16-06-2014, 02:31 PM
EXHAUST GAS RECIRCULATION IN FOUR STROKE ENGINE
[attachment=64930]
. INTRODUCTION
All internal combustion engines generate power by creating explosions using fuel and air. These explosions occur inside the engine's cylinders and push the pistons down, which turns the crankshaft. Some of the power thus produced is used to prepare the cylinders for the next explosion by forcing the exhaust gases out of the cylinder, and compressing the air or fuel-air mixture before the fuel is ignited. There are several differences between diesel engines and Petrol engines. Petrol engines combine a fuel air mixture is taken into the cylinder, while diesel engines the air compressed after inject fuel into the cylinder. Petrol engines use a spark plug to ignite the fuel-air mixture, while diesel engines use the heat created by compressing the air in the cylinder to ignite the fuel, which is injected into the hot air after compression. In order to create the high temperatures needed to ignite diesel fuel, diesel engines have much higher compression ratios than gasoline engines. Because diesel fuel is made of larger molecules than gasoline, burning diesel fuel produces more energy than burning the same volume of gasoline. The higher compression ratio in a diesel engine and the higher energy content of diesel fuel allow diesel engines to be more efficient than gasoline engines
. EXHAUST GAS RECIRCULATION
Exhaust Gas Recirculation is an efficient method to reduce NOx emissions from the engine. It works by recirculating a quantity of exhaust gas back to the engine cylinders. Intermixing the recirculated gas with incoming air reduces the amount of available O2 to the combustion and lowers the peak temperature of combustion. Recirculation is usually achieved by piping a route from the exhaust manifold to the intake manifold. A control valve within the circuit regulates and times the gas flow.
2.1. Uses of Exhaust Gas Recirculation
First, exhaust gas recirculation reduces the concentration of oxygen in the fuel-air mixture. By replacing some of the oxygen-rich inlet air with relatively oxygen-poor exhaust gas, there is less oxygen available for the combustion reaction to proceed. Since the rate of a reaction is always dependent to some degree on the concentration of itsreactants in the pre- reaction mix, the NOx-producing reactions proceed more slowly, which means that less NOx is formed. In addition, since there is less oxygen available, the engine must be adjusted to inject less fuel before each power stroke. Since we are now burning less fuel, there is less heat available to heat the fluids taking place in the reaction. The combustion reaction therefore occurs at lower temperature. Since the temperature is lower, and since the rate of the NOx-forming reaction is lower at lower temperatures, less NOx is formed
. EGR Impact on ECS
The ECM (Electronic Control Machine) considers the EGR system as an integral part of the entire ECS. Therefore the ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods of high EGR flow. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can actually be enhanced when the EGR system is functioning as designed.
2.5. EGR Theory of Operation
The purpose of the EGR system is to precisely regulate the flow under different operating conditions. The precise amount of exhaust gas must be metered into the intake manifold and it varies significantly as the engine load changes. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can be enhanced. For this an ECM (Electronic Control Machine) is used to regulate the EGR flow. When EGR is required ECM opens the EGR valve.The ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods EGR flowThe exhaust gas then flows through the pipe to the cooler. The exhaust gases are cooled by water from the vehicle’s cooling system. The cooled exhaust gas then flow through the EGR transfer pipe to the intake manifold.
CONCLUSION
Thus, as seen that using Exhaust Gas Recirculation Technique in engines, the emissions are very much controlled due to lesser amounts of NOx entering the atmosphere. Thus the emission levels to be maintained are attained by the engines. As seen, Exhaust Gas Recirculation is a very simple method. It has proven to be very useful and it is being modified further to attain better standards. This method is very reliable in terms of fuel consumption and highly reliable. Thus EGR is the most effective method for reducing the nitrous oxide emissions from the engine exhaust. Many of the four wheeler manufacturers used this technique like Ford Company, Benz Motors etc to improve the engine performance and reduce the amount of pollutants in the exhaust of the engine
[attachment=64930]
. INTRODUCTION
All internal combustion engines generate power by creating explosions using fuel and air. These explosions occur inside the engine's cylinders and push the pistons down, which turns the crankshaft. Some of the power thus produced is used to prepare the cylinders for the next explosion by forcing the exhaust gases out of the cylinder, and compressing the air or fuel-air mixture before the fuel is ignited. There are several differences between diesel engines and Petrol engines. Petrol engines combine a fuel air mixture is taken into the cylinder, while diesel engines the air compressed after inject fuel into the cylinder. Petrol engines use a spark plug to ignite the fuel-air mixture, while diesel engines use the heat created by compressing the air in the cylinder to ignite the fuel, which is injected into the hot air after compression. In order to create the high temperatures needed to ignite diesel fuel, diesel engines have much higher compression ratios than gasoline engines. Because diesel fuel is made of larger molecules than gasoline, burning diesel fuel produces more energy than burning the same volume of gasoline. The higher compression ratio in a diesel engine and the higher energy content of diesel fuel allow diesel engines to be more efficient than gasoline engines
. EXHAUST GAS RECIRCULATION
Exhaust Gas Recirculation is an efficient method to reduce NOx emissions from the engine. It works by recirculating a quantity of exhaust gas back to the engine cylinders. Intermixing the recirculated gas with incoming air reduces the amount of available O2 to the combustion and lowers the peak temperature of combustion. Recirculation is usually achieved by piping a route from the exhaust manifold to the intake manifold. A control valve within the circuit regulates and times the gas flow.
2.1. Uses of Exhaust Gas Recirculation
First, exhaust gas recirculation reduces the concentration of oxygen in the fuel-air mixture. By replacing some of the oxygen-rich inlet air with relatively oxygen-poor exhaust gas, there is less oxygen available for the combustion reaction to proceed. Since the rate of a reaction is always dependent to some degree on the concentration of itsreactants in the pre- reaction mix, the NOx-producing reactions proceed more slowly, which means that less NOx is formed. In addition, since there is less oxygen available, the engine must be adjusted to inject less fuel before each power stroke. Since we are now burning less fuel, there is less heat available to heat the fluids taking place in the reaction. The combustion reaction therefore occurs at lower temperature. Since the temperature is lower, and since the rate of the NOx-forming reaction is lower at lower temperatures, less NOx is formed
. EGR Impact on ECS
The ECM (Electronic Control Machine) considers the EGR system as an integral part of the entire ECS. Therefore the ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods of high EGR flow. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can actually be enhanced when the EGR system is functioning as designed.
2.5. EGR Theory of Operation
The purpose of the EGR system is to precisely regulate the flow under different operating conditions. The precise amount of exhaust gas must be metered into the intake manifold and it varies significantly as the engine load changes. By integrating the fuel and spark control with the EGR metering system, engine performance and the fuel economy can be enhanced. For this an ECM (Electronic Control Machine) is used to regulate the EGR flow. When EGR is required ECM opens the EGR valve.The ECM is capable of neutralizing the negative aspects of EGR by programming additional spark advance and decreased fuel injection duration during periods EGR flowThe exhaust gas then flows through the pipe to the cooler. The exhaust gases are cooled by water from the vehicle’s cooling system. The cooled exhaust gas then flow through the EGR transfer pipe to the intake manifold.
CONCLUSION
Thus, as seen that using Exhaust Gas Recirculation Technique in engines, the emissions are very much controlled due to lesser amounts of NOx entering the atmosphere. Thus the emission levels to be maintained are attained by the engines. As seen, Exhaust Gas Recirculation is a very simple method. It has proven to be very useful and it is being modified further to attain better standards. This method is very reliable in terms of fuel consumption and highly reliable. Thus EGR is the most effective method for reducing the nitrous oxide emissions from the engine exhaust. Many of the four wheeler manufacturers used this technique like Ford Company, Benz Motors etc to improve the engine performance and reduce the amount of pollutants in the exhaust of the engine