Basic of Engine Operating Characteristics

2103471 Internal Combustion Engine

Background on IC Engines
• “An internal combustion is defined as a heat engine in which the chemical energy of the fuel is released inside the engine and converted directly into mechanical work on a rotating output shaft, as opposed to an external combustion engine in which a separate combustor is used to burn the fuel.”

Background on IC Engines
Internal combustion engines are so called because the heat required to drive them is released by oxidizing a fuel inside the engine itself. This approach has advantages and disadvantages, but is still the most popular for transport and small power generation plant. We will be looking at some common types of engine, examining some ways of analysing their performance parameters, and some of the problems encountered in improving efficiency and output.

Background on IC Engines
Internal combustion engines include systems which function like "closed" systems (e.g. petrol engines) or as "open" systems (e.g. gas turbines). All the engines we will examine contain the same basic activities: invest some work to compress a working fluid, inject heat into the fluid, recover a greater amount of work, return to initial conditions by removal of some heat.

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Typical Processes for an Internal Combustion Engine

Background on the Otto Cycle
• The Otto Cycle has four basic steps or strokes:
– F-A : An intake stroke that draws a combustible mixture of fuel and air into the cylinder – A-B : A compression stroke with the valves closed which raises the temperature of the mixture. A spark ignites the mixture towards the end of this stroke. – C-D : An expansion or power stroke. Resulting from combustion. – E-F : An Exhaust stroke the pushes the burned contents out of the cylinder.

Figure idealized representation of the Otto cycle on a PV