During the past decennary, the hunt for possible alternate fuels, particularly H, has been strenuously performed by legion research workers. In this chapter, a background survey of H economic system and an overview of the effects of H add-on to hydrocarbon fuels are presented along with the aims and overall layout of the thesis.
Concerns about the energy crisis, the increasing cost of crude oil geographic expedition and processing and it inauspicious environmental effects have been the grounds for the go oning hunt for alternate energy beginnings, notably H. For the past 20 old ages, fossil fuels ingestion has increased up to 37 % ( Enerdata, 2010 ) and the turning demand might due to increasing population and industrial developments, particularly in developing states. Figure 1.1 shows the entire universe energy ingestion for the last 20 old ages, in which fossil fuels provide about 90 % of the universe ‘s entire energy.
Figure 1.1: World ‘s entire energy ingestion ( adapted from Enerdata, 2010 )
Fossil fuels burning emitted several harmful pollutants, such as C monoxide ( a chief constituent for the nursery gases ) , C dioxide, N oxides, sulfur oxides, and hydrocarbons, which can take to planetary heating and terrible air pollution jobs. By and large, the chemical equations for stoichiometric combustion of hydrocarbon in O and air ( Glassman, 1987 ) are shown in equation 1.1 and 1.2, severally.
( 1.1 )
( 1.2 )
Furthermore, the nowadays of sum suspended particulates as byproducts of the burning procedure contributes to smog and acid rain. These environmental jobs have lead to the debut of rigorous environment policies among the states. In December 2008, European Union leaders have approved several policies ( Europa, 2010 ) that aimed to:
cut down nursery gases at least 20 % by 2020 ( compared with 1990 degrees ) ,
rise renewable energy ‘s portion of the market to 20 % with 10 % of the energy beginnings for conveyance should come from biofuels, electricity or H, and,
cut down overall energy ingestion by 20 % ( compared with projected tendencies ) .
These implemented policies have initiated legion research on clean burning system and clean energy beginnings ; H being one of the energy beginnings.
Hydrogen, which can be produced from abundant beginnings and is environmentally cleaner for terminal users, has been considered as a possible campaigner for energy bearer, therefore making the term ‘hydrogen economic system ‘ . Hydrogen is non an energy beginning, but is an energy bearer which moves energy in a functional signifier from one topographic point to another, an illustration is electricity. Hydrogen can be produced by fossil fuels, atomic, solar, air current, biomass, hydro, geothermic and urban waste resources, and is a byproduct of other chemical procedures. At the minute, H is produce mostly by steam reforming and electrolysis.
Water is produced as a byproduct when it is burned in pure O and can be represented as:
( 1.3 )
The burning of H in air green goodss nitrogen oxide ( NOX ) as a byproduct:
( 1.4 )
However, the emanations are still minimum compared to those of fossil fuels and would non be discussed farther in this thesis.
Hydrogen is the lightest component known to work forces and it has the highest energy content of any common fuel per unit mass ( about three times more than methane ) , but the lowest energy content per unit volume ( about four times less than methane ) . Table 1.1 shows the important belongingss of H compared to methane and propane ( the primary component of natural gas ( NG ) and liquefied crude oil gas ( LPG ) , severally ) , and gasoline. As ascertained, H has a broad flammability scope in comparing with all other fuels.
Unfortunately, its higher flammability and lower volumetric denseness compared to those of conventional fuels make it complicated for supply and storage system where bigger storage volume is needed for H to present the same sum of energy as the other fuels. At normal temperature and force per unit area ( NTP ) , the volume of H needed to present the same sum of energy as methane is within a factor of 4.0. This job is minimised by hive awaying H either as tight gaseous H ( CGH2 ) in H armored combat vehicle at high force per unit area ( 700-900 saloon ) or as liquid H ( LH2 ) in cryogenic H armored combat vehicle at a really low temperature of 20.28 K.
However, these utmost storage and managing steps pose several safety jeopardies to the general public since hive awaying H at high force per unit area and really low temperature introduce safety hazard to environing people in the event of loss of containment. Accidental H release introduces a burning jeopardy to its milieus since it merely need 0.02 mJ ignition energy to light. On the other manus, it high diffusivity makes H a safer fuel in instance of spillage or escape ; it is the lone fuel that escapes upward and does non organize noxious exhausts. However, this phenomenon will merely be valid if merely a little sum of H is released and adequate airing is provided.
One of the of import factors for effectual usage of H as an energy bearer in the hereafter is that whether it is safe plenty for it to be applied into the bing burning procedure. This can be achieved by understanding the burning features, such as stableness and laminar combustion speed, and the alterations that might happen if H is by chance released to the environing environment and mixes with other gaseous dodo fuels. The latter can be studied by look intoing the effects of H add-on to hydrocarbon fuels on its burning features.
Some of the effects of H add-on to hydrocarbon fuels are improved ignitability, fire stableness and burning features of these mixtures, and besides cleaner emanations. Hydrogen add-on to hydrocarbon fuels can speed up the comparatively slower reaction rate of a hydrocarbon fuel, which consequences in an improved ignitability, wider scope of flammability bounds and an improved stableness even in thin combustion government.
Stability is a really of import parametric quantity where it marks the threshold of ignitibility of the fuel mixtures. Previous research by Schefer ( 2003 ) noticed that the add-on of H to methane resulted in a important extension of the thin stableness bound where the add-on of up to 20 % H reduced the thin stableness bound by about 15 % . Nevertheless, the information of the effects of H to other gaseous hydrocarbon fuels in term of its fire stableness is still deficient.
Chemical dynamicss of a burning mechanism is study on the dependance of burning rates on reactants ( fuel and oxidant ) concentrations and temperature. Each composing of the hydrogen-hydrocarbon mixtures possesses a distinguishable burning rate, hence its chemical kinetic due to different concentrations of intermediate extremist pools. Despite the theory, merely a smattering of research workers have studied the effects of H add-on to hydrocarbon fuels on its chemical dynamicss. An of import physical index to the mixtures ‘ chemical dynamicss is its ‘ laminar firing speed.
Laminar firing speed is a cardinal belongings of burning procedure where it is the velocity at which unburned gases moved through the burning moving ridge in the way normal to the moving ridge surface. During the past 20 old ages, a figure of research have been conducted to find the laminar firing speed of hydrogen-hydrocarbon mixtures. Several surveies by Yu et Al. ( 1986 ) , Choudhuri and Gollahalli ( 2000 ) , Sher and Ozdor ( 1992 ) and Wu et Al. ( 2007 ) have reported these fuel mixtures have important by different burning features from those of the primary fuels and H add-on to hydrocarbon fuels, such as methane, C2H6 and propane, can increase the laminal combustion speed of the fires. However, the elaborate effects of H composing on the laminar firing speed of the hydrogen-hydrocarbon mixtures are still equivocal.
Motivated by these issues, the present survey is undertaken to derive a better apprehension of the effects of H add-on to hydrocarbon fuels from chemical dynamicss and burning features point of positions. Methane, C2H6 and propane are used in this research since these hydrocarbons exist in gaseous signifier under atmospheric force per unit area and room temperature. Furthermore, methane and propane are the chief component of liquefied crude oil gas ( LPG ) and natural gas ( NG ) , severally. However, methane does non incorporate any C-C bonds ; hence, C2H6 is introduced in this survey to compare the effects of C-C bond on the mixture chemical dynamicss.
Aims of the Thesis
As mentioned earlier, in order to implement H safely into the bing substructure, a thorough survey of H burning features is needed to be conducted. One of the chief concerns is in the event of loss of containment where H is by chance released and mixes with other hydrocarbon fuels. This can be achieved by understanding the effects of H add-on to hydrocarbon fuels. Therefore, the overall purpose of this survey is to analyze the effects of H add-on to hydrogen-hydrocarbon mixtures on its fire stableness features and chemical dynamicss.
The aims of the research may be summarised as follow:
To by experimentation prove the burning features of hydrogen-methane, hydrogen-ethane and hydrogen-propane mixtures through a series of trials on stableness of the jet fires at different H volumetric composings,
To imitate the burning mechanism of hydrogen-methane, hydrogen-ethane and hydrogen-propane jet fires utilizing chemical kinetic burning patterning packages of KINTECUS at different H volumetric composings.
To find the effects of the H add-on on the laminar firing speed SL hydrogen-methane, hydrogen-ethane and hydrogen-propane mixtures from old research and associate it to chemical kinetic features to formalize the consequences in ( three ) .
To analyze exhaustively the chemical kinetic mechanism of hydrogen-hydrocarbon burning utilizing an set up hydrocarbon oxidization mechanism and set up a nexus between the stabilization mechanism of hydrogen-methane, hydrogen-ethane and hydrogen-propane jet fires and its corresponding chemical kinetic at different H volumetric composings.
By and large, the research is categorised into two parts and can be illustrated as follows:
Effectss of H add-on to hydrogen-methane, hydrogen-ethane and hydrogen-propane mixtures
Figure 1.2: General construct of the research
In this research, the fire stableness features hydrogen-methane, hydrogen-ethane and hydrogen-propane jet fires are determined by experimentation at 1 saloon and 293 K utilizing a individual jet diffusion burner method. The fuel composings are varied from pure H to pure hydrocarbons. The lift-off tallness, blow out and blow off speeds of these mixtures are obtained and these experimental values are compared with experimental informations of fire stabilization in the literature.
The effects of H add-on on the chemical kinetic of the mixtures are studied utilizing numerical simulation method. The burning mechanism of these mixtures numerically modeled utilizing chemical kinetic burning patterning packages of KINTECUS. Furthermore, old experimental informations on laminar firing speeds hydrogen-methane, hydrogen-ethane and hydrogen-propane jet fires are collected and the effects of H add-on on laminar firing speeds of these mixtures are analysed. Laminar firing speed is an of import parametric quantity to foretell the fire chemical kinetic and the information will formalize the consequences obtained utilizing the numerical simulations.
In order to place the relationships between fire stabilization mechanism and its chemical kinetic, a thorough chemical mechanism analysis utilizing Curran ‘s Hydrocarbon Oxidation Mechanism ( Curran et al. , 2004 ) is conducted. It totaled up to 654 reactions and consists of:
mechanism of H2 and CO,
mechanism of C1/C2 hydrocarbons oxidization, and
mechanism of C3 hydrocarbons oxidization.
Layout of the Thesis
This thesis is divided into 9 chief chapters. The first chapter summarised the information on the chief job of the survey, every bit good as the purposes and aims of the research. It besides consists of a sum-up on the construction of the thesis.
Chapter two, three and four provides a literature reappraisal of old research which contains the general background on the survey of the effects of H add-on on fire stableness features, its laminar combustion speed and chemical kinetic of hydrogen-hydrocarbon mixtures. Several stableness features such as affiliated fire, lift-off fire, blow-out and blow-off speeds are discussed. Past research on fire stableness on assorted mixtures were reviewed in this chapter including the experimental method used in these surveies every bit good as the consequences and decisions obtained. Several numerical methods to imitate fire burning are besides presented and discussed. General background on the chemical kinetic high spots the function of active extremist ( H, OH, O and CH ) in finding the rate of burning of hydrogen-hydrocarbon mixtures, therefore, its laminar combustion speed, Su.
Chapter five covers the experimental methodological analysiss that have been used in this survey, including the description of the current fire stableness experimental constellations, the lift-off monitoring attack, instrumentality and outlined programme of research lab trials. Chapter six consists of consequences and stableness features analysis at assorted H composings of the trials described in Chapter three and Chapter seven discussed the consequences obtained from the stableness trials.
The numerical mold methodological analysiss are explained in Chapter eight. The chemical kinetic mechanisms of hydrogen-hydrocarbon burning are modelled utilizing KINTECUS package bundle at different H composings. The consequences and analysis of Chapter eight are presented and discussed in Chapter nine.
Further analysis of the chemical kinetic of hydrogen-hydrocarbon burning mechanism is besides presented in Chapter nine. The nexus between stableness features of hydrogen-hydrocarbon fires and its corresponding chemical kinetic at similar composings is established.
This is followed by the concluding Chapter 10 which concluded the survey and suggested further plants in the hereafter.