Zulfiker Ali Bhutto, Roll No-931058P, Session has been accepted as satisfactory in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING on 2003. It is hereby declared that this thesis or any part thereof has not been submitted elsewhere for the award of any degree or diploma.
List of Symbols
Acknowledgments
Abstract
Introduction
Scope of the Thesis
Initially, a brief review of the diesel engine's combustion processes is presented in chapter 2, which is followed by a review of available heat emissions from natural gas and biogas for different compositions. Results obtained in this study are reported in Chapter 4 along with brief discussions of the results.
Literature Review
- Essential Features of Processes in Direct Injection CI Engines
- Natural Gas and Biogas as Alternative CI Fuel
- Modeling of Direct Injection Diesel Engine Combustion
- Modeling of Engine Heat Transfer
- Modeling of Engine Frictional Losses
The rapid pressure rise occurs due to the multiple ignition points and accumulation of fuel during the ignition delay period (Obert 1973). Other labels given to thermodynamic energy conservation based models are: zero-dimensional models (since in the absence of flow modeling, geometric features. a) Specific energy (b) Energy density of fuel-air premix. of the fluid motion cannot be predicted), phenomenological models (since additional details beyond the energy conservation equations are added for each phenomenon in tum), and quasi-dimensional models (where specific geometrical features, e.g., the diesel fuel spray shapes, are added to the basic thermodynamic approach).
Modeling of a Direct Injection (DI)
Diesel Engine
Overview of GT-Power
18 GT-Power can be used for a wide range of activities in connection with engine design and development. GT-Power can be used to predict either steady-state conditions or transient behavior of engine systems. In GT-Power, templates are the prototype structures used to define an array of objects.
Objects are the basic building blocks of the model that are created by assigning values to a template.
Overview of the Engine, Setup and Model
This should include comprehensive mapping of flow coefficients in both directions at all discontinuities in the channel. A model of the thermodynamic and gas dynamic behavior in each engine cylinder while the valves or ports are open and closed. The composition of the environment is defined in the Fstateinit object, which defines the initial state at the start of the simulation, and then the FpropGasCombust and FprsMixtureCombust objects are used to estimate the gas and mixture properties, respectively.
The heat transfer coefficient is obtained through the use of the Colburn analogy (Gamma-Technologies 2(01). Therefore, the En gCy1Geomobject object is called by the Engcylinder object to specify the geometry of the engine and steering cylinder. The Val veConn object is used to provide the cam profile that control the intake and exhaust valves.
In jPro, fileConn object is used to model the injection rate profile of liquid fuel in the engine cylinder. In the present study, Woschni model is used to estimate the engine cylinder heat transfer.
Post. Processing of the Results
Auxiliary losses (such as water pumps, radiator fans, etc.) can also be combined into the EngFrictionCF reference object. This is an empirically derived model that states that total engine friction is a function of peak cylinder pressure, mean piston speed, and mean piston speed squared.
Results,
Discussions and Conclusions
Results and Discussions
Similar gas pressures are observed in the cylinder at the end of the expansion stroke as shown in the figure. It is observed that the air-fuel ratio values decrease with increasing diesel fuel injection due to injecting more fuel while keeping the air flow essentially constant. Indicated mean effective pressure is a measure of indicated work per unit of swept volume in a form that is independent of engine size and number of engine cylinders and engine speed (Lumley 1999).
We can see that the indicator diagrams are very close to each other due to the fact that a similar amount of added heat with different fuels produced a similar amount of braking power. It is also observed that the consumption values of natural gas are lower than the consumption values of diesel fuel due to the fact that natural gas has a higher calorific value than diesel fuel. This is not surprising, since the carbon dioxide present in biogas does not release heat, but some heat is taken away with the exhaust gases.
It is seen that, in the case of pure diesel operation as shown in Fig 4.25, the experimental values of thermal braking efficiency reach the maximum value and the corresponding braking power is the rated power of the engine. Although the modeled results are within 2-3% of the experimental results up to rated power, it predicts higher thermal efficiency in all cases considered.
Conclusions
Moreover, the modeling also failed to show any decrease in thermal efficiency above the rated power due to its limitation of modeling actual combustion which causes the efficiency to decrease above the rated power due to the decrease in combustion efficiency due to the shortage of oxygen required. to completely bump the fuel. However, the modeled results show the reduction of power for higher C02 in biogas which is due to the presence of C02 which provides no energy but absorbs some heat when "exhausted in the form of increased temperature. 4.25-4.28, emphasis the fact that diebmep values effectively remove the effect of engine size and speed, and therefore no speed effect is observed in these results.
Modeling neglecting detailed combustion analysis results in a higher estimate of engine performance for the fuels considered in this study. Lower gas pressure in the cylinder and higher bulk gas temperature occur in the case of a diesel engine, which mainly uses natural gas as fuel.
Recommendations for Further Works
Maximum cylinder gas pressures and bulk gas temperatures for different amounts of diesel fuel injection per cycle. The thermal efficiency of the brakes, plotted as a function of braking power for different engine speeds, for the engine running on regular diesel. Equivalence ratio plotted as a function of the average effective brake pressure for different engine speeds, for the engine using direct diesel injection.
Equivalence ratio plotted as a function of mean effective brake pressure for various engine speeds, for the engine using a natural amount and a pilot amount of diesel injection. Equivalence ratio plotted as a function of mean effective brake pressure for various engine speeds, for the engine using BG30 biogas and a pilot amount of diesel injection. Equivalence ratio plotted as a function of mean effective brake pressure for various engine speeds, for the engine using BG50 biogas and a pilot amount of diesel injection.
Brake efficiency plotted as a function of brake mean effective pressure for different engine speeds, for the engine using direct diesel injection. Brake efficiency plotted as a function of brake mean effective pressure for different engine speeds, for the engine using natural and a pilot amount of diesel injection.
Expt
Engine Specifications
AppendixB
GT-Power ObjectIModule Review
Name of a 'FProp*' reference object that defines the composition at the start of the simulation. Carbon atoms per molecule Average number of carbon atoms in each molecule of the substance being described. Oxygen atoms per molecule Average number of oxygen atoms in each molecule of the substance being described.
Nitrogen atoms per molecule Average number of nitrogen atoms in each molecule of the substance described. In simulations where a certain species is only present as a small mass fraction of the total mass, it may be acceptable to use this default option. This object is suitable for use when the liquid is only a small mass fraction of the liquid mixture (ie the liquid is mixed with a gas).
Within a given simulation, all 'FPropLiqIncomp' reference objects must have an associated 'FPropGasCombust' reference object representing the composition of the fluid. Name of a 'FPropGasCombust' reference object that describes the properties of the liquid after it has evaporated.
Pipe. Basic Model
Options
Flexible Wall Object Name of the 'FlexWComps' reference object that defines the aeroelastic properties of the pipe walls. These numbers are automatically assigned by GT.ISE based on the direction of the arrows, so the user usually does not need to worry about them. However, if both links point into or out of a pipe (which is allowed), one of the port numbers must be edited by the user and changed so that there is a port I and a port 2. 63 EngCylinder.
Cylinder Geometry Object Name of the 'EngCylGeom', reference object that defines the cylinder geometry and piston position (crank-shift geometry). Initial State Name Name of the 'FStatelnit' reference object that describes the initial conditions within the cylinder. Name of the 'FStatelnit' reference object used strictly as a reference to calculate volumetric efficiency.
There can be more than one master cylinder as long as each one calls a different 'EngCylComb'' reference object. If the slave option is used with an 'EngCylCombSITurb' object, the simulation must be steady-state because the burn rate in the slave cylinders will be frozen once the burn rate reaches steady state (about 6 to 8 cycles).
Models
The "total" curve represents the actual flame speed taking into account the amount of turbulence. At the beginning of combustion, the "total" velocity is low because the combustion is mostly laminar, and then it usually moves towards.
EngCylGeom - Cylinder Geometry
ValveConn Connection
InjProfileConn Connection
The name of the reference object 'FPropLiqIncomp' or 'FPropGasCombust' that defines the properties of the liquid to be injected. The name of the reference object 'FPropLiqIncomp' or 'FPropGasCombust' that defines the properties of the liquid to be injected. The part of the fuel that is mixed before the start of combustion and burned in the "premix" part of the Wiebe function or the name of a dependency reference object.
Duration in crank angle degrees of the tail bump curve or the name of a dependency reference object. The duration should exclude the first 10%. and the last 10% of the area under the tailbone curve, i.e. Wiebe exponent of the premixed boom or the name of a dependency reference object. Cylinder Geometry Object Name of the 'EngCylGeomo' reference object that defines the geometry of each cylinder.
Crank.Sllder Object The name of the 'EngCrankSlider' reference object that defines the characteristics of the crank-slider mechanism. This object is used to parameterize the Chen-Flynn engine friction model described in the GT-Power user manual.
