Abstract
Human civilization has been largely influenced by the invention of engines. From the time when external combustion engines were invented to the introduction of internal combustion engines, people were highly dependent on engines to run machines that were vital in making their work easier. The spark-ignition engines which use a spark to ignite combustion of the air-fuel mixture are among the internal combustion engines that have greatly influenced the way people operate. The spark is used because these engines do not produce enough heat to enable self-ignition as is the case with compression-ignition engines. These engines can be categorized into the two-, and four-stroke ones as well as the rotor engines depending on the number of strokes present. The invention of the spark-ignition engine is credited to engineer Jean Lenoir who was the first person to practically use the engine. The advantages of the spark-ignition engine are that it is lighter, smaller in size, hence cheaper to produce, and less noisy than other engines. It can be used in light machines. However, it has some shortcomings which include its fuel inefficiency and large emissions, though, lately, technological advancements have proved that these disadvantages can be overcome.
Introduction
Human life was made easier when machines were invented which helped with some work that had been impossible hitherto. However, the invention of internal combustion engines brought another chapter to the world as it changed every aspect of people’s lives. It is nearly impossible for human beings to do anything nowadays without involving machines that use engines. Nevertheless, since the discovery of simple internal combustion engines, there have been constant improvements that have led to the emergency of rather complex and more efficient engines. Throughout history, engineers have been working to meet customers’ needs which include fuel efficiency, environmental sustainability, and affordability, thus leading to various developments on performance, besides coming up with various engine types. Spark-ignition engines were invented due to the quest for better-performing engines (Ritzinger, Koch, Lehmann and Boulouchos 2012). They underwent several developments to become what they are today.
Definition
Spark-Ignition engine is simply an engine in which a spark is used to ignite the combustion process. This is contrary to the compression-ignition engines which compression process can produce enough heat to ignite the combustion process. Additionally, in this type of engines, addition of air or fuel combustion takes place at a constant volume because it uses the Otto cycle (Ganesen 2008). The Spark-Ignition engine usually uses petrol and gasoline type of fuel though recently other types of fuel like ethanol are used. This type of engine controls both the quality and quantity of fuel and air injected unlike Compression-ignition engines.
History of Spark Ignition Engine
Thomas Savery’s steam engine was one of the very first engines that were ever developed and put into meaningful use. This engine was able to raise water by suction. This engine was later improved by Newcomen in 1712 (Meker and Schwarz 2011). Though such engines were external combustion engines, they assisted in improving the human civilization. As early as 1791, the idea of coming up with an internal combustion engine was in the minds of some people who actually tried to put it into action though they did not succeed. The spark-ignition engine was invented only in 1858 when engineer Jean Lenoir came up with the first engine to be ignited by a spark. Due to limited technology of fuel production at that time, this engine had been fueled by coal which had the main source of power though later on petroleum was used. This was, however, done after the discovery of the electric spark plug which Lenoir then used to ignite his first internal combustion engine (Klimstra 2007). Besides introduction of a new technology of electrical ignition with ability to work silently and at a higher speed, the engine had no other new improvements. These were maximum 20 horsepower engines, which were, however, relatively small.
Since the internal combustion engines did not require a boiler to function, and the explosion of the engine was rare, they became common and widely produced. In 1867, August Otto from German made an improvement in the original internal combustion engines and developed a free piston engines (Crolla and Mashadi 2011). Though this engine did not produce much power, it was more economical to operate than the first ones. All the ancient models had two strokes and did not fully compress the air-fuel mixture before combustion. Focusing on this weakness, Otto developed a four-stroke engine which was able to compress the mixture in the cylinder before combustion started, therefore, separating the charge into layers. Contrary to Otto’s first engine, this second generation was silent, more efficient and produced high power, thanks to the additional compression stroke.
After the death of Otto, Daimler went on with improving the four-stroke engine. He first worked on reducing the size of the mechanism and came up with smaller but high speed ones which were cheaper to produce. Later, he introduced fuel produced from lighter hydrocarbons to be used in fueling engines as opposed to earlier types of fuel (Govindasamy and Dhandapani 2007). Additionally, Daimler was able to increase the speed of the initial engine to720 r/min as well as adding a carburetor and hot tube ignition. It is paramount to note that the modern engines have been developed as a result of these improvements.
How spark Ignition Engine works
Spark-ignition engines can be categorized into two-stroke, four-stroke and the rotor engines depending on the number of strokes present. The two stroke engine was the first to be invented but has lately been replaced by the four-stroke one (Lo, Murphy and Cakebread 2012). The work of the four stroke spark-ignition engine can be understood by taking into consideration the functions of the suction, compression, power and exhaust strokes.
The first stroke involves intake of the air-fuel mixture through reduction of internal pressure by increasing volume. This induces the inflow of a mixture of fuel and air since the atmospheric pressure is higher than the pressure of the combustion space. As the volume of fuel and air increases, pressure also grows until it matches the atmospheric pressure and the suction valve closes (Cornilli, Gonnella, and Jacobs 2012). This ushers in the compression stroke forcing the piston up the cylinder, thus compressing the mixture of fuel and air producing heat which helps in the combustion of the fuel. The third stroke involves the ignition of the air and fuel mixture which then increases pressure substantially. This process forces the piston, which is close to the top dead center by this time, down to the bottom of the cylinder while the suction and the exhaustion valves remain closed. The last stroke involves the elimination of the burnt gases. This occurs when the piston moves back upwards while the exhaust valve is open forcing all burnt gases out through the valve (Guzzella and Onder 2009). It should, however, be noted that most of the burnt gases escape as a result of pressure from their own expansion and not of the force exerted by the movement of the piston. This completes a cycle of the four-stroke engine.
On the other hand, the two-stroke engine has both the suction and the exhaust functions performed at the same time, thus completing a power cycle in one revolution of the crankshaft (Boretti, Scalzo and Masudi 2011). These types of engines are mostly used in light machines like motor cycles and chainsaws. Two-stroke spark-ignition engines do not have specific suction and exhaustion strokes and thus use various other methods to fill and empty the cylinder.
On the same note, there is the rotary engine where a rotor is used instead of the piston. The rotor, which is attached to an eccentric shaft, is made to move round a static gear during combustion. In addition to the four strokes of a four-stroke engine, the rotary engine has a fifth stroke known as a power stroke. The rotor engine has three power pulses with the eccentric shaft doing a revolution for every pulse (Marthur and Das 1991).
Types of the Spark-Ignition Engines
Grouping engines by the use of the number of strokes that an engine has gives rise to its three major types. To begin with, the two-stroke engine is very basic and easy to operate and has only two strokes to complete an engine power cycle. These types of engines were the first ones to be invented, and the others are just improved models of a two-stroke engine. Besides having great power-to-weight ratio for narrow range rotational speeds, two-stroke engines have very few moving parts compared to the four-stroke type of the spark-ignition engines (Hooley 1999). Nevertheless, recent two-stroke engines have introduced the use of valves which open and close the exhaust, therefore, altering the port timing or the resonant frequency. These types of two-stroke engines have better low-speed power as compared to ancient types.
Besides the above type of two-stroke engine, there is also a type that has two-strokes which move in opposite directions, though in the same cylinder. At the top of the engine, there is the second crankshaft which hosts the upper pistons (Rajput 2007). The reciprocating masses of the opposed-piston engine move in the opposite directions, thus enhancing its balance. On the same note, the engine is mechanically simpler since the valves which are essential in other two-stroke engines are eliminated.
On the other hand, there is the rotary spark-ignition engine which gets its name because it uses the rotor instead of a piston. Movement of the rotor causes variations in the volume of each chamber. The chamber’s volume increases when the rotor moves towards the major diameter of the chamber and reaches its maximum when the two are parallel (Guzzella and onder 2009). The rotor is hollow, and the oil that flows through it also acts as a coolant and lubricant of the rotor and its gears. On top of the four strokes of a four-stroke engine, this type has the fifth stroke which makes it more powerful. This is the type of engines that have been improved to form the Wankel rotary engine that uses fuel economically, especially when carrying a heavy load (Kumarappa and Prabhukumar 2008).
The rotor or the Wankel engines, as they are mostly referred to, require small space and low weight per horsepower which makes them more efficient. In addition, the rotor engines are able to operate without vibrations and do not make a lot of noise when they are functioning (Marthur and Das 1991). Besides, the engines are mechanically simple due to the absence of some parts making it cheaper to manufacture. Moreover, the exclusion of the spring-closed valves allows the engine to operate effectively at high speeds contrary to the piston engines. Compared to the valves in the engines with pistons, the frequency at which the ports on rotor engines open is higher which ensures that the air-fuel mixture streams in continuously, besides making the exhausting process effective. The safety of the operators is also high when a rotor engine is used in automobiles because its low center of gravity and lower weight reduce the impact incase of a collusion.
Another type of the spark-ignition engine is the four-stroke one which is the most common. It has four strokes as the name four-stroke engine tells. It is a result of improvements done on the two-stroke engine by Otto to increase efficiency and power output. This type completes its power cycle in four strokes and produces more power as compared to two-stroke engines. During the power cycle, the engine undertakes two crankshaft revolutions and one thermodynamic cycle. The four-stroke engine was used in the manufacture of the first automobile in the late 19th century (Szwaja and Nabler 2008). It should, however, be noted that there are other categories of the spark-ignition engines which have been grouped using different criteria, for example, method of fuel management, valve type and location and cooling system.
Current Technological Improvements on the Spark-Ignition Engines
There have been some shortcomings, as far as the spark-ignition engines are concerned, which require improvements to meet the current demands. On the same note, it should be noted that people are increasingly becoming aware of the economical aspects of operating engines. Consequently, costs, such as the production and maintenance costs, need continuous enhancements in order to meet the ever rising customer demands (Rajput 2007). The other aspect of human requirements that is highly dynamic is the need to have engines that are easy to transport to and from various places, and, therefore, technological advancement is expected to come up with small, thermal efficient and affordable engines. It is important to note that for these engines to be market leaders in the highly dynamic environment based on changing customer needs, they should be economically friendly, have low emissions and at the same time afford high performance.
To begin with, the spark-ignition engines are not fuel efficient as compared to compression-ignition engines, which makes these engines expensive to operate. In this regard, new technologies like direct injection and valve actuation technology have been introduced which help in increasing the fuel efficiency of the spark-ignition engines. These technologies also reduce the level of carbon dioxide emissions to the environment, thus making the engines more environmental friendly. In addition, efforts are made to advance powertrain hybridization technology as well as come up with Nitrogenous gases aftertreatment technologies which can help in making the spark-combustion engines more environmental friendly (Ritzinger, Koch, Lehmann and Boulouchos 2012).
Technology has also been improved giving rise to lean burn spark-ignited natural gas technology which has minimal emissions of nitrogenous gases as compared to earlier engines. Additionally, efficiency is enhanced by the employment of this technology in production of engines. Direct injection technology has been quite recently put into use to help in checking the limitations that the spark-ignition engines were suffering from compared to their counterparts (Meker and Schwarz 2011). Besides reducing the sensitivity of the engines to variations in the composition of natural gases, this technology has also helped in reduction of emissions. Moreover, innovations on this technology are to maximize fuel efficiency and compression ratios, while keeping emissions low. Furthermore, efforts are being made to ensure that the spark-ignition engines can optimally operate using various alternative fuels which might be cheaper, hence reducing cost of operation.
It is of a grear importance to note that continuous improvements in technology are paramount in order to keep up with the ever changing customer tastes and needs. In addition, social and economical aspects will continue to form an important area of concentration during engine advancements since market leader engines will need to be affordable. On the same note, environmental requirements keep on being changed, thus engines need to reduce their emissions as much as possible; consequently, such issue calls for increased technological research.
Advantages of Spark-Ignition Engines
The spark-ignition engine produces higher power as compared to other engines, especially the diesel ones. This is due to improved combustion of the air-fuel mixture which is up to 95% as compared to 75% of other engines. In addition, spark-ignition engines are smaller in size, thus their cost of production is lower because of the lesser materials required in its manufacturing process. Moreover, their size makes them more portable so they can, therefore, be easily moved from one place to another, besides enabling these engines to be used on light machines, such as motorcycles (Szwaja and Nabler 2008).
Spark-ignition engines are easy to start because of the light weight of the components used to produce it as well as the lesser compression force required. This ensures that there is less damage to the engine during starting since its components are easily turned. On the other hand, spark-ignition engines have broader power band which enables them to have high power and torque at high speeds (Kumarappa and Prabhukumar 2008). They are, therefore, able to execute light high speed functions better than other engines.
The small size of the spark-ignition engines make them suitable for small and medium sized machines that require up to a maximum of 300 horsepower. Moreover, the current types of engines that are fitted with dual ignition system have proved to be more efficient in the combustion of the air-fuel mixture other than having enhanced redundancy in case of failure of one ignition system. This has the effect of increasing the performance and power that is very vital in medium-range heavy duty functions. On the same note, if a spark-ignited natural gas engine has the same combustion rate with a modern diesel engine, then the spark-ignited engines deliver substantial economic and environmental benefits due to the low cost of natural gas per unit and reduced greenhouse gas emissions (GHG) intensity of natural gas (Merker and Schwarz 2011).
Given the current innovations that have been made, spark-ignition engines are able to operate on a variety of fuels other than the traditional fuels. Some of these fuels are more remunerative, thus making the cost of operation of the spark-ignition engines cheaper as compared to counterpart ones.
Disadvantages of Spark-Ignition Engines
Compared to diesel engines, the spark-ignition engine produces lower power per unit of fuel consumed. They are, therefore, less fuel economical and less efficient. This is because the fuel conversion efficiency of the spark-ignition engines is lower, and the type of fuel used in these engines is less dense than diesel. Additionally, the spark-ignition engines have a high possibility of knocking because there is speedy combustion of fuel in the cylinder. On the same note, the types of fuel used in spark-ignition engines are poor lubricators and quite harmful to the oil film on piston rings and cylinder bores (Boretti, Scalzo and Masudi 2011). This does not only require frequent servicing of the engine but also increases cost of maintenance since the components have to be replaced time and again.
At low speeds, spark-ignition engines have low power and torque. This makes them undesirable for carrying heavy loads which mostly require a machine to move at slow speed. In this regard, they become very uneconomical in carrying out heavy commercial functions as compared to other types of engines. On the same note, spark-ignition engines have higher carbon dioxide emissions than other models, especially the diesel ones, though developments are made to reduce the emissions in the new generation engines.
It should also be noted that though it is quite beneficial for the spark-ignited engines to have high compression ratios to increase thermal efficiency, these engines stand a risk of knocking or auto ignition at certain ratios (Hooley 1999). This problem limits the high compression ratios that can be supported, thus curtailing the enhancement of thermal efficiency by increasing compression ratios. Contrary to the diesel engines which have proved to be fuel efficient and can maintain cycle efficiency in heavy-duty applications, spark-ignited engines lack these qualities, and, therefore, diesel engines can run on reduced fuel costs unlike the spark-ignited ones.
Conclusion
The spark-ignition engine has brought many changes in the way people conduct their lives since their invention. Though they might have encountered some shortcomings, technological advancements have been made improving these engines as compared to their counterparts. Since their invention, spark-ignition engines have undergone several improvements and performed certain functions that were not possible while using diesel engines. Research is, however, paramount to ensure that technology is advanced to counter the shortcomings of the spark-ignition engines, especially fuel efficiency and emissions.
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