Termal bariyer kaplamanın turbodoldurmalı bir dizel motorunun egzoz emisyonlarına etkisi

Abstract

in enhancing or renewing aircraft turbine parts with wear reducing coatings. These are applied using a process called plasma spraying. This involves blowing metal or ceramic powders at twice the speed of sound through gas that has been heated to 11.000 °C. The suddenly molten material is then just as suddenly frozen when it hits its target. The result is that the target is thinly and evenly coated with whatever material went through the gas. If the target is part of a turbine, the idea is to toughen it up. But we have begun to use its experience to clean up the insides of diesels. Most of the pollution from internal-combustion engines happens because the fuel is not burnt completely. One cause of this incomplete combustion is that the engine is not running hot enough. So we have adapted its process to deposit a thin film of insulator (or thermal barrier coating, as it prefers to call it) inside the engine's cylinders. The TBC it has chosen is zirconium oxide. Stuck to an engine's piston crowns, cylinder heads and valves, using an undercoat of cobalt alloy, it conducts heat 50 times more poorly than the cast iron to which it has been applied. As a bonus, it also reflects heat back into the combustion chamber. The trapped heat burns the fuel more completely. Since most of the unburned fuel would turn to soot and end up in either the lubricating oil or the exhaust, the engine is cleaner and needs fewer oil changes. Thermal insulation thus obtained is supposed to head, according to the second law of thermodynamics, to engine heat efficiency improvement and fuel consumption reduction. Test data published in specialist indicates that the effects achieved are less significant, than were expected from theoretical calculations. Exhaust energy rise that accompanies this can be effectively used in turbocharged engines. Higher temperatures in the combustion chamber can also have a positive effect in diesel engines, due to the self-ignition delay drop and hardness of engine operation, though a increase of nitric oxide emission may be expected as well [47]. Low Heat Rejection (LHR) engine designs promise to meet the increasingly stringent regulations in the areas of fuel economy and permissble emissions level. The LHR concept uses insulation of the combustion chamber and exhaust passages to reduce, or possibly, eliminate heat loss during the closed portion of the cycle [12]. According to the first law of thermodynamics, any energy which is not rejected to the coolant remains available to produce useful piston work. According to the second law of thermodynamics, combustion taking place at higher temperature is also more efficient, as irreversibilities decrease with increasingtemperature. The reduction in heat losses also results in increased exhaust enthalpy. This extra exhaust energy can be utilized to drive a compounding turbine or a bottoming cycle, thus improving the overall system efficiency. The changes in the combustion process due to insulation also affect exhaust emissions. Higher gas temperatures should reduce the concentration of incomplete combustion products at the expense of increases in nitric oxides. However, researchers have measured decreases in carbon monoxide, unburned hydrocarbons, and soot only under some operating conditions [42,44,51]. Adiabatic turbocompound diesel engine concept promises reduced brake spacific fuel consumption in future diesel engines as a result of three basic design revisions: XVI

. Insulating the combustion chamber.. Removing the cooling system.. Utilising the increased energy in the exhaust by turbocompounding. The advantages in operating an adiabatic turbocompound diesel engine are: reduced specific fuel consumption, reduced emission and white smoke, multi-fuel capability, improved reliability, increase piston, valve and ring life, reduced noise and vibration, reducelube oil breakdown, increase engine life, improve engine response, increase horsepower, restoration of used components. Considering the hot walls, higher charge air temperature, and oxidizing environment of the Adiabatic Engine, carbon monoxide and unburned hydrocarbons were low as expected. Being aware of current nitrogen oxide levels within an Adiabatic Engine were expected to be higher than for a conventional engine, but surprisingly they were lower when a NOx versus BSFC tradeoff was made. An additional pollutant of major importance to diesel engines is particulate loading. The particulate levels with the Adiabatic Engine over the conventional water cooled engine shows the drastic reduction. The high combustion gas temperature in the adiabatic case could be respnsible for this reduction. It should be noted that the smoke level would consistently be continued to drop as insulation or adiabaticity of the engine was increased. The hot combustion chamber wall temperatures of an Adiabatic Engine provide higher compression charge temperatures with consequent reduction in ignition delay. Short ignition delay is conductive to multi-fuel capability in compression ignition engines. In this study,the effects of thermal barrier coating on the exhaust gas emissions of a turbocharged diesel engine were investigated. The engine selected for evaluation of the thermal barrier coatings was a four-stroke, direct injection, six cylinder, turbocharged, intercooled diesel engine. First, this engine was tested, as equipped with a water cooled intercooler, at different speeds and loads conditions without coating. Then, combustion chamber surfaces of the engine wascoated with ceramic materials. Cylinder head and valves was coated with a 0.35mm thickness of CaZr03 over a 0.15mm thickness of NiCrAl bond coat. The material used on pistons was MgZr03. The coating process was made by using Plasma Spray Technique at Sakarya University Engineering Faculty Plasma Coating Laboratory. Last, the ceramic coated test engine was again tested are the same operation conditions as the standard engine. Last, the ceramic coated test engine was again tested at the same operation conditions as the standart engine. The test data of the both cases were analysed by using a computer programme and the results were compared as diagrams. The experimental results show that, thermal barrier coating greatly affects exhaust gas emission XVIIin enhancing or renewing aircraft turbine parts with wear reducing coatings. These are applied using a process called plasma spraying. This involves blowing metal or ceramic powders at twice the speed of sound through gas that has been heated to 11.000 °C. The suddenly molten material is then just as suddenly frozen when it hits its target. The result is that the target is thinly and evenly coated with whatever material went through the gas. If the target is part of a turbine, the idea is to toughen it up. But we have begun to use its experience to clean up the insides of diesels. Most of the pollution from internal-combustion engines happens because the fuel is not burnt completely. One cause of this incomplete combustion is that the engine is not running hot enough. So we have adapted its process to deposit a thin film of insulator (or thermal barrier coating, as it prefers to call it) inside the engine's cylinders. The TBC it has chosen is zirconium oxide. Stuck to an engine's piston crowns, cylinder heads and valves, using an undercoat of cobalt alloy, it conducts heat 50 times more poorly than the cast iron to which it has been applied. As a bonus, it also reflects heat back into the combustion chamber. The trapped heat burns the fuel more completely. Since most of the unburned fuel would turn to soot and end up in either the lubricating oil or the exhaust, the engine is cleaner and needs fewer oil changes. Thermal insulation thus obtained is supposed to head, according to the second law of thermodynamics, to engine heat efficiency improvement and fuel consumption reduction. Test data published in specialist indicates that the effects achieved are less significant, than were expected from theoretical calculations. Exhaust energy rise that accompanies this can be effectively used in turbocharged engines. Higher temperatures in the combustion chamber can also have a positive effect in diesel engines, due to the self-ignition delay drop and hardness of engine operation, though a increase of nitric oxide emission may be expected as well [47]. Low Heat Rejection (LHR) engine designs promise to meet the increasingly stringent regulations in the areas of fuel economy and permissble emissions level. The LHR concept uses insulation of the combustion chamber and exhaust passages to reduce, or possibly, eliminate heat loss during the closed portion of the cycle [12]. According to the first law of thermodynamics, any energy which is not rejected to the coolant remains available to produce useful piston work. According to the second law of thermodynamics, combustion taking place at higher temperature is also more efficient, as irreversibilities decrease with increasingtemperature. The reduction in heat losses also results in increased exhaust enthalpy. This extra exhaust energy can be utilized to drive a compounding turbine or a bottoming cycle, thus improving the overall system efficiency. The changes in the combustion process due to insulation also affect exhaust emissions. Higher gas temperatures should reduce the concentration of incomplete combustion products at the expense of increases in nitric oxides. However, researchers have measured decreases in carbon monoxide, unburned hydrocarbons, and soot only under some operating conditions [42,44,51]. Adiabatic turbocompound diesel engine concept promises reduced brake spacific fuel consumption in future diesel engines as a result of three basic design revisions: XVI. Insulating the combustion chamber.. Removing the cooling system.. Utilising the increased energy in the exhaust by turbocompounding. The advantages in operating an adiabatic turbocompound diesel engine are: reduced specific fuel consumption, reduced emission and white smoke, multi-fuel capability, improved reliability, increase piston, valve and ring life, reduced noise and vibration, reducelube oil breakdown, increase engine life, improve engine response, increase horsepower, restoration of used components. Considering the hot walls, higher charge air temperature, and oxidizing environment of the Adiabatic Engine, carbon monoxide and unburned hydrocarbons were low as expected. Being aware of current nitrogen oxide levels within an Adiabatic Engine were expected to be higher than for a conventional engine, but surprisingly they were lower when a NOx versus BSFC tradeoff was made. An additional pollutant of major importance to diesel engines is particulate loading. The particulate levels with the Adiabatic Engine over the conventional water cooled engine shows the drastic reduction. The high combustion gas temperature in the adiabatic case could be respnsible for this reduction. It should be noted that the smoke level would consistently be continued to drop as insulation or adiabaticity of the engine was increased. The hot combustion chamber wall temperatures of an Adiabatic Engine provide higher compression charge temperatures with consequent reduction in ignition delay. Short ignition delay is conductive to multi-fuel capability in compression ignition engines. In this study,the effects of thermal barrier coating on the exhaust gas emissions of a turbocharged diesel engine were investigated. The engine selected for evaluation of the thermal barrier coatings was a four-stroke, direct injection, six cylinder, turbocharged, intercooled diesel engine. First, this engine was tested, as equipped with a water cooled intercooler, at different speeds and loads conditions without coating. Then, combustion chamber surfaces of the engine wascoated with ceramic materials. Cylinder head and valves was coated with a 0.35mm thickness of CaZr03 over a 0.15mm thickness of NiCrAl bond coat. The material used on pistons was MgZr03. The coating process was made by using Plasma Spray Technique at Sakarya University Engineering Faculty Plasma Coating Laboratory. Last, the ceramic coated test engine was again tested are the same operation conditions as the standard engine. Last, the ceramic coated test engine was again tested at the same operation conditions as the standart engine. The test data of the both cases were analysed by using a computer programme and the results were compared as diagrams. The experimental results show that, thermal barrier coating greatly affects exhaust gas emission XVIIparameters of a turbocharged diesel engine. The emissions characteristics of the insulated engines at the same conditions appear to be attractive. Due to the more complete combustion in the insulated engine, smoke emissions were between 17% and 40% lower than the standard engine. Similarly, unburned HC levels were 24% and 44% lower for the insulated engine. The NOx concentrations were also 9% higher due to the changed nature of combustion in the insulated engine. XVM