22-10-2016, 09:41 AM
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ABSTRACT
The increasingly worldwide problem regarding rapid economy development and a relative shortage of energy, the internal combustion engine exhaust waste heat and environmental pollution has been more emphasized heavily. Out of the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work; the remaining heat is expelled to the environment through exhaust gases and engine cooling systems, resulting in to entropy rise and serious environmental pollution, so it is required to utilized waste heat into useful work .The recovery and utilization of waste heat not only conserves fuel (fossil fuel) but also reduces the amount of waste heat and greenhouse gases damped to environment.
The study shows the possibility of waste heat recovery from internal combustion engine, also describe loss of exhaust gas energy of an internal combustion engine. From various possible methods to recover waste heat from Internal combustion engines, waste heat recovery system is the best way to recover waste heat and saving the fuel. In this project, we have designed a HEAT EXHANGER to recover waste heat from Internal combustion engine.
INTRODUCTION:-
Recent trend about the best ways of using the deployable sources of energy in to useful work in order to reduce the rate of consumption of fossil fuel as well as pollution. Out of all the available sources, the internal combustion engines are the major consumer of fossil fuel around the globe. Out of the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work. The remaining heat is expelled to the environment through exhaust gases and engine cooling systems, resulting in to entropy rise and serious environmental pollution, so it is required to utilized waste heat into useful work. The recovery and utilization of waste heat not only conserves fuel, usually fossil fuel but also reduces the amount of waste heat and greenhouse gases damped to environment. It is imperative that serious and concrete effort should be launched for conserving this energy through exhaust heat recovery techniques. Such a waste heat recovery would ultimately reduce the overall energy requirement and also the impact on global warming. The Internal Combustion Engine has been a primary power source for automobiles and automotives over the past century. Presently, high fuel costs and concerns about foreign oil dependence have resulted in increasingly complex engine designs to decrease fuel consumption. For example, engine manufacturers have implemented techniques such as enhanced fuel-air mixing, turbo-charging, and variable valve timing in order to increase thermal efficiency. However, around 60-70% of the fuel energy is still lost as waste heat through the coolant or the exhaust. Moreover, increasingly stringent emissions regulations are causing engine manufacturers to limit combustion temperatures and pressures lowering potential efficiency gains.
As the most widely used source of primary power for machinery critical to the transportation, construction and agricultural sectors, engine has consumed more than 60% of fossil fuel. On the other hand, legislation of exhaust emission levels has focused on carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). Energy conservation on engine is one of best ways to deal with these problems since it can improve the energy utilization efficiency of engine and reduces emissions. Given the importance of increasing energy conversion efficiency for reducing both the fuel consumption and emissions of engine, scientists and engineers have done lots of successful research aimed to improve engine thermal efficiency, etc. However, in all the energy saving technologies studied, engine exhaust heat recovery is considered to be one of the most effective. Many researchers recognize that Waste Heat Recovery from engine exhaust has the potential to decrease fuel consumption without increasing emissions, and recent technological advancements have made these systems viable and cost effective. This project gives a comprehensive review of the waste heat from Internal Combustion engine using "SHELL AND HELICAL COIL HEAT EXCHANGER".
POSSIBILITY OF HEAT RECOVERY AND AVAILABILITY FROM I.C. ENGINE:-
Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then “dumped” into the environment even though it could still be reused for some useful and economic purpose. This heat depends in part on the temperature of the waste heat gases and mass flow rate of exhaust gas. Waste heat losses arise both from equipment inefficiencies and from thermodynamic limitations on equipment and processes. For example, consider internal combustion engine approximately 30 to 40% is converted into useful mechanical work. The remaining heat is expelled to the environment through exhaust gases and engine cooling systems. It means approximately 60 to 70% energy losses as a waste heat through exhaust (30% as engine cooling system and 30 to 40% as environment through exhaust gas). Exhaust gases immediately leaving the engine can have temperatures as high as 842-1112°F [450-600°C]. Consequently, these gases have high heat content, carrying away as exhaust emission. Efforts can be made to design more energy efficient reverberatory engine with better heat transfer and lower exhaust temperatures; however the laws of thermodynamics place a lower limit on the temperature of exhaust gases. Fig.A show total energy distributions from internal combustion engine.
Benefits of ‘waste heat recovery’ can be broadly classified in two categories:-
1. Direct Benefits:
Recovery of waste heat has a direct effect on the combustion process efficiency. This is reflected by reduction in the utility consumption and process cost.
2. Indirect Benefits:
a) Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) etc, releasing to atmosphere. Recovering of heat reduces the environmental pollution levels.
b) Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes.
c) Reduction in auxiliary energy consumption: Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption.
In automobile engines significant amount of heat is released to the environment. For example , as much as 35% of thermal energy generated from combustion in an automotive engine is lost to the environment through exhaust gas and other losses. The amount of such loss, recoverable at least partly or greatly depends on the engine load. Among various advanced concepts, exhaust energy recovery for internal combustion engines has been proved to not just bring measurable advantages for improving fuel consumption but also increase engine power output or downsizing, further reducing CO2 , and other harmful exhaust emissions correspondingly. Which was predicted that if 6% of the heat contained in the exhaust gases were converted to electric power, 10% reduction of fuel consumption can be achieved.
Possibility of Waste Heat in Internal Combustion Engine:-
Today’s modern life is greatly depends on automobile engine, i.e. Internal Combustion engines. The majority of vehicles are still powered by either spark ignition (SI) or compression ignition (CI) engines. CI engines also known as diesel engines have a wide field of applications and as energy converters they are characterized by their high efficiency. Diesel engines are used in small electrical power generating units or as standby units for medium capacity power stations.
HEAT EXCHANGER TYPES AND SELECTION:-
In order to achieve optimum process operations, it is essential to use the right type of process equipment in any given process. The selection of the proper type of heat exchangers is of critical importance. Selecting the wrong type can lead to sub-optimum plant performance, operability issues and equipment failure.
The following criteria can help in selecting the type of heat exchanger best suited for a given process:
• Application (i.e. sensible vapor or liquid, condensing or boiling)
• Operating pressures & temperatures (including startup, shutdown, normal & process upset conditions)
• Fouling characteristics of the fluids (i.e. tendency to foul due to temperature, suspended solids )
• Available utilities (cooling tower water, once through cooling water, chilled water, steam, hot oil...)
• Temperature driving force (i.e. temperature of approach or cross and available LMTD)
• Plot plan & layout constraints
• Accessibility for cleaning and maintenance
• Considerations for future expansions
• Mechanical considerations such as: 1) material of construction; 2) thermal stresses (during startup, shutdown; process upset and clean out conditions); 3) impingement protection
Shell and helical coil heat exchangers accounts for more than 50% of all heat exchangers installed. However, in many cases, there are more attractive alternatives in terms of cost and energy recovery. Any time a heat exchanger is being replaced, the opportunity should be taken to re-assess if the type used is best for the given process. Operating changes since initial installation as well as advancements in the field of heat transfer may point towards a different type as being optimal.
Heat Exchangers Types :-
Shell & tube heat exchangers
Baffle types
Compact type heat exchangers
Spiral
Helical
Air-cooled heat exchangers
In order to make the best selection, it is important to have some knowledge of the different types of heat exchangers and how they operate. The tables below offer the advantages and disadvantages of common types of heat exchangers. They can be used to arrive at a type that is best suited for a given process.
Availability of Waste Heat from I.C. Engine:-
The quantity of waste heat contained in a exhaust gas is a function of both the temperature and the mass flow rate of the exhaust gas.
Q = × Cp × ∆T
Where, Q is the heat loss (kJ/min); is the exhaust gas mass flow rate (kg/min); Cp is the specific heat of exhaust gas (kJ/kg°K); and ∆T is temperature gradient in °K. In order to enable heat transfer and recovery, it is necessary that the waste heat source temperature is higher than the heat sink temperature. Moreover, the magnitude of the temperature difference between the heat source and sink is an important determinant of waste heat’s utility or “quality”. The source and sink temperature difference influences the rate at which heat is transferred per unit surface area of recovery system, and the maximum theoretical efficiency of converting thermal from the heat source to another form of energy(i.e. mechanical or electrical). Finally the temperature range has important function for the selection of waste heat recovery system designs.