Spray and Flame Structure in Diesel Combustion

1989 ◽  
Vol 111 (3) ◽  
pp. 451-457 ◽  
Author(s):  
E. N. Balles ◽  
J. B. Heywood
Keyword(s):  
Ignition Delay ◽  
Direct Injection ◽  
Flame Structure ◽  
Combustion Process ◽  
Premixed Combustion ◽  
Fuel Spray ◽  
Fuel Vapor ◽  
Diesel Combustion ◽  
Combustion Phase ◽  
Luminous Region

The diesel combustion process in direct-injection diesel engines consists of four distinct stages: an ignition delay, a premixed phase, a mixing-controlled phase, and a late combustion phase. This paper uses geometric information from high-speed direct and shadowgraph movies and corresponding combustion chamber pressure histories, taken in a rapid compression machine study of direct-injection diesel combustion, for a coupled analysis of the diesel flame geometry and energy or heat release to develop our understanding of the diesel spray and flame structure during the ignition delay period and premixed combustion phase. It is shown that each fuel spray from a multihole fuel-injector nozzle consists of a narrow liquid-containing core centered within a much larger fuel-vapor air region, which has a distinct boundary. The liquid core does not penetrate to the chamber periphery, while the vapor containing spray interacts strongly with the boundary. Ignition occurs part way along each growing spray. Once combustion starts, the outer boundary of the fuel-vapor-containing region expands more rapidly due to the combustion energy release. Very high initial spreading rates of the luminous region boundary are observed. A comparison of enflamed areas and volumes, and burned gas volumes, indicates that the luminous region during the early stages of combustion (assumed stoichiometric) is around 1 cm thick and does not fill the full height of the chamber. During the premixed combustion phase, the burned gas volume is one-half the enflamed volume, indicating the presence of a substantial unburned (rich) fuel-vapor/air core within the luminous region of each fuel spray. A close correspondence of flame geometry to spray geometry is evident throughout the combustion process.

scholarly journals Modelling the effect of injection pressure on heat release parameters and nitrogen oxides in direct injection diesel engines

2014 ◽  
Vol 18 (1) ◽  
pp. 155-168 ◽  
Author(s):  
Levent Yüksek ◽  
Tarkan Sandalci ◽  
Orkun Özener ◽  
Alp Ergenc
Keyword(s):  
Nitrogen Oxides ◽  
Heat Release ◽  
Direct Injection ◽  
Pressure Rise ◽  
Injection Pressure ◽  
Premixed Combustion ◽  
Crank Angle ◽  
Cylinder Model ◽  
Combustion Phase ◽  
Rate Of Heat Release

Investigation and modelling the effect of injection pressure on heat release parameters and engine-out nitrogen oxides are the main aim of this study. A zero-dimensional and multi-zone cylinder model was developed for estimation of the effect of injection pressure rise on performance parameters of diesel engine. Double-Wiebe rate of heat release global model was used to describe fuel combustion. extended Zeldovich mechanism and partial equilibrium approach were used for modelling the formation of nitrogen oxides. Single cylinder, high pressure direct injection, electronically controlled, research engine bench was used for model calibration. 1000 and 1200 bars of fuel injection pressure were investigated while injection advance, injected fuel quantity and engine speed kept constant. The ignition delay of injected fuel reduced 0.4 crank angle with 1200 bars of injection pressure and similar effect observed in premixed combustion phase duration which reduced 0.2 crank angle. Rate of heat release of premixed combustion phase increased 1.75 % with 1200 bar injection pressure. Multi-zone cylinder model showed good agreement with experimental in-cylinder pressure data. Also it was seen that the NOx formation model greatly predicted the engine-out NOx emissions for both of the operation modes.

A Proposed Biodiesel Combustion Kinetics Based on the Computational Fluid Dynamics Results in an Ignition Quality Tester

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Mahmoud Elhalwagy ◽  
Chao Zhang
Keyword(s):  
Methyl Ester ◽  
Ignition Delay ◽  
Methyl Esters ◽  
Direct Injection ◽  
Combustion Process ◽  
Major Fatty Acid ◽  
Combustion Behavior ◽  
Ignition Quality ◽  
Reaction Constants ◽  
Ignition Quality Tester

In this paper, five biodiesel global combustion decomposition steps are added to a surrogate mechanism to accurately represent the chemical kinetics of the decomposition of different levels of saturation of biodiesel, which are represented by five major fatty acid methyl esters. The reaction constants were tuned based on the results from the numerical simulations of the combustion process in an ignition quality tester (IQT) in order to obtain accurate cetane numbers. The prediction of the complete thermophysical properties of the five constituents is also carried out to accurately represent the physics of the spray and vaporization processes. The results indicated that the combustion behavior is controlled more by the spray and breakup processes for saturated biodiesel constituents than by the chemical delay, which is similar to the diesel fuel combustion behavior. The chemical delay and low temperature reactions were observed to have greater effects on the combustion and ignition delay for the cases of the unsaturated biodiesels. The comparison between the physical ignition delay and overall ignition delay between the saturated and unsaturated biodiesel constituents has also confirmed those stronger effects for the physical delay in the saturated compounds as compared to the unsaturated compounds. The validation of the proposed model is conducted for the simulations of two direct injection diesel engines using palm methyl ester and rape methyl ester.

scholarly journals Modeling diesel combustion with tabulated kinetics and different flame structure assumptions based on flamelet approach

2019 ◽  
Vol 21 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Tommaso Lucchini ◽  
Daniel Pontoni ◽  
Gianluca D’Errico ◽  
Bart Somers
Keyword(s):  
Soot Formation ◽  
Flame Structure ◽  
Combustion Process ◽  
Computational Cost ◽  
Pollutant Emissions ◽  
Diesel Combustion ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Computational Fluid Dynamics Analysis ◽  
The Impact

Computational fluid dynamics analysis represents a useful approach to design and develop new engine concepts and investigate advanced combustion modes. Large chemical mechanisms are required for a correct description of the combustion process, especially for the prediction of pollutant emissions. Tabulated chemistry models allow to reduce significantly the computational cost, maintaining a good accuracy. In the present work, an investigation of tabulated approaches, based on flamelet assumptions, is carried out to simulate turbulent Diesel combustion in the Spray A framework. The Approximated Diffusion Flamelet is tested under different ambient conditions and compared with Flamelet Generated Manifold, and both models are validated with Engine Combustion Network experimental data. Flame structure, combustion process and soot formation were analyzed in this work. Computed results confirm the impact of the turbulent–chemistry interaction on the ignition event. Therefore, a new look-up table concept Five-Dimensional-Flamelet Generated Manifold, that accounts for an additional dimension (strain rate), has been developed and tested, giving promising results.

NOx emissions in direct injection diesel engines: Part 2: model performance for conventional, prolonged ignition delay, and premixed charge compression ignition operating conditions

2017 ◽  
Vol 19 (5) ◽  
pp. 528-541 ◽  
Author(s):  
Clemens Brückner ◽  
Panagiotis Kyrtatos ◽  
Konstantinos Boulouchos
Keyword(s):  
Diesel Engines ◽  
Ignition Delay ◽  
Direct Injection ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Nox Emission ◽  
Nox Emissions ◽  
Nox Formation ◽  
Parameter Variations ◽  
And Diffusion

Investigations from recent years have shown that at operating conditions characterized by long ignition delays and resulting large proportions of premixed combustion, the NOx emission trend does not correspond to the (usually) postulated correlation with an appropriately defined (adiabatic) burnt flame temperature. This correlation, however, is the cornerstone of most published NOx models for direct injection diesel engines. In this light, a new phenomenological NOx model has been developed in Brückner et al. (Part 1), which considers NOx formation from products of premixed and diffusion combustion and accounts for compression heating of post-flame gases, and describes NOx formation by thermal chemistry. In this study (Part 2), the model is applied to predict NOx emissions from two medium-speed direct injection diesel engines of different size and at various operating conditions. Single parameter variations comprising sweeps of injection pressure, start of injection, load, exhaust gas recirculation rate, number of injections, and end-of-compression temperature are studied on a single-cylinder engine. In addition, different engine configurations (valve timing, turbocharger setup) and injection parameters of a marine diesel engine are investigated. For both engines and all parameter variations, the model prediction shows good agreement. Most notably, the model captures the turning point of the NOx emission trend with increasing ignition delay (first decreasing, then increasing NOx) for both engines. The differentiation in the physical treatment of the products of premixed and diffusion with increasing ignition delay showed to be essential for the model to capture the trend-reversal. Specifically, the model predicted that peak NOx formation rates in diffusion zones decrease with increasing ignition delay, whereas for the same change in ignition delay, peak formation rates in premixed zones increase. This is caused by the high energy release in short time, causing a strong compression of existing premixed combustion product zones that mix at a slower rate and have less time to mix, significantly increasing their temperature. In contrast, the model under-predicts NOx emissions for very low oxygen concentrations, in particular below 15 vol.%, which is attributed to the simple thermal NOx kinetic mechanism used. It is concluded that the new model is able to predict NOx emissions for conventional diesel combustion and for long ignition delay operating conditions, where a substantial amount of heat is released in premixed mode.

scholarly journals THE INFLUENCE OF THE FUEL SPRAY STRUCTURE AND DYNAMICS OF ITS FORMATION ON SURFACE COMBUSTION OF BIOFUELS IN DIESEL ENGINES

Transport ◽  
2015 ◽  
Vol 31 (1) ◽  
pp. 84-93 ◽  
Author(s):  
Sergey P. Kulmankov ◽  
Sergejus Lebedevas ◽  
Vladimir Sinitsyn ◽  
Galina Lebedeva ◽  
Sergey S. Kulmankov ◽  
...  
Keyword(s):  
High Pressure ◽  
Ignition Delay ◽  
Delay Time ◽  
Combustion Process ◽  
Calculated Data ◽  
Fuel Spray ◽  
Common Rail System ◽  
Experimental Conditions ◽  
Fuel Supply ◽  
Fuel Sprays

The paper presents the results of the experimental investigation of the structure of the fuel, rapeseed oil and diesel fuel sprays obtained by analysing their optical density. The results are obtained by investigating a conventionally designed fuel supply system and a high-pressure common rail system. The experimental data on the velocity and length of fuel sprays are given. The study has shown that when high pressure fuel supply systems are used, the fuel spray is increased by about three times, while its area is increased up to 50% and homogeneity is also higher. As a result, selfignition delay time is reduced and the combustion process is intensified. The methods, taking into consideration the specific character of using the alternative types of fuel and high pressure systems, which have been tested in the experimental conditions, are suggested for calculating the time of self-ignition delay. The applied methods allow us to reduce the error of determining self-ignition delay time up to five percent. Based on the calculated data, the factors limiting the ignition of the sprayed fuel have been defined.

Mechanism of thermal efficiency improvement in twin shaped semi-premixed diesel combustion

2021 ◽  
pp. 146808742110264
Author(s):  
Kazuki Inaba ◽  
Yanhe Zhang ◽  
Yoshimitsu Kobashi ◽  
Gen Shibata ◽  
Hideyuki Ogawa
Keyword(s):  
Heat Release ◽  
Thermal Efficiency ◽  
Gas Flow ◽  
Fuel Injection ◽  
Premixed Combustion ◽  
Combustion Noise ◽  
Diesel Combustion ◽  
Combustion Mode ◽  
Secondary Stage ◽  
Combustion Phase

Improvements of the thermal efficiency in twin shaped semi-premixed diesel combustion mode with premixed combustion in the primary stage and spray diffusive combustion in the secondary stage with multi-stage fuel injection were investigated with experiments and 3D-CFD analysis. For a better understanding of the advantages of this combustion mode, the results were compared with conventional diesel combustion modes, mainly consisting of diffusive combustion. The semi-premixed mode has a higher thermal efficiency than the conventional mode at both the low and medium load conditions examined here. The heat release in the semi-premixed mode is more concentrated at the top dead center, resulting in a significant reduction in the exhaust loss. The increase in the cooling loss is suppressed to a level similar to the conventional mode. In the conventional mode the rate of heat release becomes more rapid and the combustion noise increases with advances in the combustion phase as the premixed combustion with pilot and pre injections and the diffusive combustion with the main combustion occurs simultaneously. In the semi-premixed mode, the premixed combustion with pilot and primary injections and the diffusive combustion with the secondary injection occurs separately in different phases, maintaining a gentler heat release with advances in the combustion phase. The mechanism of the cooling loss suppression with the semi-premixed mode at low load was investigated with 3D-CFD. In the semi-premixed mode, there is a reduction in the gas flow and quantity of the combustion gas near the piston wall due to the suppression of spray penetration and splitting of the injection, resulting in a smaller heat flux.

scholarly journals Analysis of the repeatability of fuel spray indexes in a spray-guided direct-injection spark-ignition engine

2016 ◽  
Vol 164 (1) ◽  
pp. 49-55
Author(s):  
Ireneusz PIELECHA
Keyword(s):  
Fuel Injection ◽  
Direct Injection ◽  
Combustion Process ◽  
Spark Ignition Engine ◽  
Fuel Spray ◽  
Injection Duration ◽  
Cylinder Test ◽  
Direct Injection Spark Ignition ◽  
Spray Velocity ◽  
Made In

The development and research works on liquid fuel injection in spark-ignited direct injection (SIDI) engines, apart from so common in recent years simulation methods, still have a significant cognitive substrate. This is related to experimental research on repeatability of combustion process using multi- and mono-cylinder test engines and Rapid Compression Machines. The repeatability of preparation and delivery processes has immediate impact on repeatability of combustion process. Except for the necessity of obtaining the repeatability of fuel amounts, the repeatability of injected fuel spray is required. The penetration range and spray area in combustion chamber have direct impact on mixture creation and formation. The optical research on fuel injection has been made in order to determinate its repeatability. The research on unrepeatability of fuel spray propagation has been conducted using piezoelectric injectors of outward-opening type, being primary elements of the spray-guided combustion systems. The results of research were presented in the form of index of variation of the selected parameters. The evaluation of the results of the optical research concerns radial spray penetration and fuel spray velocity. Unrepeatability has been presented with coefficient of variation of radial penetration in relation to the time of injection duration. It has been observed that the coefficients of various parameters are lower with longer times of fuel injection.

Normal Heptane-Diesel Combustion and Odorous Emissions in Direct Injection Diesel Engines

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Murari Mohon Roy
Keyword(s):  
Diesel Fuel ◽  
Ignition Delay ◽  
Boiling Point ◽  
Direct Injection ◽  
Volatile Components ◽  
Diesel Combustion ◽  
Gas Temperature ◽  
Eye Irritation ◽  
Heat Of Evaporation ◽  
High Latent Heat

This study investigated normal heptane (N-heptane)-diesel combustion and odorous emissions in a direct injection diesel engine during and after engine warmup at idling. The odor is a little worse with N-heptane and blends than that of diesel fuel due to overleaning of the mixture. In addition, formaldehyde (HCHO) and total hydrocarbon (THC) in the exhaust increase with increasing N-heptane content. However, 50% and 100% N-heptane showed lower eye irritation than neat diesel fuel. Due to low boiling point of N-heptane, adhering fuel on the combustion chamber wall is small and as a single-component C7 fuel, relatively high volatile components present in the exhaust are low. This may cause lower eye irritation. On the contrary, bulk in-cylinder gas temperature is lower and ignition delay significantly increases for 50% and 100% N-heptane due to the low boiling point, high latent heat of evaporation, and low bulk modulus of compressibility of N-heptane than standard diesel fuel. This longer ignition delay and lower bulk in-cylinder gas temperature of N-heptane blends deteriorate exhaust odor and emissions of HCHO and THC.

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