Dual ignition
Dual Ignitionis a system for spark-ignition engines, whereby critical ignition components, such asspark plugsandmagnetos,are duplicated. Dual ignition is most commonly employed onaero engines,[1][2]and is sometimes found on cars and motorcycles.
Dual ignition provides two advantages:redundancyin 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.
Efficiency[edit]
A dual ignition system will typically provide that each cylinder has twinspark plugs,and that the engine will have at least two ignition circuits, such as duplicatemagnetosorignition 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). TheNash Ambassadorfor 1932-1948 used twin sparkplugs on the straight eight engine, while later Alfa RomeoTwin Sparkcars use dual ignition, as do Honda cars with thei-DSI series engines,and Chrysler'sModern Hemi engine.[5]In 1980 Nissan installed twin sparkplugs on theNissan NAPS-Zengine, withFordintroducing it on the 1989Ford Rangerand 1991Ford Mustangfour-cylinder models. Several modern Mercedes-Benz engines also have two spark plugs per cylinder, such as theM112andM113engines. Some motorcycles, such as theHonda VT500and theDucati Multistrada,also have dual ignition.[6]The 2012Ducati Multistradawas 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]EarlyBMW R1100Sbikes had a single spark plug per cylinder, but after 2003 they were upgraded to dual ignition to meet emission law requirements.
Safety[edit]
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 theWorld War Iyears, when such engines as theHispano-Suiza 8andMercedes D.III,and evenrotary enginesas the laterGnome Monosoupapemodel 9N 160 hp (119 kW) versions featured twin spark plugs per cylinder.
TheHewland AE75,aninline three cylinderaero-engine created for theARV 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[edit]
While true dual ignition uses completely separate and redundant systems, somecertifiedengines, such as theLycoming O-320-H2ADuse a single engine magneto drive-shaft turning two separate magnetos. Whilst saving weight, this creates asingle point of failurein mechanical terms, that could cause both ignition systems to cease working.[2]
A simple form of partial dual ignition on someamateur-built aircraftuses 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 theHonda 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[edit]
Wankel engineshave such an elongated combustion chamber that even non-aero wankel engines may adopt dual ignition to promote better combustion. TheMidWest AE seriesWankel 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[edit]
Richard W. Dilworth of theElecto-Motive Corporationdevised 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 theGreat Depression,a railroad could save substantially on fuel costs. However, this patented ignition system saw little commercial use.[11]
References[edit]
- ^abCrane, Dale:Dictionary of Aeronautical Terms, third edition,page 177. Aviation Supplies & Academics, 1997.ISBN1-56027-287-2
- ^abcdAviation Publishers Co. Limited,From the Ground Up,(27th revised edition), page 67,ISBN0-9690054-9-0
- ^"Dual ignition - Definition and More from the Free Merriam-Webster Dictionary".Merriam-webster.com.Retrieved2013-06-12.
- ^van Elderen, Jan (2002)."Raceservice4u Twin plug systems".Retrieved5 August2011.
- ^"Honda Technology Features & Benefits | Honda NZ".www.honda.co.nz.Archived fromthe originalon March 22, 2012.
- ^"DUCATI MULTISTRADA 1000 (2004-2009) Review".motorcyclenews.com.Retrieved30 April2015.
- ^Kevin Ashin Daily Telegraph, page M18, "Motoring Section", Saturday 29 September 2012
- ^ARV Super2 Handbook
- ^Jodel.com (n.d.)."Dual ignition on auto engines without dual plugs".Archived fromthe originalon 27 September 2011.Retrieved2 August2011.
- ^MidWest Engines Ltd AE1100R Rotary Engine Manual
- ^Strack, Don."What Is Distillate Fuel?".utahrails.net.