“If I Had A Choice” By Walt Whitan Essay

Wave resemblance in Walt Whitman’s â€Å"If I Had the Choice† Although not rhythmically or metrically consistent throughout, Walt Whitman’s poem â€Å"If I Had the Choice† is very consistent in its attempt to resemble the characteristics, specifically the waves, of the sea; whether read, heard, or seen, the poem’s adaptation to a wave’s nature is clearly evident. Whitman’s use of repeated, but not uniform, rhythm in the poem exposes the â€Å"up and down† nature of waves, while the sudden, drastic change in rhythm helps depict the crashing of a wave. The metrical variation in the poem similarly attributes to the resemblance of a wave, for it goes hand in hand with the length of each line, giving the poem the physical characteristics of a wave. While the there is no metrical consistency throughout the poem (probably done because no two waves are identically alike), there is a noticeable pattern and consistency in the rhythm of the poem. The consecutive use of iambs in the first five lines of the poem help to not only emphasize the steady motion of the sea, but more importantly to give the poem a sense of the â€Å"up and down† motion of the waves in the sea; the pattern of unstressed/stressed/unstressed/stressed syllables in every line is very similar to the up and down undulation of a wave. The shift from the iambic rhythm in lines one through five to a â€Å"loud,† sudden spondee in line six clearly depicts the image of a wave crashing. The spondaic rhythm (stress/stress) of the first two words in line six, â€Å"These, these,† is an unexpected, drastic change from the prior unstressed/stressed pattern. Similar to the crashing of a wave, this change was drastic, and quick; it does not last long, hence the reason for the poem’s quick return to an iambic rhythm. The poem’s last three lines are once again consistently iambic; they are back to the quiet, pacific motion of waves in the sea. Just as the height of a wave affects the power of a wave, the meter of this poem affects it’s rhythm. Although there is no specific pattern for the number of feet per line in this poem, the meter is still greatly significant. When broken up iambically, the number of feet increase steadily from line one to four, until we reach line five, the longest (10 feet) line. The length of line five is significantly important in portraying the nature of waves; it is representative of the amplitude of a wave before it is about  to crash. Line five is ten feet long because it is followed by line six, the line in which there was a sudden rhythmical change, which portrayed the crashing of the wave. Once it crashes, the waves return to their prior size, just as the following lines of the poem go back to having the same range of feet as they did before line five. The alternating number of feet per line also allow the poem’s structure to resemble a wave; no two waves are similar in frequency (height) or amplitude (width), just as no two sentences of this poem are identical in length. As the lines approach the middle of the poem, they get longer, and then begin decreasing in size after they reached the longest point, line five. Since line five, the middle of the poem, is the longest line, when held sideways, this line is representative of the middle of a wave, it’s highest point right before it crashes. By using rhythm and meter skillfully, this poem is successful in imitating the rhythm of the sea, and the â€Å"meter† of the waves in the sea. In doing this, Whitman makes a very distinctive point; rhythm and meter affect each other, just as the height of a wave affects it’s crash. This relationship is evident whether one reads, sees or hears this poem.

United States Constitution

In the introduction of the book They Take our Jobs! : and 20 other myths about immigration written by Aviva Chomsky, Chomsky picks apart the words in the United States Constitution to support her belief that although immigrants, specifically Latino/Hispanic immigrants, are a large part in today’s U. S. society, they still do not have any rights or protection from the laws of the Constitution. She states that many of the arguments against immigrants in the United States stem from â€Å"serious misconceptions† that have been rooted from history up until present day.The view that immigration only brings about more problems and segregations for the host country has been on-going in history. When it comes down to it, a simple analogy could be made: it is difficult for the citizens or â€Å"homeowners† to be forced to house immigrants or â€Å"strangers† in their own country or home. This idea is then exaggerated and made extreme when times are tough or the peop le of the United States need a scapegoat to put their problems or the government/societal issues on.The finger is pointed at the group of outcasts—immigrants. They are easy targets. Easy because immigrants who are non-citizens are â€Å"legally deprived† of many rights the U. S. Constitution provides for citizens. What many fail to realize, as pointed out in Chacon’s Introduction in No One is Illegal is that immigrants who are here, working, living, and building a life here in the United States contribute a great deal to the overall economy and working class.They take part in the jobs that require heavy manual labor and provide the basic jobs for many large corporations in the United States at minimum wage. Rest assured, it is probable that many of their jobs should be compensated at a higher pay for the type of work they are doing, since most are jobs that many of the middle and higher class citizens cringe at when they think about it. I have speculated that th e amount of wage pay or salary today is based upon one’s credentials or experience rather than the manual load or extremities of the job at hand.This correlates to the jobs that many immigrants take on, they do a lot of work for little pay. They work for huge well known corporations and provide the labor needed to keep production at a particular rate. When times are tough and jobs are difficult to find, like right now, the blame is put upon the immigrants who hold these types of jobs. It is said that â€Å"they stole our jobs† and that is why we are unemployed and out of work. However, when looking at the core of the problem, it is not that the immigrants are ith jobs but rather the fact that the higher salary paying jobs and higher wage paying jobs are being let go first due to the downward economy and replaced with other persons who may be less qualified but could still complete the job and task at hand. As discussed, immigrants are a big part of today’s †Å"world† and the fact that they lead their daily lives just as a citizen would, immigrants are still not granted certain simple rights a newborn child is given at birth in the United States due to biases, beliefs and judgments based on history classes, politicians, and the media.

Letter from the Pope to de Las Casas Essay Example | Topics and Well Written Essays - 500 words

Letter from the Pope to de Las Casas - Essay Example It is utterly shocking and saddening to read of the atrocities committed by a man upon a fellow man. The indigenous people of the Hispaniola Island, The Taino Indians, are human just like us. They are friendly and peace loving, with utter hospitality to visitors. At no time did they ever react in a violent manner towards the Spanish visitors who went there. Columbus himself acknowledged the fact that even though they were still primitive and leading a very basic way of life, they were very hospitable. Their culture and simplicity gave them an inner joy, which glowed to the outside .This, is the life we have always wanted, and which the bible teaches us to live. It is also from our Christian teaching that we learn about treating each other like a brother and loving our neighbors as we love ourselves. Therefore, it is a shame and absolutely reproachable, when I read of your report. It is only the physical capacity and the military authority that I do not have, but culprits of such acts needed to be dealt with accordingly. The Catholic Church is going to maintain its initial push for global evangelization. The most positive bit of it is the discovery of the New World by Columbus and his team, which serves as fertile ground for evangelism. The initial task of Columbus was to spread Catholicism at a rapid rate in order to combat the spread of Islam to these regions. This is what the church was in support of. However, the church holds no support for slavery, slave trade or anything connected in whoever way, to such practices. We also abhor forced labor as learnt from your report, which is being meted upon the locals in the gold and silver mines. Your efforts in fighting for the rights and freedom of the Indians on the region shall be fully supported by the church. This is because your approach of colonization by farmers rather than soldiers, is the most effective and

Philosophy Essay Example | Topics and Well Written Essays - 2500 words

Philosophy - Essay Example Turing’s article discussed the famous Turing test, i.e. the imitation game. A similar take on Turing’s philosophy is John Searle’s Chinese room argument or thought experiment. In this essay, I would like to share something vital that I learned in our discussions in class, as well as something that I learned beyond our class discussions, since the topic was of great value to me. I shall give an overview of Turing and Searle’s philosophy of mind. Afterwards, I shall show how their philosophy is of much value to me, in this present day. For, I do believe that topics such as these are not only valuable inside classrooms but also in the real world, that is, in my life. To begin with, like Turing, the Chinese room argument or thought-experiment, advanced by John Searle (1980), specifically challenges the view of artificial intelligence or what is more commonly known as the computational theory of mind. It challenges the claim that all there is in having a mind i s the implementation of a computer program, and that as a consequence, the mental states of humans are no different in kind from the computational states of a running computer program. The Chinese room argument challenges this claim by showing that, unlike humans, computers do not know what the contents of their computational states (or the symbols they manipulate) are about or represent in the world. What computers only know of these symbols are their shapes and the ways in which they should be combined according to the rules of their programs. The Chinese room argument, in its simple form, goes this way. Imagine a native English speaker who does not understand Chinese is locked in a room with only two outlets. Outside of this room are native Chinese speakers who do not know who or what is inside the room. In one outlet, the Chinese speakers give the person inside the room several manuscripts bearing Chinese symbols and a manual of English instructions for manipulating these Chines e symbols. The person inside the room does not even know that the symbols are Chinese; he only recognizes and individuates the symbols according to their shapes or formal properties. Now imagine that the manual, which the person has immediately mastered, says that if he recognizes certain combinations of symbols in the manuscripts given to him in one outlet, then he should arrange certain combinations of symbols and send them to the persons outside the room through the other outlet. Suppose that what the person inside the room sends to the persons outside the room are correct answers to the questions that the persons outside the room ask him through the manuscripts that they send him. In this case, in so far as the persons outside the room are concerned, the person inside the room understands Chinese. But the fact is the person inside the room does not understand the symbols—he does not even know that they are Chinese; he does not know what they represent; and he simply manip ulates them according to the instructions in the manual. Technically speaking, he does not know the semantics of those symbols; he only knows their syntax. So does that count as intelligence? Similarly, an important thought experiment that is used to defend the views of artificial intelligence is the Turing test as discussed in our previous lessons. It will be recalled that according to this test, if after a series of questions and answers, the human interrogator could not tell, on

Lower Limb Prosthetics Evolution Article Example | Topics and Well Written Essays - 500 words

Lower Limb Prosthetics Evolution - Article Example Presently, there has been the use of Carbon fiber springs in the prostheses that allows improved shock absorption and mobility without increasing any weight. Additionally, the carbon fiber have allowed active amputees to wear limbs that can help in the absorption of two to four times their total body weight. In 2004, the esteemed international event aided the drive of development of lighter and more functional devices such as the gait-adaptive knee and an artificial limb that can be modified for its users2. There has been the advancement of the technology today where scientists and developed with the advent of microprocessors, robotics and computer chips have allowed amputees to get back to their accustomed lifestyle. United States., United States., & United States. (1984). Journal of rehabilitation research and development. Washington, D.C: Veterans Administration, Dept. of Medicine and Surgery, Rehabilitation R & D

Google Health and the Future of Personal Health Records Case Study

Google Health and the Future of Personal Health Records - Case Study Example Even Microsoft or Apple failed to recognize the opportunity provided by PHRs. It should be noted that Google was waiting for a breakthrough product to capture or regain market dominance. It should be noted that Google’s market share was considerably reduced in the recent past because of tight competition from prominent companies such as Apple, Facebook, Microsoft, Amazon etc. The offering of the cloud-based product Google Health in 2008 was received with high expectations. Many people though that Google at last succeeded in developing a breakthrough product to counter the challenges from competitors. Nobody can blame the consumer expectation of this product, especially because it could represent a truly consumer based PHR, given the characteristics of the company behind its design. Google was successful in incorporating all the ingredients needed for a PHR system to Google health. Google’s market reputation was huge and nobody had any doubt about the capabilities of Goo gle. Moreover the health care reform initiative in America is getting momentum after to Obama came into power. In short, the opportunity for Google health was huge. Sometimes facts are stranger than fiction. In the case of Google Health, the above statement is absolutely true. On June 24th of 2011, Google Health crashed in its intent of positioning in the difficult PHR market, leaving behind many questions and some lessons for future entrants. This paper reviews and analyses the reasons why Google Health failed as a health information solution for consumer/patient healthcare information management and the future of PHRs. Archer (2011) mentioned that â€Å"Electronic personal health record systems (PHRs) support patient cantered healthcare by making medical records and other relevant information accessible to patients, thus assisting patients in health self-management† (Archer, 2011, p.515). Current

Jacob's Creek in Australia Essay Example | Topics and Well Written Essays - 1000 words

Jacob's Creek in Australia - Essay Example This resulted in many branches of its name, for instance, Jacob’s Creek Centenary Hill Shiraz in Barossa, Jacob’s Creek St Hugo Cabernet Sauvignon in Coonawarra, and Jacob’s Creek Steingarten in Eden Valley.   Jacob’s Creek is Australia’s most known creek and it is mainly in the United Kingdom and other many countries where Jacob’s Creek wine brand is sold. Some of the international drinkers imagine Jacob’s Creek is an entire region though it’s the biggest selling label and almost one million of wine glasses are drunk each day. It is only some kilometers long via the Barossa Range near its peak, Kaiser Stuhl and gurgling down the â€Å"river red gum lined† bed into North Para River. The creek is extremely dry during the vintage time in autumn though Jacob’s Creek name conjures Amazonian of Australian the â€Å"sunshine in a bottle†. Jacob’s Creek has advertising Strategies which mainly involve unique selling proposition, brand image, resonance, emotional, generic and pre-emptive. The unique selling proposition is a strategy which ensures your offering is unique and more valuable from your competitors’ offerings and putting your idea in the minds of target groups to reach customers. Positioning attracts customers by forming a unique and positive identity in the company and its offerings. Jacob’s creek thus utilizes positioning to distinguish its products from others. The world consists of products similar to that of Jacob’s creek but the company makes its products get into advertising overload all through to gain the customer’s attention.

Mark & Spencer Essay Example | Topics and Well Written Essays - 2250 words - 1

Mark & Spencer - Essay Example The analysis has been carried out using Key performance indicators (KPI), which are essential in determining the nature of performance being shown by the company, has been outlined in the appendices. The balance scorecard and the strategy map formulated can serve as an effective guiding tool for the company, which when followed in a proper way, can be utilized to predict its effective future plan. This study contains suitable recommendations based on the key parameters used for the purpose of analysis which can serve as a benchmark for the company to evaluate its performance thereby comparing them to the performance of other peer organizations. The recommendations made can contribute significantly towards the identification of the company’s strength and weaknesses in the HR division and help it to bring about improvements in its financial and non-financial performances. In the end, critical discussion and evaluation has been done suggesting the usage of balanced scorecard anal ysis and strategy map. Table of Contents 1. Introduction 4 2. Vision and Strategy 4 3. Balanced Scorecard for Marks and Spencer PLC (Human Resource Division) 5 3.1. Financial Perspective 5 3.2. Customer perspective 6 3.3. Business Operations perspective 6 3.4. ... Having a worldwide presence, M&S offers varied line of products to its customers ranging from clothing; home ware and food retail (Reuters, 2013). The report will conduct a thorough analysis of the human resource division of M&S thereby identifying its vision and strategy. In addition to that, a balance scorecard and strategy map will be formulated from the Human Resource Division perspective depicting the alignment between the strategies adopted and their significance towards the company’s goals and targets. 2. Vision and Strategy The HR team of M&S deals with ‘people’ side of the organization which adheres to find the right mix of talented people to join them and then ensuring their happiness & growth alongside the growth of the company (Marks and Spencer, 2013). Their vision is to employ a rigid and disciplined workforce where the leadership team along with the workforce will ensure that all their tasks are directed towards the achievement of the strategic obje ctives (Marks and Spencer, 2013). Their focus lies in making the workforce understand their strategy, embrace it and motivate them towards supporting strategy execution. In addition, they also want to ensure the integration of a competent workforce (especially people holding the key positions) and imparting them the necessary knowledge and skills through various training programs whereby, the workforce can be of significant contribution towards achieving sustainable success (Huselid, 2005b). The strategies of M&S’s human resource division can be best explained by the HR architecture that they follow. Employing the right mix of qualified HR personnel whose competencies can be aligned to the needs of the business (Marks and Spencer, 2013).

My Eldest Cousin Essay Example for Free

My Eldest Cousin Essay Many people admire singers, movie stars, who make so much money that they could do everything they want and are famous. However, they don’t even know the person or their personality whom they admire. To me, admiration is a kind of respect. But there aren’t a lot of people who deserve this sort of respect from me in this world. Respecting my parents who raised me is the important thing that I have to do for the rest of my life. Besides my parents, my eldest cousin is the only person who made me look at things differently. He is two years older than me. His name is Khoi. I can remember when I was a high school kid. My family used to live in a rural town that was far away from my school. For convenience, I had to stay temporarily in my aunt’s house for studying. My aunt has only one son who is my eldest cousin. He has curly hair, tall with dark skin and his body was built with muscle. Those things made him look extremely strong. I could imagine that he is like a stone, like Bruce Lee. He was very good at sports. Read more:  Most admirable person  essay Playing basketball was his favorite one. Whenever he played, his team won most of the time. It was interesting to observe how extremely emotionally involved he was in the game. He had many fans in our school, many people liked him. I can remember one of his games. His team was down by three points and they had only five seconds left, he had the ball from a teammate and then he made a three pointer to make the game in a tie. They went over time. Finally, his team won by five points. After finishing the game, some of his fans carried him and ran around the basketball court for celebrating. Sport was always for him a source of fun, emotions, experiences, which are important ingredients in his spiritual life. Not only he was very good at sports, but also his knowledge was broad. He was the person who had the highest grades in the school. All teachers loved him, they always told us â€Å" Khoi is a good student, he deserves to be the person for you to learn from†. He did too great in the school. Consequently, few people hated him because they were jealous. Despite of the fact that he was a good student in our school, he wasn’t haughty. He always thought that he had to learn more and more every day even though he was only 18 years old by that time. At home, he was also a good son. He always respected his parents and elders. He helped his mother to clean house, wash dishes, mop floors more and more†¦ He also helped me on my homework, helped me whenever I got in troubles. Our neighbors liked him too. One of our neighbor talked to his parents and said â€Å"You have a great son, you must be proud of him†. His parents were very happy. My cousin never stopped learning new things. He always got advices from other people even though he had his ideas to solve his problems. He became a business man successfully after finishing his major. He was glad to help everyone who was in our family whenever we had troubles. He taught me about life experience and helped me when I got in troubles. For example, after a long day of work he was really tired and just wanted to go home and took a nap. Instead, he spent time and listened to me about troubles that I had. And then he solved the problems and gave me some advices before taking the shower. In conclusion, I admire my eldest cousin because he taught me about life, and tried to help me when I needed him. He is the greatest person that I’ve ever known. He is the person that I would like to learn from. He advised me that I need to treat people respectfully; I should not stop learning new things and try to help people if they need me. Otherwise, my life will be meaningless.

Ignition Timing Advance Of The Petrol Engine Engineering Essay

Ignition Timing Advance Of The Petrol Engine Engineering Essay Ignition Timing: as applied to the spark ignition engines (petrol engines) is a process of setting the time at which the spark plug should fire in the combustion chamber during the compression with respect to the piston position and the crankshaft angular velocity. The spark plug should fire before TDC and the flame should terminate after TDC. Setting the appropriate ignition timing is very crucial as it decides the time available for combustion of the air-fuel mixture. Hence, the ignition timing affects many variables including fuel economy and engine power output. Earlier engines that use mechanical spark distributors rely on the inertia of rotating weights and springs and manifold vacuum in order to set the ignition timing throughout the RPM range of the engine; whereas the latest engines consists of an ECU (engine control unit) which uses a computer to control the ignition timing throughout the engines RPM range. Factors influencing ignition timing: Type of ignition system used. Engine speed. Load of the engine: with more load (larger throttle opening) requiring less advance (as the mixture burns faster). Components used in the ignition system. Settings of the ignition system components. Temperature of the engine; lower temperature allows for more advance. The ignition timing to some extent also depends on the octane number of the fuel, and the air-fuel ratio as this determines the speed with which the fuel burns. Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine. Timing Advance: refers to the number of degrees before top dead centre (bTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the compression stroke. In contrast to that, timing retard refers to the changing in ignition timing, so that the fuel ignition takes place later than the manufacturers specified time. As an example, if the set ignition time was 12Â ° bTDC, then when the fuel ignition starts later than 12Â ° bTDC, it is known as ignition retard; similarly when the air-fuel mixture is ignited at an angle greater than 12Â ° bTDC, it would be known as ignition advance. Timing advance is necessary because it takes time for the combustion of the air-fuel mixture to complete. Igniting the mixture before the piston ends its compression stroke would maximize the limit to which the mixture burns completely, and hence help to build up maximum pressure soon after the piston reaches the TDC. This would ensure maximum power output by maximizing the force with which the piston is pushed down, by maximizing the pressure as soon as the piston starts going down when the power stroke is initiated. Ideally, the mixture should be completely burnt by 20Â ° aTDC (after TDC). If the ignition occurs at a position that is too advanced relative to the piston position, the rapidly expanding air-fuel mixture can actually push against the piston still moving up, causing detonation and lost power; whereas if the ignition is too retarded relative to the piston position, the maximum cylinder pressure will occur after the piston has already travelled too far down the cylinder. This would result in lost power accompanied by high emissions and unburnt fuel. Why is Ignition timing advance required? The ignition timing needs to be increasingly advanced (relative to the TDC) as the engine speed increases, so that the air-fuel mixture has the correct amount of time to burn completely. As the engine speed increases, the time available to burn the mixture decreases while the burning itself proceeds at the same speed; this requires the burning to start earlier to complete in time. The correct timing advance for a given engine speed will allow for maximum cylinder pressure to be achieved at the correct crankshaft angular position. Combustion in SI Engines: The combustion process in SI engines consists of three major parts: Ignition and flame development, Flame propagation, and Flame termination. Consumption of the first 5-10% of the air-fuel mixture is generally considered as the flame development. During the flame development period, the spark plug fires and the combustion process starts, but very little pressure rise is observed (graph-1). Almost all the useful work is produced in an engine cycle during the flame propagation period of the combustion process. During this period 80-90% of the air-fuel mass is burnt; the cylinder pressure is greatly increased which provides the force to produce work in the expansion stroke. The final 5-10% of the air-fuel mass which burns is classified as flame termination. During this time, pressure drops and combustion is finally terminated. The combustion process ideally consists of an exothermic sub-sonic flame progression through a premixes almost homogenous air-fuel mixture. The spread of the flame front is greatly enhanced by the induced turbulence and swirl within the cylinder. Ignition and Flame Development: The process of combustion is initiated by an electric discharge across the electrodes of a spark plug anywhere between 10Â ° to 30Â ° bTDC, depending on the geometry of the combustion chamber. The high-temperature plasma discharge between the electrodes ignites the air-fuel mixture in the immediate vicinity, and the flame spreads outwards from here. Graph . The increase in pressure rise is very slow after ignition during the flame development period. This results in a slow pressure force increase on the piston and a smooth engine cycle. Maximum pressure occurs 5Â ° to 10Â ° aTDC. The combustion starts very slowly due to the high heat losses to the relatively cold spark plug and the gas mixture. The flame can generally be detected at about 6Â ° of crank rotation after the spark plug firing. The applied potential across the spark plug is usually 25,000-40,000 V. overall spark discharge lasts about 0.001 second with an average temperature of about 6000 K. The discharge of the spark plug delivers about 30 to 50 mJ of energy, most of which is lost by heat transfer. Ignition Systems: The few commonly used methods used to produce the high voltage potential, which is required to cause the electrical discharge across the spark plug electrodes, are: Battery-coil combination: Most automobiles use a 12-volt electrical system, including a 12-volt battery. This voltage is multiplied many times by the coil that supplies the very high potential delivered to the spark plug. Capacitor Discharge: Some systems use a capacitor to discharge across the spark plug electrodes at the proper time. Magneto system: Most small engines and some larger ones use a magneto driven off the engine crankshaft to generate the needed spark plug voltage. Some engines have a separate high-voltage generation system for each spark plug, while the others have a single system with a distributor that shifts from one cylinder to the next. The Spark Plug: The gap between the electrodes on a modern spark plug is about 0.7 to 1.7 mm. smaller gaps are acceptable if there is a rich air-fuel mixture or if the pressure is high (i.e. high inlet pressure by turbocharging or a high compression ratio). Normal temperature of spark plug electrodes between firings should be about 650Â ° to 700Â ° C. A temperature above 950Â °C risks the possibility of surface ignition, and a temperature below 350Â °C tends to promote surface fouling over extended time. For older engines with worn piston rings that burn an excess of oil, hotter plugs are recommended to avoid fouling. Hotter plugs have a greater heat conduction resistance than colder plugs. Modern spark plugs have a greater life span than the old ones. Some of the high quality spark plugs with platinum-tipped electrodes are made to last 160,000 km or more. Harley Davidson uses gold-tipped spark plugs. One reason this is desirable is the difficulty in replacing spark plugs in some modern engines due to the complexity and compactness of engine and increased amount of engine equipment. Figure . An NGK spark plug Spark plug firing: When a spark plug fires, the plasma discharge ignites the air-fuel mixture between and near the electrodes. This creates a spherical flame front that propagates outward into the combustion chamber. At first, the flame front moves very slowly because of its original size; it does not generate enough energy to quickly heat the surrounding gases and thus propagates very slowly. As a result of this, the cylinder pressure is not raised quickly and very little compression heating is experienced. Once the first 5-10% of the air-fuel mass is burnt, the flame velocity reaches higher values with corresponding rise in pressure, the flame propagation region. It is desirable to have a rich air-fuel mixture around the electrodes of the spark plug at ignition, as it ignited easily and more readily, has a faster flame speed and initiates the combustion process well. Spark plugs are generally located near the intake valves to assure a richer mixture, especially when starting a cold engine. Latest developments in spark plug/ignition system technology: The efforts to develop better ignition system continue. Spark plugs with several electrodes and two or more simultaneous sparks are now available. They give a more consistent ignition and quicker flame development. One of the modern systems still under development gives a continuing arc after the initial discharge; this additional spark will speed up combustion and give a more complete combustion as the air-fuel mixture swirls through the combustion chamber. Development work has been done to create a spark plug with variable electrode gap size. This would allow flexibility in ignition for different operating conditions. At least one automobile manufacturer is experimenting with engines that use a point on top of the piston as one of the spark electrodes. Using this system, spark ignition can be initiated across the gaps of 1.5 to 8 mm with a reported lowering of fuel consumption and emissions. Flame Propagation: Induced turbulence and swirl causes the flame propagation speed to increase by 10 times than if there were a laminar flame front moving through a stationary gas mixture. These motions also cause the flame front to expand spherically from the spark plug in stationary air and is greatly distorted and spread. As the gas mixture burns, the temperature and pressure rise to high values. Figure . A typical flame propagation pattern. The burnt gases behind the flame front are hotter than the unburnt gases before the flame front, with all the gases at about the same pressure. This decreases the density of the burnt gases and expands them to occupy a greater percentage of the total combustion chamber volume. Compression of the unburnt gases raises their temperature by compressive heating. In addition, radiation heating emitted from the flame reaction zone, which is at a temperature on the order of 3000 K, further heats the gases in the combustion chamber, unburnt and burnt, raising the pressure further. Heat transfer by conduction and convection are minor as compared to radiation, due to very short real time involved in each cycle. The environment inside the combustion chamber is such that the progressive increase in temperature and pressure in taking place, causing the reaction time to decrease and flame front speed to increase. The temperature of the burnt gases is not uniform. It is higher near the spark plug where the combustion had initiated. Ideally, the air-fuel mixture should be around two-thirds burnt at TDC and almost completely burnt at about 15Â ° aTDC. This causes the maximum pressure and temperature of the cycle to occur somewhere between 5Â ° and 10Â ° aTDC. A lesser pressure rise rate gives lower thermal efficiency and danger of knock. The combustion process is therefore a compromise between the highest thermal efficiency possible and a smooth engine cycle with some loss of efficiency. Burn angle, Ignition and Ignition advance: The typical burn angle, the angle through which the crankshaft turns during combustion, is about 25Â ° for most engines. If combustion is to be completed at 15Â ° aTDC then ignition should occur at about 20Â ° bTDC. If ignition is too early, the cylinder pressure will increase to undesirable levels before TDC, and useful work would be wasted in compression stroke. If ignition is late, peak pressure will not occur early enough, and work will be lost at the start of power stroke due to lower pressure. Graph . Average flame speed in the combustion chamber. Lean air-fuel mixtures have slower flame speeds, with maximum speed occurring when slightly rich mixture at an equivalence ratio near 1.2 Actual ignition timing is typically anywhere from 10Â ° to 30Â ° bTDC, depending on the fuel used, engine geometry, and engine speed. For any given engine, the combustion occurs faster at higher engine speed. Real time for combustion is therefore less, but real time for engine cycle is also less, and the burn angle is only slightly changed. This slight change is corrected by advancing the spark as the engine speed in increased. This initiates combustion slightly earlier in the cycle, peak temperature and pressure remaining at about 5Â ° to 10Â ° aTDC. At part throttle, ignition timing is advanced to compensate for the resulting slower flame speed. Graph . Burn angle as a function of engine speed. Timing adjustment in Modern engines: Modern engines automatically adjust ignition timing with electronic controls. These not only use engine speed to set the timing but also sense and make fine adjustment for knock and incorrect exhaust emissions. Earlier engines used a mechanical timing adjustment that consisted of a spring-loaded ignition distributor that changed with engine speed due to centrifugal forces. Ignition timing on many small engines is set at an average position with no adjustment possible. Graph . Average combustion chamber flame speed as a function of engine speed for a typical SI engine. Flame Termination: 90 95% of the air-fuel mass has been combusted by 15Â ° to 20Â ° aTDC and the flame front has reached the extreme corners of the combustion chamber. The last 5 10% of the mass has been compressed into a few percent of the combustion chamber volume by the expanding burning gases behind the flame front. Although at this point the piston has already moved away from TDC, the combustion chamber volume has only increased on the order of 10 20% from the very small clearance volume. This means that the last mass of air and fuel will react in a very small volume in the corner of the combustion chamber and along the chamber walls, at a reduced rate. Near the walls, turbulence and mass motion of the gas mixture have dampened out and there is a stagnant boundary layer. The large mass of metal cylinder walls also act as a heat sink and conduct away much of the energy being released in the reaction flame. Both these mechanisms reduce the rate of reaction and flame speed, and the flame is finally terminated as it slowly dies out. Although very little additional work is delivered by the piston during the flame termination, it still is a desirable occurrence. Because the rise in cylinder pressure tapers off slowly towards zero during this flame termination, the forces transmitted to the piston also taper off slowly resulting in smooth engine operation. Self Ignition: During the flame termination period, self-ignition will sometimes occur in the end gas and engine knock will occur. The temperature of the unburnt gases in front of the flame front continues to rise during the combustion process, reaching a maximum in the last end gas. The maximum temperature is often above self-ignition temperature. Because the flame front moves slowly at this time, the gases are often not consumed during ignition delay time, and self-ignition occurs. The resulting knock is usually not objectionable or even noticeable. This is because there is so little unburnt air-fuel left at this time that self-ignition can only cause very slight pressure pulses. Maximum power is obtained from an engine when it operates with very slight self-ignition and knock at the end of the combustion process. This occurs when maximum pressure and temperature exist in the combustion chamber and knock gives a small pressure boost at the end of combustion. Abnormal Combustion: Abnormal combustion is referred to a combustion process in which a flame front may be started by hot combustion chamber surfaces either prior to or after spark ignition, or a process in which some part or all of the charge may be consumed at extremely high rates. Figure . Phenomenon of abnormal combustion The two important abnormal combustion phenomena of major concern are: Knock, and Surface Ignition They are of major concern, because: When severe, they can cause major engine damage; and Even if not severe, they are regarded as an objectionable source of noise by the engine or vehicle operator. Knock: is the name given to the noise which is transmitted through the engine structure when essentially spontaneous ignition of a portion of the end gas. This is when the fuel, air, residual gas, mixture ahead of the propagating flame occurs. When this process takes place, there is an extremely rapid release of much of the chemical energy in the end gas, causing very high local pressures and the propagation of pressure waves of substantial amplitude across the combustion chamber. Surface Ignition: is ignition of the fuel-air mixture by a hot spot on the combustion chamber walls such as an overheated valve or spark plug, or glowing combustion chamber deposit: i.e. by any other means other than the normal spark discharge. It can occur before the occurrence of the spark (pre-ignition) or after (post-ignition). Following the surface ignition, a turbulent flame develops at each surface-ignition location and starts to propagate across the chamber in an analogous manner to what occurs with normal spark ignition. Types of Abnormal Combustion in SI Engines: Spark Knock: A knock which is recurrent and repeatable in terms of audibility. It is controllable by the spark advance; advancing the spark increases the knock intensity and retarding the spark reduces the intensity. Surface Ignition: hot spots combustion chamber deposits: Surface ignition is ignition of the fuel-air mixture charge by any hot surface other than the spark discharge prior to the arrival of the normal flame front. It may occur before the spark ignites the charge (pre-ignition) or after normal ignition (post-ignition). Surface ignition can be of two types: Knocking surface ignition: Knock which has been preceded by surface ignition. It is not controllable by spark advance. Non-Knocking surface ignition: Surface ignition which does not result in knock. Run-on: It is the continuation of engine firing after the electrical ignition is shut off. Runaway surface ignition: Surface ignition which occurs earlier and earlier in the cycle. It can lead to serious overheating and structural damage to the engine. Wild Ping: Knocking surface ignition characterized by one or more erratic sharp cracks. It is probably the result of early surface ignition from deposit particles. Rumble: A low-pitched thudding noise accompanied by engine roughness. It is probably caused by high rates of pressure rise associated with early ignition or multiple surface ignitions. Knock primarily occurs under wide-open-throttle operating condition. It is thus a direct constraint on engine performance. It also constraints engine efficiency, since by effectively limiting the temperature and pressure of the end-gas, it limits the engine compression ratio. The occurrence and severity of the knock depend on the knock resistance of the fuel and on the anti-knock characteristics of the engine. Measures to avoid knocking: The ability of the fuel to resist knock is measures by its octane number; higher octane numbers indicate greater resistance to knock. Gasoline octane ratings can be improved by refining processes, such as catalytic cracking and reforming, which convert low-octane hydrocarbons to high-octane hydrocarbons. Also, antiknock additives such as alcohols, lead alkyls, or an organomanganese compound can be used. The octane number requirement of an engine depends on how its design and conditions under which it is operated affect the temperature and pressure of the end-gas ahead of the flame and the time required to burn the cylinder charge. An engines tendency to knock, as defined by its octane number is increased by factors that produce higher temperatures and pressures or lengthen the burning time. Octane Requirement: can be defined as the octane rating of the fuel required to avoid knock. Thus knock is a constraint that depends on both the quality of the available fuels and on the ability of the engine designer to achieve the desired normal combustion behavior while holding the engines tendency to knock at a minimum. Some major steps: The use of a fuel with higher octane number. The addition of octane-increasing additives in the fuel Ignition Timing Retardation . Use of a spark plug of colder heat range, in cases, where the spark plug insulator has become a source of pre-ignition leading to knock. Reduction of charge temperature e.g. through fuel evaporation inside the cylinder (GDI) Anti knock combustion chamber design. Consequences of engine knock: The engine can be damaged by knock in different ways: -piston ring sticking breakage of the piston rings failure of the cylinder head gasket -cylinder head erosion piston crown and top erosion -piston melting and holing Examples of component damage due to pre ignition and knock are shown below: Stroboscope: A stroboscope in an instrument used to make cyclically moving object appear to be moving slow or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating strings are common examples. In its simplest form, a rotating disc with evenly-spaced holes is placed in the line of sight between the observer and the moving object. The rotational speed of the disc is adjusted so that it becomes synchronised with the movement of the observed system, which seems to slow and stop. The illusion is caused by temporal aliasing, commonly known as the stroboscopic effect. In electronic versions, the perforated disc is replaced by a lamp capable of emitting brief and rapid flashes of light. The frequency of the flash is adjusted so that it is an equal to, or a unit fraction below or above the objects cyclic speed, at which point the object is seen to be either stationary or moving backward or forward, depending on the flash frequency. Observations: Engine Speed Throttle Position Degree Advance 475 5% 10Â ° 580 8% 17Â ° 657 22% 22Â °