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Abstract
In this research paper we would be discussing the basic functionality as well as the concept of search engine analysis. An engine can be considered as a mechanical device which is supposed to turn out some output from a given input. When we talk of an engine, we need to understand that the basic functionality of an engine is based upon the input output function, wherein the input is in the form of fuel source and the output is in the form of kinetic energy. The fuel source in an engine is also known as a prime mover and is considered to be the most effective means of running an engine. An engine consists of a power source, which in turn is a machine which generates kinetic energy from other variants of energy. Some of these variants include electricity, the usual flow of hydraulic fuel and compressed air.
Summary
Whenever we set about explaining the basic cycle of an engine, we need to try and symbolize it with the functionality of an automobile. A vehicle has a starter motor, which is needed to start the vehicle and it also contains an additional motor, which in turn is necessitated to drive the pumps. In this situation, the pumps are indicated through the means of power steering and the fuel inoculation system. Here, the power plant, which has the ability to drive the engine, is denoted by the engine. While discussing the life cycle of an engine, we also need to understand that the term “motor” was initially used to distinguish those engines which were originally powered by the internal combustion engine with those that were powered by the earlier engines, such as the steam engines.
While describing engines, the petrol engine is denoted by the term internal combustion engine whereas a steam roller or a motor roller is denoted by the steam engine. Engines are also utilized for military functions and they are ideally used as blockade engines, battering rams, large catapults and trebuchets. An engine was originally a mechanical device that was used to convert force into motion (Anonymous, 2000). Catapults are military machines which are also referred to as siege engines. If we go into the basics, then the word engine has been derived from the French word, engine. Some are of the belief that it is derived from the “Latin” word, “ingenious”. During the industrial revolution, most devices that were used were termed as engine, and hence, the name came into prominence. Devises that perform mechanical work are considered to be engines. The work here is supplied through the means of torque, which is also used for operating machinery, pump water, extract natural gas and generate electricity (Anonymous (a), 2004)
Engines are also made up of propulsion systems, which are mainly used in the context of air-breathing engines. As compared to a rocket, an air breathing engine makes use of the atmospheric air in a bid to oxidize the fuel as compared to an oxidizer, which is mainly used in a rocket. The word engine is also used in computer science. It is used in the context of a search engine. There is also usage of 3D graphic game engine, the text to speech engine, apart from the commonly used, rendering engine. In terms of computer science, the term search engine is not completely devoid of a mechanical computing device, nor does it have any relation with steam or smoke (Anonymous (b), 2004)
Overview
The Ancient Engines
An engine cycle has often been presented as an effective means of showcasing the internal mechanism of an engine. While there are various kinds of engines that are available in the market today, the basic engine types that are supposedly used in the present era are the diesel engine, the petrol engine, the rocket engine, the nuclear engine and the steam engine. Engines have evolved over a period of time. The most primitive style of engine was in the form of club and oars, which were also considered as simple machines. Then with time, power started being derived from wind, animals, steam and water but the engines in those days were still regarded as antique engines. Capstan, windmill, treadmill, block and tackle, were also considered as machines that made use of power and could well be considered as engines of the olden days.” The blockade engines of the Ancient Rome and the ship crafts of the Ancient Greece were also considered as engines.” (Benham, Crawford & Armstrong, 1996).Writers such as Pliny and Elder treated these engines as common occurrence and hence the engines may have been introduced long before they were born.
Strabo, a renowned writer, categorically states that the water mill was used in the 1st century AD and during this time; it was widely used in the kingdom of Mithridates. Thereafter, it was used for various centuries in Ancient Rome. During those days, dams and sluices, as well as different varieties of gears were also used on a random basis. The wind and steam power were successfully demonstrated by the hero of Alexandria in the 1st century, although they were not applied to practical use (Benham, Crawford & Armstrong, 1996).
The Medieval Engines
The 7th century was the establishment era of Muslim Agricultural Revolution. In the beginning of the 7th century, engineers developed and strapped up energy through the means of tidal, wind, fossil as well as fossil fuels. Even products such as petroleum were used in factory complexes the world over and these were also known as tiraz in the Arabic language. Watermills were used in the context of industrialization in the 7th century. With time, the vertical as well as the horizontal water wheels started being used for industrial as well as agricultural purposes and became a highlight of the 9th century. “In the beginning of 9th century, numerous mills came into existence like saw mills, paper mills, sugar refineries, windmills, paper mills, haulers, gristmills, steel mills and tide mills. In is interesting to note that by the end of 11th century, almost all Islamic nations around the world had industrialized mills into operation” (bayraktar, 2003).
In those days water turbines and crank shafts were also discover and put to use. With the introduction of gear based systems as well as the water raising machines, dams were constructed, which in turn raised the existing water levels of the dams. In the medieval Islamic world, the concept of manual labour was slowly replaced by mechanized labour. The Industrial Revolution of the 18th century took birth owing to these concepts. Al-Jazari, invented the crank shaft as well as the connecting rod in the year 1206. With this invention, the rotary motion was transformed into a reciprocating motion. This is also considered to be parallel to inventions such as the steam engine and the internal combustion engine. Taqi-al-Din, in the year 1551 introduced the steam turbine as well as the prime mover, which in turn was used for rotating a split.
The Era of Modern Invention
The modern era of the engine lifecycle could be attributed to the contributions by Sir Samuel Moreland, who happened to introduce the concept of utilizing gunpowder in an attempt to drive water into pumps. This occurred in the 17th century. It was in this period when the traditional internal combustion engine was replaced by the concept of two stroke engines. It is interesting to note that the conceptual designing and execution of the two stroke engine was given shape by Sadi Carnot, of France, in the year 1824. Another interesting aspect regarding the conceptualization of the two stroke engine was the first patenting rights, which in this aspect were conveniently granted to the American businessman Samuel Morey, in the year 1826. Sir Douglas Clark (1854-1932), manufactured the first workable two stroke engine in the year 1878and had it patented in England in the year 1881. the production of automobiles has never looked back ever since and have given birth to a wide variety of energy conversion systems, which included steam, turbine, solar, piston type and rotary internal combustion engines. The modern era was a pioneering force behind the introduction and development of various technological improvements, which in turn led to the overall development of the engine types and forms. The engines have been on the rise ever since and their production has also been growing at a rapid pace. Owing to the widespread increment in the overall development of mechanized production, engines have been able to keep pace with the rising demands of production. Owing to the rise in demands, there have also been cases wherein the technological improvements of engines have increased four folds and the usage of new techniques is on the rise (Hwang, 2004)
The Concept of Engine Cycle
The engine cycle is a simple mechanism which clearly defines the workability of petrol as well as a diesel engine, which may or may not belong to the category of a two stroke engine r a four stroke engine. The internal combustion engine of petrol works on a four stroke Otto cycle and it is considered to be fairly successful with automobiles. On the other hand, the diesel engine works on a similar operating functionality but is considered more effective for heavier automobiles. The new engines of the modern era were pioneered by Karl Benz. He started work in the year 1878 and proved to be fairly efficient in devising and creating reliable two stroke engines which functioned on gas. The two stroke gas engine was a powerful engine that was formulated on the designs of Nikalous Otto, who in turn was responsible for the overall development of the four stroke engine. Karl Benz was a pioneer of sorts and he devised one engine after the other. After a while he was able t successfully formulate and device engines that were completely free from flaws and those which could be used on a random basis, with regards to automobiles. Benz got a patent for the same in the year 1879.
The Horizontal Opposition of Pistons
Karn Benz was once again supposed to be a pioneer of sorts when he managed to get a patent for designing and formulating the horizontally opposed piston. In the present scenario, numerous BMW motorbikes are using a similar structure to enable a better functionality.
The design was based on the principles of horizontal movements, wherein the pistons moved at horizontal basis and corresponded with the pistons on the top dead centre simultaneously. This acted as a balancing momentum wherein each piston was provided with adequate power, which in turn allowed the engines to function in a smooth power, thereby providing the much needed power to the running automobile. Such engines are called as flat engines and if we compare its efficiency from other engines then it is much effective then. It is unique in its design and as they are flat in shape, they called as flat shaped engines. It contains an even number of cylinders and they could either be two, four or six. The Volkswagen beetle engine is a perfect example of a horizontally opposed piston engine. Such designs are also used as a perfect medium to power jets and while most of them are used to enhance and improvise the overall functionality of propeller aircrafts, the concept has picked speed and is comparably more effective and well suited when compared to traditional engines. There are numerous automobiles which are able to catch on to the concept of Porsche and Subaru.
The Development Cycle of Engine
The improvement of engine control systems is often looked on as an essential tool for the continued use of the internal combustion engine for automobiles. Nowadays, there have been a lot of improvements in terms of the overall improvement of engines. One such example is the availability of onboard computers which provide support to the overall engine efficiencies. The electrically controlled fuel injection system is also looked on as an essential means of enhancing the overall development of an engine’s performance.
In order to increase the overall efficiency of an engine, there have been various processes that have allowed it to achieve efficiencies that are way beyond the comprehension of ordinary engine groups, which in this context, were officially used in the olden days. In order to increase the power outputs for engines, the concept of forced air induction through the mediums of supercharging as well as turbo charging, has often been looked upon as an effective means of achieving optimum performance. Small diesel engines too have been fortified with similar alterations so as to provide the missing power and allow them to come at par with petrol engines. Large diesel engines, with relatively larger torque are still used in trucks and busses, while smaller cars in Europe are being fortified with enhanced diesel engines. The biggest advantage of the internal combustion engine was its ability to offer flexibility over a wide range of speed options. Likewise, the power of the weight engine was reasonable and it had the ability of being readily used in either fuel or petrol options.
The Norms of Pollution
The engine life cycle has often come under strict scanner owing to the increasing levels of pollution the world over. Although there have been a steady increase in the number of battery operated vehicles, it needs to be understood that owing to the cost and convenience factor, the concept of electrically charged vehicles has not yet picked speed. The twenty first century engine is therefore considered to be the diesel engine but as of now, the overall concept and the charm of a highly fuel efficient gasoline engine is yet to be challenged in the automobile market.
Increased Power
Owing to the sudden demand in the production of the internal combustion engines, it has been noticed that the overall demand for speed has seen a sudden surge and automobiles, with special regards to the American models, are often designed to raise the overall capacity of an engine. During the engine life cycle analysis, an attempt is made to improve the efficiency of the engines by increasing their existing pressure, enhancing the existing size of the engine and allowing increasing the speed at which power is generated in the engine. Owing to the higher forces and pressures, the size as well as the noise levels in the engine started to increase. In order to contain this problem, engineers as well as mechanics came up with the V shaped design module. Not only did it create lesser amount of noise and vibration, it also led to the alteration of layouts, with the cylindrical layouts being slowly replaced by the sleeker, straight line arrangements.
The V-8 layouts in terms of passenger cars were devised on the foundation of greater piston dislocation. All vehicles with more than 250 cubic inches of displacement were eligible for this form of layout, while those with less than a 4 litre capacity could not fit in a V-8 engine module. In order to increase the power of an engine, mechanics followed various technical procedures and while the basic engine cycle remained more or less the same, an attempt was made to enhance the overall functionality of the existing mechanism. Likewise, the technicians had to enhance and improve the existing engines on the basis of the international requirements as well as the existing norms of pollution.
Engine Life Cycle and Combustion Efficiency
The engine life cycles saw a lot of ups and downs owing to the changing demands of the society. There were numerous changes and there were a lot of variations as well. Owing to the economic and pollution check scenarios, it was decided that the engine be modified in order to suit the present environmental conditions. In a bid to improve the existing combustion capacity of the engine, new engines were introduced, which in turn could be fitted within small cars and those that had the ability to last for a relatively longer on twisty roads. Owing to this various small engines, with a horsepower of 40 were introduced and six cylinder engines had an output of as low as 60 horse-powers. On the other hand V-8 engines had a power rating and capacity of belting 250 to 350 horse powers of output at one go.
The Configurations of Engines
In the early days, engines used to be of a much larger volume. Engines ranged from one to sixteen cylinders and were distinguished on the basis of the overall size, piston displacement, weight, cylinder bores and the number of cylinders. Majority of vehicles made use of nineteen to a hundred and twenty horse power variants. There were also three cylinders, two stroke cycle models which grew in demand and had in-line cylinders in place. There also existed two and four cylinder makes which horizontally opposed. The engines in the olden days employed the use of camshafts and there were several vehicles which had air cooled engines located at the rear. This caused the compression ratio to slacken considerably.
During the 70s and 80s, the introduction of V-6 engines as well as the four cylinder layouts led to the introduction of fuel efficient engines. There have been engines which are powered by a series of V-8 engines and there have also been variants that are known to produce immense output owing to the W16 engine format. Over here, two V-8 engines are placed side by side and the placement creates a W shape. The Bugatti Veyron operates on a similar model. The Wartsila Sulzer RTA96-C is the biggest internal combustion engine which was developed to run the largest container ship in the world, the Emma Maersk. The weight of the engine is 2300 tons and it generates 109,000 bhp of power whilst running at 102 rpm. The engine is very effective and gives maximum output but consumes13.7 tons of fuel each hour.
The Concept of Air Breathing Engines
Internal combustion engines which make use of air in order to produce the required power through the process of oxidation are known as air breathing engines. Rather than carrying an oxidizer, the air breathing engines derive power from the surrounding air. Such kinds of engines are mainly used in the context of rocket engines. Engine cycle analysis ideally takes the help of such engines and can often lead to the development and enhancement of air breathing engines. Air breathing engines are designed in a way which allows a constant stream of air to flow at a regular pace. The flowing air undergoes through the process of compression then they are mixed with fuel and ignited before being expelled in the form of exhaust. It is interesting to note that the thrust which is produced by an air breathing engine is eight times greater than the original weight of the engine.
Air breathing engines have a limited breathing velocity of about one to three kilometres whereas hydrogen based engines of the same designs possess four times the velocity of a normal engine. There are various kinds of air breathing engines which are readily available and explicitly used in the present scenario. Major engines include reciprocating engines, gas turbine engines, jet engines, turbo propeller engines, IRIS engines, scramjet engines, ramjet engines, pulse detonation engines, liquid air cycle engines and reaction engines SABRE.
Environmental Effects of Engines
Engines have a negative impact on the environment. Combustion engines are supposed to be the major cause of noise and air pollution. The exhaust of an engine comprises of both harmful as well as non harmful elements. While the non harmful elements include water vapour as well as nitrogen, the harmful ingredients consist of carbon dioxide, nitrogen oxides as well as hydrocarbons. The carbon monoxide gas is extremely poisonous and it can create extremely high levels of carbon monoxide poisoning. It is therefore recommended that the carbon monoxide gas should never be allowed to be built up in a confined space. This is one of the main reasons why diesel as well as patrol engines should never be allowed to run indoors. Engines use catalytic converters to reduce harmful emissions but they cannot get rid of them completely. The greenhouse effect has also been caused owing to the escalations in the green house gasses present in the environment. Global warming has also identified carbon dioxide as an effective pollutant and hence, the need to curb it is very essential.
Noise pollution is also considered a major drawback with engines. Large automobiles plying at slow speeds are a major cause for the rise in noise pollution. Engines are therefore fitted with mufflers in a bid to reduce the existing noise levels.
Aims of Dissertation
The basic aim of this research paper is to unveil the true meaning of an engine besides of course, highlighting the overall functionality of an engine. With special regards to the engine cycle analysis, an attempt has been made to ensure that the research paper tries to probe each and every aspect of the engine. An attempt has also been made, in the review section, to ensure that the end user is made aware of the various studies that have been initiated by eminent scholars, who have done so in order to ensure that the readers have a clear idea regarding the lifecycle of an internal combustion engine. In the previous sections, an attempt has been made to explain the overall functionality of an engine. We have also defined and explained the basic qualities of an engine. These features have been considered as an essential means of ensuring that the end user clearly understands the basics of an engine in a suitable manner.
The dissertation has also provided ample opportunity to explain various research methodologies, before finally trying to conclude the analysis through the means of relevant data. In the latter half of the dissertation, an attempt has been made to ensure that the dissertation has ample scope for discussions as well as conclusions before being providing recommendation for future work. In the end, a section on personal reflection has been sought to analyze and deduce the overall project through an individualized perspective.
Objectives
The objectives of this dissertation are to ensure that the end user has a clear understanding on the life cycle of an engine. An engine has always been used for the betterment of the society and its usage can be dated to the prehistoric times. While the evolution has made drastic changes in the overall concept, design and functionality of an engine, the fact still remains that an engine has often been pegged as the single most important entity for ensuring a safe and speedy transport.
The dissertation therefore makes an attempt to ensure that the basic lifecycle of an engine is discussed in the most appropriate manner. An attempt is made, through the means of the literary review section, to ascertain the life cycle of an engine through the means of numerous case studies, which have been performed by a diverse group of individuals with a different perspective in mind.
Through the means of the dissertation, an attempt has been made to explain the mechanism of an engine and although this dissertation is quite different from the others as it does not contain unnecessary equations and diagrams, the case study is a fulfilling experience in itself. Data and analysis has been performed and an effort has been made to gather the required information which is considered a prerequisite to ensure the complete functionality of an internal combustion engine.
In the end, a section has been left primarily for individualistic views. In this section, the author has tried to express his views on the life cycle of an engine. The understanding of the author cannot be critically examined through facts or scientific data but can be understood and applied through individualistic reasoning and application.
Introduction
The free piston atmospheric engine was formulated by Nikolaus Otto, an engine that had been invented by Etienne Lenoir. Otto allowed the engine to run of liquid fuel and through the means of the four stroke piston cycle internal combustion engine, Otto was able to create a niche in the overall life cycle of an engine. In May 1876, when Otto finally came up with this technology, the engine was deemed as the perfect alternative to the steam engine. Then engine was thus named the Otto Engine Cycle, after the name of its inventor. The calculations and values were based on the fact that the engine was running at a wide open throttle without the aid of any pumping loss. The Otto Cycle was not like the four stroke engine and it had certain features which were fairly different from an ordinary four stroke engine.
For many years researchers as well as technicians have made efforts to improvise the existing engine life cycles. The research studies concerning internal combustion engines have often been considered theoretical as well as experimental, wherein the engine design, the operational ability, the testing of new engine systems as well as the other theoretical methods are often looked on and considered an essential means of determining the lifecycle of an engine. The mathematical model of an engine is often established with a point of view of realistic assumptions which are often validated through the means of the design and development study. Internal combustion engines are a sum total of thermodynamics, which in turn include, the cylinder, the intake as well as the exhaust manifold (Bayraktar, 1997; Heywood, 1988).
The systems enable the transfer of mass, enthalpy as well as energy, which in turn is derived through work and heat (Poulos & Heywood, 1983). The study of the engine cycle analysis often contains the determination of the thermodynamic state of the charge involved.
Background Information
In this dissertation, we would be discussing a spark ignition engine cycle, which also happens to be quail dimensional in nature. In this procedure, the combustion is represented as a process which is based upon turbulent flame propagation. During the process of combustion, it is stated that the charge in the cylinder consists of both burnt as well as un-burnt gas zones. To analyze this process, a computer code was developed through which then engine, which was operating at a particular condition and performing within the parameters which were characterized under the combustion parameters, could be analyzed through a mathematical cycle model. The overall performance of an engine is therefore computed through the means of a computer generated code, which in turn is linked with different geometrical codes. The predicted values of these theoretical examinations are compared with the experimental data and a good arrangement is reached between the predicted as well as the experimented results. The comparison between the two is ideal for allowing a researcher to reach a conclusion and state whether the present model is reliable enough analyzing spark ignition engine cycles or not. The engine’s operation, design as well as testing of the new system, is possible through practical methods but it requires more time than theoretical methods. The mathematical model of the engine cycle can therefore be proposed with realistic assumptions, which in turn are arranged in a computer generated code.
Literature Review
In order to improve the functionality of spark ignition engines, researchers have made considerable efforts and conducted various research studies which are considered both experimental as well as theoretical. Quasi-dimensional models are used for the analysis. These models are useful for predicting the detailed spatial information regarding the cylinder charge during the engine cycle analysis. Such dimensional models are not feasible for the parametric studies, which effects with the changes in the operational variability and the design of the engine performance, its efficiency and its performance.
The present theoretical study has been performed to analyze and assess the spark ignition engines operating conditions, fuels as well as varying geometric calculations. Taking this debate further, we have devised a quasi dimensional spark engine cycle. Through the means of this paper, a mathematical model of the engine cycle has been presented. The application of this model includes the checking and reliability of the presented methods and the comparative analysis of the results which have been derived from various related studies. At the end of the article, there is a brief section which categorically states the discussions related with the engine life cycle besides providing solutions for the same. The concepts of using alternative fuels have been left for future discussions and in this context, only the theoretical aspects are being discussed.
Research Methodology
The Mathematical Model
In order to establish the theoretical investigation of the spark engine cycle, we need to first establish a mathematical model. Through the means of this mathematical model, we can establish the charge of the cylinder. During the course of the study, we developed a quasi dimensional engine cycle model. A broad description of this model was provided by Bayraktar (1997) and then Durgun (1997). The spark engine cycle consists of four different processes, namely intake, compression, combustion-expansion and expansion.
All four processes are different and hence they should be computed with different equations and different estimates. In a bid to ascertain the thermo dynamical state of the cylindrical contents, expressions pertaining to the temperature and pressure need to be established at the earliest given opportunity. The first laws of thermodynamics and gas law, the following equations could be derived. They are based upon the first time rates of pressure and temperature.
The dots here denote the differentiation in time, wherein the equation () denotes the net rate of the aggregation of enthalpy. The total transfer to the wall is denoted by the symbol Q. W=pV, which in turn denotes the work done by the gas on the piston. H denotes enthalpy.
These ordinary, first order equation, should ideally be resolved through the means of equation 1 and 2 respectively. During the process, this cycles aught to be aught to be arranged with reasonable assumptions. The assumptions are process specific as each process has a distinct chemical as well as physical process. The exhausts as well as the intake processes are calculated by the method that was formulated by Durgun and Bayraktar (1997).
The equations regarding the combustion, expansion as well as compression is denoted in a separate pattern and their solutions are listed right below. Now we are going to discuss each and every one of them as a separate assumption.
The Intake Procedure
The intake process is denoted by the temperature as well as the intake pressure, which in turn is denoted by a simple method formulated by Bayarktar (1997). According to this method, the pressure loss is denoted by (), which in turn is analyzed through the Bernoulli equation. The calculation is based on the one dimensional no compressible flow, through which the intake pressure is specified.
Over here, po, is specified as the ambient pressure. Likewise, the intake temperature is calculated through the following formula Bayraktar (1997).
Over here To is denoted by the ambient temperature, (triangle T) is denoted by the increase in temperature within the intake system, Tr is the exhaust temperature, which was mentioned in the previous cycle, and finally Yr is the coefficient which in turn is comprised by the residual gasses. The volumetric efficiency is defined as-
Wherein () is referred to as the charge up efficiency and () is denoted by the compression ratio.
The Compression Process
During the analysis of the compression process, the equations (1) and (2) need to be arranged in a specific manner so as to reach a suitable assumption. The basic assumptions for this procedure are as listed. The system is considered consistent for instantaneous contents, in relation to a single cylinder. The variable volume in a cylinder is spatially uniform in pressure. The following assumptions are also valid for other strokes as well. During the process of compression, the overall cylinder charge comprises of a judicious mixture of fuel, gas, air and fuel vapour. The ideal gasses are in reacting in nature and are characterized by a single mean temperature. In the system, the total mass is always considered as a constant and this remains steadfast throughout the entire engine cycle analysis. In accordance with the above mentioned assumptions, the equations (1) and (2) are arranged in the following manner.
Over here, the un burnt gas is denoted by the symbol u, the instantaneous total cylinder volume is denoted by V, the total heat transfer to the wall is denoted by the symbol Q, the density is denoted by the symbol p, and cp= (), is the specific heat at a constant pressure. The rate on the change of the cylinder pressure is denoted by
The Combustion Pressure
The fuel air residual gas mixture, which in turn is compressed within the compression chamber, is ignited by a spark, after which the process of combustion is stated to begin. From the point of view of experimental observations, (Beratta et al., 1983; Gatowski et al., 1984; Namazian et al., 1980; Tagalian and Heywood, 1986), an observer needs to understand that three different zones exist during the process of combustion. These zones are recognized as the unburned fuel air mixture zone which is ahead of the flame front, and a fully flame zone which lies under the flame zone.
In the above scenario, the un-burnt mixture i=u. In the context of the burnt mixture i=b. through the means of conversion (mass), it is evident that mb= -mu.
The Expansion Process
Once the entire charge is burnt within the cylinder, the expansion procedure is set to begin. During the process of expansion, the cylinder charge is totally composed of fully burnt gasses while the total mass is always constant. If we go by the above assumptions in terms of the expansion process, the equation (1) and (2) can be written as:
Wherein, Aa as well as Bb are the same form as the form that was denoted in the combustion process.
The Exhaust Process
The exhaust process is denoted by the symbol pr, while the temperature is denoted by the symbol Tr. The exhaust process is calculated by a simple process which is dented by a simple method which in turn is developed by Durgun and is given by Bayraktar (1997). The exhaust pressure is specified depending upon the ambient pressure and the ambient pressure is denoted by po.
Tr, which is symbolic to the exhaust temperature, is specified using the gas burned process temperature, which is denoted by Tb, at the end of the expansion process.
In this scenario, if the predicted difference between the chosen as well as the predicted values of Tr is within the prescribed limits, the last value of Tr is considered to be acceptable in nature. In case if it is not, then the cycle needs to be computed all over again in order to derive the last value of Tr.
The Sub Models
In the previous cessions, we gave different equations for both temperature as well as the pressure. In order to solve these equations in a numeric manner, we need to determine the numeric values of T as well as P. the term in the equations should therefore be determined through the means of reasonable approximations. We would now be discussing the various sub models included in the engine life cycle.
The Thermodynamic Properties
In a bid to ascertain the life cycle of an engine, the thermodynamic properties of both the burned as well as the unburned gasses need to be looked at on a regular basis. Interestingly, the unburned gas is stated to comprise of three non reacting gasses, which in turn are ideal in nature. The gasses are air fuel vapor and residual gasses. A sub model was devised by Komiyama and Heywood (1973), in a bid to calculate the mixture composition and thermodynamic properties along with their particle derivatives with respect with the temperature and pressure. A model developed by Olikara and Borman (1975) was used in a bid to calculate the combustion and expansion of the burned gasses. According to this method, the burned gasses are reacting gasses that are based upon a chemical equilibrium. Through the means of the sub model, the composition of mixture and thermodynamic derivatives are computed simultaneously at any given time.
The Transfer of Heat
The transfer of heat between gasses and cylinders has to be specified. Heat transfer in a spark engine cycle is caused due to the properties of combustion and radiation. In a bid to determine the instantaneous heat transfer coefficient, several empirical correlations have been developed and put into practice. The correlations were provided by Borman and Nishiaki (1987). The empirical formula on the other hand has been developed by Annand (1963) and it is widely used for this study. According to this formula, the Qw is specified as.
Here, a, b and c are constant variables and are chosen as a=0.35-0.8, b=0.7 and c=4.3×10-9 W/m2K4. This is in regards to combustion and expansion. The cylinder bore is denoted by D, subscript i can also be u, which is the unburned gas, or b, which is the burned gas. Finally Tw is denoted as the wall temperature. Re, the Reynolds number is calculated empirically (Heywood, 1988).
The Geometric Model
The geometric model is mainly used to analyze the instantaneous cylinder volume, which s denoted by symbol V and its differentiation with regards to the time, t, as well as the crank angle o (V). All these are then merged with the flame front area as well as the combustion chamber which in turn comes in contact with burned as well as unburned gasses. It is easy to calculate the total cylinder volume as well as its derivative V, regardless of the crank angle. Nonetheless, the geometric features of the flame, regardless of the instant of combustion need to be analyzed through the means of a specific calculation method. In accordance to the experimental observations, the geometry of the flame in spark engine analysis is approximately spherical in nature (Beratta et al., 1983; Gatowski et al., 1984; Namazian et al., 1980).
In order to ascertain the instantaneous flame geometry, a commonly used mathematical mode ideally used in combusting modelling studies was used. It was devised by Annand (1970). The enflamed volume Vf as well as the surface area have been calculated regardless of the piston position on the basis of the instantaneous flame radius Rf. The chamber height h is derived by the use of Simpson’s integration scheme. During the process of combustion, the volume enveloped by the flame front is depicted by the following formula.
According to the equation, the entrained mass by flame front is denoted by me, while mb is denoted by the burned mass. The Newton-Raphson iteration method is used to compute the all contact area f the gasses which corresponds to the instantaneous burned gas volume as well as the flame front area that corresponds to the volume enclosed by flame, denoted by the symbol Vf.
The Burn Rate Model
The combustion chamber in the spark engine cycle is ignited with the aid of a park discharge. In the outset, the flame consists of a smooth surface and it s also spherical in nature. The 1 mm kernel grows spherically for a few degrees (Gatowski et al., 1984; Namazian et al., 1980; Tagalian and Heywood, 1986). Using this phase, a negligible fraction of the mass is burnt and the calculated initial burned speed is fairly close to the laminar burn speed (Tagalian and Heywood, 1986). His stage is also referred to as the initial burn stage. The turbulent flow fields then interacts with the flame, which in turn produces a wrinkled and a highly convoluted outer surface of the flame (Gatowski et al., 1984; Tagalian and Heywood, 1986). At this stage the burn speed is directly proportional to the turbulent flame speed. The phase is also referred to as the faster burning phase. S per various experimental studies, it has been noticed that a specified amount of gas is still left unburned after the flame propagation process has been completely terminated. This is the last stage and it is also known as the final burning stage. These summarizations have been based on various experimental observations, which in turn have been proven by statistical data.
In order to gather realistic predictions, the realistic models need to be modelled after considering the turbulent flame propagation procedures. For this very reason, numerous studies have also been performed on a random basis. (Heywood, 1980; Blizard and Keck, 1974; Tabaczynski et al., 1977; Beratta et al., 1983; Tabaczynski et al., 1980). He models mentioned above were originally based upon the observations of Blizard and Keck (1974). The process was later provided an extension by Keck and coworkers (1982). In this theory, the turbulent eddies have a radius lt, which are entrained into the flame zone at the entertainment velocity of Ue. The burned is a characteristic time which is denoted by tb. The combustion can therefore be describer through the following equations.
In this scenario, tb=Lt/ Sl. This is the reaction time which is required to burn the mass of an eddy which is the size of lt, me is the mass which is entrained by the flame front, the characteristic speed is denoted by Ut and the laminar flame speed is denoted by Sl. In this study, the geometrical model is used to calculate the flame surface area Af which corresponds with the enflamed volume Vf. The empirical correlations are computed through the means of Sl, which in turn has been provided by Bayraktar (1997) and Heywood (1998). The mean inlet gas speed is directly responsible for the computation of Ut. It is also proportional to the ratio of the unburned gas density and the actual gas density (Keck, 1982). The empherical calculation is based on the maximum intake valve lift Liv as well as the density ratio pi/pu (Keck, 1982). The formulas used are as follows.
Ut=0 during the initial burning phase. Once the flame is fully propagated, the equations 16 and 17 are used. During the final burning phase, Af=0 and the burning rate is computed through the following formulae.
Here, F is symbolic to the conditions that were prevalent at the end of the flame propagation.
The Simulation Process
This mathematical engine cycle analysis has been developed through the means of a computer code. The input that are needed to begin the computing process include, speed n, the equivalence ratio, the distance of the ignition point from the edge of the chamber (the location of the spark plug) a, the spark advance angle, the properties of fuel, ambient pressure, intake valve geometry and finally, the temperature.
After the intake conditions have been determined, the next step is to predict the thermodynamic state of the cylinder charge. For this, first order differential equations for each process with appropriate crank angle increments are needed. In order to integrate the equations, the Euler predictor corrector technique is put to practice. Variables at each step are computed through the means of equations in the sub models.
The combustion starts with this scenario (at θs before Top Dead Centre–TDC), wherein the initial value of the burned gas temperature is evaluated as the adiabatic flame temperature. The cosine burn rate formula is applied to compute the initial value for the mass fraction burned.
The laminar burning is said to have begun when the ignition delay period has already begun. After the eddy has started burning, the combustion process is computed as a fully developed turbulent flame process. During the entire process of combustion, the thermodynamic state of burned as well as unburned gasses is determined in a separate sphere. During this process, the cylinder charge is made up of fully burned combustion products. Once the piston reaches the bottom dead centre, the exhaust stroke is started automatically. If the previous value of the temperature is close to the predicted value, the engine cycle analysis is said to be terminated. If it is not, the cycle computation procedure is once again repeated to produce the desired results.
Table-1 SI engine parameters
D H Lc Liv a θs
Numerical Applications
The computer program is ideally run for various engine geometries and it is also analyzed and tested at varying operating conditions, in a bid to compare the predicted results with the other experimental deductions that have been analyzed by various researchers. Table 1 show the basic geometric parameters of the engine types which are used in the final calculations. Listed below are the comparative results.
Predicted Vs the Experimental Results
In a bid to determine the validity of the spark engine lifecycle, the predicted parameters of various engines at varying operating conditions have been compared with the experimental data, which is mentioned in the literature (Abraham et al., 1985; Bayraktar, 1991; Benson and Baruah, 1977; Blizard and Keck, 1974; Heywood et al., 1979; McCuiston et al., 1977; Tabaczynski et al., 1980; Tomita and Hamamoto, 1988). In accordance with this study, the burned mass fraction Xb, the burn duration, which is also known as the burn interval, the pressure of cylinders p, and performance parameters, which include effective power, effective efficiency and specific fuel consumption, were chosen and later applied in the form of comparison parameters. The experimental data of mass fraction burned, as stated by Blizard and Keck (1974), Tabaczynski et al. (1980), and Tomita and Hamamoto (1988), are used and depicted in the following figure, for the detailed analysis of the combustion procedure.
As per the figures, the computed values of the mass fraction burned are in tandem with the measured results. Figure 4 shows the comparison of combustion in relation with the experimental and theoretical burn duration values. It is interesting to note that the equivalent as well as the computed ratios is in agreement with each other. Even the measured burning intervals are in tandem with the rest.
The cylinder pressure variations are often looked on as an essential means of obtaining a general insight on the engine cycle analysis. Over here, the predicted pressure values are compared and analyzed with the measured pressure data, which in turn has been defined by Heywood et al. (1979), Benson and Baruah (1977), and Abraham et al. (1985). The last assessment has been performed to judge the efficiency parameters. These parameters have been taken from the measured data from the engine geometry as stated by Bayraktar (1991) and then compared with the predicted values. The prediction of the engine performance parameters have been accurately predicted through the means of the following figures. (Fig: 5-7).
Conclusion
We have successfully developed a quasi dimensional spark engine cycle model. We have also used the First Law of Thermodynamics in a bid to determine the first order differential equations in order to measure the engine cycle through pressure and temperature. The process of combustion has been formulated as a turbulent flame propagation procedure, wherein the basic details of the simulations are clearly present. Computed results were compared in a bid to determine the validity of the model with the results of various other engine geometries stated by various eminent authors. Cording to this engine cycle analysis, the present mode can be used for predicting combustion parameters, cycle parameters as well as the performance parameters in an adequate manner. The investigational results were in good agreement with the predicted results. The engine cycle analysis of spark can easily be applied for examining the effects of fuel type, the engine geometry, the operating parameters on combustion as well as the cycle and performance.
Ratios
The intake and exhaust process in this model have been calculated through the aid of a simple methodology. Likewise, the mechanical losses have been provided with an empirical calculation through the aid of mean piston speed. The model’s validity can be improved through the means of strokes and losses. The characteristics of Ut in the combustion process and the characteristics of the length Lt have been calculated on the basis of an empirical analysis. Once their scales are computed via detailed turbulence modelling, the reliability of the combustion process can be further improvised.
In the above study, the models have been displayed in great detail and the practical utility as well as the validity of the SI engine cycle has been proved through an analytical approach. In the studies which follow, an attempt would be made to compare the various effects of parameters, through the means of the presented mathematical model.
Personal Reflections
The internal combustion engine has revolutionized the way we live and it has also transformed the way we travel. There was a time when travel was made easier with the invention of the wheel. Now, with the invention of the internal combustion engine, not only has travel been made easy, there has also been a rapid increase in the quality of engines produced. Through the means of this research paper, we have tried to discuss the basics of the spark engine life cycle through a detailed format. What we have missed discussing is the engine knock. The engine knock is still a cause for concern and it has often limited the capacity of the spark ignition gasoline engine compression ratios and hence an attempt needs to be made to improvise it so as to enhance engine efficiency as well as the torque.
Knock is often defined as the unburned gas auto ignition of sufficient strength. Low intensity auto ignition can often occur and it produces a knocking noise, which in turn is an audible sound. Knock is a resultant of the unnatural combustion of the unburned end gas portion of the charge mixture before its arrival in the form of the turbulent flame front. Acceleration under load is often defined as a possible reason behind knock and it can also be caused under state high load operation.
The after effects of the knock can often lead to destructive consequences, including engine failures but the end result depends completely on the intensity of the knock. Hence, nowadays, engine constructors are applying one or more technique in a bid to prevent the occurrence of an engine knock.
A few techniques that are considered essential and useful in resolving the engine knock include compression ratio limits, delays in spark timings, enrichment of the fuels and its controls. Owing to these measures, the fuel efficiency of an engine is greatly reduced, which increases the overall expenditure. Spark timing thus needs to be retarded from the best torque levels in a bid to avoid knock during transitions to high torque levels during low engine speeds. Engine knock is therefore considered to be a dominant factor in deciding upon the engine compression ratios. It also needs to be noted that the operational conditions that often produce the knock effect, low speeds and high loads are infrequently used by many drivers. When the engine f forced into a high load low speed case, in terms of vehicle acceleration, the knocking prone condition thus created can be effectively reduced through the mitigation by reducing throttle or by increasing the speeds of the engine wherein the recurrence of knocking is greatly reduced.
The goal of all investigating procedures should therefore be diverted at analyzing whether delay exists on the onset of the acceleration procedure. This is done to ascertain the optimum spark timing schedules in order to minimize the timing effects of the retardation procedure.
While there have been numerous experiments and various case studies have been conducted with regards to this concept, very few have ideally managed to draw a suitable conclusion. Through the means of the WOT experiments, which in turn are conducted on the modified CFR SI gasoline engine with the first WOT cycle having advanced spark with varied fuelling, the following results were drawn.
The Conclusions of the Knock Experiment
The following conclusions were drawn on the basis of advanced spark with varied fuelling.
- Audible knock was said to be audible in 60 to 80 percent of the cases, when the knock ration was in between 1.05 to 1.35. KI was supposed to be greatest when the knock percentage was in between 1.1 and 1.2.
- Fuelling was considered a necessity during the first WOT cycle. In this scenario, the in cylinder concept allowed the ratio to lower stoichinometric the audible volume of the KI to a considerable extent.
- The concept of stoichinometric fuelling also led to the provision of the strongest g.i.m.e.p, owing to the appropriate combustion phase without the need for the knock.
- Despite of slightly rich fuelling conditions, which are considered highly effective for knock, it has been noticed that the knock ration may remain low owing to its micro local nature.
In the end, it would not be inappropriate to state that the knock experiments as well as other enhancements are a must if the engine is supposed to enhance and function for the betterment of the human society. While there have been considerable improvements and achievements in the existing life cycle of the engine ever since the internal combustion engine came into existence, there have often been instances wherein the engine, regardless of whether it was a four stroke or a two stroke engine, had the ability to be improvised to suit certain conditional parameters, which in turn were supposed to be essential for the improved functionality and performance of an automobile. While we have limited our efforts with just two aspects of the engine life cycle, there are hundreds and even thousands of improvisations, going on at this point of time.
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