquid mass transport effects and might be used to better determine the magnitude of liquid mass transport present in microgravity experiments.

To experimentally validate single and bicomponent droplet combustion models, microgravity methanol and methanol/water droplet combustion experiments were conducted in the 2.2-s drop tower facility at NASA Lewis Research Center. The experiments were then simulated using a transient, bicomponent droplet combustion model developed earlier. Tests were performed in oxidizing environments of 18%–35% O2/N2 with initial liquid water contents of 0–20%. Instantaneous droplet diameter measurements were made using back-lit, high-speed photography. The instantaneous flame position was determined by monitoring the chemiluminescence from electronically excited hydroxyl radicals (OH*). Analysis of the flame and droplet diameter data yielded burning rates and flame standoff ratios for a wide array of methanol and methanol/water droplet combustion conditions. For initially pure methanol droplets, the available burn time (≈1.5 s) was not, in general, sufficient to observe extinction or significant nonlinearity in the regression of diameter squared with respect to time. For each oxygen content, the numerical model predicted the burning rate to within 10% and the flame position to within one normalized diameter without any independent parameter adjustment. In the case of 10% and 20% initial water content, substantial nonlinearity in diameter squared was observed. The numerical model, which accurately accounts for changes in liquid transport properties caused by variable liquid water content, did not predict the nonlinearity to the extent that it was observed. A possible explanation is that with the addition of initial water content to the droplet, the internal mass and thermal transport is enhanced as a result of increased internal mixing. The sources of this internal mixing are likely multifold but are not due to relative gas/liquid convection effects at the droplet surface.

A procedure is outlined that uses hydroxyl (OH) radical chemiluminescence measurements along with detailed numerical modeling to determine flame position and gain further insight into the structure of microgravity droplet flames. To validate this procedure, microgravity n -heptane and methanol droplet combustion experiments were conducted using the 2.2-second drop tower and the ero Gravity Facility at NASA Lewis Research Center. The spontaneous emission from electronically excited hydroxyl radicals (OH o ) within the envelope diffusion flame was measured with a UV-sensitive video camera. The OH o emission data was deconvoluted using an inverse Abel transform to determine the time evolution of the location of peak intensity within the flame. Chemical reactions describing the production, emission, and quenching of OH o were incorporated into a transient, spherically symmetric droplet combustion model. The modeling and experimental results indicate differences in the route of OH o production between n -heptane and methanol flames. For n -heptane, the production of OH o emission-intensity profiles which agree well with experiment (both in terms of shape and location of maximum intensity) and are shifted from the position of maximum ground-state OH concentration. For methanol flames, which produce very little CH, the OH o appears to be the result of thermal excitation within the flame rather than from a specific chemiluminescent reaction. In both cases, the location of maximum OH o emission intensity is very near the location of maximum flame temperature, suggesting that OH o imaging is a good approach for measurement of the flame position.

Recent developments in numerical techniques and computational processing power now permit time-dependent, multi-dimensional computational fluid dynamic (CFD) calculations with reduced chemical kinetic mechanisms (approx. 20 species and 100 reactions). Such computations have the potential to be highly effective tools for designing lean-burn, high BMEP natural gas engines that achieve high fuel efficiency and low emissions. Specifically, these CFD simulations can provide the analytical tools required to design highly optimized natural gas engine components such as pistons, intake ports, precombustion chambers, fuel systems and ignition systems. To accurately model the transient, multi-dimensional chemically reacting flows present in these systems, chemical kinetic mechanisms are needed that accurately reproduce measured combustion data at high pressures and lean conditions, but are of sufficient size to enable reasonable computational times. Presently these CFD models cannot be used as accurate design tools for application in high BMEP lean-burn gas engines because existing detailed and reduced mechanisms fail to accurately reproduce experimental flame speed and ignition delay data for natural gas at high pressure (40 atm and higher) and lean (0.6 equivalence ratio (ϕ) and lower) conditions. Existing methane oxidation mechanisms have typically been validated with experimental conditions at atmospheric and intermediate pressures (1 to 20 atm) and relatively rich stoichiometry. These kinetic mechanisms are not adequate for CFD simulation of natural gas combustion in which elevated pressures and very lean conditions are typical. This paper provides an analysis, based on experimental data, of the laminar flame speed computed from numerous, detailed chemical kinetic mechanisms for methane combustion at pressures and equivalence ratios necessary for accurate high BMEP, lean-burn natural gas engine modeling. A reduced mechanism that was shown previously to best match data at moderately lean and high pressure conditions was updated for the conditions of interest by performing sensitivity analysis using CHEMKIN. The reaction rate constants from the most sensitive reactions were appropriately adjusted in order to obtain a better agreement at high pressure lean conditions. An evaluation of this adjusted mechanism, “MD19”, was performed using Converge CFD software. The results were compared to engine data and a remarkable improvement on combustion performance prediction was obtained with the MD19 mechanism.Copyright © 2012 by ASME

Scaling behavior of burning rate constant with initial droplet diameter is investigated for a single component, sooting fuel under going spherically symmetric combustion in microgravity. Three different regions were identified: the D2-law region where the burning rate constant is independent of initial droplet size, the sooting region, and the non-luminous radiative loss region. In the last two regions the burning rate constant is shown to decrease as D0 -1/4 where D0 is the initial droplet size. This decrease is primarily due to temperature dependent property variation. An estimate for the critical diameter that divides the first two regions is developed using a semi-empirical formulation for sooting.

International audience; A detailed chemical kinetic model has been used to study methyl butanoate (a model compound for biodiesel fuels) oxidation over a wide range of conditions. New experimental results obtained in a jet stirred reactor (JSR) at 0.101 MPa, Φ = 1.13 and 800 < T (K) < 1350 were obtained and used to test and modify an earlier model. In addition, new experimental data generated in an opposed-flow diffusion flame at 0.101 MPa and in the Princeton variable pressure flow reactor (VPFR) at 1.266 MPa, 0.35 < Φ < 1.5 and 500 < T (K) < 900 are presented and compared against the revised model. The numerical model consists of 295 chemical species and 1498 chemical reactions and gives a good description of the data. Experimentally, the oxidation of methyl butanoate shows very little low temperature and negative temperature coefficient behaviour, with hot ignition occurring at about 800 K. Modeling results show similar diminished low temperature oxidation character, but reasonably reproduce hot ignition behaviour found in the VPFR. At higher temperature conditions, the model well describes the intermediate species found in the jet stirred reactor and in opposed flow diffusion flame experiments.