Technology - Transports
diesel engine - How Diesel engines work


How Diesel Engines Work

Like a gasoline engine, a diesel is an internal combustion engine that converts chemical energy in fuel to mechanical energy that moves pistons up and down inside enclosed spaces
called cylinders.

The pistons are connected to the engine’s crankshaft,which changes their linear motion into the rotary motion needed topropel the vehicle’s wheels. With both gasoline and diesel engines, energy is released in a series of small explosions (combustion) as fuel reacts chemically with oxygen from the air.

Diesels differ from gasoline engines primarily in the way the explosions occur. Gasoline engines start the explosions with sparks from spark plugs, whereas in diesel engines, fuel ignites on its own.Air heats up when it’s compressed.

This fact led German engineer Rudolf Diesel to theorize that fuel could be made to ignite spontaneously if the air inside an engine’s cylinders became hot enough through ompression. Achieving high temperatures meant producing much greater air compression than occurs in gasoline engines, but Diesel saw that as a plus. According to his calculations, high compression should lead to high engine efficiency. Part of the reason is that compressing air concentrates fuel-burning oxygen.

A fuel that has high energy content per gallon, like diesel fuel, should be able to react with most of the concentrated oxygen to deliver more punch per explosion, if it was njected into an engine’s cylinders at exactly the right time.

Four Strokes
Marine Engine Uses

Emergency Diesel Generators (EDG)
Certain amphibious landing ships
Mine warfare ships
Patrol craft
Tug boats
Small boats
Outboard motors

Thermodynamic Principles

All internal combustion : Open cycle, heated Engine

Gasoline (Otto) Engine : Spark ignition ,Compresses air-fuel mixture

Diesel Engine : Compressed ignition,Compresses air only.

Structural Components

Cylinder Block :Part of engine frame that contains cylinders in which piston moves
Supports liners & head.

Cylinder Head/Assembly : Serves to admit, confine, and release fuel/air
Cover to cylinder blockSupports valve train.

Crankcase : Engine frame section that houses the crankshaft

Oil sump :Reservoir for collecting and holding lube oil

Moving Components

Three Groups – according to motion
Reciprocating only (pistons and valves)
Reciprocation & rotary (connecting rods)
Rotary only (crankshafts and camshafts)

Piston : Acted on by combustion gases Lightweight but strong/durable
Piston Rings Transfer heat from piston to cylinder Seal cylinder & distribute lube oil
Piston Pin Pivot point connecting piston to connecting rod
Connecting Rod Connects piston & crankshaft reciprocating otating motion.

Crankshaft : Combines work done by each piston Drives camshafts, generator, pumps, etc.
Flywheel : Absorbs and releases kinetic energy of piston strokes -> smoothes rotation of crankshaft.

Intake: open to admit air to cylinder (with fuel in Otto cycle)
Exhaust: open to allow gases to be rejected
Camshaft & Cams Used to time the addition of intake and exhaust valves
Operates valves via pushrods & rocker arms.


Increased pressure of combustion gases acts on piston -> converted to rotary motion
Can be 2 or 4 stroke engines
2-stroke: 1 power stroke per 1 crankshaft rev
4-stroke: 1 power stroke per 2 crankshaft rev

Engine stroke
A stroke is a single traverse of the cylinder by the piston (from TDC to BDC)
1 revolution of crankshaft = 2 strokes of piston

Four-Stroke Diesel Engine

Intake stroke
Intake valve open, exhaust valve shut Piston travels from TDC to BDC
Air drawn in.

Compression stroke
Intake and exhaust valves shut Piston travels from BDC to TDC
Temperature and pressure of air increase.

Power stroke
Intake and exhaust valves shut Fuel injected into cylinder and ignites
Piston forced from TDC to BDC

Exhaust stroke
Intake valve shut, exhaust valve open Piston moves from BDC to TDC
Combustion gases expelled.

Strokes : Intake , Compression ,Power and Exhaust.

Two-Stroke Diesel Engine

1 power stroke every crankshaft revolution (vice every two w/ 4-stroke)
Uses pressurized air to simultaneously supply new air and expel combustion gases

Scavenging : Exhaust valve open, inlet port exposed
Pressurized air enters, expels combustion gases
Piston near BDC

Compression : Intake and exhaust valves shut Piston travels from BDC to TDC
Temperature and pressure of air increase.

Power stroke : Intake and exhaust valves shut Fuel injected into cylinder and ignites
Piston forced from TDC to BDC.

Supporting Systems

Ignition system : Diesel has compression ignition Gasoline has spark plugs

Cooling system :Uses fresh water and/or salt water to cool

Lubrication system : Provide lubrication and cooling

Drive Train – Direct or Indirect

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diesel engine - How Diesel engines work (Technology - Transports)    -    Author : segarin - India

50044 visitors since 2009-12-14
Last update : 2011-07-24 >> Technology >> Blog #13481

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