Heat engine

Let Us Learn About Heat Engine

Heat engine is defined as a device that converts heat energy into mechanical energy or more exactly a system which operates continuously and only heat and work may pass across its boundaries.

A heat engine typically uses energy provided in the form of heat to do work and then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work. The first law and second law of thermodynamics constrain the operation of a heat engine

The Heat Engine as Part of a System

Heat engines enable heat energy to be converted to kinetic energy through the medium of a working fluid.

The diagram opposite shows the system heat flow. Heat is transferred from the source, through working fluid in the heat engine and into the sink, and in this process some of the heat is converted into work.

Heat engine theory concerns only the process of converting heat into mechanical energy, not the method of providing the heat, the combustion process. Combustion is a separate conversion process and is subject to its own efficiency losses. In some practical systems such as steam turbines these two processes are physically separate, but in internal combustion engines, which account for the majority of engines, the two processes take place in the same chamber, at the same time.

A heat engine is any machine which converts heat into useful work for example, a steam engine or a car engine. Real heat engines are complex and there are many ways of converting heat energy into useful work. We can abstract and generalise the workings of any heat engine into three parts:

• The Hot Resevoir - heat energy is created by some process such as combustion of a fuel to provide the heat energy.
• The working body - converts the heat energy into work. In real heat engines, the conversion process is never 100% efficient, so the work output is always less than the heat energy supplied. However we frequently idealise and assume reversibility.
• The cold resevoir - the energy that cannot be turned into work is dumped and goes to heat up the cold resevoir. In practice, the cold resevoir is usually the atmosphere. We also assume that the temperature of the cold resevoir does not increase, it has an infinite heat capacity.