Suitable turbocharger matching with naturally aspirated gas engine in order to control volumetric efficiency and compression ratio

Master's Thesis

Automotive Power Orientation

Abstract

In this thesis, which is presented under the title of turbocharger adaptation suitable for the EF7 engine in order to improve volumetric efficiency, the history of the invention and use of the turbocharger is first discussed. Then, naturally aspirated and turbocharged engines are compared, which results in clarifying the purpose of using this system. After that, a brief overview of the performance, components and types of turbocharging systems is done. Then the changes of the engine to be equipped with a turbocharger in order to achieve the best performance mode, the problems of turbocharging and its reduction methods are stated. In the following sections, the equations governing the turbocharger, the selection and adaptation of the appropriate turbocharger are discussed first, and after presenting the necessary theory, the equations and modeling method of the engine and turbocharger in the GT POWER software are explained. This model predicts engine behavior in different input conditions. Then, to ensure the accuracy of this model's performance, the results obtained at full load and partial load when 25% of the throttle is open have been calibrated so that all the model's predictions of the engine's performance are in good agreement with the test results. In this regard, the calibration method is explained and its results are compared with the results of experimental tests. Then, by making some changes in the geometric and design specifications, a suitable turbocharger that works in the high efficiency area and also provides the required power and torque increase is selected. Since in order to make any changes in order to improve the performance of the engine as well as complying with the existing restrictions, it is necessary to know the sensitivity of the different parameters of the engine to the changes applied. Next, a sensitivity analysis has been performed for the EF7 engine, in which the impact of each variable such as the conditions of the intake air, valve timing, spark timing, the presence of the turbine exhaust valve, cooling efficiency, air-to-fuel ratio, compression ratio and change in the geometry of the intake and exhaust system on the performance parameters of the engine and turbocharger has been measured. will be Finally, the supercharging of the turbocharged engine in order to increase the boost pressure at low engine speeds that the turbocharger is unable to provide due to its low speed is explained, the appropriate supercharger is selected, and then the results of superturbocharging the gas-burning EF7 engine are shown. style="direction: rtl;">      The average concentration of pollutants such as carbon monoxide, unburned hydrocarbons and nitrogen oxides in many parts of Tehran is higher than the limit recommended by the World Health Organization. Due to the rapid growth of traffic, the situation will worsen in the future.

     Considering that 89% of Tehran's air polluting sources are related to cars, the replacement of cleaner fuels that are both economically more economical and less polluting in terms of environmental effects has been taken into consideration and presented as a social necessity [1].

     Gas is a cheap fuel with less pollution and in the case of Providing the possibility of more access is one of the best alternative fuels to gasoline and diesel. By burning cars with gas, carbon monoxide, unburned hydrocarbons, sulfur dioxide and suspended particles resulting from combustion are significantly reduced. In addition, lead as one of the most harmful pollutants is completely removed and the engine noise is also reduced. Comparing gas engines with gasoline engines, the power is reduced by about 10 to 15 percent. The two main reasons for this reduction are the gaseous state of CNG fuel when injected into the engine, which occupies some of the air entering the engine and causes a decrease in volumetric efficiency.This factor shows that the gas-burning engine needs more air than the gasoline engine, in other words, if we can enter that amount of gas into the engine that the amount of energy released is equal to the amount of gasoline entered into the engine, more air should enter the engine than in gasoline mode. Because the amount of air entering the engine in gas mode is even less than the amount in gasoline mode, therefore, in gas-powered engines, more air is needed to improve performance. Due to the resistance of natural gas against self-ignition, the reduced power can be compensated by different methods. If we want to encourage people to use natural gas, reducing power when using natural gas is not acceptable. The method presented in this article to obtain more power is to use a turbocharger in order to increase the mass flow rate of air and subsequently increase the volumetric efficiency and power of the engine. Also, by using fuel injection, some of the engine pollutants can be kept at a lower level with more aeration or so-called lean burning of the engine. style="direction: rtl;"> 

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Chapter One

Introduction and research review Done in the past

1-1- History

Turbocharging of internal combustion engines was an idea that came up shortly after the invention of internal combustion engines. In 1885, Daimler received a paper on the use of a fan or compressor to add intake air to the engine. In 1902, Louis Renault built a centrifugal turbocharger for the first time and installed it on a prototype engine. This turbocharger was connected to the crankshaft by a belt and rotated at five times its speed. The first moving supercharger with exhaust fumes (turbocharger) was developed between 1909 and 1912 by Dr. Alfred Bucci of Switzerland. He presented the first example of a diesel engine equipped with a turbocharger in 1915 [2]. In the Buchi turbocharger, both the turbine and the compressor were axial flow type, which were connected to the engine crankshaft by a mechanical connection. Today, this type of engine is called a compound engine. A few years later Bucci came up with a modified model in which the mechanical connection between the engine and the turbocharger was removed, but the mechanical connection between the turbine and the compressor remained. The first turbocharger made by Bucci was of the uniform flow type, which did not meet with success. In 1925, Bucci introduced a successful shock turbocharging system [1], known as the Bucci model. The further boom of turbocharging started when turbochargers were installed on the cylinder and piston engines of airplanes and increased the amount of flight ceiling. Because in this plane, there was this problem that when the plane took off due to pressure drop, the output power of the engine was greatly reduced and this limited the flight ceiling. By using turbochargers and increasing the inlet pressure, it helped a lot to increase the flight height. Until World War II, the turbocharger industry was greatly developed. Using a turbocharger on a diesel engine was the best way to reduce fuel consumption costs, reduce the space required for the engine and reduce engine weight, increase efficiency and reduce noise. In the 1970s, the use of turbochargers for gasoline engines became very popular, and companies presented their sports cars with turbocharger engines, but due to the delay in the operation of the turbocharger, these engines were not welcomed by consumers.