Injection Combustion Research Articles

Injection strategy for simultaneous reduction of NOx and soot emissions using two-stage injection in DME fueled engine

The ultimate purpose of this study is the reduction of exhaust emissions from a dimethyl ether (DME) fueled diesel engine without deterioration of engine performance, such as indicated mean effective pressure (IMEP) and indicated specific fuel consumption (ISFC). In this study, we applied multiple injection strategies to achieve the research goal. In a comparison between diesel and DME single injection combustion, the IMEP in both fuels was similar around the top dead center (TDC) injection condition (this is the typical injection timing). However, the nitrogen oxide (NOx) emission in DME was higher than that in diesel. The single injection combustion in DME and diesel was compared on the basis of the same energy input condition. When the injection timing was advanced in order to reduce the DME NOx emission, the IMEP in DME decreased below the diesel level. Therefore, multiple injection strategies, including pilot injection, split injection, and advanced+post injection, were applied in this study. In the experimental results, the pilot injection strategy with advanced main injection (2nd injection) resulted in the lowest NOx, HC, and CO emissions. In the case of soot emission, DME itself has soot free combustion, and emitted an ignorable amount of soot. Moreover, the pilot injection strategy showed the highest IMEP level and the lowest ISFC level in the test conditions.

Effects of Injection Nozzle Specifications and Combustion Chamber Shape on Smoke Reduction by Post Injection in a Diesel Engine

Effects of Injection Nozzle Specifications and Combustion Chamber Shape on Smoke Reduction by Post Injection in a Diesel Engine

Effect of fuel injection pressure and injection timing of Karanja biodiesel blends on fuel spray, engine performance, emissions and combustion characteristics

In this investigation, effect of 10%, 20% and 50% Karanja biodiesel blends on injection rate, atomization, engine performance, emissions and combustion characteristics of common rail direct injection (CRDI) type fuel injection system were evaluated in a single cylinder research engine at 300, 500, 750 and 1000bar fuel injection pressures at different start of injection timings and constant engine speed of 1500rpm. The duration of fuel injection slightly decreased with increasing blend ratio of biodiesel (Karanja Oil Methyl Ester: KOME) and significantly decreased with increasing fuel injection pressure. The injection rate profile and Sauter mean diameter (D32) of the fuel droplets are influenced by the injection pressure. Increasing fuel injection pressure generally improves the thermal efficiency of the test fuels. Sauter mean diameter (D32) and arithmetic mean diameter (D10) decreased with decreasing Karanja biodiesel content in the blend and significantly increased for higher blends due to relatively higher fuel density and viscosity. Maximum thermal efficiency was observed at the same injection timing for biodiesel blends and mineral diesel. Lower Karanja biodiesel blends (up to 20%) showed lower brake specific hydrocarbon (BSHC) and carbon monoxide (BSCO) emissions in comparison to mineral diesel. For lower Karanja biodiesel blends, combustion duration was shorter than mineral diesel however at higher fuel injection pressures, combustion duration of 50% blend was longer than mineral diesel. Up to 10% Karanja biodiesel blends in a CRDI engines improves brake thermal efficiency and reduces emissions, without any requirement of hardware changes or ECU recalibration.

Porous Inserts for Passive Control of Noise and Thermo-Acoustic Instabilities in LDI Combustion

In this study, ring-shaped porous inserts made from high-strength, temperature-resistant ceramic materials are utilized within the combustor to passively reduce noise and thermo-acoustic instabilities in lean direct injection (LDI) combustion. Inserts of 85% porosity; pore density of 18 pores per cm; and converging, diverging, and hyperbolic configurations are considered. Kerosene fuel atomized by an air-blast fuel injector is introduced in the swirl-stabilized combustor operated at atmospheric pressure. For a fixed equivalence ratio, emissions and acoustics measurements are obtained at different heat release rates and atomizing air to liquid mass ratios. Results show negligible effects of porous inserts on NOx and CO emissions at the combustor exit. Porous inserts are, however, very effective in suppressing both noise and thermo-acoustic instabilities for a range of operating conditions. The measured trends in acoustic absorption are predicted using a simplified thin-layer model of the porous material, and an important flow mechanism to explain the observed trends is discussed.

Time-Resolved Particle Image Velocimetry Measurements of Nonreacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry (PIV) to measure the turbulent flow field in a nonreacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the proper orthogonal decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core (PVC), which would ultimately affect the acoustic behavior in a favorable manner.

A Reduced Chemical Kinetic Mechanism for Low Temperature Diesel Combustion and Soot Emissions

A reduced diesel surrogate fuel chemical kinetic mechanism of n-heptane/toluene/1-hexene including poly-aromatic hydrocarbons (PAHs) formation was developed for prediction of the diesel combustion process and soot emissions. The proposed mechanism, which includes 60 species and 123 reactions, agrees well with experimental ignition delays in shock tubes. The proposed mechanism was coupled with the KIVA-3V Release 2 computational fluid dynamics (CFD) code to predict the combustion process and soot emissions in constant volume spray chamber and diesel direct injection combustion cases. The simulation results predict the combustion processes for diesel fuel under various conditions well. However, the predicted soot emissions have notable deviations compared to the experimental data when C2H2 or phenanthrene (A3) were chosen as precursors in the soot model at lower oxygen concentration conditions. The predicted soot emissions at different oxygen concentrations have better agreement with the experimental data when pyrene (A4) was chosen as the soot precursor. Compared to C2H2 or A3, A4 is a more suitable precursor for soot predictions in the LTC simulations. The overall results show that the present mechanism can be used to predict the combustion process and soot emissions of low temperature diesel combustion.

Flame Dynamics During Combustion Instability in a High-Pressure, Shear-Coaxial Injector Combustor

We present a large-eddy simulation based investigation of combustion instability in the Continuous Variable Resonance Combustor (CVRC); a high-pressure, shear-coaxial injector combustor studied experimentally at Purdue University. An important characteristic of the CVRC setup is the role that the oxidizer injector length plays in the stable/unstable combustion dynamics occurring within the combustor. We perform three simulations corresponding to different stability regions; one is a semi-stable case whereas the other two cases are unstable. The acoustic pressure fluctuation exhibits a limit cycle behavior in all cases. An abrupt change in the predicted amplitude between stable and unstable cases is also observed, consistent with the experimental trends. Further investigations to characterize the mechanism driving such abrupt change in the stability pattern when the oxidizer injector length is varied, show that acoustic interactions with the flow field lead to subtle changes in the vorticity (and mixing) dynamics, which significantly alters the distribution of species and heat release. In addition, aspects related to flame stabilization such as the mean flame anchoring location and the mode of burning, premixed or non-premixed, are also affected. The analysis of flame structures shows the presence of multi-mode burning regions where premixed and non-premixed flames appear to coexist. However, the dominant burning mode switches from premixed to non-premixed within an acoustic cycle, potentially playing an important role in flame stabilization.

Characterization and Modeling of a Spinning Thermoacoustic Instability in an Annular Combustor Equipped With Multiple Matrix Injectors

Oscillations in fully annular systems coupled by azimuthal modes are often observed in gas turbine combustors but not well documented. One objective of the present study is to characterize this type of oscillation in a laboratory scale system, allowing detailed pressure measurements and high speed visualization of the flame motion. The experiment is designed to allow detailed investigations of this process at a stable limit cycle and for an extended period of time. Experiments reported in the present article are carried out in the MICCA facility which was used in our previous work to analyze instabilities arising when the chamber backplane was equipped with multiple swirling injectors (Bourgouin et al., 2013, “Self-Sustained Instabilities in an Annular Combustor Coupled by Azimuthal Acoustic Modes,” ASME Paper No. GT2013-95010). In the present study, these units are replaced by a set of matrix injectors. The annular plenum feeds 16 such devices confined by two cylindrical quartz tubes open to the atmosphere. The multiple flames formed by the matrix injectors are laminar and have a well documented describing function. This constitutes an ideal configuration allowing systematic investigations of thermo-acoustic oscillations coupled by longitudinal or azimuthal modes while avoiding complexities inherent to swirling turbulent flames studied previously. Optical access to the chamber allows high speed imaging of light emission from the flames providing instantaneous flame patterns and indications on the heat release rate fluctuations. Eight waveguide microphones record the pressure signal at the combustor injection plane and in the plenum. Among the unstable modes observed in this setup, this analysis focuses on situations where the system features a spinning azimuthal mode. This mode is observed at a frequency which is close to that associated with the 1A mode of the plenum. A theoretical analysis is then carried out to interpret the angular shift between the nodal lines in the plenum and chamber, and the measured flame describing function (FDF) is used to quantify this shift and determine the linear growth rate.

Study of Pilot Injection for the Improvement of Combustion and Emissions Characteristics in a Heavy-Duty Diesel Engine

A 6-cylinder, turbocharged, common rail heavy-duty diesel engine was used in this study. The effect of pilot injection strategies on diesel fuel combustion process, heat release rate, emission and economy of diesel engine is studied. The pilot injection strategies include pilot injection timing and pilot injection mass to achieve the homogeneous compression ignition and lower temperature combustion of diesel engine. The two-color method was applied to take the flame images in the engine cylinder and obtain soot concentration distribution. The results demonstrate that with the advance of pilot injection timing, the peak in-cylinder pressure becomes lower, the ignition delay of the main combustion is shortened, the NOXand soot emissions are reduced, but the HC and CO emissions are increased. With the increase of pilot injection fuel mass, the heat release rate of the pilot injection combustion and the maximum rate of pressure rise increase, NOXand HC emissions are higher, and PM and CO emissions are reduced. The pilot combustion flame is non-luminous.

Experimental Study of a Multinozzle Combustor at Elevated Pressures

Emissions measurements and chemiluminescence imaging were performed on a novel multipoint lean direct injection combustor designed for low-NOx emissions and with the flexibility to operate at both high- and low-power settings. The combustor has five rows of fuel nozzles that can be staged in three independent circuits as required. The fuel nozzle stages are not identical; instead, they are optimized for different power settings. NOx, CO, and unburned hydrocarbons were measured for a variety of settings, including lean blowout, idle, intermediate power, and simulated full power. Effects of pressure, inlet temperature, equivalence ratio, and fuel flow distribution were studied. chemiluminescence was used to observe flame structure and interpret emissions trends. The local equivalence ratio, calculated with the fuel and air flow rates particular to each combustor stage, was a useful parameter for interpreting emissions. The combustor demonstrated the ability to operate at a wide range of conditions, from an overall equivalence ratio of 0.55 to lean blowout at 0.079. Low-NOx operation was achieved at high power by using all fuel stages and controlling fuel flow to obtain an even distribution among the nozzles and reduce peak temperatures while using staging to provide good stability at low power.

A review on hydrogen industrial aerospace applications

This article depicts the scenario in which hydrogen appears as the best candidate fuel for long range transportation with potentially zero emissions. Main characteristics of hydrogen that make it appealing and exploitable in applications are described and compared to those of other common fuels. A historical journey through aerospace industry applications of hydrogen since its discovery is provided, considering turbojet, ramjet, scramjet and rocket engines. Current and future technology levels are reported. • Historical journey of hydrogen use as fuel in aerospace applications. • Main propulsion characteristics of hydrogen compared with those of other fuels. • Hydrogen lean direct injection and micro-mix combustion strategies for gas turbines. • State-of-the-art of H 2 fueled engines for supersonic passengers' transportation.

Concentration of nitrogen oxides in fuel-combustion products

Methods of predicting the formation of nitrogen oxides in the combustion products of gaseous fuel are considered. Predicted concentrations of nitrogen oxides in the smoke gases are obtained for the combustion of natural gas in burners with different methods of mixing the fuel and air. Other conditions being equal, the minimum content of nitrogen oxides in the combustion products is seen in burners with open flames (flat-flame burners and radiant burners) and in burners with improved mixing. The content of nitrogen oxides is somewhat higher in burners without preliminary mixing of the fuel and air. The most toxic smoke gases are formed in injection burners. On heating the air for combustion, the content of nitrogen oxides in the smoke gases increases by a factor of 2–3. The discrepancy between the results obtained by the methods considered is 5–7% for high-temperature furnaces and 20% or more for low-temperature furnaces. With considerable air heating, the discrepancy increases.

MULTIDIMENSIONAL MODELING OF COMPRESSED BIO GAS (CBG) ENGINE FOR ULTRA LOW EMISSION

The purpose of this study is to find out in-cylinder flow characteristics of a four-cylinder, 2,3 liter diesel engine before the fuel injection and also properly simulate the atomization process in order to improve the combustion efficiency and emission parameters. A complete intake stroke with Compressed Bio Gas (CBG) port injection, compression stroke, pilot fuel injection at the end of the compression and exhaust stroke simulated in 3D. Both naturally aspirated and turbo-charged modes of operations were studied. In this study, cold flow structure, fuel atomization for different spray models and dual fuel combustion are investigated. A comprehensive model for atomization of liquid sprays under high injection pressures has been employed. Finally, a calculation on an engine configuration with compression, spray injection and CBG-diesel combustion in a direct injection dual fuel diesel engine is presented. In 3D CFD study, selected proper cases modeled using full geometry of diesel engine. Fine grids were tested with 1,700,000 hexahedral cells. In this paper, fine grid results are evaluated. CBG fuel induced during intake process in dual fuel diesel combustion engine and then mixed with air before the premixed gas enters the cylinder. It is ignited by the injection of pilot diesel fuel near the Top Dead Center (TDC). This lean combustion and diluted gas mixture cause low in-cylinder temperature and resulting in a NOx emission. The results are in agreement qualitatively with the previous studies in the literature.

Characterization of Swirl-Venturi Lean Direct Injection Designs for Aviation Gas Turbine Combustion

Injector geometry, physical mixing, chemical processes, and engine cycle conditions together govern performance, operability, and emission characteristics of aviation gas turbine combustion systems. The present investigation explores swirl-venturi lean direct injection combustor fundamentals, characterizing the influence of key geometric injector parameters on reacting flow physics and emission production trends. In this computational study, a design space exploration was performed using a parameterized swirl-venturi lean direct injector model. From the parametric geometry, 20 three-element lean direct injection combustor sectors were produced and simulated using steady-state Reynolds-averaged Navier–Stokes reacting computations. Species concentrations were solved directly using a reduced 18-step reaction mechanism for Jet A. Turbulence closure was obtained using a nonlinear model. Results demonstrate sensitivities of the geometric perturbations on axially averaged flowfield responses. Output variables include axial velocity, turbulent kinetic energy, static temperature, fuel patternation, and minor species mass fractions. Significant trends have been reduced to surrogate model approximations, intended to guide future injector design trade studies and advance aviation gas turbine combustion research.

A review of engine application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas

The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this paper. Discussions include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas, visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel, and the fundamental study of turbulent premixed combustion of hydrogen enriched natural gas. The effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.

A Review on Numerical and Experimental Results of Hydrogen Addition to Natural Gas in Internal Combustion Engines

Conventional fossil fuel for combustion system, such as gasoline and petroleum have long been recognized as powerful energy source, however these have a number of problems related to emissions and energy security. The use of hydrogen blends with natural gas is a viable alternative to pure fossil fuels because of the expected reduction of the total pollutant emissions and increase of efficiency. Enhancement of chemical reaction with hydrogen addition is regarded as the increase of H, O and OH free radical mole fraction in the flame. Also in SI engines will move the lean limit to leaner mixture, increasing the combustion speed and temperature. Results show that the hydrogen has a catalyzing effect in the ignition of hydrocarbons with only a few percent addition of hydrogen by volume and by adding it to the pure natural gas (CNG) this difference in spark advance of the engine may be reduced, as a result of the higher flame speed of hydrogen. In this paper, we present the advances and development made on internal combustion engines which operate with mixture of hydrogen/CNG, doing more emphasis in the combustion process, ignition energy and injection systems. Also this paper mentions a comparison that experimental and numerical results match quite well expect for extremely fuel lean condition. The nozzle geometry has an important influence on injection process and combustion development and shows that degree of conicity can be evaluated for each nozzle by the K- Factor.

Impact of DME as an Oxygenated Alternative Fuel on Combustion and Emissions Reduction in a Transportation Vehicle at Low Load Condition

AbstractThis study investigates the impact of dimethyl ether (DME) on the combustion and exhaust emission characteristics at low engine load operating and pilot injection conditions in a four-cylinder diesel engine that was modified for DME application. The combustion characteristics were analyzed based on the combustion pressure, the rate of heat release, the accumulated heat release, and the premixed combustion characteristics. The emission characteristics were analyzed through the analysis of the nitrogen oxides (NOx), soot, hydrocarbon (HC), and carbon monoxide (CO). The heat release amount per unit crank angle in DME combustion is higher than that in diesel combustion in a pilot injected combustion mode. The accumulated heat release of DME during the main combustion is higher than that of diesel fuel. The pilot injection combustion of DME fuel started earlier than single-injection combustion does. The advanced pilot injection timing caused a decrease of premixed combustion duration and a retardation ...

Large eddy simulations for radiation-spray coupling for a lean direct injector combustor

Large Eddy Simulations (LESs) for a lean-direct injection (LDI) combustor are performed and compared with experimental data. The LDI emissions characteristics, and radiation-spray coupling effect on the predictions are analyzed. The flamelet progress variable approach is employed for chemistry tabulation coupled with a stochastic secondary breakup model. Good comparisons are shown with the experimental data mean and root mean square for both the gas phase and spray droplets profiles. The effect of combustion is found to change the shape and structure of the central recirculation zone to be more compact in length but larger in diameter in the transverse direction. In-addition the results show that the gas phase radiation alters the spray dynamics by changing the local gas-phase temperature distribution. This impacts the spray evaporation rate, the local mixture fraction, and consequently the combustion heat released rate and the predicted emissions. The simulation with no radiation modeling shows over prediction in the temperature distribution, pollutants emissions, higher fuel evaporation rate, and narrower range of droplet size distribution with lower number density for the smaller size particles. The current study suggests that, even for low pressure systems, radiation modeling can be important for accurate emissions prediction.

Effectiveness of jet location on mixing characteristics inside a cavity in supersonic flow

The incorporation of cavities within supersonic combustion chambers is an effective means of slowing down the flow for fuel injection and consequent stable combustion. Understanding the flow physics associated with such flows, especially with the injection of a gas to replicate fuel injection, are essential for the optimum design of supersonic propulsion mechanisms. An experimental investigation was performed on a rectangular open cavity with upstream injection model in a Mach number of 1.9 using a trisonic indraft wind tunnel. A rectangular open cavity of dimensions L/D=5, 100mm in length (L) and 20mm deep (D), was adopted, and it was embedded into the lower wall of the test section. An air jet with a jet-to-freestream momentum flux ratio of J=1.2, 2.7 and 5.3 was injected upstream of the cavity. To evaluate the effect on mixing and flow stability the jet position, measured from the front edge of the cavity, was varied between 0.1L and 1L. The flow field was visualized using schlieren photography, particle image velocimetry, and oil flow measurements. It is found that the mixing characteristic within the cavity when the jet is positioned 0.1L is enhanced independent on the J value because the turbulence intensity of the flow velocity within the cavity is strongly influenced by the jet interaction which lifted the flow from the floor of the cavity compared to the other jet positions. However, the flow over the cavity is unstable at all jet positions. The separation shock formed at the front edge of the cavity oscillates significantly for the case where the jet is located at 0.1L because the separation shock location coincides with the compression shock behind the jet.

Effects of Fuel Temperature on Injection Process and Combustion of Dimethyl Ether Engine

To investigate the effects of fuel temperature on the injection process in the fuel-injection pipe and the combustion characteristics of compression ignition (CI) engine, tests on a four stroke, direct injection dimethyl ether (DME) engine were conducted. Experimental results show that as the fuel temperature increases from 20 to 40 °C, the sound speed is decreased by 12.2%, the peak line pressure at pump and nozzle sides are decreased by 7.2% and 5.6%, respectively. Meanwhile, the injection timing is retarded by 2.2 °CA and the injection duration is extended by 0.8 °CA. Accordingly, the ignition delay and the combustion duration are extended by 0.7 °CA and 4.0 °CA, respectively. The cylinder peak pressure is decreased by 5.4%. As a result, the effective thermal efficiency is decreased, especially for temperature above 40 °C. Before beginning an experiment, the fuel properties of DME, including the density, the bulk modulus, and the sound speed were calculated by "ThermoData." The calculated result of sound speed is consistent with the experimental results.