Wasted spark
Encyclopedia
The wasted spark system is an ignition system
used with some four-stroke cycle
internal combustion engine
s. In a wasted spark system, the spark plug
s fire in pairs even though one is on its compression stroke and one is on its exhaust stroke. The extra spark on the exhaust stroke has no effect and is thus "wasted". This design halves the number of components in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts on the lifespan of modern ignition components.
Series I and newer, Harley Davidson V-Twin
, air-cooled BMW Motorcycles
, Citroën 2CV
, Mazda B engine
, Chrysler V10, PSA TU Engine
s, Volkswagen
Mark 3 2.8 VR6 (other than 2.0 ), Saturn Corporation 4 cylinders, and Chrysler Neon engine
s. Some Ford engines also do. Many Honda
and Kawasaki
motorcycle and PWC
engines also follow a similar design, to allow for a smaller number of more powerful coils to replace a larger number of smaller coils in the same limited space.
In practical use, a V-6 engine would only need three coil packs instead of six. Each individual coil fires the spark plugs in two cylinders simultaneously, the spark plug in one cylinder on a compression stroke where the power comes from, and the spark plug in the other cylinder on an exhaust stroke.
As well as the build-weight and maintenance advantages of this system, there is a tuning advantage. Mounted directly on the end of the crankshaft all the stress that spark generation would otherwise place on the camshaft chain (or another special purpose half-speed drive) is avoided, while there is virtually none of the strain
that necessarily degrades the ignition timing in systems relying on chains or gears.
Unlike the multi-cylinder systems noted above (which fire two plugs simultaneously from a double-ended coil) the coil in this system has only a single HT
lead running to the single plug. The flywheel magneto provides other services in, for instance, small motorcycles, as it can easily be built to provide direct-current battery-charging power at almost no additional cost or weight.
), or better combustion performance by initiating the flamefront at opposing points simultaneously (e.g. Alfa Romeo
). None of these are counted as wasted spark systems, as their sparks all take place after the useful compression stroke, rather than "wasted" in the exhaust stroke.
Ignition system
An ignition system is a system for igniting a fuel-air mixture. Ignition systems are well known in the field of internal combustion engines such as those used in petrol engines used to power the majority of motor vehicles, but they are also used in many other applications such as in oil-fired and...
used with some four-stroke cycle
Four-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...
internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s. In a wasted spark system, the spark plug
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...
s fire in pairs even though one is on its compression stroke and one is on its exhaust stroke. The extra spark on the exhaust stroke has no effect and is thus "wasted". This design halves the number of components in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts on the lifespan of modern ignition components.
Practical examples of 'wasted spark'
This system has been widely used, including such engines as the Buick V6 engineBuick V6 engine
The Buick V6, initially marketed as Fireball at its introduction in 1962, was a large V6 engine used by General Motors. The block is made of cast iron and all use two-valve-per-cylinder iron heads, actuated by pushrods....
Series I and newer, Harley Davidson V-Twin
V-twin
A V-twin engine is a two-cylinder internal combustion engine where the cylinders are arranged in a V configuration.- Crankshaft configuration :Most V-twin engines have a single crankpin, which is shared by both connecting rods...
, air-cooled BMW Motorcycles
BMW motorcycles
BMW's motorcycle history began in 1921 when the company commenced manufacturing engines for other companies. Motorcycle manufacturing now operates under the BMW Motorrad brand...
, Citroën 2CV
Citroën 2CV
The Citroën 2CV |tax horsepower]]”) was an economy car produced by the French automaker Citroën between 1948 and 1990. It was technologically advanced and innovative, but with uncompromisingly utilitarian unconventional looks, and deceptively simple Bauhaus inspired bodywork, that belied the sheer...
, Mazda B engine
Mazda B engine
The Mazda B-series engine is a small-sized, iron-block, inline four-cylinder with belt-driven SOHC and DOHC valvetrain ranging in displacement from 1.1L to 1.8L. It was used from front-wheel drive economy applications to the turbocharged full-time 4WD 323 GTX and rear-wheel drive Miata as well as...
, Chrysler V10, PSA TU Engine
PSA TU engine
The PSA TU engine is a family of small four-cylinder engines used in the Peugeot and Citroën range of cars. It was introduced in 1986 with the Citroën AX, replacing the X family, although it shared many components with its predecessor...
s, Volkswagen
Volkswagen
Volkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is...
Mark 3 2.8 VR6 (other than 2.0 ), Saturn Corporation 4 cylinders, and Chrysler Neon engine
Chrysler Neon engine
The Chrysler 1.8, 2.0, and 2.4 are inline-4 engines designed originally for the Dodge and Plymouth Neon compact car. These engines were loosely based on their predecessors, the Chrysler 2.2 & 2.5 engine, sharing the same 87.5 mm bore...
s. Some Ford engines also do. Many Honda
Honda
is a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
and Kawasaki
Kawasaki Motorcycle Corporation
Kawasaki motorycles are manufactured by the Motorcycle & Engine division of Kawasaki Heavy Industries at plants in Japan, USA, Philippines, Indonesia and Thailand. The motorcycles have been produced since 1954.-History:...
motorcycle and PWC
Personal water craft
A personal water craft , also called water scooter, is a recreational watercraft that the rider rides or stands on, rather than inside of, as in a boat....
engines also follow a similar design, to allow for a smaller number of more powerful coils to replace a larger number of smaller coils in the same limited space.
In practical use, a V-6 engine would only need three coil packs instead of six. Each individual coil fires the spark plugs in two cylinders simultaneously, the spark plug in one cylinder on a compression stroke where the power comes from, and the spark plug in the other cylinder on an exhaust stroke.
Single cylinder use
Most single cylinder four-stroke engines use the wasted spark system in order to capitalise on the simplicity and reliability of the flywheel magneto. These engines need a flywheel to run smoothly, and the heavy current-generating magnets help provide the momentum while delivering a zero-maintenance drive to the ignition system. Bolted directly on the end of the crankshaft this flywheel turns and operates at twice the speed that ignition is required.As well as the build-weight and maintenance advantages of this system, there is a tuning advantage. Mounted directly on the end of the crankshaft all the stress that spark generation would otherwise place on the camshaft chain (or another special purpose half-speed drive) is avoided, while there is virtually none of the strain
Strain
Strain can refer to:* Strain , variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes* Strain , a chemical stress of a molecule...
that necessarily degrades the ignition timing in systems relying on chains or gears.
Unlike the multi-cylinder systems noted above (which fire two plugs simultaneously from a double-ended coil) the coil in this system has only a single HT
High tension
High tension is a synonym for high voltage.It can also mean:* The HT, high tension or B battery supply to a traditional vacuum tube circuit, see HT * Haute Tension, a French horror film released as High Tension in North America...
lead running to the single plug. The flywheel magneto provides other services in, for instance, small motorcycles, as it can easily be built to provide direct-current battery-charging power at almost no additional cost or weight.
Effect on component life
In modern conditions, this method has a very small impact on the length on the service intervals of the vehicle and the longevity of individual components. Modern ignition systems do not have breaker points, which have been almost entirely replaced by electronic systems. Modern ignition coils outlast most other components of the vehicle and modern spark plugs have excellent service life, though there is a slight-difference between the two plugs as to erosion suffered at the centre electrode.Twin plug combustion
Some engines, since the earliest petrol engines, have used twin spark systems. These have twin spark plugs, supplied by separate sources. There may be several reasons for this: reliability (typically aircraft), starting (e.g. Model TFord Model T
The Ford Model T is an automobile that was produced by Henry Ford's Ford Motor Company from September 1908 to May 1927...
), or better combustion performance by initiating the flamefront at opposing points simultaneously (e.g. Alfa Romeo
Alfa Romeo Twin Spark engine
Alfa Romeo Twin Spark technology was used first time in Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars to enable it to achieve a higher power output from its engines...
). None of these are counted as wasted spark systems, as their sparks all take place after the useful compression stroke, rather than "wasted" in the exhaust stroke.