A review of research on low heat rejection engines, to incorporate various systems of ceramic materials in intermittent combustion engines, and on the use of ceramics in these engines is presented. The reduction of heat loss from the combustion chamber of diesel engines improves fuel efficiency only by 3 or 4 per cent. Some other gains may be possible from a smaller cooling system, recovery of exhaust energy, and improvements in aerodynamics. The use of thermal barrier coatings (TBCs) to increase the combustion temperature in diesel engines has been pursued for over 20 years. Increased combustion temperature can increase the efficiency of the engine, decrease the CO and (possibly) the NOx emission rate. However, TBCs have not yet met with wide success in diesel engine applications because of various problems associated with the thermomechanical properties of the coating materials. Although, the in-cylinder temperatures that can be achieved by the application of ceramic coatings can be as high as 850-9000C compared to current temperatures of 650-7000C. The increase in the in-cylinder temperatures helped in better release of energy in the case of biodiesel fuels thereby reducing emissions at, almost the same performance as the diesel fuel. The purpose of this paper is to explain the effect of insulation on engine performance, heat transfer characteristics, combustion and emission characteristics. Many researchers have carried out a large number of studieson Low Heat Rejection Engine (LHRE) concept. Some of them are experimental work and many are theoretical studies. In the case of LHR engines almost all theoretical studies predict improved performance but many experimental studies show different picture. This paper analyses the reason for this deviation. The operating conditions, under which the experimental and simulation studies are carried out, have been clearly discussed. The factors, which affect thermal efficiency, combustion, and exhaust emissions in LHR engine, are deduced and their influences discussed.
An experimental Lanthanum Zirconate (La2Zr2O7) ceramic powder has been used as a thermal barrier coating material to study its effect on performance and exhaust emissions of a single cylinder diesel engine operated using diesel and biodiesel. Pongamia vegetable oil has been used to prepare biodiesel through transesterification process. Lanthanum doped thermal barrier coatings are found to be promising candidates for applications such as in diesel engines besides the conventional YSZ TBCs with lower thermal conductivity, high sintering resistance, low oxygen permeability and with catalytic activity. This experimental study has shown that the performance of the engine is improved significantly on the account of brake thermal efficiency and specific fuel consumption. Emissions, on the other hand are also improved, especially the smoke opacity which is significantly low at all Low Heat Rejection (LHR) operations.
In the present work, results of a numerical study carried out using finite volume method, to investigate the fluid flow and heat transfer characteristics of Alumina ( Al2O3 ) nanoparticles in the base fluid (water) in a square cavity under natural convection mode are presented. The Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm was used to solve the discretized momentum and energy equations. Constant temperature heat sources of same strength are placed on bottom and left vertical surfaces whereas the right surface was kept cold, while the top surface was maintained as adiabatic. The impact of Rayleigh number (RaN) ( 1000 to 106 ) and nanoparticles volume fraction (Φ = 0 %, 5 %, 10 %, 15 % and 20 %) on fluid and heat flow characteristics were numerically investigated and presented in the form of streamlines, isothermal lines, mid line horizontal and vertical velocity components, local Nusselt number ( Nuloc ) and average Nusselt number ( Nuavg ). The obtained results indicate, for lower RaN ( i.e; 103 ), conduction dominates over convection near heated surfaces and results in lower fluid velocities and poor heat transfer. For higher values of RaN ( RaN = 105 and 106 ) and volume fraction of nanoparticles, there was a significant increase in mid horizontal and vertical velocity components, Nuloc and Nuavg due to increase in convective heat transfer and thermal conductivity of nanofluid.
Natural convective fluid flow and heat transfer in a square cavity filled with Copper (Cu) nano particles, mixed in a base fluid (water) has been numerically studied using finite volume method. The Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm has been used to solve the transport equations (momentum and energy). Two constant temperature heat sources of same magnitude are placed on bottom surface and the two vertical surface temperatures are kept cold, while the top surface is maintained adiabatic. The influence of Rayleigh number (RaN) (varied from 1000 to 10 6) and nanoparticle volume fraction (Φ = 0%, 5%, 10%, 15% and 20%) on fluid and heat flow characteristics has been numerically investigated and presented in the form of streamlines, velocity vectors, constant temperature lines, vertical velocity component at mid horizontal line, local and average Nusselt number. The obtained results indicate, for higher values of RaN (RaN=10 5 and 10 6) and volume fractions of nanoparticles, there is a significant increase in vertical velocity component, local and average Nusselt numbers due to increase in buoyancy forces and thermal conductivity of nanofluid.
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