Bsfc, Thermal Efficiency And Heat Balance

Introduction:

Specific fuel consumption is defined as the amount of fuel consumed for each unit of brake power developed per hour. Thermal efficiency of an engine is defined as the ratio of the output to that of the chemical energy input in the form of fuel supply.

Brake Specific Fuel Consumption

Specific fuel consumption is defined as the amount of fuel consumed for each unit of brake power developed per hour. It is a clear indication of the efficiency with which the engine develops power from fuel.

Brake specific fuel consumption (bsfc) 

This parameter is widely used to compare the performance of different engines.

Thermal Efficiency and Heat Balance

Thermal efficiency of an engine is defined as the ratio of the output to that of the chemical energy input in the form of fuel supply. It may be based on brake or indicated output. It is the true indication of the efficiency with which the chemical energy of fuel (input) is converted into mechanical work. Thermal efficiency also accounts for combustion efficiency, i.e., for the fact that whole of the chemical energy of the fuel is not converted into heat energy during combustion.

• The energy input to the engine goes out in various forms – a part is in the form of brake output, a part into exhaust, and the rest is taken by cooling water and the lubricating oil.

•  The break-up of the total energy input into these different parts is called the heat balance.

•  The main components in a heat balance are brake output, coolant losses, heat going to exhaust, radiation and other losses.

•  Preparation of heat balance sheet gives us an idea about the amount of energy wasted in various parts and allows us to think of methods to reduce the losses so incurred.

Exhaust Smoke and Other Emissions

• Smoke and other exhaust emissions such as oxides of nitrogen, unburned hydrocarbons, etc. are nuisance for the public environment. With increasing emphasis on air pollution control all efforts are being made to keep them as minimum as it could be.

• Smoke is an indication of incomplete combustion. It limits the output of an engine if air pollution control is the consideration. Exhaust emissions have of late become a matter of grave concern and with the enforcement of legislation on air pollution in many countries; it has become necessary to view them as performance parameters.

Specific Weight

Specific weight is defined as the weight of the engine in kilogram for each brake power developed and is an indication of the engine bulk. Specific weight plays an important role in applications such as power plants for aircrafts.