apaloosa

I was wodering what is the point in having 2 glow plugs on the engine head rather than 1 though they are rare. some gas engines do follow this method as well -2spark plugs. anyone have an idea ???

w8ye

My Feedback: (16)

Typically, the second glow plug didn't need a ignitor. When the engine started, it would heat up the 2nd plug?

Enjoy,

Jim

ZAGNUT

My Feedback: (1)

if one plug dies the other will keep the engine going...that's my theory anyway. could be useful, especially in competition


dave

Mighty Mouse-RCU

My Feedback: (145)

Possibly better combustion thus resulting in a bit more power. In theory anyway.
Dont think there are any engine out there any more like that. Saito had one DP. Maybe others.

Rendegade

Mintor does a double plug head for their 170's and I think as a replacement for the OS 140 RX.

downunder

Early Fox, Merco and OS had twin plugs in their large engines but it should be noted they were all the old cross flow (baffled piston) designs. I've never come across the real reason they were used so I'd have to guess it was to overcome the (probably) poor turbulence and give two ignition points for two flame fronts for a faster pressure rise. I doubt it made too much difference though and one day maybe I'll find out by fitting a dead plug into my OS 80 and checking the revs.

I believe some large high performance (ducted fan and boat) engines use twin plugs to get that same two ignition points. On ignition, the flame front travels at a certain speed all the time and with a large combustion chamber there just may not be enough time for the flame front to travel from one side to the other especially at high revs. This is why most very high performance car engines use twin plugs.

ajcoholic

My Feedback: (10)

I thought they were mainly used in 60 size pattern engines (merco, OS, ST) in case a plug failed in flight, you could finish the round.

AJC

jessiej

The old Super Cyclone 60 was available with dual spark plugs, I have one in fact.

I understand from those who have run both single and double versions there is no difference in performance. The dual plug version sure looks neat though.

Flypaper 2

I still have a Merco 49 with both heads. Barely enough difference to read on a tach.

FlyingPilgrim

My Feedback: (26)

I believe the theory behind the double plugs was better ignition and lower reliable idle. As stated above, though, it did not provide the benefit of either, and was discontinued.

Pilgrim

Hobbsy

My Feedback: (102)

The Saito 182T, 300TD, 325 radial and 450 radial still use dual plugs.

Sport_Pilot

There are two reasons to use two plugs; better flame front and reduced detonation, and improved reliability. In aircraft engines two plugs are used in large high compression engines for both of the above reasons. But smaller aircraft engines really only benefit from improved reliability. I suspect the later for glow engines.

BTW with the lower powered aircraft engines you will have an RPM drop when running on one ignition system. That doesn't necessarily mean that the engine performs better on two plugs. When you have two plugs the ideal ignition timing is retarded, so when running on one plug its like retarding your distributer a few degrees.