Dual ignition
Encyclopedia
Dual Ignition is a system for spark-ignition engines, whereby each cylinder has every critical ignition component duplicated, including spark plug
s, magneto
s and ignition circuits, rather than the more usual single spark plug or circuit. It is commonly employed on both two-stroke and four-stroke aero engines 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. In aircraft, redundancy is the most important consideration, but in other vehicles combustive efficiency is the prime aim.
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 that could cause both ignition systems to cease working.
Another form of partial dual ignition that has been used on amateur-built aircraft uses a single spark plug, but duplicates the coil and pick-up for better redundancy than traditional single ignition.
A further form of dual ignition on motorcycles has twin plugs but a single coil per cylinder. The HT current does not return via earth but via a second HT lead on the second plug. This system allows the cylinder to fire even if one plug becomes fouled; and the continuing combustion may burn off deposits, possibly enabling the fouled plug to clear.
Dual ignition promotes engine efficiency by initiating twin flame fronts, thereby obtaining faster and more complete burning and increasing power. Although a dual ignition system is a very effective method of
achieving optimum combustion and better fuel consumption, it remains rare in cars and motorcycles because of difficulties in siting the second plug. Alfa Romeo Twin Spark cars (by definition) use dual ignition, as do some motorcycles, such as the Honda VT500
and the Honda NT400 Bros
.
Wankel engine
s 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.
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, magneto
Magneto
A magneto is a type of electrical generator.Magneto may also refer to:* Magneto , permanent magnetic alternating current rotary generator* ignition magneto, magnetos on internal combustion engines...
s and ignition circuits, rather than the more usual single spark plug or circuit. It is commonly employed on both two-stroke and four-stroke aero engines 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. In aircraft, redundancy is the most important consideration, but in other vehicles combustive efficiency is the prime aim.
Design
The provision of dual ignition in aero-engines is a safety feature to allow an aircraft to continue flying and land 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.While true dual ignition uses completely separate and redundant systems, some certified
Type certificate
A Type Certificate, is awarded by aviation regulating bodies to aerospace manufacturers after it has been established that the particular design of a civil aircraft, engine, or propeller has fulfilled the regulating bodies' current prevailing airworthiness requirements for the safe conduct of...
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 that could cause both ignition systems to cease working.
Another form of partial dual ignition that has been used on amateur-built aircraft uses a single spark plug, but duplicates the coil and pick-up for better redundancy than traditional single ignition.
A further form of dual ignition on motorcycles has twin plugs but a single coil per cylinder. The HT current does not return via earth but via a second HT lead on the second plug. This system allows the cylinder to fire even if one plug becomes fouled; and the continuing combustion may burn off deposits, possibly enabling the fouled plug to clear.
Dual ignition promotes engine efficiency by initiating twin flame fronts, thereby obtaining faster and more complete burning and increasing power. Although a dual ignition system is a very effective method of
achieving optimum combustion and better fuel consumption, it remains rare in cars and motorcycles because of difficulties in siting the second plug. Alfa Romeo Twin Spark cars (by definition) use dual ignition, as do some motorcycles, such as the Honda VT500
Honda VT series
The Honda VT series comprises motorbikes with two-cylinder V engines. More sporting V engined bikes are given "VTR" model numbers. Four-cylinder V-engined Hondas are designated VF or VFRs, while Honda motorbikes with inline engines mostly belong to the CB and CBR series.* VT125C* VT250* VT250F*...
and the Honda NT400 Bros
Honda NT650
The Honda Hawk GT NT650 motorcycle was designated as model RC31 and was designed by Toshiaki Kishi, and was the second Honda with "Pro-Arm" suspension bike after the RC30 VFR750R. The Japanese model was named the Bros...
.
Wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...
s have such an elongated combustion chamber that even non-aero wankel engines may adopt dual ignition to promote better combustion. The MidWest AE series
MidWest AE series
| -See also:-External links:*...
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.