Thedevelopment of turbocharger overcame the general perception thatlarge size engines are the most efficient. The turbochargertechnology began in early twentieth century, but is a commercialapplication occurred in the late twenties. The basic workingprinciples of the turbocharger include a significant increase in themass flow of oxygen that enters the engine and the possibility ofusing the waste exhaust to generate power. Some of the majorcomponents of turbocharger that leads to successful downsizinginclude turbine, compressor, and center hosing rotating assembly.Market trends indicate that demand for downsized engines willcontinue increasing, especially in the developed economies. Some ofthe key advantages of turbocharger technology include a significantreduction in fuel consumption, carbon emission, increasedhigh-altitude performance, and power-to-size ratio. Some of the keydisadvantages associated with turbocharger technology include turbolag, installation problems, and excessive heating. The use of aturbocharger in downsizing engines is the best way to go.
Keywords: Downsizing, turbocharger technology, fuel consumption, engineefficiency.
Overthe years, people have held a general perception that the size of theengines is directly associated with its efficiency. However,technological advancement, especially in the automotive industry hasproven that engine downsizing can be achieved without foregoing fuelefficiency and the overall performance of the engine. Enginedownsizing refers to a process in which the load or speed operatingpoint moved to a region that is more efficient, a process that isachieved by reducing the capacity of the engine, while maintainingfull lead performance through pressure charging (Stephen, 2012, p.2). In other words, the process of engine downsizing involves thesignificant reduction in the cubic capacity of an engine with theobjectives of enhancing engine’s efficiency reduce fuelconsumption, and lower carbon dioxide emission. This process shouldbe accomplished using developmental and clever engineering methods toensure that performance and power generation as well as usage is notcompromised. The turbocharger is one of the modern technologies thathave made a significant contribution towards the process ofdownsizing of engines.
Thedevelopment of the turbochargers dates back to early twentiethcentury, when the first model was developed by Alfred Buchi between1909 and 1912 (Akden, 2013, p. 1). However, this discovery was notrecognized until in the late twenties when aggressive research workswere initiated following the increase in the need to reduce emissionof carbon dioxide and fuel consumption without reducing efficiency ofthe engine (Grissom, 2013, p. 6). The first engine was successfullydeveloped in 1925 by Alfred Buchi and resulted in an increase inpower by 40 %. This made an official entry of engines downsized usingthe turbocharger technology in the automobile industry. The researchand the process of commercial development of turbocharger downsizedengines were halted in the 1960s, following the realizing that theengines had very low levels of safety (Akden, 2013, p. 1). However,the issues of oil crises and climate change have increased thesignificance of the idea of engine downsizing in order to address theemerging economic and environmental challenges.
Initially,it was generally perceived that turbochargers could only be used forvery large engines. However, extensive research has allowed engineersto use turbochargers in smaller engines, include the engines designedfor sport cars. The first sport car (include the Formula 1 design)and passenger cars utilizing the turbocharger technology weredeveloped in the 1970s (Akden, 2013, p. 1). The real performanceturbocharger units were developed in 1978 by different companies(including Mercedes Benz) that aimed at increasing efficiency oftheir engines and reduce fuel consumption in order to meet thecustomer demands. Today, researchers have managed to increase thelevel of safety of these engines, reduce energy consumption, emissionof carbon dioxide, and increase power generation.
Theworking principle of the turbocharger
Theturbocharger is mainly used in increasing power in engines withinternal combustion. Turbocharger accomplishes this mission byincreasing the rate of mass flow of air that enters the engine. Therate is increased by turbine action that is driven by the exhaust(Muqeem, 2012, p. 38). The similar principle is applied in enginesdesigned for automobiles, aircrafts, and motorcycles. Theturbocharger is made up of a compressor and a turbine mounted on ashared shaft. The turbine section, which is a heat engine, convertsheat energy that is released through the exhaust into power. Thepower generated from this conversion is then used to drive thecompressor, which in turn compress ambient air. The compressed air isthen delivered to the air intake section at a higher pressure, whichresults in the entry of a greater mass of air entering the engine.Compressed air may at times be passed through the intercooler systembefore its introduction to the manifold. Since the turbochargers areheat engines that convert wasted exhaust into power, they compressthe air more efficiently than the superchargers.
Despitethe differences in air compression efficiencies between theturbocharger and the supercharger, their primary objective is thesame to enhance the size-to-output efficiency (Quan, 2012, p. 2).This is achieved by overcoming the cardinal challenge of slow airintake as a result of low pressure differences between the atmosphereand the interior of the engine. Turbocharger addresses this challengeby increasing pressure at the point of air entry into the cylinder.Additional air increases the possibility of fuel addition, which inturn increase torque and power output of the downsized engine. Theintake pressure is controlled by regulating the rotational pace ofturbocharger in order to avoid the risk of detonation as well asphysical damage. The waste-gate performs this control function byrouting part of the exhaust away from the turbine. The routingprocess, in turn regulates the speed of the shaft and air pressure inthe manifold.
Theprocess of increasing pressure at the intake air intake section usinga compressor is achieved through forced induction. Air compressionoccurs in the same fashion in both the turbocharger and thesupercharger, but they differ in the source of energy to do thecompression. Supercharger uses energy from the engine to get a netgain, but this should be provided in the total output of a givenengine. Turbocharger, on the other hand, functions by convertingexhaust into useful energy (Yao, 2011, p. 76. This results in asignificant improvement in volumetric efficiency following anincrease in the density of the intake air. Although the primaryobjective of designing turbocharger was to increase power, efficiencycan be achieved without any increase in power. This is accomplishedby feeding waste exhaust back into the intake of the engine. This isaccompanied by an increase in temperature, which in turn increasesCarnot efficiency.
Componentsof turbocharger that support engine downsizing
Turbochargeris composed three major components that are responsible for itscapacity to increase power and efficiency of the engine. First, theturbine has several housings that direct air through the turbine andit spines at about 250,000 rpm (Gan, 2014, p. 1). Both the shape andthe size of the turbine housings indicate different performancefeatures of the turbocharger. In addition, the size of the impellerwheel combined with the size of the impeller is the key determinantsof the amount of exhaust or air that flows through the system.
Thecompressor is the second components of the turbocharger and itfunctions as a centrifugal system (Williams, 2014, p. 1). The primaryfunction of the compressor is to increase the mass of intake oxygenthat is in the process of passing through the combustion chamber. Thecompressor is made up of a diffuser and an impeller that are housedwithin its casing. The role of impeller (made of aluminum) is to drawair, accelerate its velocity, and then force it into the diffuser(Pool, 2011, p. 37). The diffuser, on the other hand, decelerates theair, raises the temperature as well as the pressure inside thecompressor housings, compress it, and then direct it to the engine.An increase in the efficiency of the compressor is characterized byan intake of denser (cooler) air, which leads to an improvement inpower generation.
Third,the center housing rotating assembly is a component that connects theturbine and the compressor. This component has a bearing system thatsuspends the turbocharger’s shaft, thus enhancing its capacity torotate at a high velocity, but with minimal friction (Muqeem, 2013,p. 4). Modern turbochargers are fitted with air-foil bearings thatreduce the risk of extreme heating.
Figure1: Components of a turbocharger
Source:Muqeem (2013, p. 4).
Trendsin the market and the needs for engine downsizing
Enginedownsizing is not a new concept, but its significance has beenincreasing with time. Market trends related to engine downsizing havefive major characteristics. First, study shows that the share ofturbocharger has been increasing exponentially, especially in thedeveloped economies as well as in the medium income countries. Someof the countries that have reported a tremendous increase in theshare of gasoline turbo include the European countries and China,while Japan has a moderated increase in the share of the turbocharger(Schmltter, 2014, p. 24). Secondly, the number of research projectsaimed at enhancing engine downsizing has been increasing continuouslywith no signs of decline in the near future. For example, it isanticipated that the number of 3-cylinder engines will increase inChina compared to the share of 8 and 6-cylinder engines that willcontinue reducing with time.
Trendsalso show that the gasoline aluminum blocks will increase from 62 %in the year 2011 to 76 % in the 2017 (Schmltter, 2014, p. 26). Thesame study also indicated that the aluminum diesel engines are likelyto increase from 18 % in the year 2011 to 21 % in 2017 on conditionthat the original equipment manufacturers will come up with plans toexpand their shares of diesel engines. Coating of engine blocks withaluminum provides significant advantages with regard to the reductionof the engine size, recycling, and reduction of the scrap rate. Inaddition, trends show that the share of steel pistons will continueincreasing with time. Lastly, the peak cylinder pressure and themaximum specific power for LV gasoline as well as diesel engines willincrease at a high rate. All these trends suggest that the technologysector is ready to keep pace with the increase in demand for engineminimization, especially the application of the turbocharger.
Advantagedof turbocharger and engine downsizing
Enginedownsizing using the turbocharger has four major benefits over thenaturally aspirated automotive engines. First, the use ofturbocharger results in significant reduction in the rate of fuelconsumption. This implies that an engine fitted with a turbochargerand the engine without the turbo producing the same power would do sousing different amounts of fuel. For example, an engine downsizedusing the turbocharger technology can produce 200 horsepower usingfour cylinders, while a normal engine without a turbocharger wouldrequire 6 cylinders to produce the same amount of energy (Borretti,2013, p. 150).
Secondly,the use of turbocharger reduces the rate of carbon dioxide emission.Turbocharger utilizes the waste exhaust by converting it into usableenergy, thus reducing the rate at which the exhaust gas is releasedinto the atmosphere. The application of exhaust gas in powerproduction instead of spewing it out into the atmosphere reduces thelevels of carbon emission, which is part of environmentalconservation (Michigan, 2013, p. 1). This is part of waste recyclingthat is targeted at reducing environmental pollution.
Third,turbocharger increases the high-altitude performance of the engine.Under normal circumstances, engines produce less power at higheraltitudes because of the low pressure (Michael, 2013, p. 1). One ofthe primary roles of a turbocharger is to increase the density of allair that enters the engine. This helps the downsized engine producemore power at higher altitudes compared to engines without theturbocharger. This is because of the pressure difference between theair in the exhaust and the air at turbocharger.
Fourth,the power-to-weight ratio of the downsized engine is much better thanthe normal engine. This is because a downsized engine would requirefewer cylinders compared to the normal engine to produce the sameamount of energy (Michael, 2013, p. 1). This means that one would berequired to use a heavier and a bigger normal engine to produce thesame among of energy that an engine with the turbocharger wouldproduce.
Althoughturbocharger had addressed most of the pressing challenges (such asenvironmental pollution and excessive consumption of fuel), it hasseveral disadvantages like any other type of technology. First, turbolag is a challenge that is experienced by nearly all turbochargersystems that are installed in cars. Turbo lag refers to the amount oftime taken by the turbocharger to accumulate sufficient pressure inits chamber to ensure that the full potential of the car’sperformance is reached (Kress, 2013, p. 1). This means that drivershave to do careful timing to avoid the problem of turbo lag. Turbolag can make a driver lose control of the vehicle, especially whennegotiating sharp corners.
Secondly,installation of the turbo system is paramount to its effectiveness.This means that the capacity of the system to achieve the intendedgoals depends on the level of expertise applied during theinstallation phase. An improperly installed turbocharger can resultin serious damage to the engine. Many vehicles function properly withadditional power and experience minor tuning between 5 and 7 PSI.However, levels of 8 to 12 PSI require some reinforced internals,including heavy duty valve train as well as special pistons (Kress,2013, p. 1). Turbochargers operating above 12 PSI require someprofessional modifications to be done in the engine in order toprevent damage to its internal components. However, even someproperly installed turbochargers that have been negligently drivenare still likely to cause serious damage to the engine. This impliesthat the successful installation of the turbocharger is an issue ofprobability since the installation is not a perfect situation.
Third,in most cases turbochargers results in excessive heating of theengine that increases the risk of detonation or damage of the othercomponents fitted close to the engine. This is a common occurrencewhen the turbocharger is fitted in the engine without an intercooler.Excessive heat can also result in the melting of critical plasticcomponents of the engine, overheating breakdowns, and fires (Kress,2013, p. 1).
Opportunitiesfor further improvement
Althoughthe extensive research has resulted in successful downsizing, it isevident that further studies are required to address the limitationshindering the maximum downsizing. There is a need to design dieselengines with lower displacements. The main focus of engine developersshould be to enhance the functionality of the common-rail injectionsystem in order to the engine performance further (Pool, 2011, p.39). The common rail injection refers to a system that mixes air withfuel in the internal combustion compartments. A smaller turbochargeris used to raise the levels of pressure and enhance pressurebuild-up. By raising the pressure build-up further, engineers will beable to regulate the injection of fuel into the engine with anincreased frequency and accuracy, which will in turn increase power.
Despitethe significant decline in the level of carbon emission, which hasbeen achieved since the discovery of turbocharger, there is stillsome room for improvement. Most of the present research projects inthe automotive engineering are targeting the discovery ofcarbon-cutting techniques since the global emission limits are yet tobe realized (Pool, 2011, p. 39). The main focus should be on theexploration of combustion control, which can be achieved using thecombustion chamber pressure sensor. In addition, there is a need todo further investigation of the best approaches that can be used forenergy recovery from exhaust heat in order to enhance automotiveefficiency. The achievement of these targets will result ineconomical driving and help the scientists in meeting the stringentcarbon emission targets (Pearson, 2014, p. 1).
Achievingthe fuel cut off targets is essential following the increase in fuelcrisis and economic challenges that have elevated the demand forvehicles that consume less. The fuel cutoff technology is still atits infancy stage where the main focus is being given to the lighthybrid engine system. In this system an electric motor and a batteryare installed in the vehicle together with the downsized engine(Copeland, 2013, p. 1). However, the main role of the electric motoris to start, smooth out cranks, and accelerate the downsized engine.This results in further decrease the rate of fuel consumptionfurther. Although the addition of the motor and the battery decreasesfuel consumption, it is suggested that the development of aneffective turbocharger has not reached the maximum. This means thatthere still a room for the development of downsized engine that willrequire a simultaneous installation of the motor and the battery.
Turbochargeris not a relatively new technology, but it has evolved for nearly acentury with significant improvements being achieved each at a time.Some of the primary factors that pressured researchers to dedicatetime and resources in this technology are the need to reduce carbondioxide emission and reduce consumption of fuels. The two objectivescould be achieved by engines that could consume less fuel andgenerate maximum power from any amount of fuel injected into theengine. The basic principles that have given success to researchersinclude the use of waste exhaust to generate more power beforereleasing it into the environment. The successful development ofturbocharger reduced the amount the carbon dioxide emitted into theatmosphere by downsized engines, significant reduction in fuelconsumption, increased performance in high altitude, and improvedpower-to-size ration of the downsized engines. However, thistechnology is still facing some challenges (such as turbo lag,excessive heating, and installation problems) that call for furtherresearch.
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