CLASSIFICATION OF IC ENGINES

There are several bases for classification of IC engines, some of the important bases can be explained as

• Number of strokes per cycle.
• Nature of thermodynamic cycle.
• Ignition systems.
• Fuel used.
• Arrangement of cylinders.
• Cooling systems.
• Fuel supply systems.

Number of Strokes per Cycle: IC engines can be classified as four stroke engines (4S) and two stroke engines (2s). In four stroke engines, the thermodynamic cycle is completed in four strokes of the piston or two revolutions of the crankshaft whereas in two stroke engines, the thermodynamic cycle is completed in two strokes of the piston or one revolution of the crankshaft.

Nature of Thermodynamic Cycle: IC engines can be classified as Otto cycle, diesel cycle, and dual cycle engine. In Otto cycle engine, heat addition, and heat rejection occur at constant volume; therefore, this is also known as constant volume engine whereas in diesel cycle engine, heat addition occurs at constant pressure, and heat rejection occurs at constant volume. In dual cycle, heat addition occurs partly at constant volume and partly at constant pressure but heat rejection occurs fully at constant volume.

Ignition Systems: There are two modes of ignition of fuel inside the cylinder: spark ignition and self or compressed ignition. In spark ignition, sparking starts at the end of compression stroke from spark plug while in compressed ignition the temperature of the fuel is increased to the self-ignition point by compressing the air alone and at the end of compression fuel is injected inside the cylinder.

Fuel Used: On the basis of fuel used, IC engines can be classified as:

• Gas engines like CNG, natural gas, etc.
• Petrol engine.
• Diesel engine.
• Bi-fuel engine.

In bi-fuel engine two types of fuel are used like gaseous fuel and liquid fuel.

Arrangement of Cylinders: According to arrangement of cylinders (Figure 6.1), IC engines can be classified as:

• In-line engines.
• V-engines.
• Opposed cylinder engines.
• Opposed piston engines.
• X-type engines.
• Radial engines.

Figure 6.1 Classification of IC Engines on the Basis of Cylinders Arrangement

In an in-line cylinder engine, all the cylinders are arranged linearly and transmit power through a single crankshaft. V-engines have two banks of cylinders arranged in the shape of English letter V and single crankcase and crankshaft is used to transmit the power. In opposed cylinder engines, all the cylinders lie in same plane but the cylinders are arranged on both sides of the crankshaft at 180°. It is inherently well balanced. When a single cylinder houses two pistons each of which drives a separate crankshaft, it is called an opposed piston engine. The moments of the pistons are synchronized by coupling two crankshafts. It is also inherently well balanced. X-type engines have four cylinders with single crankcase and single crankshaft. The cylinders are arranged in the shape of English letter X. In radial engine, cylinders are arranged in radial directions like the spokes of a wheel and are connected to a single crankshaft. These engines are used in conventional air-cooled aircraft engines.

Cooling Systems: There are two types of cooling systems in IC engines: water cooling and air cooling. In water cooling, coolant, and radiators are provided to cool the cylinder. In air cooling, fins are provided on the surface of the cylinder to radiate the heat into the atmosphere. Low power engines like motorbikes are equipped with air cooling systems whereas large power producing engines like car, bus, truck, etc. are equipped with water cooling systems.

Fuel Supply Systems: On the basis of fuel supply systems, IC engines can be classified as:

• Carburettor engine.
• Air injection engine.
• Airless or solid or mechanical injection engines.

In a carburettor engine, air, and fuel are properly mixed into the carburettor and then fed into the cylinder. In air injection engines, fuel is supplied to the cylinder with the help of compressed air. In mechanical injection engines, the fuel is injected inside the cylinder with the help of mechanical pump and nozzle.