Types of Engine

In the automotive world, different types of engine used depending on the application. Engine types mainly classified as internal combustion engine and external combustion engines.

Internal Combustion Engine – Petrol (gasoline) engine & diesel engine.

‘Steam engine’ is an external combustion engine. Steam engines no longer used in the industry. It’s an outdated technology.

In this blog, we will focus on the internal combustion engine.

Types of Engine

Types of Engine - By Knowledge Swami
Types of Engine

Following factors also considered for classification of engines,

  1. 2 Stroke Engine
  2. 4 Stroke Engine
  3. Types of Ignition (Spark Ignited / Compression Ignited)
  4. Single-cylinder or multiple cylinders or V-Type cylinder
  5. Air-cooled engine or water-cooled engine
  6. SOHC – Single Overhead camshaft or DOHC- Double overhead camshaft
  7. Naturally aspirated engine or Turbo Charged engine
  8. Rotary engine.

Before we move to the next section of this blog, let’s understand internal combustion engine terminology.

Internal combustion engine terminology

Engine Terminology & Compression Ration Formula - by knowledge-swami.com
Engine Terminology & Compression Ration Formula

2 Stroke Engine:

2 stroke engine generates power in each revolution of the crankshaft. In 2 stroke engine following cycle completed in two cycles (in one revolution of the crankshaft)
a. Suction
b. Compression
c. Power
d. Exhaust

Air & fuel mixture generated in the carburetor and it is feed inside the crankcase trough in-let port. During the upward movement of the piston, the air-fuel mixture enters inside the crankcase. When the piston reaches the top dead center (T.D.C) air-fuel mixture is compressed and this compressed charge is ignited by a spark plug. Once combustion takes place the piston moves towards the bottom dead center (B.D.C). During piston moving towards B.D.C, exhaust ports opens and exhaust gases in a cylinder is pushed out from exhaust port. The entire cycle is completed in two strokes of piston (BDC to TDC to BDC) that’s why this engine is known as 2 stroke engine.

4 Stroke Petrol / Gasoline Engine:

To understand quickly about 4 stroke engine watch following animation. 4 stroke engine equipped with spring-loaded valves on top of the cylinder head.

Suction Stroke:

In the suction cycle, air and fuel mixture sucked inside the cylinder due to the vacuum effect. In the suction cycle, the cylinder moves from T.D.C to B.D.C, and suction/inlet valves open. The exhaust valve of the engine will remain closed during the suction cycle. The opening and closing of the valve are controlled by a camshaft, cam, and compression spring. The camshaft is driven by a crankshaft.

Compression stroke:

In the compression cycle, the air-fuel mixture is compressed by the piston as piston moves from B.D.C to T.D.C. In the compression cycle, both suction and exhaust valve will remain closed. In the compression cycle, the pressure inside the cylinder increases. Typically pressure inside ranges from 850 kPa to 1000 kPa. The pressure range inside the cylinder is fully dependent on the compression ratio. The compression ratio in the petrol engine ranges from 8 to 11.

Power Stroke:

Once compression stroke complete, the combustion of an air-fuel mixture (charge) initiated by the spark plug. Due to the combustion of air-fuel mixture heat generated and burning gases expands. In gasoline engine pressure in power-stroke ranges from 4500 to 6000 kPa. Expansion of gases pushes the piston towards B.D.C. This cycle is known as a power stroke.

Exhaust Stroke:

At the end of the power stroke, an exhaust valve opened by a camshaft. In the exhaust cycle, the piston moves from B.D.C to T.D.C. In this cycle pressure inside cylinder drops as most of the exhaust/burnt gases are pushed out by piston through the exhaust valve and pressure drops inside the cylinder to atmospheric level. The suction valve will remain closed during this cycle.

Working Cycle of 4 Stroke Petrol Engine
Working Cycle of 4 Stroke Petrol Engine

In the internal combustion engine, Why exhaust valve is smaller than the inlet valve?

  • The main reason for the bigger valve size for the inlet valve is to improve the volumetric efficiency of the engine, by providing a larger opening in the inlet valve, air-fuel mixture (charge) flows with less or no restrictions.
  • The pressure of exhaust gases inside the cylinder is always higher than the atmospheric pressure. If exhaust gases not pushed out completely, it leads to knocking or pre-ignition of the engine. To avoid this, exhaust gases must be pushed out from the engine cylinder as quickly as possible. In exhaust stroke, the piston pushes burnt gases through exhaust valves. By providing a small valve opening (as compared to inlet valve), the velocity of exhaust gases increased. This increased velocity of exhaust gases and the pressure difference between the cylinder and atmospheric pressure, exhaust gases are quickly pushed out from the cylinder. (Basic Physics principal: High-pressure gas moves towards the low-pressure area)

4 Stroke Diesel Engine:

To understand quickly about 4 stroke engine watch following animation.

Diesel engine: 4 stroke diesel & gasoline engine both are equipped with suction and exhaust valve. The only difference between the two engines is the ‘ignition’ of fuel & air mixture. In diesel engine ignition take place due to compression of air and fuel mixture. That’s why the diesel engine is known as a compression-ignition (CI) engine. Whereas, in the petrol (gasoline) engine, the air-fuel mixture is ignited by a spark plug. That’s why the petrol engine is known as a spark ignition (SI) engine.

Who has invented the Diesel engine?

A German engineer and scientist ‘Rudolf Diesel’ invented the diesel engine. To know more about Rudolf Diesel please watch the following video.

4 Stroke Petrol Engine Vs. 4 Stroke Diesel Engine

Petrol EngineDiesel Engine
Fuel Type – Petrol (Gasoline)Fuel Type – Diesel
Working Principle – Otto Cycle
(Constant Volume)
Working Principle – Diesel Cycle
(Constant Pressure)
Air & fuel is compressedOnly air is compressed
Air-fuel mixture ignited by spark plug Ignition initiated by injecting diesel inside combustion chamber
Compression Ratio – 8:1 to 12:1Compression Ratio – 14:1 to 24:1
Higher running (fuel) costLower running (fuel) cost
Comparatively low initial costHigher initial cost
Comparatively diesel engine lower thermal efficiencyHigher thermal efficiency
Spark plug, carburetor or fuel injection system required.Only fuel injection system required
Runs smoothlyNoisy
Comparison between 4 Stroke Petrol Engine & 4 Stroke Diesel Engine

Wankel Engine (Rotary Engine):

The major difference between the rotary engine and the IC engine, is piston displacement. In the Wankel engine, the piston rotates, and in a conventional engine, the piston reciprocates.

We hope, this blog helps you to understand the types of engines and it’s working principle. Sharing is caring!

Please read other blogs too: How to maintain a car during lock-down.

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