What is Engine Cycle ?

The term "engine cycle" typically refers to the sequence of events that occur within an internal combustion engine during one complete operation. There are several types of engine cycles, but the most common ones are the Otto cycle and the Diesel cycle.

1. Otto Cycle: This is the cycle used in gasoline engines. It consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing the air-fuel mixture to enter the combustion chamber as the piston moves down.
   • Compression Stroke: Both intake and exhaust valves close, and the piston moves up, compressing the air-fuel mixture.
   • Power Stroke: When the air-fuel mixture is compressed, a spark plug ignites it, causing an explosion that drives the piston down, producing power.
   • Exhaust Stroke: Finally, the exhaust valve opens, and the piston moves up, pushing the burnt gases out of the combustion chamber.

2. Diesel Cycle: This cycle is used in diesel engines and is similar to the Otto cycle but differs in the method of ignition. It also consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing air into the cylinder.
   • Compression Stroke: The air is compressed highly, raising its temperature. Fuel is then injected directly into the cylinder near the top of the compression stroke.
   • Power Stroke: The injected fuel ignites due to the high temperature of the compressed air, driving the piston down.
   • Exhaust Stroke: The exhaust valve opens, and the piston moves up, expelling the exhaust gases.

These cycles are fundamental to the operation of internal combustion engines and are the basis for the efficiency and performance characteristics of various engine designs.

Standard diesel engine cycle

The standard diesel engine cycle, also known as the Diesel cycle, is a theoretical thermodynamic cycle that represents the operation of a diesel engine. It was first proposed by Rudolf Diesel, the inventor of the diesel engine. The Diesel cycle consists of four distinct processes:

1. Intake Stroke: The intake valve opens, and fresh air is drawn into the cylinder as the piston moves downward. Unlike in gasoline engines, no fuel is introduced during this stroke.

2. Compression Stroke: Once the intake valve closes, the piston moves upward, compressing the air within the cylinder. This compression process raises the temperature of the air significantly, typically to temperatures high enough to ignite diesel fuel.

3. Power Stroke: Near the top of the compression stroke, fuel is injected into the highly compressed, hot air. The fuel instantly ignites due to the high temperature, causing rapid combustion and an increase in pressure within the cylinder. This pressure forces the piston downward, producing power.

4. Exhaust Stroke: As the piston reaches the bottom of its stroke, the exhaust valve opens, and the piston moves upward again, pushing the burnt gases out of the cylinder.

The Diesel cycle is characterized by constant-pressure heat addition (combustion) and constant-volume heat rejection (exhaust). This cycle is different from the Otto cycle, which is used in gasoline engines, primarily in the method of ignition—diesel engines rely on the heat generated by compression to ignite the fuel, while gasoline engines use spark plugs for ignition. Diesel engines are known for their high efficiency and torque output, making them popular in applications such as heavy-duty trucks, buses, and industrial machinery.