Search

Remote or off-grid communities in Canada and across the world heavily rely on diesel-fueled generators to meet their electrical power and heating needs. Reducing diesel consumption of these generators with locally produced sustainable fuels such as syngas has the double benefit of reducing the greenhouse gas (GHG) emissions and the cost of transporting diesel to remote locations. In remote/off-grid areas, syngas can be produced from local biomass or waste through gasification or pyrolysis. The aim of this study was to investigate the combustion and emission performance of a syngas-diesel dual-fuel generator at a constant load condition under varying syngas flow rate and composition. This experimental study was carried out using a 30-kilowatt (kW) generator with a four-stroke, four-cylinder, turbo-charged, and electronically controlled direct injection diesel engine. The intake manifold of the engine was modified to introduce syngas upstream of the engine’s turbocharger. Syngas was simulated using individually controlled flow rates of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2) and nitrogen (N2) from compressed gas cylinders before their mixing and introduction into the engine intake manifold. Two practical syngas compositions with varying CO/H2 ratios were evaluated. The engine was operated with a programmable engine control unit to control the diesel direct injection events. Electrical load on the generator was controlled by a load bank set to 11 kW (5.25 bar IMEP) and the engine speed was 1800 rpm. The experimental results revealed that increasing the syngas flow rate at a fixed diesel injection timing and duration caused the indicated thermal efficiency (ITE) of the engine to decrease. NOx emissions decreased with increasing syngas flow rate but CO, particulate matter (PM) and CO2 emissions increased. Increasing the CO/H2 ratio in the syngas caused the ITE to decrease and the CO and CO2 emissions to increase. The laminar flame speed (LFS) and ignition delay (ID) of syngas-air mixture were calculated to develop a further insight into the experimental results.

A zero-mean flow fan-stirred chamber is used to gather data on suspended fuel droplet evaporation at turbulence intensities, q1/2, approaching 4.30 m/s. This research is driven by the oft-cited but unconfirmed belief that the droplet evaporation rate, K, eventually plateaus with increasing turbulence kinetic energy. Further motivation comes from numerous real-world examples, including combustion systems, where droplets are exposed to turbulence intensities far beyond the experimental capabilities reported in the literature to date. Decane, ethanol, and heptane fuels are selected and grouped into two categories based on the similarity of their vapor pressures, Pv, and mass diffusivity coefficients, DAB, in an effort to discern which thermophysical properties are important to vaporization enhancement, or lack thereof, in high turbulence. Individual droplets with constant initial diameters, d0, of 500 µm are placed in the central region of a highly homogeneous and isotropic turbulent flow field using a novel multi-fiber intersection technique. Neither alkane fuel exhibits any sign of reduced effect of turbulence, as K/K0 remains a strongly linear function of turbulence intensity throughout the test conditions. Conversely, the normalized evaporation rate of ethanol begins to plateau at the higher levels of intensity. Although equalizing the vapor pressures of ethanol and heptane was sufficient to match K/K0 values at low intensity, their divergence as q1/2 increases implies that the thermodynamically-predicted vapor quantity at the droplet surface does not enforce an upper limit on turbulence effectiveness at moderately elevated temperatures. This is confirmed by decane, which has the lowest volatility and yet experiences the greatest improvement in evaporation rate at the highest levels of turbulence.

This paper presents a step-forward extension of the well-known chemistry/flow interaction Eddy Dissipation Concept approach for modelling both, non-premixed and premixed, combustion regimes in a Re...

For decades, experimental investigations of turbulent droplet evaporation have generally followed one of two distinct paths: wind tunnel experiments, which generate significant mean flow but low turbulence intensity, and stirred chamber configurations, which yield the opposite characteristics. The present study bridges the gap between these two established techniques by modifying a fan-stirred spherical chamber to incorporate a controllable mean flow while retaining the attributes of highly-energetic homogeneous and isotropic turbulence. Heptane droplets with a fixed initial diameter, d0, of 500 ± 10 µm are suspended on the intersection of two microfibers and evaporated in pockets of high-intensity turbulence (27%

The effects of different baffled configurations of acoustic dampers placed downstream of the dump plane of a combustor on the mean flowfield, coherent structures, acoustics, stability and dynamics of partially premixed methane flames were experimentally investigated. Particle image velocimetry (PIV) was used to capture the instantaneous flowfield downstream of the dump plane or the baffles and proper orthogonal decomposition (POD) was used to analyze coherent structures. High-speed imaging was used to capture flame dynamics, and a Bruel and Kjaer microphone was used to perform acoustics measurements. Two interchangeable baffle configurations were tested; one consists of eight-blade radial baffles attached to a circumferential baffle and placed underneath of a circumferentially-slotted cup (AD#1), and another consists of eight-blade radial baffles attached to a circumferential baffle (AD#2). The results revealed significant improvement in flame stability when using baffles. This is attributed to several factors. First, the burner baffled configurations caused a significant reduction in the amplitude of coherent structures and acoustics. Second, the presence of baffles promoted either a very narrow CRZ (in case of AD#2) or no ORZ with a weak CRZ (in case of AD#1). This positive axial velocity convected vortical structures farther downstream of AD#1. Third, both flame–flame interaction in AD#1 configuration (resulting from the axial flow off the circumferential slots and that from the swirling flow in the core flow region) and flame-baffles interaction in AD#2 configuration (resulting from the interplay between baffles’ tips and the swirling flame in the core region) helped reducing the azimuthal mean velocity and its rms component in the flow core region. This consequently resulted in a significant change in the azimuthal acoustic waves’ behavior within the combustor/confinement. The results revealed that the baffled burner configurations enhanced mixing as witnessed by the more flame bluish color and consequently its stability.

The effect of mixing tube length (partial premixing level) on the amplitude of coherent structures and acoustics, and stability of partially premixed flames (PPFs) of methane off a concentric flow ...

This paper presents an assessment study of a modification introduced to a recently developed extended version of Eddy Dissipation Concept (EDC) chemistry/flow interaction approach for modeling Mode...

The effect of the mixing tube length and fuel nozzle geometry on coherent structures and acoustics’ characteristics of partially premixed swirling methane flame is experimentally studied. Particle image velocimetry (PIV) is used to document the flowfield inside the transparent confinement tube. Proper orthogonal decomposition along with phase averaging are used to capture coherent structures. High-speed imaging is carried out to shed light on the flame front dynamics within the outer shear layer (OSL). The acoustic waves are measured using a Bruel & Kjaer type 4189 microphone. A radial-type swirl generator with a swirl number (S) of 1.15 is adopted. Two different lengths of the mixing tube and two different geometries of the fuel nozzle with a similar equivalent diameter are tested. The swirling airflow and fuel flowrates are kept constant. The results showed a significant difference in the energy of coherent structures between the two central nozzle geometries with the same mixing length. Both, the mixing length and central nozzle geometry, are found to alter the integral length scale and the central recirculation zone (CRZ). The mixing length is found to alter the amplitude of the acoustics modes when using the same central nozzle geometry. However, keeping the same mixing tube and varying the central nozzle geometry has the same effect. The flame front dynamics within the outer recirculation zone (ORZ) is found to depend on both the central nozzle geometry and mixing tube length (i.e., level of mixing). High amplitude coherent structures are found to contribute to flame roll-up within the outer shear layer. The results showed that the mixing length is not the only parameter to mitigate combustion instabilities. That is, combustion stability can be improved using a single-orifice nozzle with a long mixing length or a multi-orifice nozzle with a short mixing length.

This paper proposes a new combustion model for the simulation of biomass combustion. It is developed based on the framework of the well-known Eddy Dissipation Concept (EDC) approach, which has the ...

The design of a new solid particle seeding generator for laser-based velocity measurements in gaseous flows is reported. Performance tests revealed that the new seeder has the ability to control the concentration of seeding particles in a flow independently of the flowrate. It also can provide a steady supply of seeding particles, operate over an extended range of flowrate, and break up agglomerates into smaller particles. These features give this seeder advantages over its counterparts, especially at low volumetric flowrate.

Natural gas–diesel dual fuel (NDDF) engine has the potential to significantly reduce carbon dioxide (CO2) and particulate matter (PM) emissions while retaining the diesel engine’s high efficiency and reliability. The operation and performance of the NDDF engine depend on natural gas energy fraction (%NG), which ranges from low %NG, where diesel fuel provides most of the combustion energy, to high %NG, where diesel fuel is used only to initiate combustion. Although pertaining published studies demonstrated that the effect of %NG on the combustion performance and emissions of the NDDF engine depend upon the engine load, none of these studies discussed the reasons behind this dependence. The present study attempts to shed light on this issue by experimentally and numerically investigating the effect of different %NGs on the NDDF engine under different load conditions. Both experimental and numerical results revealed that the peak pressure rise rate (PPRR) first increases and then drops with increasing %NG under all load conditions. The calculated local equivalence ratio and charge temperature contours showed that increasing %NG to a certain limit increases local equivalence ratio inside the ignition kernel, which implies that more premixed natural gas–air mixture participates in reactions during the premixed combustion stage. This results in an increased flame temperature and higher PPRR right after ignition. However, increasing %NG beyond this range decreases local equivalence ratio inside the ignition kernel, which leads to lower PPRR. Increasing %NG retards the combustion phasing at low-to-medium load conditions. However, increasing %NG generally advances the combustion phasing under medium-to-high load conditions due to the fact that the flame propagation speed of natural gas–air mixture increases with %NG at medium-to-high load conditions. Methane emissions grow with increasing %NG under all examined engine load conditions. However, this growth becomes much smaller under medium-to-high engine load conditions. Increasing %NG significantly increases greenhouse gas (GHG) emissions under lower load conditions. However, using advanced diesel injection timing decreases GHG emissions of the NDDF engine under lower load conditions. Increasing %NG decreases GHG emissions by 6%–11% under medium-to-high load conditions.

Two perforated plates with different solidity ratios, S=50% and 67%, were used to investigate the effect of the velocity fluctuations of a subsonic gaseous crossflow on the spray characteristics of a liquid jet including droplet size and velocity distributions. The experiments were conducted over a range of jet-to-crossflow momentum flux ratio of q=16.5-172, and two gas Weber numbers of Weg=2.7 and 5.9, corresponding to the enhanced capillary breakup and bag breakup regimes, respectively. The experimental results of this study revealed that the distribution of droplets size associated with a turbulent and a uniform crossflow for each specific breakup regime were approximately identical. The bimodal and single peak distributions of droplets size, respectively, associated with enhanced capillary and bag breakup regimes were generally consistent with the literature reports. However, the transition of the liquid primary breakup regime from enhanced capillary to bag breakup mode was delayed in a turbulent crossflow compared to its uniform counterpart. The general behavior of droplets size-velocity profiles were also consistent with the literature reports. Nonetheless, complex variations in the distribution of droplets velocity when changing the crossflow turbulence intensity were observed and linked with the presence of instabilities on the liquid jet's surface. Finally, the present experiments allowed shedding more light on the reason why the breakup mechanisms of a liquid jet in a conventional uniform crossflow should not be generalized to predict the distinct breakup process of a liquid jet in a turbulent crossflow.

Past research has shown that advancing diesel injection timing is a promising approach to decrease the unburned methane and greenhouse gas (GHG) emissions of natural gas/diesel dual-fuel engines at lower engine loads. However, this benefit may not persist under medium to high load-low speed conditions. To explore this, the present paper uses experiments and detailed computational fluid dynamic (CFD) modeling to investigate the impacts of diesel injection timing on the combustion and emissions performance of a heavy-duty natural gas/diesel dual-fuel engine under four different engine load-speed conditions. The results showed that advancing diesel injection timing increases the peak pressure, thermal efficiency, and NOx emissions for all examined engine load-speed conditions. Advancing diesel injection timing also significantly decreases the unburned methane and CO2-equivalent (GHG) emissions of the dual-fuel engine under low load-low speed and medium load-high speed conditions. The concentration of OH and CH4 revealed that the central part of the combustion chamber is the main source of the unburned methane emissions under low load-low speed and medium load-high speed conditions, and advancing diesel injection timing significantly improves the combustion of natural gas-air mixture in this region. However, advancing diesel injection timing slightly increases the unburned methane emissions trapped in the crevice volume. However, this slight increase in the unburned methane emissions in the crevice volume is much lower than its significant decrease in the central region of the combustion chamber. At medium to high load-low speed conditions, there is almost no unburned methane in the central part of the combustion chamber, and the crevice region is considered as the main source of unburned methane emissions. As a result, advancing diesel injection timing does not improve the combustion of natural gas-air mixture in the central part of the combustion chamber but slightly increases the unburned methane trapped in the crevice region. This is the main reason that advancing diesel injection timing slightly increases the unburned methane emissions under medium to high load-low speed conditions. Overall, advancing diesel injection timing significantly increases thermal efficiency and decreases the unburned methane and GHG emissions under low load-low speed and medium load-high speed conditions. It improves the thermal efficiency under medium to high load-low speed conditions, but comes at the expense of increased methane and unchanged GHG emissions.

The effect of fuel nozzle geometry and swirling airflow on the flashback and its relationship with the coherent structures of partially premixed methane flame is investigated experimentally. Particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) are used to document flow characteristics, and Schlieren imaging technique is used to study flame appearance and vortex shedding frequency downstream of the burner exit. Proper orthogonal decomposition (POD) technique is applied to capture the coherent structures, along with phase averaging of the linear superposition of the first four POD modes. Seven different fuel nozzle geometries and two swirl number (S = 0.79 and 1.15) are tested. The nozzles are categorized into three groups, with each has similar equivalent diameter; namely, a symmetric nozzle (used as a reference), nozzles with polygonal orifices (group A), and angled multi-orifice nozzles (group B). The results of the flow field inside the mixing tube show that the strength of coherent structures and flashback propensity increase with the swirling airflow Reynolds number, swirl number, nozzle bluff body area, and the number of the peripheral angled orifices of the fuel (central) nozzle. On the other hand, the results of flame appearance outside of the mixing tube indicate that methane flame experiences symmetric vortex shedding at high swirl number and low Reynolds number, while it experiences PVC near blowout conditions at low swirl number and high Reynolds number. Furthermore, the frequency of coherent structures is found to depend on the swirling airflow Reynolds number, swirl number, and fuel nozzle geometry. Additionally, the flashback’s mean region inside the mixing tube is found directly proportional to the strength and frequency of the coherent structures.

Recent regulation on pollutant and greenhouse gas (GHG) emissions has exerted great pressure on diesel engine industries which generate significant amount of GHG and pollutants. The concept of lean burn pilot ignited natural gas/diesel dual-fuel (NDDF) combustion is considered as one of the most suitable engine platforms to meet emissions and fuel economy regulations over a short to medium term. However, a major challenge is the slightly lower fuel efficiency and high level of methane (CH4) and carbon monoxide (CO) emissions, especially under low to medium engine load conditions. This paper numerically investigates the influence of swirl ratio on the combustion performance and emissions of a NDDF engine under low to high load conditions. The results at low load-low speed condition and retarded injection timing of 14 crank angle degrees before top dead center (BTDC) suggest that increasing swirl ratio from 0.5 to 1.5 significantly improves fuel efficiency and CH4 and CO emissions. However, under the same engine load-speed condition but at advanced injection timing of 30 crank angle degrees BTDC, increasing swirl ratio deteriorates the fuel efficiency and CH4 and CO emissions. Under a medium load-high speed condition, swirl ratio significantly improves diffusion combustion and turbulent flame propagation of natural gas. The results show that OH radical propagates more rapidly in the azimuthal direction when increasing the swirl ratio from 0.5 to 1.5. Further increase in the swirl ratio causes the peak pressure to exceed the limit (160 bar). At high load-low speed condition, increasing the swirl ratio significantly improves diesel diffusion and flame propagation of natural gas, which consequently enhances fuel efficiency. Under this engine load-speed condition, OH radical distribution shows that the combustion progresses rapidly within each jet in both the azimuthal and radial directions. Considering fuel efficiency and emissions, a swirl ratio of 1.5 is found to be the optimum. Overall, it is concluded that swirl motion may provide better mixture preparation, diesel diffusion, and natural gas flame propagation. However, this benefit may not persist under very high swirl ratio (swirl ratio > 1.5) due to higher heat losses.

The ability of the standard Eddy Dissipation Concept (EDC) approach to account for the chemical kinetic rates during the interaction between chemistry and turbulent flow field made it a suitable scheme for simulating gas-phase combustion. However, its application poses a challenge for modeling weakly turbulent reacting flow conditions, as well as reacting flows with comparable flow and chemical time scales. A modified version of EDC (referred to here as extended EDC) has recently been developed for predominantly non-premixed turbulent flames. This led to significant improvement in the predictions of species and temperature fields of biomass-derived gas jet flames over a wide range of turbulence conditions (from weakly to highly turbulent flow conditions). The present study examines the application of this extended EDC approach for the simulation of a small-scale updraft biomass combustor. The predictions of the model are compared with those of the standard EDC and their counterparts’ experimental temperature and species concentrations. In addition, the pathway of formation/destruction of gas-fuel species and pollutants (e.g., NOx) is investigated. The findings of the present study reveal a significant improvement in the predictions of temperature field and species of the gas-phase of grate-firing biomass combustion.

Small-scale grate-firing biomass combustors generate high level of pollutants as a result of poor air/fuel mixing and short residence time of combustion. Reliable gas-phase combustion modeling can play a key role in the improvement and optimization of the design of a biomass furnace. This paper proposes a new combustion model based on the framework of the well-known eddy dissipation concept (EDC) approach. The ability of EDC to incorporate detailed chemical reactions in turbulent reacting flows has made it attractive for modeling combustion. However, its application poses a challenge especially for modeling weakly turbulent reacting flow conditions, as well as reacting flows with comparable flow and chemical time scales. The newly proposed combustion scheme can reasonably describe the interaction of chemistry and turbulent flow over a wider range of turbulence conditions. To validate the model, simulations are carried out using diffusion and partially premixed jet flames covering weakly to highly turbulent flow conditions. Moreover, the capability of the new model in predicting NOx emissions, based on fuel bound nitrogen source as well as thermal NOx, is investigated. All numerical results are compared with their counterparts’ experimental measurements of temperature and species concentrations. Compared to the standard EDC, the results of the new EDC approach reveal noticeable improvement in the predictions, especially for slow-forming and kinetically dominated species such as CO and NOx.

This paper presents an extensive experimental study regarding the effect of turbulence and droplet size on the evaporation rate of suspended monocomponent alkane droplets at elevated temperature and pressure conditions of up to 100 °C and 10 bar, respectively. Individual droplets of n-heptane and n-decane were suspended at the intersection of two crossed micro-fibers in the center of a fan-stirred spherical vessel. The droplet size was varied in the range between 110 and 730 µm. Eight axial fans generated a controlled turbulent flow field with quasi-zero mean velocity and turbulence intensity up to 1.5 m/s. The results reveal a linear relationship between the initial droplet size and its turbulent steady-state evaporation rate, where larger droplets evaporate at a faster rate than their smaller counterparts at all elevated temperature and pressure conditions. The normalized turbulent evaporation rate increases with pressure, whereas elevated temperature produces the opposite effect. The ratio of the Kolmogorov length scale to initial droplet diameter is shown to be of paramount importance for interpreting the effect of turbulence, as the normalized evaporation rate increases dramatically at lower values of this ratio under all test conditions. However, the ability of turbulence to enhance the vaporization rate vanishes when this ratio approaches unity, suggesting that only droplets which are initially larger than the smallest turbulent eddies experience enhanced evaporation. In addition, the widespread belief that turbulence enhances less volatile fuels more than their high volatility counterparts also depends on the ambient pressure and initial droplet size. The ability of turbulence to generate small-scale structures and, subsequently, the interaction of these eddies with the available fuel concentration gradient at the surface of the droplet governs the relationship between fuel type, initial droplet size, and ambient temperature and pressure. A turbulent Reynolds number or a vaporization Damkohler number is used to correlate turbulent droplet evaporation rates at all explored test conditions.

The role of natural convection in droplet evaporation is experimentally investigated for a range of micro-sized alkane fuel droplets at moderately elevated pressure and temperature. This paper assesses the impact of buoyant mass transfer from two perspectives; the resulting variation in steady-state evaporation rate, and the potential relation to non-linear temporal d2 profiles. The steady-state evaporation rate is found to increase linearly with initial droplet diameter at all tested conditions, where the relative improvement in evaporation rate depends upon the fuel type, pressure, and temperature. In addition to modifying the steady-state evaporation rate, the various environmental conditions also impact the occurrence and timing of d2 deviation, which manifests as a strong reduction in evaporation rate near the end of a droplet’s lifetime. Pressure tends to encourage the appearance of d2 deviation for both heptane and decane by increasing the proportion of evaporation for which natural convection is responsible. The effect of temperature depends upon the droplet volatility, and the results differ between the two test fuels. Overall, the relative importance of natural convection, as compared to pure molecular diffusion, appears to govern both the expected improvement in, and potential deviation from, steady-state evaporation. Proposed Grashof correlations justify the above hypothesis.

Natural gas/diesel dual-fuel combustion is currently one of the most promising LTC strategies for the next generation of heavy-duty engines. While this concept is not new and it has been deliberated lengthily in the past two decades, several uncertainties still exist. A major shortcoming of this concept is associated with its low thermal efficiency and high level of unburned methane and CO emissions under low engine load conditions. The present paper reports an experimental and numerical study on the effect of different injection strategies (single and two pulses injection of pilot diesel fuel) on the combustion performance and emissions of a heavy duty natural gas/diesel dual-fuel engine at 25% engine load. The results of single diesel injection mode showed that advancing diesel injection timing from 10 to 30 °BTDC reduced unburned methane and CO emissions by 62% and 61% and increased thermal efficiency by 6%; however, NOx emissions increased by 74%. In order to achieve NOx – CH4 and NOx – CO trade-off and increased thermal efficiency at low load conditions, the effect of split injection strategy was experimentally and numerically examined. The results of split injection mode revealed that split injection strategy considerably increases the in-cylinder peak pressure compared to that of single injection (10 °BTDC). The results showed also that the heat release produced by the first injection of diesel fuel considerably increased the in-cylinder charge temperature before the start of the second injection. The flame zone of the split injection mode is markedly higher than that of the single injection due to larger heat release produced during the first injection which promotes the combustion of the second one. When the first injection timing is close to the second injection timing, the MPRR of split injection mode is higher than that of single injection (10 °BTDC). However, further advancing of the first injection timing continuously decreased the MPRR. OH radical analysis showed that for advanced first injection timings (38–50 °BTDC), the overall growth rate of OH radical becomes slower and its distribution is narrower as indicated by the wider non-reactive blue zones compared with those observed at a late first injection timing in the initial stages of combustion. However, OH radicals gradually grow during last stages of combustion in the expansion stroke, indicating that a more premixed combustion takes place in these cases. For very advanced first injection timing of 55 °BTDC, the OH distribution is similar to that of the single injection mode with lower OH intensity at initial stages of combustion and they barely grow during the late expansion stroke. At this condition, the ignition of premixed mixture is mainly controlled by the second diesel fuel injection. The trade-off between NOx – CH4 and NOx – CO is achieved when applying split injection. Compared to single injection (10 °BTDC), the first injection timing of 50 °BTDC decreased unburned methane and CO emissions by 60% and 63%, respectively, and increased the thermal efficiency by 8.9%. However, NOx emissions were maintained at the same level as single injection mode (10 °BTDC).

The combination of diesel and natural gas fuels has superior performance in terms of nitrogen oxides (NOx) and particulate matter (PM) emissions when compared to conventional diesel engine. However, this advantage does not hold at low load operating conditions as indicated thermal efficiency (ITE), carbon monoxides (CO), and unburned hydrocarbon (HC) emissions deteriorate. Most published studies tried to resolve this drawback using diesel split injection. However, the present study evaluates natural gas split injection strategy as an alternative to improve the performance and emissions of diesel/natural gas dual-fuel engines at low load conditions. The results show that natural gas split injection with proportional split injection ratio (ISR) and small dwelling timing improves NOx, CO, and HC emissions. Moreover, split injection of natural gas with proportional ISR after intake valve closing (IVC) is found to improve SFC, ITE, and power. Conversely, natural gas split injection strategy with proportional ISR after intake valve opening (IVO) yields poor engine performance. Overall, split injection of natural gas with low ISR yields the greatest engine performance at long dwelling time, whereas it worsens emissions compared to single injection of natural gas at 560°CA ATDC, which serves as the baseline condition. However, very low CO and HC emissions of natural gas split injection is achieved at low ISR and short dwelling time. Finally, this study reveals also that stratification of air/natural gas mixture due to natural gas split injection strategy can significantly improve the performance and emissions of dual-fuel diesel/natural gas engine at low load conditions.

The stability of turbulent non-premixed biogas flame was studied experimentally by varying the fuel composition (i.e., changing the carbon dioxide content in the fuel, which is mainly composed of CH 4 and CO 2 ) and altering the fuel nozzle geometry. The fuel was discharged through a central nozzle surrounded by a co-axial airflow passing through a low-swirl (25°-angle vanes) generator. The results revealed that the biogas flame stability limits are highly sensitive to fuel composition in that a small increase in carbon dioxide content can lead to a significant shrinkage in the flame stability operating conditions. On the other hand, the results showed that the fuel jet momentum (fuel nozzle geometry) plays a key role in reducing the dependency of the stability of swirling non-premixed flame on fuel composition. The experimental data with varying both the fuel composition and fuel nozzle geometry was used to develop semi-empirical non-dimensional correlations capable of describing both the lower and upper flame stability limits of both biogas and methane fuel. The validity of these correlations was extended to include both non-premixed and premixed swirling flames.

Natural gas/diesel dual-fuel combustion compression ignition engine has the potential to reduce NOx and soot emissions. However, this combustion mode still suffers from low thermal efficiency and high level of unburned methane and CO emissions at low load conditions. The present paper reports the results of an experimental and numerical study on the effect of diesel injection timings (ranging from 10 to 50 °BTDC) on the combustion performance and emissions of a heavy duty natural gas/diesel dual-fuel engine at 25% engine load. Both experimental and numerical results revealed that advancing the injection timing up to 30 °BTDC increases the maximum in-cylinder pressure. However, with further advancing the injection timing up to 50 °BTDC, the maximum in-cylinder pressure decreases which is mainly due to the lower in-cylinder temperature before SOC. Moreover, the analysis of OH spatial distribution shows that, at very advanced diesel injection timings, the non-reactive zones are much narrower than later injection timings during the last stages of combustion, indicating a more predominant premixed combustion mode. At retarded diesel injection timings, the consumption of premixed fuel in the outer part of the charge is likely to be a significant challenge for dual-fuel combustion engine at low engine load conditions. However, with advancing the diesel injection timing, the OH radical becomes more uniform throughout the combustion chamber, which confirms that high temperature combustion reactions can occur in the central part of the charge. Diesel injection timing of 30 °BTDC appears to be the conversion point of all conventional dual-fuel combustion modes. Further advancing diesel injection timing beyond this point (30 °BTDC) results in noticeable reduction in NOx and unburned methane emissions, while CO emissions exhibit only slight drop. However, at very advanced diesel injection timings of 46 and 50 °BTDC, NOx and unburned methane emissions continue to drop, whereas CO emissions tend to increase. The results showed also that the highest indicated thermal efficiency is achieved at these very advanced diesel injection timings of 46 and 50 °BTDC. Finally, the results revealed that, by advancing diesel injection timing from 10 °BTDC to 50 °BTDC, NOx, unburned methane, and CO emissions are reduced, respectively, by 65.8%, 83%, and 60% while thermal efficiency is increased by 7.5%.

This paper presents the results of an experimental investigation of the effect of droplet size on the fuel vaporization process in a turbulent atmosphere at standard ambient conditions. Single droplets of n-heptane and n-decane are formed and evaporated at the intersection point of two micro-fibers placed in the center of a fan-stirred spherical vessel which is maintained at room temperature and pressure. The droplet initial diameter varies in the range between 145 and 730 µm. A controlled isotropic and homogeneous turbulent flow field with nearly zero mean velocity and intensity ranging between 0.25 and 1.5 m/s is generated inside the vessel by means of eight axial fans. The results indicate that the droplet normalized squared diameter varies quasi-linearly with time, suggesting the applicability of the d 2 law at all examined conditions. More importantly, the results reveal that the droplet initial diameter becomes a significant contributing factor in determining the evaporation rate in a turbulent environment, as the rate of vaporization is found to increase with both turbulent intensity and droplet size. However, droplet size produces no effect on the vaporization rate in quiescent (no flow) surroundings. The results also emphasize that as the ratio of the Kolmogorov length scale over droplet initial diameter approaches unity, the effect of turbulence becomes negligible, illustrating the importance of the small-scale eddies, and their relation to droplet size, in the transport/transfer of mass. The coupled effect of droplet size and turbulence on the vaporization rate is correlated in terms of either a turbulent Reynolds number or a vaporization Damkohler number.

This paper presents a computational study to evaluate the influence of turbulence and combustion models as well as chemistry schemes on the combustion of a 8–11 kW small lab-scale biomass furnace. The analysis is conducted in the zone above the bed (freeboard) where the volatiles are burned. The turbulence models tested are standard k - e , RNG k - e and Realizable k - e ; and the combustion models are SFM (Steady Flamelet Model), UFM (Unsteady Flamelet Model) and EDC (Eddy Dissipation Concept). In addition, several chemical mechanisms with different complexity (reduced and detailed chemical kinetics) are considered. The predictions of the velocity, species, and temperature fields are compared with their counterparts’ experimental measurements. The present findings reveal that all tested combustion models (SFM, UFM and EDC) are capable of predicting temperature and major species profiles; whereas only EDC is able to reliably predict slow-chemistry species.

This study examines the effect of fully developed turbulent flow at the exit of nozzle/injector on the trajectory and column breakup location of a liquid jet injected transverly into a gaseous crossflow. Liquid jet trajectory and column breakup for different nozzle geometries at different velocities of liquid jet and crossflow are analytically and experimentally Investigated. Shadowgraph imaging technique is used to determine the jet trajectory and breakup location of a transverse liquid jet in a uniform airflow. Particle image velocimetry (PIV) is used to measure the near-field velocity profile of a liquid jet discgarged into a quiescent atmosphere. The experimental results show a higher penetration and breakup height for the liquid jet ensuing from a nozzle with a smaller length to diameter ratio. This is due to the surface irregularities of the liquid column of a turbulent jet, which breaks up and consequently follows the cross airflow sooner. In order to capture the effect of turbulence, the analytical trajectory correlation developed in our previous studies is modified to account for the discharge coefficient of a nozzle. The discharge coefficient is estimated indirectly by comparing the liquid column trajectory predicted by the modified analytical correlation with that determined experimentally. The indirectly determined discharge coefficient is then used in the analytical correlation for predicting the breakup height of a transverse liquid jet. The results predicted using this approach are in good agreement with the experimental data of the present study at standard temperature and pressure (STP) test conditions.

Energy fraction of the main (premixed) fuel and pilot injection timing are important in dual-fuel pilot diesel ignition engine. In the present study, natural gas, which is the main premixed fuel, is induced into the engine through the intake port, while the pilot diesel fuel (for ignition) is indirectly injected into the engine. A computational fluid dynamic (CFD)-chemistry platform based on AVL FIRE-CHEMKIN is used to simulate the combustion and emissions characteristics of a dual-fuel pilot diesel ignition engine operating on premixed natural gas. The effect of natural gas energy fraction and diesel injection timing at constant engine total fuel energy on combustion performance and emissions is investigated at low engine load (25% load and IMEP = 3 bar). The results revealed that at injection timings of 12 and 20 °BTDC, the maximum ITE (26.7%) occurs at 50% natural gas energy fraction. This is attributed to the improved cylinder charge conditions as a result of high swirling motion produced by the introduction of pre-combustion chamber. Moreover, a drastic reduction of NO x emissions was observed at 60% natural gas energy fraction in comparison with that of only diesel combustion (i.e., 0% natural gas energy fraction). On the other side, the combustion of fuel starts in the pre-combustion chamber and propagates into the main chamber. As a result, the combustion peak temperature drops which significantly reduces NO x formation. The results revealed that unburned methane emissions under dual-fuel operation mode become much higher compared to that under diesel combustion mode, which implies that a considerable amount of gaseous fuel escapes the combustion process at low load. However, using pre-combustion chamber is found to decrease unburned methane emissions by 46% on average compared to dual-fuel engine without pre-combustion chamber.

This paper presents an experimental study of the effect of fuel nozzle geometry on swirling partially premixed methane flames, where the focus is put on the ensuing flowfield and its role on coherent structures' suppression. The burner consists of a central interchangeable fuel nozzle surrounded by a swirling co-airflow where both discharge into a short mixing tube. The nozzle geometry is classified into two groups, namely, single- and multi-orifice nozzles. The swirling motion of the co-airflow is produced using a radial-type swirl generator with a swirl number of 1.15. The flowfield characteristics and coherent structures are documented using particle image velocimetry (PIV). Flame front dynamics are captured using Mie scattering technique. Quantitative laser sheet (QLS) is used to qualitatively shed light on the mixing characteristics downstream of the mixing tube exit, and laser Doppler velocimetry (LDV) is used to extract the coherent structures' peak frequency from the power spectra. The results revealed that the fuel nozzle geometry significantly affects the mean flowfield, mean, and root-mean-square (RMS) of the flame front location, flame front asymmetry, and coherent structures' amplitude. Higher spread rate and faster decay caused by single-orifice nozzles inside the mixing tube result in divergent flames with higher degree of flame front asymmetry downstream of the mixing tube exit. On the other hand, multi-orifice nozzles mitigate coherent structures, enhance mixing, and hence, promote the most appropriate conditions for coherent structures' suppression.

The effect of lip thickness of fuel nozzle on the liftoff of an attached diffusion methane flame with and without a coflow was experimentally and analytically investigated. Three fuel nozzles made of a long pipe with the same internal diameter but different nozzle lip thickness were tested. The co-airflow was also varied to assess its impact on the liftoff of jet diffusion flame. The results showed that the effect of fuel nozzle lip thickness on the liftoff of a free jet flame (i.e., no coflow) is marginal. However, the presence of a weak to moderate coflow (0.05 m/s < Uco < 0.3 m/s) reduced the liftoff velocity of an attached flame. The reduction rate of the liftoff velocity with co-airflow was found to be more significant for the fuel nozzle with the smaller lip thickness. At a relatively higher coflow (Uco > ∼0.3 m/s), a more pronounced drop in the liftoff velocity with coflow was observed. Flow field characteristics obtained using PIV measurements showed that the coflow stream experienced a transition to the turbulent regime for Uco > ∼0.3 m/s range which is believed to cause the inception of the flame liftoff to occur. A model for predicting the liftoff velocity of an attached flame in the presence of a coflow was developed based on the stoichiometric mixture velocity equation. This model showed good agreement with the present experimental data. However, although it can predict successfully the observed trends in the literature, further experiments are required to generalize it.

Replacing diesel by natural gas in diesel engine is of great interest for transportation and power station industry due to larger availability and lower environmental impact of natural gas compared to diesel fuel. However, natural gas/diesel dual-fuel (NDDF) engine has lower thermal efficiency and produces higher greenhouse gas (GHG) emissions than its counterpart diesel engine at low load conditions when conventional diesel combustion strategy is used. In order to overcome this drawback, the present paper experimentally and numerically investigates the coupling of two strategies; namely increasing diesel injection rail pressure and splitting diesel injection of a heavy-duty NDDF engine at low engine load conditions. The results revealed that increasing the injection rail pressure decreases thermal efficiency of the NDDF engine with split injection as a result of overly advanced combustion phasing. However, a higher thermal efficiency (37.2%), than that of the diesel-only and the NDDF engine with a single injection, can be achieved under optimized combustion phasing. Increasing the injection rail pressure significantly reduces the unburned methane emissions of the NDDF engine with split injection, especially at lower split ratios (mass of the injected diesel in the first pulse divided by that of the total injected diesel). However, increasing the injection rail pressure does not affect the unburned methane emissions under a split ratio of 65%. This is due to the fact that a larger portion of diesel fuel impinges onto the cylinder wall surface as revealed by the simulation results. The optimum methane emissions of the NDDF engine with split injection is reduced by 50% compared to the best condition of the NDDF engine with a single injection. Moreover, the indicated specific carbon dioxide equivalent (ISCO2-equivalent) emissions of the NDDF engine with split injection are reduced by 11% compared to those of the NDDF engine with a single injection and diesel-only engine. All in all, the present study demonstrated that thermal efficiency and GHG emissions of the NDDF engine can be further improved when simultaneously varying diesel fuel injection split ratio and rail pressure increase. This strategy is also found to help reducing pressure rise rate (PRR) and NOx and soot emissions.

In this study the effect of two diesel injection strategies named main-post and pre-main-post on natural gas/diesel dual-fuel (NDDF) combustion at high load conditions is investigated. In the main-post diesel injection strategy, part of diesel is injected after the main injection in the late expansion stroke (post-injection). In the pre-main-post injection strategy, part of diesel fuel is injected before main injection in the early compression stroke (pre-injection) and part of diesel fuel is injected after main injection in the late expansion stroke. The results revealed that the main-post diesel injection strategy did not change the start of combustion compared to single injection strategy. However, the pre-main-post injection strategy significantly increased the cylinder pressure and advanced the start of combustion. The maximum measured indicated fuel efficiencies (IFE) of NDDF engine with both single and pre-main diesel injection strategies were 41.50%. The main-post diesel injection strategy slightly decreased IFE of NDDF (i.e., 40.35%). However, an optimized combustion phasing and pre-main-post injection strategy made it possible to achieve similar or higher IFE than single injection strategy. Moreover, the pre-main-post diesel injection strategy significantly decreased unburned methane emissions. The lowest measured unburned methane emissions when using pre-main-post diesel injection was 0.37 g/kW.h, which was lower than that of single injection (0.80 g/kW.h). Compared to single diesel injection, optimized combustion phasing along with pre-main-post injection strategy reduced GHG and NOx emissions by 10% and 47%, respectively.

This article reviews published literature on the characteristics of a liquid jet injected transversally into a subsonic gaseous crossflow. The review covers the following aspects: (і) liquid jet primary breakup regimes, (іі) liquid jet trajectory and penetration, (ііі) liquid jet breakup length, and (іv) droplets features and formation mechanisms. The focus is on analyzing the role of different prominent parameters which include gaseous and liquid properties, and liquid injector geometry. The review revealed that gas Weber number plays a crucial role in defining non-turbulent primary breakup regimes, while liquid jet Weber number is of great importance for the transition to turbulent primary breakup. Jet-to-crossflow momentum flux ratio is the most important parameter for predicting the trajectory, penetration, and breakup length of a liquid jet in a crossflow. The characteristics of droplets disintegrated during the primary breakup are mostly influenced by the nozzle exit conditions, whereas the characteristics of droplets produced via the secondary breakup are strongly dependent on the velocity of cross airflow. Although the review revealed that substantial progress has been made in understanding this complex two-phase flow phenomenon, there still remain several shortcomings which require further research.

The eddy dissipation concept (EDC) model has the ability to incorporate detailed chemistry in turbulent combustion, which makes it attractive for simulating a wide range of industrial combustion systems. However, its application for modeling weakly turbulent reacting flows and slow chemistry poses a real challenge. The present study examines the influence of the EDC model’s coefficients, with respect to turbulent flow field characteristics. In order to assess the sensitivity of EDC model’s constants, simulations of two distinct jet flames covering weakly and highly turbulent flow conditions are performed. The predictions are compared with published experimental measurements. The findings of this study revealed that EDC predictions of the characteristics of weakly turbulent reacting flow can be improved by changing the model’s constants. The study also showed that, in comparison with the standard EDC, modifying the model’s coefficients produced improved predictions of the characteristics of highly turbulen...

Laminar flame speed of a newly developed biodiesel surrogate, 1,3-dimethoxyoctane, has been experimentally determined at standard atmospheric pressure and 433 K using a spherical combustion chamber. The 29 L combustion chamber has two pairs of fused silica windows for optical access and is also equipped with 4 pairs of axial fans for generating isotropic turbulence, which is used here to prepare homogeneous combustible mixtures of fuel and air. Schlieren technique was used to visualize and document the temporal evolution of the outwardly propagated spherical 1,3-dimethoxyoctane/air flame. An in-house developed Matlab code was employed for postprocessing of the flame front images and determining the time histories of its radius. Validation of the experimental setup and methodology was achieved by measuring the laminar flame speed of n-heptane/air mixtures at atmospheric pressure and 353 K, and compared with published reports. The results revealed that the proposed biodiesel surrogate, 1,3-dimethoxyoctane, ...

The main focus of this paper is to investigate the impact of fuel type on HCCI combustion under different engine loads. A coupled chemical kinetics-computational fluid dynamic (CFD) model is developed to investigate the combustion performance and emissions characteristics of a HCCI engine with pre-combustion chamber fueled with natural gas, natural gas/10% dimethyl ether (DME) mixtures, or methanol. The simulation results indicate that the probability of partial combustion increases when using natural gas under low engine load. However, methanol and natural gas/DME experience complete combustion under low engine load. In contrast, for both methanol and natural gas/DME the rate of pressure rise and heat release at high engine load is very high which induces engine knock. At leaner mixtures (ER 0.26). NOx emissions of natural gas fueled HCCI engine are much lower than that of methanol and natural gas/DME, especially at high engine loads. However, natural gas/DME and methanol offer superior combustion control and NOx, carbon monoxide (CO), and unburned hydrocarbon (UHC) emissions under low to moderate engine loads. However, the use of natural gas in HCCI combustion is suitable for moderate to high engine loads.

A hybrid Eulerian–Lagrangian approach was used to develop a model for predicting the penetration of a liquid jet in a subsonic gaseous crossflow. This was achieved by taking into account the effect of all forces acting on the jet, including drag, gravitation, and surface tension, as well as the mass shedding from the liquid column. The effect of mass shedding from the liquid column and jet Reynolds number on the spray penetration height was also studied. It was found that, although the momentum flux ratio q plays a predominant role in the prediction of a liquid jet column, the liquid jet penetration can be affected when changing the ambient temperature and pressure (or gas to liquid density and viscosity ratio), especially when holding constant q and jet velocity vj. Two correlations were developed in the form of sinusoidal-exponential and logarithmic function for the prediction of liquid column and droplets’ plume regions, respectively. The proposed correlations are capable of predicting jet penetration ...

Advancing the start of diesel injection timing is an effective way to enhance thermal efficiency and reduce greenhouse gas (GHG) emissions of natural gas/diesel dual-fuel (NDDF) engine. However, severe thermodynamic conditions under high engine load conditions may increase the propensity for engine knocking when advancing the start of diesel injection (SODI). In this study, the strategy of split diesel injection (two-pulse injection) is used and its feasibility as a method to reduce knocking intensity and improve thermal efficiency of NDDF engine is investigated. The results reveal that advancing single diesel injection timing significantly increases knocking intensity, whereas split diesel injection strategy decreases knocking intensity. The results also show that, when using split diesel injection, the flame kernels do not propagate as fast and deep as in the case of single diesel injection. This slows down the pressure and temperature rise rate in the unburned end-gas region and thus reduces knocking tendency. Moreover, the early partially burning of the premixed natural gas – air mixture in the squish region dilutes the unburned end-gas and consequently makes it resistant to auto-ignition. NDDF engine with split diesel injection can reach a maximum thermal efficiency that is comparable to that observed under knocking conditions of single diesel injection. Using either, single or split, diesel injection strategy reduces GHG emissions of NDDF engine (up to 12%) compared to its counterpart diesel engine. However, the lowest GHG emissions of NDDF engine with single diesel injection strategy is recorded under knocking conditions.

This is the post-print version of the following article: "An analysis of the droplet support fiber effect on the evaporation process", which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S001793101833196X?via%3Dihub; International audience; This paper presents an analysis of the effect of the droplet support fiber on the droplet evaporation process. This effect is evaluated for a droplet evaporating in a hot environment at atmospheric pressure using the experimental results of the present study and those in the literature. Selected published results are acquired using similar test conditions and experimental setups as the present data. The only main difference between these studies is the droplet support fiber diameter which varies between 14 µm and 225 µm. The ambient temperature explored in these studies ranges from room temperature up to 973K. n-heptane is selected because it is the most common fuel used in these studies. The main findings are that the cross-fiber technique, which uses 14 µm fiber diameters, induces no noticeable heat transfer into the droplet and consequently does not interfere with the evaporation process. In contrast, the classical fiber technique, which uses relatively larger fibers, greatly enhances the droplet evaporation rate as a consequence of increased conduction heat transfer through the fiber. A correlation is proposed to quantify the level of this increase as a function of ambient temperature and the fiber cross-sectional area, 2 .

Biogas is a renewable source of energy produced by anaerobic digestion of organic material and composed mainly of methane (CH4) and carbon dioxide (CO2). Despite its lower heating value, biogas can still replace fossil fuels in several engineering stationary power generation and other industrial applications. Although numerous published studies were devoted to advance our understating of biogas combustion, experimental data of some parameters such as turbulent burning velocity (St) under certain operating conditions is still lacking. The present study aims to experimentally determine biogas turbulent burning velocity under normal temperature and pressure conditions. Turbulent premixed biogas–air flame was ignited at the center of a 29 L fan-stirred spherical combustion chamber of nearly homogeneous and isotropic turbulence. Test conditions consisted of varying turbulence intensity and biogas surrogate composition. Outwardly propagating biogas flames were tracked and imaged using Schlieren imaging technique. The results showed that, by increasing turbulence and reducing methane percentage in the surrogate, the flammability of the mixture shrinked. In addition, the curve fits of biogas turbulent burning velocity versus the equivalence ratio exhibited two different trends. The peak of turbulent burning velocity shifted away from nearly lean equivalence ratio toward the stoichiometric at a fixed turbulence intensity and higher CH4 percentage in the surrogate. However, for the same biogas surrogate composition, the peak of turbulent burning velocity shifted away from stoichiometric toward leaner equivalence ratio with increased turbulence intensity.

A multi-dimensional computational fluid dynamics (CFD) model coupled with chemical kinetics mechanisms was applied to investigate the effect of various premixed fuels and equivalence ratios on the combustion, performance, and emissions characteristics of a dual-fuel indirect injection (IDI) pilot diesel ignition engine. The diesel fuel is supplied via indirect injection into the cylinder prior to the end of the compression stroke. Various premixed fuels were inducted into the engine through the intake manifold. The results showed that the dual-fuel case using hydrogen/diesel has a steeper pressure rise rate, higher peak heat release rate (PHRR), more advanced ignition timing, and shorter ignition delay compared to the natural gas/diesel and methanol/diesel dual-fuel cases. For leaner mixtures (ΦP 0.32). For instance, with an equivalence ratio of 0.35, the ITE is 56.24% and 60.85% for hydrogen/diesel and methanol/diesel dual-fuel cases, respectively. For an equivalence ratio of 0.15, the natural gas/diesel simulation exhibits partial burn combustion and thus results in a negative IMEP. At equivalence ratios of 0.15, 0.2, and 0.25, the methanol/diesel case experiences misfiring phenomenon which consequently deteriorates the engine performance considerably. As for the engine-out emissions, the hydrogen/diesel results display carbon monoxide (CO) free combustion relative to natural gas/diesel and methanol/diesel engines; however, considerable amount of nitrogen oxides (NOx) emissions are produced at an equivalence ratio of 0.35 which exceeds the Euro 6 NOx limit. Due to the larger area exposed to high temperature regions and the higher content of oxygen with increased methanol, soot and CO emissions are significantly reduced for richer premixed methanol mixtures. According to these findings, a dual-fuel engine operating on methanol and diesel performs better at rich conditions, whereas the performance of hydrogen and diesel is superior to that of natural gas/diesel and methanol/diesel mixtures at lean conditions.

There is an urgent need to develop new combustion strategies such as homogeneous charge compression ignition (HCCI) mode to meet current and future emissions regulations. In this study, experiments and a coupled AVL-CHEMKIN CFD (computational fluid dynamic) model were adopted to compare combustion phasing, engine performance and emissions in term of equivalence ratio for both HCCI combustion engines with and without pre-combustion chamber to investigate the effect of pre-combustion chamber on HCCI combustion engine. Results revealed that with an equivalence ratio of 0.2, HCCI engine with pre-combustion chamber (comet MK.V) tolerates misfiring process, while HCCI engine without pre-combustion chamber (modified chamber) experiences a complete combustion. HCCI engine with modified chamber has higher combustion pressure, narrower heat release rate (HRR), more advanced start of combustion (SOC) and higher indicated mean effective pressure (IMEP) in comparison with comet MK.V chamber. For equivalence ratios between 0.2 and 0.5, the average increase in IMEPs is 49.3%. Furthermore, HCCI engine with modified chamber generates higher work per kg fuel compared to comet MK.V chamber. While a high level of nitrogen oxide (NO x ) emissions is produced by HCCI combustion with modified chamber, both carbon monoxide (CO) and hydrocarbon (HC) emissions decreased drastically. In terms of combustion phasing, engine performance and emissions, the HCCI engine with modified combustion chamber is preferred at low equivalence ratios ( Φ

New experimental data on the effect of turbulence on the combustion of n-heptane and n-decane droplet at elevated pressure are reported. Turbulent flow field in the central volume of a spherical vessel was generated by a set of eight axial fans. Flow characterization demonstrated that turbulence is isotropic and homogeneous within the 40 mm central volume of the vessel. The combustion of n-heptane and n-decane droplet was examined by varying turbulence intensity via the fans rotational speed and ambient pressure and temperature inside the vessel/chamber. Results showed that droplet burning rate becomes sensitive to turbulence only at elevated ambient pressure. Droplet flame extinction was found to depend on the heat loss from the droplet envelop flame, which increases with turbulence intensity.