HEAT OF AN IC ENGINE
Jabinth.J , 3rd Mechanical
St.Xaviers catholic college of engineering, Chunkadai.
The refrigerating units currently used in road transport vehicle are of Vapour Compression Refrigeration system (VCRS). This system utilizes power from the engine shaft as the input power to drive the compressor of the refrigeration system, hence the engine has to produce extra work to run the compressor of the refrigerating unit utilizing extra amount of fuel. This loss of power of the vehicle for refrigeration can be neglected by utilizing another refrigeration system i,e. a Vapour Absorption Refrigeration System (VARS).
It is well known that an IC engine has an efficiency of about 35-40%, which means that only one-third of the energy in the fuel is converted into useful work and about 60-65% is wasted to environment. In which about 28-30% is lost by cooling water and lubrication losses, around 30-32% is lost in the form of exhaust gases and remainder by radiation, etc. In a Vapour Absorption Refrigeration System, a physicochemical process replaces the mechanical process of the Vapour Compression Refrigeration System by using energy in the form of heat rather than mechanical work. The heat required for running the Vapour Absorption Refrigeration System can be obtained from that which is wasted into the atmosphere from an IC engine.
1. CONVENTIONAL A/C SYSTEM USED IN VEHICLES
The air conditioning system used usually in a vehicle is a vapor compression refrigeration system. It consists of a compressor, condenser, expansion valve, an evaporator blower set and a refrigerant which is circulated through the system. This system works by compressing the refrigerant using a compressor, which increases the pressure and temperature of the refrigerant and it vaporizes. The refrigerant is then passed through the condenser where the latent heat of the refrigerant is removed and is liquefied. This refrigerant is then passed through the expansion valve where its pressure is reduced reducing the temperature. This chilled refrigerant is then passed through the evaporator to produce the cooling effect. The blower blows the air through the evaporator to produce the required cooling inside the cabin of the vehicle. The refrigerant absorbs the heat of the air and vaporizes, which is then passed through the compressor. Hence cooling effect is produced inside the vehicle. The main disadvantage of such a system is that the required power to run the compressor is taken from the engine main shaft, hence to maintain the same power the engine has to produce more work consuming more fuel thereby reducing the mileage of the vehicle. Fig 1. 1 Conventional refrigeration system used in automobiles
2.Vapour compression cycle
All vapour compression refrigeration systems are designed and built around these basic thermodynamic principles. * Fluids absorb heat while changing from a liquid phase to vapour phase and reject heat in changing from a vapour phase to a liquid phase. * The temperature at which a change in phase occurs is constant during the change, but this temperature will vary with the pressure. At one fixed pressure vaporization takes place only at fixed corresponding temperature. However, the temperatures of vaporization at a particular pressure are different for different fluids. * Heat will flow from a body at higher temperature to a body at lower temperature. * In Selecting metallic parts of cooling and condensing units, metals are selected which have high heat conductivity. * Heat energy and other forms of energy are mutually convertible with directional relationship imposed by second by second law of thermodynamics.
The vapour absorption refrigeration is one of the oldest methods of producing refrigerating effect. The principle of vapour absorption was first discovered by Michael Faraday in 1824 while performing a set of...