Dual ignition

Last updated
A Jabiru 5100 flat-8 four-stroke aircraft engine with dual ignition, with two spark plugs per cylinder and two distributors. Jabiru5100-180hp.jpg
A Jabiru 5100 flat-8 four-stroke aircraft engine with dual ignition, with two spark plugs per cylinder and two distributors.

Dual Ignition is a system for spark-ignition engines, whereby critical ignition components, such as spark plugs and magnetos, are duplicated. Dual ignition is most commonly employed on aero engines, [1] [2] and is sometimes found on cars and motorcycles.


Dual ignition provides two advantages: redundancy in the event of in-flight failure of one ignition system; and more efficient burning of the fuel-air mixture within the combustion chamber. [1] [2] In aircraft and gasoline-powered fire fighting equipment, redundancy is the prime consideration, but in other vehicles the main targets are efficient combustion and meeting emission law requirements.


BMW R1100S with dual ignition. The second spark plug is concealed below the cylinder head. BMW R1100S - Flickr - mick - Lumix.jpg
BMW R1100S with dual ignition. The second spark plug is concealed below the cylinder head.

A dual ignition system will typically provide that each cylinder has twin spark plugs, and that the engine will have at least two ignition circuits, such as duplicate magnetos or ignition coils. [3]

Dual ignition promotes engine efficiency by initiating twin flame fronts, giving faster and more complete burning and thereby increasing power. [4] Although a dual ignition system is a method of achieving optimum combustion and better fuel consumption, it remains rare in cars and motorcycles because of difficulties in siting the second plug within the cylinder head (thus, many dual ignition systems found on production automobiles typically were of a two valve design rather than a four valve). The Nash Ambassador for 1932-1948 used twin sparkplugs on the straight eight engine, while later Alfa Romeo Twin Spark cars use dual ignition, as do Honda cars with the i-DSI series engines, and Chrysler's Modern Hemi engine. [5] In 1980 Nissan installed twin sparkplugs on the Nissan NAPS-Z engine, with Ford introducing it on the 1989 Ford Ranger and 1991 Ford Mustang four-cylinder models. Several modern Mercedes-Benz engines also have two spark plugs per cylinder, such as the M112 and M113 engines. Some motorcycles, such as the Honda VT500 and the Ducati Multistrada, also have dual ignition. [6] The 2012 Ducati Multistrada was upgraded with "twin-plug cylinder heads for smoother, more efficient combustion", the change contributing to a 5% increase in torque and a 10% improvement in fuel consumption. [7] Early BMW R1100S bikes had a single spark plug per cylinder, but after 2003 they were upgraded to dual ignition to meet emission law requirements.


A 160 hp (119 kW) Gnome 9N Monosoupape with dual ignition provision. Gnome 9N 1917 160 hp.jpg
A 160 hp (119 kW) Gnome 9N Monosoupape with dual ignition provision.

Dual ignition in aero-engines should enable the aircraft to continue to fly safely after an ignition system failure. Operation of aero engines on one magneto (rather than both) typically results in an rpm drop of around 75 rpm. [2] Its existence on aviation powerplants dates back to the World War I years, when such engines as the Hispano-Suiza 8 and Mercedes D.III, and even rotary engines as the later Gnome Monosoupape model 9N 160 hp (119 kW) versions featured twin spark plugs per cylinder.

The Hewland AE75, an inline three cylinder aero-engine created for the ARV Super2, had three ignition circuits, each circuit serving a plug in two different cylinders. If just one of the three circuits failed, all three cylinders still received sparks, and even if two circuits were to fail, the remaining circuit would keep the engine running on two cylinders. [8]

Partial dual ignition

While true dual ignition uses completely separate and redundant systems, some certified engines, such as the Lycoming O-320-H2AD use a single engine magneto drive-shaft turning two separate magnetos. Whilst saving weight, this creates a single point of failure in mechanical terms, that could cause both ignition systems to cease working. [2]

A simple form of partial dual ignition on some amateur-built aircraft uses a single spark plug, but duplicates the coil and pick-up for better redundancy than traditional single ignition. [9]

A further form of partial dual ignition (such as on the Honda VT500) is for each cylinder to have a single HT coil which sends the current to one plug and completes the circuit via the second plug, rather than via the earth. This system requires a voltage sufficient to jump both plug gaps, but an advantage is that if one plug fouls, the fouled plug may burn itself clean while the engine continues running.

Wankel engines

Wankel engines have such an elongated combustion chamber that even non-aero wankel engines may adopt dual ignition to promote better combustion. The MidWest AE series Wankel aero-engine has twin plugs per chamber, but these are placed side-by-side, not sequentially, so their main purpose is to give redundancy rather than improved combustion. [10]

Distillate fuel

Richard W. Dilworth of the Electo-Motive Corporation devised a system, using four spark plugs and one carburettor per cylinder, in order to burn "distillate" fuel in train car engines. Because such heavy, but cheap, fuel was hard to ignite, a quadruple system of ignition was used in order to burn fuel roughly equivalent to kerosene or home heating fuel. By using this distillate fuel, that cost as little as one-fifth the price of gasoline before the Great Depression, a railroad could save substantially on fuel costs. However, this patented ignition system saw little commercial use. [11]

Related Research Articles

Ignition magneto electricity-producing device

An ignition magneto, or high-tension magneto, is a magneto that provides current for the ignition system of a spark-ignition engine, such as a petrol engine. It produces pulses of high voltage for the spark plugs. The older term tension means voltage.

Wankel engine Combustion engine using an eccentric rotary design

The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion.

Spark plug Device that generates sparks in internal combustion engines

A spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a ceramic insulator. The central electrode, which may contain a resistor, is connected by a heavily insulated wire to the output terminal of an ignition coil or magneto. The spark plug's metal shell is screwed into the engine's cylinder head and thus electrically grounded. The central electrode protrudes through the porcelain insulator into the combustion chamber, forming one or more spark gaps between the inner end of the central electrode and usually one or more protuberances or structures attached to the inner end of the threaded shell and designated the side, earth, or ground electrode(s).

Petrol engine Internal combustion engine designed to run on gasoline

A petrol engine or gasoline engine is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.

An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines, oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark ignition internal combustion engines is in petrol (gasoline) road vehicles such as cars and motorcycles.


A distributor is an enclosed rotating shaft used in spark-ignition internal combustion engines that have mechanically timed ignition. The distributor's main function is to route secondary, or high voltage, current from the ignition coil to the spark plugs in the correct firing order, and for the correct amount of time. Except in magneto systems and many modern computer controlled engines that use crank angle/position sensors, the distributor also houses a mechanical or inductive breaker switch to open and close the ignition coil's primary circuit.

CVCC Reduced-emissions engine by Honda

CVCC, or Compound Vortex Controlled Combustion, is an internal combustion engine technology developed and trademarked by the Honda Motor Company.

Gnome Monosoupape

The Monosoupape, was a rotary engine design first introduced in 1913 by Gnome Engine Company. It used a clever arrangement of internal transfer ports and a single pushrod-operated exhaust valve to replace the many moving parts found on more conventional rotary engines, and made the Monosoupape engines some of the most reliable of the era. British aircraft designer Thomas Sopwith described the Monosoupape as "one of the greatest single advances in aviation".

A wasted spark system is a type of ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a cylinder on its exhaust stroke. The extra spark during the exhaust stroke has no effect and is thus "wasted". This design halves the number of components necessary in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts the lifespan of modern ignition components. In a typical engine, it requires only about 2–3 kV to fire the cylinder on its exhaust stroke. The remaining coil energy is available to fire the spark plug in the cylinder on its compression stroke.

Alfa Romeo Twin Spark engine Motor vehicle engine

Alfa Romeo Twin Spark (TS) technology was used for the first time in the 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. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.

Ignition coil Automobile fuel ignition system component

An ignition coil is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car's 12-volt supply. The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads. Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser). More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. A modern passenger automobile may use one ignition coil for each engine cylinder, eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses.

Motorcycle engine Engine that powers a motorcycle

A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.

Capacitor discharge ignition

Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds. The capacitive-discharge ignition uses capacitor discharge current to the coil to fire the spark plugs.

Sunbeam Matabele

The Sunbeam Matabele was a British 12-cylinder aero engine that was first flown in 1918. The Matabele was the last iteration of one of Sunbeam's most successful aero engines, the Cossack.

High tension leads

High tension leads or high tension cables or spark plug wires or spark plug cables, colloquially referred to as HT leads, are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal combustion engine. "High tension lead" or "cable" is also used for any electrical cable carrying a high voltage in any context. Tension in this instance is a synonym for voltage. High tension leads, like many engine components, wear out over time. Each lead contains only one wire, as the current does not return through the same lead, but through the earthed/grounded engine which is connected to the opposite battery terminal. High tension may also be referred to as HT.

Sunbeam Cossack

The Sunbeam Cossack was a British 12-cylinder aero engine that was first run in 1916. The Cossack spawned a family of engines from Sunbeam.

Inductive discharge ignition systems were developed in the 19th century as a means to ignite the air–fuel mixture in the combustion chamber of internal combustion engines. The first versions were low tension coils, then low-tension and in turn high-tension magnetos, which were offered as a more effective alternative to the older-design hot-tube ignitors that had been utilized earlier on hot tube engines. With the advent of small stationary engines; and with the development of the automobile, engine-driven tractors, and engine-driven trucks; first the magneto and later the distributor-type systems were utilized as part of an efficient and reliable engine ignition system on commercially available motorized equipment. These systems were in widespread use on all cars and trucks through the 1960s. Manufacturers such as Ford, General Motors, Chrysler, Citroen, Mercedes, John Deere, International Harvester, and many others incorporated them into their products. The inductive discharge system is still extensively used today.

Small engine

A small engine is the general term for a wide range of small-displacement, low-powered internal combustion engines used to power lawn mowers, generators, concrete mixers and many other machines that require independent power sources. These engines often have simple designs, for example an air-cooled single-cylinder petrol engine with a pull-cord starter, capacitor discharge ignition and a gravity-fed carburettor.

The Hewland AE75 is a lightweight aircraft engine that was manufactured in the mid-1980s by Hewland in Maidenhead, United Kingdom. The engine, a two-stroke inverted inline triple of 750 cc (46 cu in) displacement, is liquid-cooled and yields 75 hp (56 kW)

Trembler coil

A trembler coil, buzz coil or vibrator coil is a type of high-voltage ignition coil used in the ignition system of early automobiles, most notably the Benz Patent-Motorwagen and the Ford Model T. Its distinguishing feature is a vibrating magnetically-activated contact called a trembler or interrupter, which breaks the primary current, generating multiple sparks during each cylinder's power stroke. Trembler coils were first used on the 1886 Benz automobile, and were used on the Model T until 1927.


  1. 1 2 Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 177. Aviation Supplies & Academics, 1997. ISBN   1-56027-287-2
  2. 1 2 3 4 Aviation Publishers Co. Limited, From the Ground Up, (27th revised edition), page 67, ISBN   0-9690054-9-0
  3. "Dual ignition - Definition and More from the Free Merriam-Webster Dictionary". Merriam-webster.com. Retrieved 2013-06-12.
  4. van Elderen, Jan (2002). "Raceservice4u Twin plug systems" . Retrieved 5 August 2011.
  5. "Honda Technology Features & Benefits | Honda NZ". www.honda.co.nz. Archived from the original on March 22, 2012.
  6. "DUCATI MULTISTRADA 1000 (2004-2009) Review". motorcyclenews.com. Retrieved 30 April 2015.
  7. Kevin Ash in Daily Telegraph, page M18, "Motoring Section", Saturday 29 September 2012
  8. ARV Super2 Handbook
  9. Jodel.com (n.d.). "Dual ignition on auto engines without dual plugs". Archived from the original on 27 September 2011. Retrieved 2 August 2011.
  10. MidWest Engines Ltd AE1100R Rotary Engine Manual
  11. Strack, Don. "What Is Distillate Fuel?". utahrails.net.