Injection Combustion Research Articles

The Characteristic of Flow Field and Emissions of a Concentric Staged Lean Direct Injection (LDI) Combustor

The characteristic of flow field and emissions was investigated by numerical simulation for a concentric staged lean direct injection combustor, the non-reaction and reaction flow fields were studied under idle and takeoff conditions, and the effect of combustion heat release on flow field was analyzed, then the influence of injection angle on emissions were obtained. The investigation results indicated that the steady central recirculation zone could be formed under non-reaction and reaction conditions by medium swirl strength which the swirl angle is 32°, however, the size and reverse mass flow at reaction conditions is significantly increased than non-reaction conditions; the combustion reaction zone moves toward the outlet as the decrease of fuel injection angle, which reduce the resistant time of hot gas in combustor, and then the production of nitrogen oxides would be decreased.

DFT and canonical ensemble investigations of gasoline additives at the gas phase: ETBE, MTBE, DIPE, ethanol and methanol

A quantum analysis was performed with Density Functional Theory and a canonical ensemble, in order to predict thermodynamic properties of gasoline with additives at the gas phase. These calculated quantities included standard gasoline mixed with the following oxygenate additives: methyl tert-butyl ether, ethyl tert-butyl ether, diisopropyl ether, ethanol and methanol. For each gasoline and additive mixture, thermodynamic potential variations were calculated between room and the approximate ignition temperatures at 1 atm, where an analysis of the additive effect was performed in order to estimate relevant fuel properties at similar conditions to the injection step and combustion. Some thermodynamic quantities for combustion were obtained, showing substantial concordance with experimental data, relative errors being lower than 2%, thus establishing an excellent method for calculating and predicting the thermodynamic properties of combustion reactions for gasoline with additives.

Tailored Fuel Injection for Performance Enhancement in a Mach 12 Scramjet Engine

To investigate the potential performance benefits of tailored fuel injection in a scramjet engine, flow through a rectangular-to-elliptical shape-transitioning scramjet was simulated with two different combustor injection geometries: one with uniform film injection, and the other with oblique-angle cross-flow porthole injectors targeting the flow structures observed in engine simulations. Both engines used inlet injection to promote rapid ignition and burning of the combustor-injected fuel. The simulations were compared with experimental data for validation purposes. The tailored-injection engine fuelled to an equivalence ratio of 1.24 realized higher performance than the film-injection configuration, achieving oxygen-based mixing and combustion efficiencies of 98.9% and 84.9%, respectively. Tailored injection shows promise as a method for improving scramjet performance, allowing higher fuel efficiency with simplified fuel injection, and potentially shorter combustor sections.

Bio-ethanol additive effect on direct injection diesel engine performance, emission and combustion characteristics – an experimental examination

ABSTRACT The present investigation explores the effect of dairy scum oil methyl ester (DSOME) blends and ethanol additive on TV1 Kirloskar diesel engine performance, combustion and emission characteristics. From the experimental study, it is concluded that DSOME-B20 (20% dairy scum biodiesel + 80% diesel) has shown appreciable performance and lower HC and CO emissions among all other blends. Hence DSOME-B20 is optimised as best fuel blend and it is carried for further investigations to study the effect of bio-ethanol additive on diesel engine performance. From the study it apparent that diesel engine operated with ethanol additive and 20% dairy scum biodiesel blended fuels shown the satisfactorily improved emission characteristics when compared to petroleum diesel fuel operation. Finally, from the experimental investigation, it concludes that addition of ethanol shown the slightly higher HC, CO emission and improved BTE, BSFC, NOx and CO2 than sole B20 biodiesel blend. Among all three (3%, 6% and 9%) ethanol additive ratios, E6% (6%-ethanol with B20) ethanol additive exhibits slightly better BTE, BSFC, cylinder pressure and heat release rate hence 6% ethanol additive with B20 biodiesel blend would furnish beneficial effects in the diesel engine.

Optimization of the injection parameters and combustion chamber geometries of a diesel/natural gas RCCI engine

This study aims at finding the favorable combinations of the diesel injection parameters and combustion chamber shape of a diesel/natural gas dual fuel engine to achieve lower fuel consumption and pollution emissions. The genetic algorithm NSGA-II coupled with the KIVA-3V code was employed for the multi-objective optimizations. The results show that the straight combustion chamber is effective to reduce the CH4 emission and improve the fuel economy, and the indicated thermal efficiency reaches 50.2% with an injection timing of −16.45 °CA ATDC. The NO emissions are the lowest when the reentrant-type combustion chamber is used, while CH4 emissions and ISFC are higher than the other two types of the combustion chamber. When the injection timing is far away from the top dead center, the NO emissions, CH4 emissions and ISFC are very close to each other for the three types of the combustion chamber. Slightly narrow spray angle is favorable to improve the performance of the dual fuel engine.

Fundamental investigations for lowering emissions and improving operability

This paper first highlights recent developments in lean direct injection (LDI) combustion technology. In view of the needs and opportunities to lower emissions and expand the operability range of LDI, fundamental research has been undertaken to elucidate the effects of air swirler vane angle, air swirler rotation direction, and overall equivalence ratio on the LDI flow field and flame structure/response. Moreover, additional investigation has been conducted to understand the fundamental differences between representative LDI and airblast injectors in order to highlight the importance of the flare feature to LDI venturi geometry. The results of these fundamental studies are discussed to help identify possible areas for optimization to generic LDI designs that may improve individual swirler performance.

Combustion characteristics of natural gas injected into a constant volume vessel

The combustion characteristics of injected natural gas based on experiments were carried out in a constant volume vessel. The influences of equivalence ratio, temperature and premix ratio on the flame morphology and combustion characteristics were analyzed. The flame front is wrinkled and twisted during the flame propagation, which shows the extreme randomness of injection combustion caused by the strong turbulence. The maximum pressure and maximum heat release rate of injection combustion are larger than premixed combustion, with less time reaching the maximum pressure, according to the progress of the pressure in the vessel. The initial and main combustion durations of the injection combustion are also shorter than that of premixed combustion.

Supercritical combustion of gas-centered liquid-swirl coaxial injectors for staged-combustion engines

The combustion characteristics of gas-centered, liquid-swirl coaxial injectors typically used in oxidizer-rich staged combustion cycle engines are numerically investigated at supercritical conditions. Turbulence closure is achieved using large-eddy-simulation techniques, and turbulence/chemistry interaction is modeled by a steady laminar flamelet approach. Gaseous oxygen (GOX) at 687.7 K is injected into the center post while kerosene at 492.2 K is delivered tangentially into the outer coaxial annulus. The operating pressure is 25.3 MPa. Detailed flow structures and flame dynamics are explored. The entire flowfield can be divided into four regimes: propellant injection, flame initialization, flame development, and intensive combustion. The diffusion-dominated flame is anchored in the wake of the GOX post and further enhanced in the downstream taper region. The surface of the coaxial annulus and taper is covered by fuel-rich mixtures and thus protected from thermal flux in the flame zone. Effects of the recess length (from the end of GOX post to the entrance of taper region) on the flow and flame evolution are investigated in depth. The efficiency of propellant mixing and subsequent combustion is found to increase with increasing recess length. The kerosene film is nearly depleted before the exit of the recess region for cases with long recess length, and the flame spreads upwards in the taper region for cases with reduced recess length due to insufficient mixing between GOX and kerosene. In a fully recessed injector without fuel shielding, the injected kerosene behaves like a liquid jet in a crossflow. Two recirculating zones containing fuel-rich mixtures are formed between the injection slit and the headend. A broad flame region is established at the exit of the recess region. In a non-recessed injector, the occurrence of combustion is delayed to the taper region. The flame resides along the taper surface and the injector faceplate, with most of GOX convecting downstream unburned. Results obtained from the present study can also be used to characterize combustion responses to local flow oscillations.

Effect of Swirl Strength on the Flow and Combustion Characteristics of Pulverized Biomass Flames

ABSTRACTThis article reports on the effect of swirl intensity on the flow and combustion characteristics of pulverized olive waste (OW) burning. Numerical simulations are carried out using the computational fluid dynamics (CFD) Commercial Software “Fluent ANSYS14” by choosing appropriate model parameters. The biomass furnace consists of a vertical cylinder equipped with a swirling co-flow injection burner. The particles of pulverized biomass (OW) are injected transversally into the furnace just near the co-flow exit, via four square-shaped injection nozzles. The non-premixed combustion model with mixture fraction/PDF model for turbulence-chemistry interactions is used. Standard k-ε turbulence model closure, discrete phase model (DPM) for tracking the motion of individual particle and P-1 radiation model for flame radiation inside the combustor are used in the numerical simulation. Four different swirl numbers Sn = 0.38, 0.95, 1.2 and 1.42 are used in this study in order to investigate the swirl intensity effect on the flow and combustion behavior. The results showed that the flow and the flame characteristics such as axial velocity, streamlines, gas temperature, flame length and CO2, CO and O2 concentrations are affected by the swirl intensity.

Parametric investigation of combustion instabilities in a single-element lean direct injection combustor

Self-excited combustion dynamics in a liquid-fueled lean direct injection combustor at high pressure (1 MPa) are described. Studied variables include combustor and air plenum length, inlet air temperature, equivalence ratio, fuel nozzle location, and fuel composition. Measured pressure oscillations were dependent on combustor geometry and ranged from about 1% of mean chamber pressure at low equivalence ratio, up to 20% at high equivalence ratio. In the most unstable cases, strong pressure modes were measured throughout the frequency spectrum including a band around 1.2–1.5 kHz representing the 4th longitudinal mode, and another band around 7 kHz. The oscillation amplitudes have a non-monotonic dependency on air temperature, and are affected by the placement of the fuel nozzle relative to the throat of the subsonic swirling air flow. The parametric survey provides a rich dataset suitable for validating high-fidelity simulations and their subsequent use in analyzing and interpreting the complex combustion dynamics.

Investigation of Discharge Coefficients for Single Element Lean Direct Injection Modules

Lean direct injection (LDI) combustion has a high potential as a low pollution combustion method for gas turbines. The present research aims to further investigate the discharge coefficient of an LDI module, axial swirler and convergent outlet under non-reaction and reaction conditions by theoretical, numerical and experimental methods. The functional relationship between the discharge coefficient of the LDI module, axial swirler and convergent outlet was established, and the effect of swirl angle (30°, 32°, 34°, 36°, 38°, 40°) and vane number (11, 12, 13, 14, 15, 16) on discharge coefficient was studied, and finally the differences in effective flow area of LDI combustor under different inlet conditions were analyzed. The results indicate that the flow separation on the suction side increases as the swirl angle increases, which leads to a decrease of the discharge coefficient of the axial swirler, however the discharge coefficient of the convergent outlet remains unchanged first and then decreases. As the vane number increases, the flow separation on the suction side decreases and the flow friction loss increases, so that the discharge coefficient of the axial swirler and convergent outlet will first increase with the increase of vane number and then decrease with further increases. The effective flow area of combustor changes as the conditions change, but it is approximately equal under high power conditions and normal temperature and pressure conditions.

Efficient Thermo-Chemistry Tabulation for Non-Premixed Combustion at High-Pressure Conditions

Propellant injection and turbulent combustion in high-pressure engines is often dominated by real-gas effects. However, previous studies suggested that the departure of the fluid properties from an ideal gas behavior has only a limited effect on the laminar flame structure. This is due to the fact that chemical reactions take place in the flame zone where the temperature is sufficiently high and molecular interactions are negligible, i.e., the ideal gas assumption is valid. On the other hand, various experimental and numerical studies of injection processes at high-pressure conditions demonstrated that real-gas effects can have a strong impact on the turbulent flow. Mixing is influenced by the rapid change of fluid properties. In this work, we exploit the gap in the fidelity of the thermodynamics model needed to describe the laminar flame structure and that needed to describe the turbulent flow field. We then propose a new real-gas flamelet model with increased numerical performance. The computational cost of the new formulation is not significantly higher than that of an ideal gas simulation. The performance of the method is analyzed and the error that is introduced by our assumptions is assessed by comparison to more complete modeling. Finally, the method is used to simulate a turbulent jet flame emanating from a coaxial injector at supercritical pressure and cryogenic oxidizer temperature. The results are compared with experimental OH∗ images giving evidence of the suitability of the present method.

Energy-Efficient Gas-Powered Burner for the Pyrotechnical Equipment of Oil and Gas Enterprises

A design of a fuel-spray injection burner for replenishing the fuel of users of the equipment of oil and gas companies is proposed. A schematic diagram of the newly developed burner design is presented and engineering designs by means of which lesser specific metal content is achieved than in existing constructions described, the operational reliability improved, and the overhaul life increased. Effective mixing of the fuel and air is realized in the new burner, overheating of the burner stabilizer prevented, and failures in firing are eliminated. The burner supports efficient combustion of gas fuel, including as well the liquid phase components.

Including real fuel chemistry in LES of turbulent spray combustion

Large Eddy Simulation (LES) is progressively becoming a crucial design tool for the next generation of aeronautical combustion chambers. However, further improvements of the predictive capability of LES is required especially for predictions of pollutant formation. In general, the exact description of real fuel combustion requires to take into account thousands of unique chemical species involved in complex and highly non-linear chemical reaction mechanisms, and the direct integration of such chemistry in LES is not a viable path because of excessive computational demands and numerical stiffness. Modeling of real aeronautical transportation fuel is further complicated by the fact that kerosenes are complex blends of a large number of hydrocarbon compounds and their exact composition is very difficult to determine. In this work, we propose a new framework relying upon the Hybrid Chemistry (HyChem) approach and Analytically Reduced Chemistry (ARC) to allow a direct integration of real fuel chemistry in the compressible LES solver AVBP. The HyChem-ARC model is coupled with the Dynamically Thickened Flame LES model (DTFLES) and a Lagrangian description of the spray to investigate the turbulent two-phase flow flame in a lean direct injection combustor, fueled with Jet-A. The LES results are compared to experimental data in terms of gas velocity, temperature and species (CO2, H2O, CO, NO) mass fractions. It is found that the proposed methodology leads to very satisfying predictions of both the flow dynamics and the NOx levels. Additionally, the refined level of chemistry description enables to gain valuable insights into flame/spray interactions as well as on the NOx formation mechanism in such complex flame configurations. To improve further the results, a more detailed experimental characterization of the liquid fuel injection should be provided.

Experimental and numerical investigation of combustion characteristics on GO2/GH2 shear coaxial injector

This study presents the results of a visualization investigation of the gas–gas injection combustion characteristics using a shear coaxial injector of non-premixed gaseous oxygen and gaseous hydrogen (GO2/GH2) under elevated ambient pressures. Advanced optical diagnostic approaches, including hydroxyl (OH) planar laser-induced fluorescence (PLIF) and high-speed imaging, are employed to capture the spatial distribution of the OH radical and the instantaneous flame dynamics near the faceplate. Experimental results indicate that an instantaneous reaction zone represents an apparent local extinction and re-ignition phenomenon, but does not affect the overall time-averaged reaction distribution. In addition, this study adopts the same ignition device and sequence used in a previous study; however, a different ignition process occurs. The reasons for this difference may be attributed to the fact that the exorbitant pressure peak disturbs the originally stable, downstream, cold-flow fields near the axis, which radically change the initial ignition and flame propagation processes. In order to demonstrate the feasibility and effectiveness of the applicability of computational fluid dynamics (CFD), several different associations of Reynolds averaged Navier–Stokes (RANS) approaches are compared with each other and with the experimental results. This proves that the turbulent model plays a dominant role in affecting the flow field structure. Based on the comparison with optical diagnostic results, a numerically-aided approach using RANS simulation is proposed to quantify the experimental results. This study is a first attempt to establish a standard corresponding relation between the simulation results and the optical diagnosis results.

Numerical Analysis of the Mixture Formation in a Two-Stroke Wall-Guided LPG DI Engine for Extended-Range Electric Vehicle

The use of automotive LPG characteristics which are easy to evaporate vaporization and carry. The paper presents a design of extended-range electric vehicle for wall-guided two stroke LPG engine with direct injection combustion system. Based on the modified vehicle LPG spray model, a database describing the characteristics of vehicle LPG fuel was built and imported into the CFD software. And the accuracy of the model is verified by the Schlieren experimental results. The concentration and velocity field of the mixture in the cylinder under different load conditions are numerically analyzed. The analyzed result indicated that the start injection time θ = 60°–70°CA BTDC under part load condition, the plug electrode near the gathering of a richer mixture is easy to be fired at spark ignition time, the obvious formation of mixture in cylinder is formed and the overall air-fuel ratio is above 40: 1. The start-transition working condition and large load conditions in the piston moves upward before closing the exhaust port to start injection LPG. The optimized LPG injection start time θ ensures that the fresh gas is locked in the cylinder when the exhaust port is closed (63°CA ABDC). In the ignition time of the spark plug, an ideal homogeneous mixture in the cylinder is realized.

Effects of injection condition and combustion chamber shape on performance and exhaust emissions of supercharged natural-gas/diesel dual-fuel engine

Effects of injection condition and combustion chamber shape on performance and exhaust emissions of supercharged natural-gas/diesel dual-fuel engine

Alcohol fuels for spark-ignition engines: Performance, efficiency and emission effects at mid to high blend rates for binary mixtures and pure components

The paper evaluates the results of tests performed using mid- and high-level blends of the low-carbon alcohols, methanol and ethanol, in admixture with gasoline, conducted in a variety of test engines to investigate octane response, efficiency and exhaust emissions, including those for particulate matter. In addition, pure alcohols are tested in two of the engines, to show the maximum response that can be expected in terms of knock limit and efficiency as a result of the beneficial properties of the two alcohols investigated. All of the test work has been conducted with blending of the alcohols and gasoline taking place outside the combustion system, that is, the two components are mixed homogeneously before introduction to the fuel system, and so the results represent what would happen if the alcohols were introduced into the fuel pool through a conventional single-fuel-pump (dispenser) approach. While much has been written on the effect of blending the light alcohols with gasoline in this way, the results present significant new findings with regard to the effect of the enthalpy of vaporization of the alcohols in terms of particulate exhaust emissions. Also, in one of the tests, two mid-level blends are tested in a highly downsized prototype engine – these blends being matched for stoichiometry, enthalpy of vaporization and volumetric energy content. The consequences of this are discussed and the results show that this approach to blend formulation creates fuels which behave in the same manner in a given combustion system; the reasons for this are discussed. One set of tests using pure methanol alternately with cooled exhaust gas recirculation and with excess air shows a significant increase in thermal efficiency that can be expected as the blend level is increased. The effect on nitrous oxide emissions is shown to be similarly beneficial, this being primarily a result of the enthalpy of vaporization of the alcohol cooling the charge coupled with the lower adiabatic flame temperature of the alcohol. Whereas it is normally a beneficial characteristic in spark-ignition combustion systems, one disadvantage of a high value of enthalpy of vaporization is shown in another series of tests in that, in admixture with gasoline, it is a driver on flash boiling of the hydrocarbon component in the blend in direct injection combustion systems. In turn, this causes the particulate emissions of the engine to increase quite markedly over those of ethanol–gasoline blends at the same stoichiometry. The paper shows for the first time the dichotomy of the potential efficiency improvement with the challenge of particulate control. This effect poses a challenge for the future introduction and use of such high blend rate fuels in engines without particulate filters. Although it must be stated that the overall particulate emissions of the methanol–gasoline blend are lower than for gasoline, the effect is only present at extremely low load, and that there is a likelihood that particulate filters will be adopted in production vehicle anyway, nullifying this issue.

Emission Characteristics for a Homogeneous Charged Compression Ignition Diesel Engine with Exhaust Gas Recirculation Using Split Injection Methodology

Due to the serious issues caused by air pollution and global warming, emission regulations are becoming stricter. New technologies that reduce NOx and PM emissions are needed. To cope with these social exhaust gas regulation demands, many advanced countries are striving to develop eco-friendly vehicles in order to respond to stricter emissions regulations. The homogeneous charged compression ignition engine (HCCI) incorporates a multi-stage combustion engine with multiple combustion modes, catalyst, direct fuel injection and partial mixing combustion. In this study, the HCCI combustion was applied to analyze and review the results of engines applying HCCI combustion without altering the conventional engine specifications. The optimization of exhaust gas recirculation (EGR) and compression ratio changes provides an optimal fuel economy. In this study, potential for optimum economy within the range of IMEP 0.8 MPa has been evaluated.

An equilibrium phase spray model for high-pressure fuel injection and engine combustion simulations

High-pressure fuel injection impacts mixture preparation, ignition and combustion in engines and other applications. Experimental studies have revealed the mixing-controlled and local phase equilibrium characteristics of liquid vaporization in high injection pressure diesel engine sprays. However, most computational fluid dynamics models for engine simulations spend much effort in solving for non-equilibrium spray processes. In this study, an equilibrium phase spray model is explored. The model is developed based on jet theory and a phase equilibrium assumption, without modeling drop breakup, collision and finite-rate interfacial vaporization processes. The proposed equilibrium phase spray model is validated extensively against experimental data in simulations of the engine combustion network Spray A and in an optical diesel engine. Predictions of liquid/vapor penetration, fuel mass fraction distribution, heat release rate and emission formation are all in good agreement with experimental data. In addition, good computational efficiency and grid-independency are also seen with the present equilibrium phase model. The examined operating conditions cover wide ranges that are relevant to internal combustion engines, which include ambient temperatures from 700 to 1400 K, ambient densities from 7.6 to 22.8 kg/m3 and injection pressures from 1200 to 1500 bar for diesel sprays.