Does using dual spark plugs per cylinder make any difference?

Click For Summary

Discussion Overview

The discussion revolves around the use of dual spark plugs per cylinder in internal combustion engines, specifically focusing on a 180CC single cylinder petrol engine marketed with "twin spark technology." Participants explore the potential impacts on performance, efficiency, and reliability, questioning whether this technology is a marketing gimmick or a meaningful advancement.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express skepticism about the actual performance benefits of dual spark plugs, suggesting it may be more of a marketing strategy than a significant technological improvement.
  • Others argue that dual spark plugs can enhance combustion efficiency by ensuring more complete fuel burning, particularly in engines with specific combustion chamber designs.
  • It is noted that the speed of flame propagation can limit engine performance, and dual plugs may help achieve better combustion at higher RPMs, especially in two-stroke engines.
  • Some contributions highlight historical examples, such as the Bristol series of radial aero engines, where dual plugs were used primarily for reliability rather than performance enhancement.
  • Participants discuss the potential for dual plugs to allow for higher compression ratios and better fuel efficiency, particularly in smaller engines, though the actual performance gain may be marginal.
  • One participant references dyno data from larger engines, suggesting that dual plugs can lead to increased power and reduced emissions, though the relevance to smaller engines remains uncertain.
  • Concerns are raised about the cost-effectiveness of adding a second spark plug in smaller engines like the 180CC bike in question.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effectiveness or necessity of dual spark plugs in smaller engines. Multiple competing views are presented regarding their impact on performance, efficiency, and reliability.

Contextual Notes

Some discussions reference specific engine designs and historical contexts, indicating that the effectiveness of dual spark plugs may depend on various factors such as combustion chamber shape, engine size, and intended use. Limitations in available test data and the need for further empirical studies are acknowledged.

  • #31
berkeman said:
So each of the magnetos feeds one set of spark plugs for redundancy? Interesting...
During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".
 
  • Informative
  • Like
Likes   Reactions: Flyboy and berkeman
Engineering news on Phys.org
  • #32
Flyboy said:
I haven't touched a radial since school three years ago...

Lol, I haven't touched a radial since A&P school. . . 50 years ago. ( 1973 )

.
 
  • #33
When I was about 14, I wandered into the local Euro-Sports-Auto sales lot. They had a red Ferrari with the hood up. I spent quite a few minutes looking at the engine. Counted the 12 spark plug wires. Eventually I asked the sales guy "why are there two spark plugs per cylinder?" -- annoyed, he told me "that's a twelve cylinder engine, kid."

Much later I had a hot-rodded HD sportster with dual plugs. As mentioned above, this does allow for less spark advance, a lot less.
 
  • Haha
Likes   Reactions: berkeman
  • #34
I recall seeing Honda Odyssey many years ago with two plugs. (Not the car) It was only a single cylinder engine. Two stroke I would assume.
s-l400.jpg
 
  • #35
And according to eBay, here is one.
s-l1600.jpg
 
  • #36
Sometimes, the second "plug hole" is for a compression release. Seen on old Brit bikes, if they don't have a "valve lifter."
 
  • #37
Baluncore said:
During WW2, the test before takeoff was to run the engine up to temperature and speed, then cut one magneto at the time to check the fall in RPM. A "magdrop" of more than say 150 RPM, cancelled the flight.

I have a double toggle switch panel somewhere here, labelled "Magnetos".
Exactly right. Still done today on light piston planes, although it's more of a maintenance check every so often.
 
  • #38
gmax137 said:
Sometimes, the second "plug hole" is for a compression release. Seen on old Brit bikes, if they don't have a "valve lifter."
That could be but I do recall a plug in each hole and a wire on each. The Odyssey I used to ride only had one and I don't recall a comp release.
 
  • #39
Averagesupernova said:
That could be but

Sorry @Averagesupernova , my comment was not directed at your photo. More of a general comment.
 
  • #40
gmax137 said:
Sorry @Averagesupernova , my comment was not directed at your photo. More of a general comment.
Hey that's ok.
 
  • Like
Likes   Reactions: gmax137

Similar threads

  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 8 ·
Replies
8
Views
4K
Replies
7
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 14 ·
Replies
14
Views
1K
  • · Replies 25 ·
Replies
25
Views
11K
  • · Replies 25 ·
Replies
25
Views
13K
  • · Replies 3 ·
Replies
3
Views
37K
Replies
14
Views
5K
  • · Replies 19 ·
Replies
19
Views
6K