Formation Of Pollutant Emissions Research Articles

Investigation on novel natural gas fueled homogeneous charge compression ignition engine based combined power and cooling system

A significant part of energy of fuel supplied is lost in internal combustion engines in the form of atmospheric discharge of engine exhaust gases which are considered as a big source of engine inefficiency and formation of pollutant emissions. To address this issue, a bottoming cycle combining the transcritical CO2 (T-CO2) refrigeration cycle and the supercritical CO2 (sCO2) power cycle is employed, aiming to produce cooling for food preservation by utilizing the exhaust heat of homogeneous charge compression ignition (HCCI) engine powering the refrigerated truck. The operative variables and their effect on thermal and exergetic efficiency of HCCI engine and the combined system are investigated. At the base case operative conditions, the thermal and exergy efficiencies of natural gas fueled HCCI engine are improved significantly from 48.69% to 61.28% and from 41.14% to 42.79%, respectively, after employing the sCO2 powered T-CO2 refrigeration cycle. Promotion of equivalence ratio from 0.3 to 0.9 enhances the thermal and exergy efficiencies of HCCI engine from 47.44% to 49.54% and from 40.14% to 42.12%, respectively. Increasing of engine speed from 1400 r.p.m to 2200 r.p.m provides marginal improvement in HCCI engine efficiencies but the efficiencies of combined cycle are significantly improved from 57.67% to 65.18% and from 40.64% to 45.06%, respectively. Finally, exergy analysis applied to determine the sources of non-idealities within the system revealed that out 361 kW (100%) fuel exergy supplied to the system, HCCI engine destroys 93.31 kW (25.85%), catalytic convertor destroys15.49 kW (4.29%), and the in-cylinder heat transfer losses and system exhaust losses are found as 35.72 kW (9.91%) and 16.61 kW (4.61%), respectively.

CFD Modeling of Reacting Diesel Sprays with Primary Reference Fuel

<div class="section abstract"><div class="htmlview paragraph">Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels - binary mixtures of n-heptane and iso-octane. Simulations were initially carried out to evaluate and compare the performance of two kinetic models in homogeneous reactors and laminar diffusion flames, followed by turbulent reacting spray simulations considering different fuels, ambient temperatures, and oxygen concentrations. The sensitivity study of the turbulent Schmidt number was then conducted, and results in terms of ignition delay and lift-off length were compared with experimental data to determine a more appropriate global constant. Finally, parametric variations of ambient temperature and oxygen concentration were performed for six fuel blends ranging from PRF0 (n-heptane) to PRF100 (iso-octane), confirming the validity of the TFPV model.</div></div>

PM reduction and flame confinement in biomass combustion using a porous inert material

The present study aims to determine the effects caused by the inclusion of a ceramic porous material in an experimental biomass combustor. The burner is an underfed fixed-bed facility that allows air staging wood pellet burning. Air staging determines the proportion of air entering by the primary inlet below the bed and the secondary inlet above it. The value used is 30/70 (%primary/%secondary). Due to the inclusion of a porous inert material (PIM) in a specific place in the combustor, the outlet gas flow from the combustion chamber is unaffected, but the behaviour of the combustion process is remarkably altered. Tests are performed by changing the total air flow from 0.223 kg/m2s, 0.279 kg/m2s and 0.334 kg/m2s and the position of the PIM at heights of 380 and 540 mm above the bed. The results show a significant reduction in particulate matter (PM) emissions, with some quantities reaching a reduction above 50% of the original values. The best results are achieved with the material positioned closest to the bed but always above the secondary air inlet.The concentration and distribution of PM were studied. Preliminary results of analysing the temperature profile along the combustor gas phase suggest that the effect of PIM inclusion is flame confinement. A higher rate of radiation is reflected back to the bed (solid combustion) due to the PIM insertion, increasing the temperature of the whole volume beneath. This temperature increase could slightly improve the combustion process in the gaseous phase, leading to a decrease in pollutant emission formation (especially PM).

Testing of formulated fuel with variable aromatic type and contents in a compression-ignition engine

Fuels used in various combustion engines necessitate deep understanding of the fuel components before being used as a feedstock with present engine technology. Fuel components impact the efficiency of the engine along with the formation of pollutant emissions. Aromatics are important component of the fossil-based diesel fuel, which highly affects the tailpipe emissions. Therefore, the study of aromatics has a great significance for diesel engine. A comprehensive study with a total of 13 different aromatics was performed to investigate the impact of their structure and content on diesel engine characteristics. Diesel, pure higher chain alkanes and single added aromatics were blended as ternary mixture. Detailed spray investigations were carried out at an injection pressure of 200 bar using a three-hole nozzle of diesel engine. The aromatic structure and content highly influenced the emission and performance characteristics. A blending ratio of 10% aromatics in base fuel shows promising results compared to 5% and 15% blending content of aromatics in the base fuel. Higher aromatics blending in ternary mixture led to higher particulate matter, carbon monoxide, and unburnt hydrocarbon emissions. Due to higher degree of unsaturation, polycyclic single and double ring aromatics produce higher pollutant emissions compared to single ring monocyclic aromatics.

Quasi-Dimensional Multi-Zone Combustion Diagnostic Tool for SI Engines with Novel NOx and CO Emissions Models

<div class="section abstract"><div class="htmlview paragraph">In this work a quasi-dimensional multi-zone combustion diagnostic tool for homogeneous charge Spark Ignition (SI) engines is analytically developed for the evaluation of heat release, flame propagation, combustion velocities as well as engine-out NOx and CO emissions, based on in-cylinder pressure data analysis. The tool can be used to assess the effects of fuel, design and operating parameters on the SI engine combustion and NOx and CO emissions formation processes.</div><div class="htmlview paragraph">Certain novel features are included in the presently developed combustion diagnostic tool. Firstly, combustion chambers of any shape and spark plug position can be considered due to an advanced model for the calculation of the geometric interaction between a spherically expanding flame and a general combustion chamber geometry. Also, the temperature stratification of the burned gas developed during the combustion phase, which has to be captured for the theoretically realistic estimation of the in-cylinder formation of pollutant emissions, is taken into account by a multi-zone thermodynamic treatment. According to this, multiple spherically allocated burned zones are sequentially generated at specified (user-defined) crank angle intervals, forming overlapping shells. Moreover, complex chemical equilibrium compositions are computed, which can include any user-defined mixture of species in the combustion products, using an advanced modular method based on the minimization of Gibbs energy. Furthermore, NOx and CO engine-out emissions are calculated based on novel in-cylinder formation models presented by the authors in the past. Specifically, NOx emissions are evaluated by a global algebraic NOx emissions formation model, accounting for both thermal and N<sub>2</sub>O pathway NO formation, based on the calculation of the characteristic timescales of the relevant NO formation mechanisms. CO emissions are assessed using a new kinetics-based model, consisting of a single Ordinary Differential Equation (ODE) that can be analytically integrated. The CO emissions model is derived considering the dynamics of a representative pool of active radicals in post-flame gases and explicitly describes the CO oxidation quenching process.</div><div class="htmlview paragraph">The combustion diagnostic tool is applied to a lean burn gas engine at various engine speeds under full load conditions and constant lambda value. Various combustion and NOx and CO emissions related results are presented and discussed to illustrate the capabilities of the tool for combustion diagnosis, while at the same time calculated engine-out NOx and CO emissions are found to be in satisfactory agreement with measured ones.</div></div>

Close Nozzle Spray Characteristics of a Prefilming Airblast Atomizer

The formation of pollutant emissions in jet engines is closely related to the fuel distribution inside the combustor. Hence, the characteristics of the spray formed during primary breakup are of major importance for an accurate prediction of the pollutant emissions. Currently, an Euler–Lagrangian approach for droplet transport in combination with combustion and pollutant formation models is used to predict the pollutant emissions. The missing element for predicting these emissions more accurately is well defined starting conditions for the liquid fuel droplets as they emerge from the fuel nozzle. Recently, it was demonstrated that the primary breakup can be predicted from first principles by the Lagrangian, mesh-free, Smoothed Particle Hydrodynamics (SPH) method. In the present work, 2D Direct Numerical Simulations (DNS) of a planar prefilming airblast atomizer using the SPH method are presented, which capture most of the breakup phenomena known from experiments. Strong links between the ligament breakup and the resulting spray in terms of droplet size, trajectory and velocity are demonstrated. The SPH predictions at elevated pressure conditions resemble quite well the effects observed in experiments. Significant interdependencies between droplet diameter, position and velocity are observed. This encourages to employ such multidimensional interdependence relations as a base for the development of primary atomization models.

KESAN SUDUT PUSARAN TERHADAP PEMBAKARAN MENGGUNAKAN PEMUSAR JEJARIAN DWI ALIRAN

Development of combustion systems which involves retrofitting or design of new burners, is made to reduce the formation of pollutant emissions. The reduction of this pollutant emission results from the complete mixing of fuel and air during the combustion process. Meanwhile, non-complete mixing of fuel and air during combustion process can cause ignition problem and create problems in terms of flame stability and combustion efficiency. This article describes a study on the effects of swirling flow generated by a double radial swirler on flame characteristics that is related to the emission of NO. The double radial swirlers used in this study have the angles of 30°/40°, 30°/50° and 30°/60°. Diesel is used as a fuel in this study. The results show that all double radial swirlers used have different effects on the flame characteristics and temperature profile. From all these double radial swirlers, the one with an angle of 30°/60° produces flame with high temperature, short flame length with blue colour and wide spread.

Experimental investigation of the primary combustion zone during staged combustion of wood-chips in a commercial small-scale boiler

In this work the primary combustion zone of a modified, commercial, small-scale boiler was investigated during staged combustion of wood-chips. Experimental research on thermal conversion of biomass in fixed beds is necessary to supply reliable data for gas phase combustion model validation and optimization. Furthermore, scruting of pollutant emission formation and combustion efficiency enhancement can be conducted. Two different fuel moistures were used while the primary combustion zone of a small-scale boiler was investigated as a function of the primary air ratio. The combustible products leaving the fuel layer were analyzed under continuous operation by an extractive method. This approach is new in the field of small-scale biomass combustion research and considers the strong coupling between the products leaving the fuel bed and the heat fluxes emitted by the flame of the secondary combustion zone. Additionally, fine particulate matter emissions were quantified to study the effect of varying primary air ratio and different fuel moisture on particulate formation. Results show that the primary air ratio and the fuel moisture have a significant influence on the primary combustion products composition, on the fuel bed behavior and on fine particulate matter emissions. At low primary air ratios, tars constitute a significant part of the heating value of primary combustion products. The smallest amount of particulate emissions was found at low primary air ratio and low fuel moisture. Experimental data was validated with an elemental balance, which showed perfect accordance.

Towards a more sustainable transport sector by numerically simulating fuel spray and pollutant formation in diesel engines

Diesel engines account for approximately 50% of new passenger-car sales in the European market and are the major contributor to pollutants that adversely affect human health and the environment. The most adverse pollutants emitted by the combustion of diesel fuel are NOx, soot, CO and HC. Numerous studies have been carried out to determine the influence of engine design, fuel injection, fuel-air mixing and combustion on pollutant emissions. Information gained through experimental research of in–cylinder processes is limited, and the body of knowledge can be improved by the use of numerical modelling and computer simulations. Computational Fluid Dynamics (CFD) has become a valuable tool that decreases the time and the cost of experimental research. Therefore, CFD is being increasingly used in development of combustion systems. This paper presents how the development of CFD models is the proper approach towards achieving a cleaner and more sustainable transportation sector. The physical models for the liquid fuel disintegration, evaporation and pollutant formation are used and implemented into the commercial CFD code FIRE. The models are capable of predicting complex in–cylinder processes and, ultimately, the formation of pollutant emissions. The results from numerical simulations, such as NOx and soot concentrations, in–cylinder pressure and temperature are found to be in good agreement with the existing experimental data.

Conversion of oxygenated and hydrocarbon molecules to particulate matter using stable isotopes as tracers

Fuels are continuing to be derived from fossil sources, but as production technology improves, biofuels and synthetic fuels are expected to emerge as scalable long-term sources of liquid fuels. Efforts are being made to ensure that this next-generation of fuels is cleaner burning than the last. In order to inform the production and processing of cleaner burning fuels, more needs to be known about how molecular structure influences the formation of pollutant emissions. Reducing airborne quantities of particulate matter (PM) is of particular interest for human health and the environment. This publication presents a 13C labelling technique, which has been developed and applied to identify the influence of local molecular structure on the formation of PM. The paper applied the technique based on the 13C stable isotope to trace the conversion of individual carbon atoms to PM in the case of several oxygenated and hydrocarbon molecules. A laminar tube reactor facility has been used for generating and collecting samples of PM under pyrolysis conditions. A number of single-component oxygenated and hydrocarbons (ethanol, propanol, pentanol, cyclopentanol, ethyl acetate, and toluene) have been enriched with 13C at specific carbon atom locations and the 13C/12C isotope ratios of PM were measured. The contribution to PM of particular carbon atoms within a molecule was evaluated, and the results shed new light of how individual carbon atoms in a molecule convert to PM. It was found that the conversion to PM of different atoms within a molecule varies widely, depending on the identity of their neighbouring moiety. Furthermore, it was shown that oxygen-containing functional groups have a significant influence on the formation of particulates, partly through a reduction in the conversion to PM of carbon atoms, which are adjacent to oxygen atoms.

Comparison of well-mixed and multiple representative interactive flamelet approaches for diesel spray combustion modelling

The application of detailed chemistry to the computational fluid dynamics simulation of combustion process in diesel engines has many potentials, including the possibility to predict auto-ignition, diffusion flame structure, stabilisation and soot formation in a wide range of operating conditions, also taking into account the effects of different fuel types. Among the approaches that were proposed over the years, the ones that are mostly used in practical calculations can be divided into two main categories: the first assumes each cell to be a well-stirred reactor, while the second employs the flamelet assumption to describe both auto-ignition and turbulent diffusion flame propagation. Despite the fact that both types of model have been widely validated over the years, a detailed comparison between them appears to be very useful in order to understand better the relevant parameters governing auto-ignition, flame stabilisation and the formation of pollutant emissions. This work is focused on a comparison of two different combustion models that were recently implemented by the authors in an open-source code. The first assumes each cell to be a homogeneous reactor and neglects interaction between turbulence and chemistry, while in the second, multiple laminar flamelets are used to represent the structure of a turbulent diffusion flame. Suitable techniques for online reaction rate tabulation and chemical mechanism reduction are also incorporated, to make the use of bigger mechanisms possible (up to 150 species). The two models are compared and validated by simulating constant-volume diesel combustion in a wide range of operating conditions, including variations of ambient temperature and oxygen concentration. Comparison between the computed and experimental data on flame structure, auto-ignition and flame lift-off enables an understanding of the main relevant differences between the models in the way both auto-ignition and flame stabilisation processes are predicted.

Improvement and validation of a multi-zone model for HCCI engine combustion concerning performance and emissions

The main objective of the present work is to improve and validate a multi-zone model developed by the authors for HCCI combustion. The multi-zone model describes the heat and mass transfer mechanisms and simulates combustion and pollutant formation using a reduced chemistry reaction mechanism and chemical kinetics. The division of the combustion chamber into zones is based on geometrical considerations. Heat and mass is exchanged between zones and the cylinder wall according to their spatial configuration, throughout the compression and expansion strokes, i.e. for the closed part of engine operation. The model is improved by modelling crevice flow through the description of the motion of unburned and burned mixture in and out of the crevice regions. These regions are a significant source of unburned hydrocarbons and contribute to the formation of CO. Using the model, a description of the formation of pollutant emissions in the zones is described. For model validation, cylinder pressure, performance data and emissions obtained from the simulation are compared to experimental data taken from an engine operating on HCCI mode for three different load cases.

The Effect of Combustion Dynamics on the Formation of Pollutant Emissions by Co-Firing the Wood Biomass with Gaseous Fuel

The Effect of Combustion Dynamics on the Formation of Pollutant Emissions by Co-Firing the Wood Biomass with Gaseous Fuel