Engine Ignition

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Contents

Description

Ignition System

Introduction: The internal combustion engine is an amazing machine that has evolved for more than 100 years. It continues to evolve as automakers manage to squeeze out a little more efficiency, or a little less pollution, with each passing year. The result is an incredibly complicated, surprisingly reliable machine. In other words, the ignition system of an internal-combustion engine is an important part of the overall engine system that provides for the timely burning of the fuel mixture within the engine. All conventional petrol (gasoline) engines require an ignition system. The ignition system is usually switched on/off through a lock switch, operated with a key or code patch.


Types

The two main types of iginition system are:

1- Mechanically Timed Ignition System Most four-stroke engines have used a mechanically timed electrical ignition system. The heart of the system is the distributor which contains a rotating cam running off the engine's drive, a set of breaker points, a condenser, a rotor and a distributor cap. External to the distributor is the ignition coil, the spark plugs, and wires linking the spark plugs and ignition coil to the distributor.

2- Electronic Ignition System In the initial systems, points were still used, but they only handled a low current which was used to control the high primary current through a solid state switching system. Soon, however, even these contact breaker points were replaced by an angular sensor - either optical, where a vaned rotor breaks a light beam, or more commonly using a Hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft. The sensor output is shaped and processed by suitable circuitry, then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil. The rest of the system (distributor and spark plugs) remains as for the mechanical system.


Core Components

Spark Plug

1- Fly Wheel: Flywheel is a rotating disk used as a storage device for kinetic energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft when a fluctuating torque is exerted on it by its power source such as a piston-based (reciprocating) engine, or when the load placed on it is intermittent (such as a piston pump). The flywheel is really a heavy wheel in an engine that helps keep it running and smooths its motion. The crankshaft in a petrol engine has a flywheel at one end, which keeps the crankshaft turning in between the intermittent power strokes of the pistons. It also comes into contact with the clutch, serving as the connection between the engine and the car's transmission system.

2-Key: A small metallic piece under the flywheel that keeps it intact so that the flywheel moves with the crankshaft.

3-Magnetron: The Magnetron ignition system was introduced in the mid-1980's. This system was developed to replace the older breaker point system which provides greater reliability and efficiency with fewer parts. Often when an engine will not start, it is the ignition system that is the cause. The engine spins a magnet inside a coil, and also operates a contact breaker, interrupting the current and causing the voltage to be increased sufficiently to jump a small gap. The spark plugs are connected directly from the magneto output. Magnetos are not used in modern cars, but because they generate their own electricity they are often found on piston aircraft engines and small engines such as mopeds, lawnmowers, snowblowers, chainsaws, etc.

4-Governor: Historically, in 1698 the first engine was built by the English engineer Thomas Savery. In 1769 the French engineer Nicolas Cugnot built the first pseudo-automobile, a steam-powered tricycle. Between the years 1775 and 1800 Scottish engineer James Watt in partnership with industrialist Matthew Boulton produced some 500 engines. A governor is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the Watt or fly-ball governor, which uses weights mounted on spring-loaded arms to determine how fast a shaft is spinning, and then uses proportional control to regulate the shaft speed. There are two types of automobile governors, one limiting the rotational speed of the engine, the other limiting the speed of the vehicle. In small, low power applications, governors are used to protect the engine from damage due to excessive rotational speed, or pushing the engine past its peak abilities.

5-Spark Plug: A spark plug (also, very rarely nowadays, in British English: a sparking plug) is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. Spark plugs have an insulated center electrode which is connected by a heavily insulated wire to an ignition coil or magneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder.

6-Spark Plug Connector: Spark Plug is connected by a heavily insulated wire, also called spark plug connector, to an ignition coil or magneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder. Early patents for spark plugs included those by Nikola Tesla (in U.S. Patent 609,250 for an ignition timing system, 1898), Richard Simms (GB 24859/1898, 1898) and Robert Bosch (GB 26907/1898). Karl Benz is also credited with the invention.


How it works

The follwoing phases will explain how the ignition system actually works:

TIMING: When the fuel/air mixture in the cylinder burns, the temperature rises and the fuel is converted to exhaust gas. This transformation causes the pressure in the cylinder to increase dramatically and forces the piston down.

In order to get the most torque and power from the engine, the goal is to maximize the pressure in the cylinder during the power stroke. Maximizing pressure will also produce the best engine efficiency, which translates directly into better mileage. The timing of the spark is critical to success.

There is a small delay from the time of the spark to the time when the fuel/air mixture is all burning and the pressure in the cylinder reaches its maximum. If the spark occurs right when the piston reaches the top of the compression stroke, the piston will have already moved down part of the way into its power stroke before the gases in the cylinder have reached their highest pressures.

VOLTAGE: The spark plug must have an insulated passageway for this high voltage to travel down to the electrode, where it can jump the gap and, from there, be conducted into the engine block and grounded. The plug also has to withstand the extreme heat and pressure inside the cylinder, and must be designed so that deposits from fuel additives do not build up on the plug.

CURRENT FLOW: Current flows from the battery through the primary winding of the coil.

NEXT TWO STEPS: The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don't actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder. When you do a tune-up, one of the things you replace on your engine is the cap and rotor -- these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.

PRECIS: Thus, all these steps together make an engine work.


Evolution

History The earliest petrol engines used a very crude ignition system. This often took the form of a copper or brass rod which protruded into the cylinder, which was heated using an external source. The fuel would ignite when it came into contact with the rod. Naturally this was very inefficient as the fuel would not be ignited in a controlled manner. This type of arrangement was quickly superseded by spark ignition, attributed to Karl Benz, a system which is generally used to this day, albeit with sparks generated by more advanced circuitry. Early low-speed stationary engines often used a moving contact which protruded into the cylinder. This contact was quickly closed and reopened at the precise instant, producing a spark across the contacts, generated by a coil.

Some of the main types are explained as following, but before reading on it should be kept in mind that constant efforts exist to enhance this product:

Magneto system

The simplest form of spark ignition is that using a Magneto. The engine spins a magnet inside a coil, and also operates a contact breaker, interrupting the current and causing the voltage to be increased sufficiently to jump a small gap. The spark plugs are connected directly from the magneto output. Magnetos are not used in modern cars, but because they generate their own electricity they are often found on piston aircraft engines and small engines such as mopeds, lawnmowers, snowblowers, chainsaws, etc.

Switchable systems

In this mode of operation, the coil would "buzz" continuously, producing a constant train of sparks. The entire apparatus was known as the Model T spark coil (in contrast to the modern ignition coil which is only the actual coil component of the system), and long after the demise of the Model T as transportation they remained a popular self-contained source of high voltage for electrical home experimenters, appearing in articles in magazines such as Popular Mechanics and projects for school science fairs as late as the early 1960s. In the UK these devices were commonly known as trembler coils and were popular in cars pre-1910, and also in commercial vehicles with large engines until around 1925 to ease starting.

Battery operated ignition

With the universal adaptation of electrical starting for automobiles, and the concomitant availability of a large battery to provide a constant source of electricity, magneto systems were abandoned for systems which interrupted current at battery voltage, used an ignition coil (a type of autotransformer) to step the voltage up to the needs of the ignition, and a distributor to route the ensuing pulse to the correct spark plug at the correct time. The first reliable battery operated ignition was developed by the Dayton Engineering Laboratories Co. and introduced in the 1910 Cadillac.


References

Reference.com

How Things Work

Wikipedia

3D parts

Subassembly Bill of Materials
Part Name # Req'd Function Mfg Process Material CAD File Image
Magnetron 1 Contact breaker in the flywheel interrupts the current and causes an increase in voltage. Sheet Metal Forming Sheet Metal Magnetron
Magnetron.jpg
Spark Plug 1 Current jumps a small gap and causes a spark. Various Cast Iron & Aluminum Oxide Spark Plug
Spark plug.jpg
Magnetron Coil 1 Connects magnetron to spark plug. Various Wire, Insulator, Magnet Magnetron Coil
Magnetron coil.jpg
Magnetron Bolt 2 Secures magnetron to block Machined Steel Magnetron Bolt
Magnetron bolt.jpg
Flywheel 1 Stores kinetic energy. Cast Cast Iron & Aluminum Flywheel
Flywheel 1.jpg
Ignition Assembly 1 Ignites the fuel air mixture in the combustion chamber. Various Various Ignition Assembly
Ignition assem.jpg


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