Future of Mobile Global Business Assignment Example | Topics and Well Written Essays - 3000 words

Future of Mobile Global Business - Assignment Example This study evaluates some of these case studies to provide some valuable insight about the contribution of mobile use, and application in commerce and what the prospects for the future are in the mobile industry. It will critically analyse the potential futures in different perspectives such as the competition, role of stakeholders, political, technical, and social issues, and collaboration of mobile in m-business. To get an accurate insight into the contribution of the mobile industry in business, this study will focus on evaluating mobile systems such as MPS (Mobile Payment System), Mobile Ticketing System, and Mobile Learning Systems (M-Learning). In addition, the paper aims to investigate the drivers of mobile applications, their various applications and some the projections in future business world. Through evaluation and analysis of the past researches it also analyses the the past statistics and compares the present trend in the mobile industry. Apart from analysing the contri bution of mobile technology in the business world, this paper will look at how mobile applications such as M-Learning, M-ticketing, and M-Payment systems influence the future development of mobile commerce. It also evaluates the various scenarios of how mobile devices can be used in mobile commerce, their disadvantages, advantages, and the challenges posed in terms of acceptance by people, and the implementation of the technology itself. Key words Mobile mobility; mobile technology; mobile payment system; M-Learning; mobile ticketing system; Short Message Service (SMS); mobile application Introduction One of the most powerful and famous portable technology is mobile technology. It comprises of mobiles phones, PDAs (Personal Digital Assistances), and laptop computers. Mobile services have the capacity to enable and provide services of spatial and temporal constraints. As opposed to other interpersonal services such as online services, which are delivered on the spot, mobile services allow users access to information and services when on the move without being bound to a one spot. In addition, it offers accessibility, ease of use, and flexibility. For instance, through the Mobile Ticketing Service (M-Ticketing), users are able to make bookings and purchase tickets for games, transport, and theatres (Alfawaer, 2011, p848). The advent of mobile phone technology has allowed consumers access to services and content anywhere, anytime. For instance, through wireless devices, mobile phone technology users are able to carry out sell or buy transactions, pay bills, track stock quotes, access bank accounts, make orders, or receive promotions anytime, anywhere. This has been through electronic commerce (E-commerce), which is carrying out business over the internet. This definition is so general and says nothing about the devices used. Normally, a person can access the internet via a wired LAN (connected to a desktop pc) or through a wireless network (phones, PDAs, Laptops, etc.). When we access e-commerce via wireless networks such as through a mobile phone, we refer to it as mobile commerce (M-Commerce). Through mobile devices such as PDAs and mobile phones, mobile business services have a promising future. Applications functions such as news, ticketing, can be optimized for business functionality (Abdelkarim & Nasereddin, 2004, p52). In the business world, information is considered the most valuable aspect of business than money. Given this importance, accuracy, volume, and the swiftness of available information is equally significant. Modern businesses today bases their future profits on the timeliness of information concerning the development of customers’

Environmental Microbiology Assignment Example | Topics and Well Written Essays - 250 words - 2

Environmental Microbiology - Assignment Example flu in humans are very similar to conventional influenza which generally involves muscular pains, cough, general body weakness, chills, fever, severe migraine and general discomfort. Human to human infection of this virus is also prevalent in a manner similar to that of the common flu, namely through coughing & sneezing of infected individuals or by touching something with flu virus on it and then eating food without washing the hands etc. Swine flu is also transmitted to humans by eating pork products which are not cooked to at least 160Â °F, which kills the swine flu virus and other dangerous bacteria and viruses. It has been noted that although conventional treatment for swine flu exits, natural medicines have also been quite successful in treating and preventing pandemic outbreaks of this virus, especially homeopathic and herbal medicine therapies. (Kruzel p.2) Now even vaccines for swine flu prevention are available and public awareness campaigns and education programs have helped increase awareness about this virus to the masses. The best treatment for swine-flu is possible if a physician is contacted within 1-2 days of noticing the swine flu

World Literature Essay Example | Topics and Well Written Essays - 1250 words

World Literature - Essay Example Set in Corinth in Greece, the whole play is enacted in a single scene in front of Medea's house. The nurse and chorus act as conscious-keepers of Medea and the attenders and messengers are employed by the playwright to depict scene shifts through their speech. In fact, the very opening of the play sets the tone of the horrific nature of events to follow. With a voice of doom of one of the nurses of Medea clearly indicates that her mistress, a victim of fate, is out to contrive some untoward scheme. The nurse acts as a foreteller of deeds to ensue. Through her speech we learn how in love she was with Jason and how her dangerous mood was capable of so much anger evil. "There is a subtle but fascinating theme of ethnic tension as Medea and Jason clash" (Mazza, Michael J) throughout the play. Medea lies fasting and weeping ever since she learnt that she was wronged by her husband, recalling memories of her dear father, her country and her home, which she gave up to come away with the man who now holds her in dishonor. Medea had antagonized her father and even killed her own brother in order to run away from a barbarious land to a land of promise along with Jason whom she blindly loves. "My love for you was greater than my wisdom" (lines 571-72) she says. After a series of adventures in which Jason is helped by Medea, they seek asylum in Corinth. Here they lead a respectable life and beget two children till they almost reach their middle age. Trouble brews when Jason gets restless with his complacent life. He wants a secure, wealthy future for his wife and children and hence resorts to infidelity. He wins the heart of Glauce, the daughter of Creon, king of Corinth. He tells Medea that it was not for love that he had promised to marry the princess, but to win wealth and power for himself and his sons. But Medea is infuriated and her unfailing love immediately turns to sheer anger. In a sense, it is Medea's own nature and vicious temper that proves her undoing. "Women don't like violence, but when their husbands desert them, that is different. In life, the worst disasters come from passion" (lines 467-69) Medea gets into a constant state of confusion and anxiety. Initially she weeps over her hapless situation. She feels women are most wretched because they care for one man only. But she gains a little confidence when Aegeus, King of Athens grants her asylum in exchange for helping him beget children by her skills in sorcery. Aegeus realizes that her scorn is justified and sees her as a woman with remarkable forethought. "A brain like yours is what is needed" he says. He fully believes in her powers of creation which is equal to her powers of destruction, which is why he uses her witchcraft to make his queen beget children. With the success of each scheme Medea devises, her resolve hardens and reaches a point of no return. "One can clearly trace the progression within the play of a victim with certain heroic traits who, because of her ill fate and her ruthlessness, becomes a villain" (Kliegl, Michael) Deciding to take her plans forward, she manages to buy a day's time from Creon befor e she is sent on exile. Creon's fate is sealed even though he knows that Medea is "A clever woman, very experienced in evil ways" (lines

Reducing Incidences of Child Obesity Research Proposal

Reducing Incidences of Child Obesity - Research Proposal Example The imbalance leads to such weight differences and redefines the way children will develop later in life. Genetic factors also form a huge part of the obesity trends. Many children are seen to be susceptible to obesity-conducive genes, which makes it easier to develop such weight problems if the parents do not offer a chance to capitalize on retaining a healthy lifestyle always. Â  The important thing is to generate new understanding of what obesity is all about. The case involving the utility of the resources available for the sake of intervening in the very early years as a way of preventing the obesity from taking shape and allowing the society to move from a rational way of dealing with the issue to an emotional one. Many of the parents fear that keeping their children from the junk they are used to may be a way of keeping them away from themselves (Rippe, 2013). This means that they do not offer them any guidance that could provide them with a chance of dealing with the issue when it is still in its early stages (Gorard, 2013). Evidence from difference sources highlights the impact that lifestyle choices could have in tracking obesity and allowing adults to lose weight and keep fit, as well as allow the children to choose better lifestyles. The purpose of introducing the changes from a tender age is the fact that they are easily receptive at this age ( Rippe, 2013). Preventing its occurrence is essential as a way of managing the weight issues amongst the children. Â  Obesity amongst children has in many developed countries reached epidemic levels. This means that so many children are falling into this trap when they are much younger than they should be. At least 25% of the children in the US alone are in the overweight category with 11% of these falling into the obese category (Ahima, 2013).

Mgt checkpoint 3 Essay Example | Topics and Well Written Essays - 250 words

Mgt checkpoint 3 - Essay Example The article also considers the personnel professionals to be responsible for managing substance abuse in the work place. This include offering guidance and counseling to people affected by substance abuse. Employees are able to perform and meet their expectations if they are free from destructive habits. Most employees get involved in substance abuse due to work related issue such as stress. Personnel professional such as supervisors are charged with the responsibility of ensuring that employees within an organization perform to their expectations. Supervisors are therefore responsible for ensuring that employees within their organization lead a life that is free from substance abuse. Supervisors within an organization face issue of diversity in their daily responsibilities. Substance abuse is common factor that contribute to the diversity of employees within an organization. Supervisors can use information contained in Smits and Pace article to formulate policies for the management of substance abuse in their workplace. The information can also be used to articulate workers such that they avoid getting involved in drug abuse. This will greatly help the organization to meet its

Meaning of life, Life Essay Example for Free

Meaning of life, Life Essay Suffering is an inevitable part of life. We all live in this big labyrinth of suffering. Th only way out of the labyrinth is death. † To live is to suffer, to survive to find meaning in the suffering. Few peopl e actually commit suicide to liberate themselves form suffering. Most people find meaning or purpo se for their life so that they have the motivation to live on. Some think that suffering make them wis er, some think that suffering is a test of faith, there will be rewards for them in the after life if they c an endure the suffering on earth. Some people couldnt understand but keep going on with their life for their loved ones. Some people keep themselves busy to dodge from the question. My view on this question is that suffering does not make life any more or any less meaningful. Beca use as an atheist, I believe that there is no God, the Universe does not have a divine plan for us. Tha t the existence of life is just purely a miraculous accident. When we die, we stop existing. The time we spend on Earth will not amount to anything in an afterlife in another dimension. Therefore, life i s inherently meaningless, with or without pain and suffering. Human are powerless in the face of m eaninglessness . The only way we can deal with life is to embrace the fact that there is no intrinsic va lue in life. We can only create our own meanings. One can create meaning of life with or without su ffering. But since suffering is an inseparable part of our life, it more or less give us insights on mean ing of life. Dr. Bernard Rieux can best exemplifies my point of view. When the plague got out of control and O ran was placed under quarantine, it didn’t stop the doctor form battling the plague, fighting the war t hat was doomed to fail. At this point, many would wonder what is meaning of of the doctor’s action s when they are all in vain. The answer can be found in a dialogue he shared with Tarrou. Tarrou asked the doctor why he was so committed to fighting the plague if he does not believe in G od. The doctor replied that whether or not God exist is irrelevant and he didn’t have the time to thin k about what waits him in the future and what will come out of his actions. The only thing he knew that there were sick people suffering and they needed to be cured. Even though he admitted that his struggles against death would only be temporary victories and that the plague was what he referred as an†endless struggle†, he said that this was not the reason to give up struggle. From the dialogue, we can see the doctor was aware of the intrinsic meaninglessness of his life, bec ause he said he wouldnt waste time to think about the existence of God and what his action will lea d to him. If he deemed his life has inherent meaning, he should have thought about the above questi ons. Thought he considered that his life is inherently meaningless, the plague gave me the meaning. The meaning lies in the other people. The doctor was fully aware that his attempts at lifting people out of misery is an impossible task as more and more people became infected and die. And there were no effective cure. Basically, his sitti ng around and doing nothing or wearing himself off to save the patients might just possibly lead to s ame outcome. However, the doctor did not stop his work in face of his powerlessness to alter the situation. Becaus e under this situation, he was left with only two choices, ignore it or act on it. There was no third op tion. The doctor chose the later one because he couldnt bear to see people suffer and doing nothing about it. It’s meaningless to battle the unwindable battle against the plague. It was not defeating the plague that gave meaning to the doctor. It was the people gave him meaning. It was his compassion for others that keep him going in times of suffering. From the case of Dr. Rieux and his battle against the plague, we can see similarities in the real worl d. The plague is like the amoral universe, and Dr. Rieux represents all the human beings. We are po werless in face of the meaningless of life, just as Dr. Rieux was powerless in face of the plague. But we do have a choice, we can create meanings for ourselves just as Dr. Rieux has learnt from sufferin g and found meanings in helping people. Winston Smith from 1974 1984 somewhat share some similarities with Dr. Rieux in terms of action upon the unchangeable, though he was not such a noble and heroic person as Dr. Rieux. In his case, the unchangeable was the Big Brother. Winston Smith lived in a state where every moves, every wo rds ands every thoughts he made were monitored by the Party. In the instance of living in an extrem e state where even having disloyal thought against the party is in violation of law. The meaning of li fe for Smith was not to start a revolution and topple the party, and change the system entirely. Thou gh Smith had thought about it and desired it to happen. Deep down he believed that it was impossibl e to achieve the goal and sooner or later he would be arrested by the Party. Nevertheless, he set out t o challenge the limits of the Party. He kept a diary which has† Down with the Big Brother† written o n it over and over again. He had an forbidden affair with Julia. Also he joined the Brotherhood whic h he believe is the enemy of the Party. I think the meaning for Smith did not lie in being the hero. What was important for him was to stay as human as possible. Through the rebellious acts against the Party in his own ways, he got to keep his spirit and his human side. That was the meaning he could find for himself. Despite the fact that he was completely compromised at last when he was brought into Room 101, where he was tortured to an extreme degree and indoctrinated to cure his â€Å"insaneness†. He was com pletely broke and dehumanised. His passionate hatred towards the Big Brother turned into absolute l oyalty and love. He should not be blamed for betraying Julia and not upholding what he believed in the first place in such extreme conditions. After all, he did try to rebel against the Big Brother even t hough deep down he knew he couldn’t do anything to overthrow the Big Brother. Dr. Rieux and Winston Smith resolved the question of meaning through their rebellious acts against the plague and the Big Brother. There are people who find suffering itself reveals the meaning of lif e. Father Paneloux is a good example to illustrate this point of view. In his first sermon addressing t he plague. He said that the plague was a punishment by God. That it was the result of the sin of all c itizens. He criticised the people for not attending church and repenting for their sins. Therefore the p lague was reminder of God’s power and the Oran residents should start to change their habits and st art to fear God again. Unlike Dr. Rieux, who is an atheist, Father Paneloux based his life and work on his christian faith. F rom a Christian point of view, everything happens on earth has purpose and fit into the grand plan o f God. Therefore, it was his job to make sense of the suffering of the plague so that he and the peopl e listening to him will be able to endure and continue to believe in God. From his interpretation of s uffering, the meaning of life for Father Panels was more easily understood than Dr. Rieux and Winst on Smith. The meaning of life was really simple, that is to serve and honour God in his will. Though he changes his view on suffering drastically after witnessing the death of an innocent child. He did not view suffering as a punishment anymore. He said that the reason why a innocent child sh ould suffer was not something that human would necessarily understand no matter how hard they tri ed. They just had to keep in mind that it was God’s will. One must keep his faith and God and find t he good in bad situation. In spite of a changing tone, the meaning for Father Paneloux remained the same- to serve God. To conclude, life itself is inherently meaningless. Not even religion can provide an universal answer to the meaning of life. There are no answers for that and never will be. Suffering does not make one’ s life meaningful. But through suffering one might find meanings in life and live a meaningful life. Wu Ngai Ching, Ivy 20189319 Grade: 21/25 ? 19/25 (due to 2-day late submission) Comments: ?Ivy – In terms of the main thesis of the essay, you’ve done a good job delineating your own atheist view on the meaning of life and drew 3 examples from the 2 works to discuss what m ight be the meaning of life for them. Your argumentation is quite right and your analysis of e ach of their reaciton and thoughts on this difficult question is right on. ?However, you simply â€Å"narrated† through the whole essay without really giving detailed or c oncrete evidences from the book. I wish you could provide some passages or quotes from se veral particular moments in the book to clearly illustrate your point. This is one of the ways t o demonstrate that you’ve actually done the reading, and that is also what we’ve been doing in class – making your point across by providing specific passages/instances in the book as c oncrete evidence. So please remember to do so for your final paper!

Advantages Of Internal Combustion Engines Engineering Essay

Advantages Of Internal Combustion Engines Engineering Essay The most widely used heat engine is the internal combustion engine. The advantages that it has over gas turbines have seen its widespread usage in passenger car applications. [1] All the components of internal combustion engines work at an average temperature which is below the maximum temperature of the working fluid in the working cycle. This is because the high temperature of the working fluid in the cycle persists only for a very small fraction of the cycle time. As a result, fluids with high working temperatures can be used to increase thermal efficiency at moderate maximum working pressures. Weight to power ratio is less than that of steam turbine and gas turbines. It is therefore possible to develop reciprocating IC engines of very small power output with reasonable thermal efficiency and cost. Higher brake thermal efficiency can be obtained as only a small fraction of heat energy of the fuel is dissipated to the cooling system. Initial cost is low. Materials used in the manufacture of gas turbines must be strong and heat resistant in order to sustain the heat generated. Machining operations required for gas turbines construction are also more complex. Reciprocating IC engines are more efficient at idle speeds than gas turbines in terms of fuel consumption at idling. Gas turbines have delayed responses to different power requirements changes. Gas turbines must be removed for overhaul and servicing, which is usually not the case in internal combustion engines. Gas turbines require more air than IC engines for its normal operation. It also consumes more fuel whenever the load fluctuates, which is common in the domestic usage. All these explain why passenger cars do not use gas turbine engines, but use internal combustion engines instead. Question 2 Define the following parameters and give typical values for spark-ignition and compression ignition IC engines: Specific fuel consumption, Specific fuel consumption (SFC) is the fuel flow rate per unit power output []. It measures how efficiency of an engine in using the fuel to produce useful work. The equation for the specific fuel consumption is: Where: Ke= specific fuel consumption K: Fuel Consumption, kg/s Pe=Useful work per cycle, i = 0.5 for 4ÃŽ, 1 for 2ÃŽ ne=real efficiency HÃŽÂ ± =Heat of Combustion = 42.000 KJ/Kg Low values of SFC are obviously desirable. For SI engines typical values of brake specific fuel consumption are about 270 g/kWh. Range (345 285 g/kWh) For CI engines, values are lower and in large engines can go below 200 g/kWh. Range (285 190 g/kWh) [2] Mean effective pressure, Relative engine performance measure is obtained by dividing the work per cycle by the cylinder volume displaced per cycle. The parameter so obtained has units of force per unit area and is called the mean effective pressure (mep). Where: W=Indicated Work: Vh=Piston Displacement (cylinder) Volume (cc, cm3, lt) H=Length TDC Length BDC For, Naturally aspirated spark ignition engines, maximum values are in the range 850 to 1050 kPa at the engine speed where maximum torque is obtained (about 3000 rev/min). Turbocharged automotive spark-ignition engines the maximum bmep is in the 1250 to 1700 kPa range. Naturally aspirated four-stroke diesels, the maximum bmep is in the 700 to 900 kPa range Turbocharged four-stroke diesel maximum bmep values are typically in the range 1000 to 1200 kPa Turbocharged aftercooled engines this can rise to 1400 kPa Two-stroke cycle diesels have comparable performance to four-stroke cycle engines. Large low-speed two-stroke cycle engines can achieve bmep values of about 1600 kPa. [2] Power-torque relation as function of engine rpm, Engine torque is measured using a dynamometer. The engine is clamped and the output shaft is connected to the dynamometer rotor. The rotor is coupled electromagnetically, hydraulically, or by mechanical friction to a stator, which is supported in low friction bearings. The stator is balanced keeping the rotor stationary. The torque exerted on the stator with the rotor turning is measured by balancing the stator with weights, springs, or pneumatic means. Fig.1 Brake dynamometer- engine torque test [2] Torque is a measure of an engines ability to do work; and power is the rate at which work is done. The value of engine power measured as described above is called brake power Pb. This power is the usable power delivered by the engine to the load-in this case, a brake. Fig.2 Engine power, torque vs. speed plot [3] Correlation between measured force and engine torque: Measured power: (1 PS = 0.736 kW) Conversion between different units may be necessary for power, torque, or angular speed. For example, if rotational speed (revolutions per time) is used in place of angular speed (radians per time), a factor of 2à Ã¢â€š ¬ radians per revolution have to be multiplied. Dividing on the left by 60 seconds per minute and by 1000 watts per kilowatt gives us the following. mbox{power (kW)} = frac{ mbox{torque (N}cdotmbox{m)} times 2 pi times mbox{rotational speed (rpm)}} {60,000} Volumetric efficiency Volumetric efficiency is the ratio of the mass inside the engine cylinder to the mass of air of the displacement volume at atmospheric conditions. It measures the effectiveness of an engines induction process. Volumetric efficiency is used for four-stroke cycle engines which have a distinct induction process and not for two stroke engines. Where pai is the inlet air density Alternatively volumetric efficiency can also be defined as, Indicative values: 4ÃŽ-Otto: 0.7 0.9 2ÃŽ-Otto: 0.5 0.7 Typical maximum values of ÃŽÂ ·v for naturally aspirated engines are in the range 80 to 90 percent. The volumetric efficiency for diesels is somewhat higher than for SI engines. [2] Engine real efficiency as function of engine power, fuel consumption and fuel calorific value The real engine efficiency of an engine can be found out using the relation Where, ne=real efficiency nth= theoretical thermodynamic efficiency ng=quality coefficient (0.4-0.7 Otto; 0.6-0.8 Diesel) nm=mechanical efficiency (0.8) ni=actual efficiency (nth.ng=Pi/Q) K= fuel consumption Kg/s HÃŽÂ ± =Heat of Combustion = 42.000 KJ/Kg Question 3 Describe with simple terms the main air flow path developing inside the cylinder of IC engines relative to the piston motion; make a simple schematic to indicate them. Laser Doppler Velocimetry (LDV) helps us to visualise the charge motion within the cylinder with the help of optically transparent research engines. Computational Fluid Dynamics (CFD) can help in validating the average flow field in the cylinder but the process is expensive. One such CFD software is KIVA-4v, which helps to predict the air charge motion. Swirl flow Swirl is defined as the micro mass rotational motion of charge within the cylinder. It is generated by constructing the intake system to give a tangential component to the intake flow as it enters the cylinder. This is done by shaping and contouring the intake manifold, valve ports, and sometimes even the piston face. Swirl enhances the mixing of air and fuel to give a homogeneous mixture in a short time in modern high-speed engines. It is also responsible for very rapid spreading of flame front during the combustion. Fig.3 Swirl flow in the engine cylinder [3] Swirl flow can be generated by changing the geometry of the inlet port Fig.4 Geometry of inlet port affecting swirl flow [3] (a) Deflector wall (b) directed (c) shallow ramp helical (d) steep ramp helical Similarly inlet valve approach geometry can also generate swirl flow by producing net in-cylinder angular momentum of the charge. Fig.5 Inlet valve geometry affecting swirl flow [2] Squish flow When the piston approaches TDC at the end of the compression stroke, the volume around the outer edges of the combustion chamber reduces drastically. New combustion chamber designs have the clearance volume near the centerline of the cylinder. As the piston approaches TDC, the gas mixture occupying the volume at the outer radius of the cylinder is forced radially inward as this outer volume is reduced to near zero. This radial inward motion of the gas mixture is called squish. It adds to other mass motions within the cylinder to mix the air and fuel, and quickly spreads the flame front. Maximum squish velocity usually occurs at about 10 °bTDC. During combustion, the expansion stroke begins and the volume of the combustion chamber increases. As the piston moves away from TDC, the burning gases are propelled radially outward to fill the now-increasing outer volume along the cylinder walls. This reverse squish helps to spread the flame front during the latter part of combustion Piston motion influences squish as in the case of wedge shaped and bowl-in combustion chambers. Fig.6 Piston motion generating squish [2] (a) Wedge shaped SI combustion chamber (b) bowl-in-piston DI Diesel combustion chamber Tumble As the piston nears TDC, squish motion generates a secondary rotational flow called tumble. This rotation occurs about a circumferential axis near the outer edge of the piston bowl Fig.7Tumble- result of piston motion and squish [3] Turbulence Due to the high velocities involved, all flows into, out of, and within engine cylinders are turbulent flows. The exception to this is those flows in the corners and small crevices of the combustion chamber where the close proximity of the walls dampens out turbulence. As a result of turbulence, thermodynamic transfer rates within an engine are increased by an order of magnitude. Heat transfer, evaporation, mixing, and combustion rates all increase. As engine speed increases, flow rates increase, with a corresponding increase in swirl, squish, and turbulence. This increases the real-time rate of fuel evaporation, mixing of the fuel vapor and air, and combustion. Intake turbulent mixture flow Turbulence superimposed on mixture swirl Fig.8 Turbulence of the charge within cylinder [4] Question 4 The Figure below shows a conceptual model of a quasi-steady Diesel combustion plume, as presented by Dec et al in 1997. Indicate the following areas shown on this schematic: liquid fuel , rich vapour fuel-air mixture , fuel-rich premixed flame, initial soot formation , diffusion flame boundary , thermal NO production zone , soot oxidation zone , 25398f1.jpg Fig.9 Quasi-steady Diesel combustion plume [5] The above figure describes the formation and features of a quasi-steady diesel fuel jet. This model is applicable to large bore, quiescent chamber combustion or a free fuel jet without wall interactions. At the point of fuel injection, fuel penetrates into the combustion chamber and air which is at a high temperature due to end of compression stroke begins to mix with the spray. Fuel absorbs energy from the hot air and evaporates. This process continues until a point where no liquid fuel is present. The point at which this occurs is called the liquid length. This liquid length reduces after the start of combustion but thereafter remains constant until the end of injection. Beyond the liquid length, the rich premixed fuel and air are still heated by the surroundings until they start to react in the rich premixed zone. The products of rich combustion continue downstream and diffuse and mix radially outward until reaching the surrounding cylinder gases. At a location where the rich prod ucts and cylinder gases mix to produce a stoichiometric mixture, a diffusion flame is produced. The diffusion flame surrounds the jet in a thin turbulent sheet, which extends upstream towards the nozzle. The axial distance from the nozzle exit to the diffusion flame is the lift-off length. The lift-off length controls the amount of oxygen mixed into the fuel jet and therefore the stoichiometry. Soot is burned out and NOX is produced on the outside of the diffusion flame, where temperatures are high and oxygen and nitrogen are abundant. Question 5 What are the main requirements of the fuel injection system for a direct injection engine? In recent years, significant progress has been made in the development of advanced computer-controlled fuel injection systems, which has had much to do with the research and development activities related to Direct Injected engines being expanded. [6]The main requirements of the fuel injection system for a direct injection engine are: Well atomised fuel spray independent of chamber pressure conditions Injection during the compression stroke against pressures up to 20bar Injection during the intake stroke against atmospheric pressures with stoichiometric homogeneous mixture To have uniform distribution of fuel in a multi cylinder engine To improve breathing capacity of an engine i.e. volumetric efficiency To reduce or eliminate detonation To prevent fuel loss in the form of scavenging in the case of two stroke engines. For an efficient combustion of a stratified mixture, a stable and compact spray geometry is necessary Injection pressure has been determined to be very important for obtaining both effective spray atomization and the required level of spray penetration. Accurate fuel metering (generally a +2% band over the linear flow range); Desirable fuel mass distribution pattern for the application; Minimal spray skew for both sac and main sprays; Good spray axisymmetry over the operating range; Minimal drippage and zero fuel leakage, particularly for cold operation; Small sac volume; Good low-end linearity between the dynamic flow and the fuel pulse width; Small pulse-to-pulse variation in fuel quantity and spray characteristics; Minimal variation in the above parameters from unit to unit. Question 6 Describe the injection process requirements for direct injection Diesel engines and the evolution of the fuel injection equipment over the last few decades. The functional requirements of the fuel injection system are as follows Accurate fuel metering per engine working cycle Injection timing to ensure maximum power, good fuel economy and low emissions Obtain the desirable heat release pattern by control of injection rate Atomisation of the fuel Proper spray pattern to ensure better mixing of fuel and air Uniform distribution of fuel droplets in the combustion chamber Supply equal quantities of fuel to all cylinders, in the case of multi cylinder engines Eliminate dripping of fuel droplets into the combustion chamber by eliminating injection lag between start and end of injection Evolution of fuel injection equipment: In-line pump Fig.10 Layout of In-line fuel injection pump [7] Though in-line pumps are primitive injection systems, they are still in use among heavy duty marine engines. Individual fuel pumps fuel each of the injectors Engine operational speed has a major influence on the fuel injection pressures As a result, there is a hydraulic delay between the pressure increase and the start of injection Fuel flows through high pressure connecting pipes Fuel injection pressures range from 600 1200 bar Injector with discharging in the combustion chamber (the nozzle with one or more holes) Distributor type pumps These are still used in a number of engines Though it started as mechanically operated, now electronic control modifications have been made It has a mechanism which controls the spill valve responsible for cutting off the high pressure generated inside the pumping chamber, and thus, responsible for the termination of injection One pumping chamber delivers high pressure to all the injectors of the engine Pressure depends on engine speed, so a hydraulic delay exists between the pressure generation and start of injection Relatively low injection pressures (up to 1200bar) Fig.11 Distributor type pump (Lucas CAV) [7] Unit injectors Consists of the pump and the injector integrated into one body, which does not require a high pressure connection pipe High fuel pressure is generated close to the nozzle exit, which can be upto 2500 bar. These gave accurate control over injection Each cylinder has its own individual system High pressure developed depends of the engine rpm and the load. Fig.12 General Layout of Unit injector [7] [6]Delphi Diesel Systems electronic unit injectors (EUI fig13.) control the quantity and the timing of injection electronically through a solenoid actuator. The solenoid can respond very quickly (injection periods are of the order 1 ms), to control very high injection pressures (up to 1600 bar or so). The solenoid controls a spill valve, which in turn controls the injection process. The pumping element is operated directly from a camshaft (or indirectly via a rocker), and the whole assembly is contained within the cylinder head. Fig.13 Electronic Unit injector (Lucas EUI system) [7] [6]An alternative approach to the EUI is the Caterpillar Hydraulic Electronic Unit Injector (HEUI, also supplied by other manufacturers). HEUI uses a hydraulic pressure intensifier system with a 7: 1 pressure ratio to generate the injection pressures. The hydraulic pressure is generated by pumping engine lubricant to a controllable high pressure. Similar to CR injection systems, there is control of the injection pressure. The HEUI uses a two-stage valve to control the oil pressure, and this is able to control the rate at which the fuel pressure rises, thereby controlling the rate of injection, because a lower injection rate can help control NOx emissions. Common Rail fuel injection systems One of the last improvements to the fuel injection system is the Common Rail System that was implemented first by the Fiat Company. Fig.14 Common rail fuel injection system [8] Common rail (CR) fuel injection systems decouple the pressure generation from the injection process and have become popular because of the possibilities offered by electronic control. The key elements of a CR fuel injection system are as follows: A (controllable) high-pressure pump The fuel rail with a pressure sensor Electronically controlled injectors An engine management system (EMS) The injector is an electro-hydraulic device, in which a control valve determines whether or not the injector needle lifts from its seat. The engine management system can divide the injection process into four phases: two pilot injections, main injection, and post-injection (for supplying a controlled quantity of hydrocarbons as a reducing agent for NOx catalysts). Common rail injection also enables a high output to be achieved at a comparatively low engine speed Fuel injectors Fig.15 Types of nozzles used in Diesel fuel injectors [1]