Do F1 engines run with one or two sparkplugs? What would the advantage be?
I ask as honda use two sparkplugs in there small petrol engine and alfa use a twin sparkplug setup.
I would suggest that using two sparkplugs is not ideal as there would be two flame fronts created? have they added two plugs on the road engines to reduce the CO2 emissions?
Is it possible to pre-ignite one plug followed by the second?
As a formally trained aero engine technician, I can tell you some advantages of having multiple ignition sources.
I aviation, redundancy is essential, because aircraft and their components have to be as fail safe, or fail tolerant as possible. In a reciprocating aircraft engine, you will almost always find two completely independant ignition circuits. And those circuits are designed to be as fail safe as possible. They are magnetos.
As an added note, on the aircraft we flew, we had each ignition circuit hooked up to an oscilloscope, and we ran a full check of the plugs and circuits before flight. Warm the engines up, run them up to a high RPM, check each sparkplug on the scope....... and that's routine.
In drag racing, they run two sparkplugs because the conditions inside the combustion chamber are hostile to ignition. So they run an obscenely strong spark, in the hopes that one plug will ignite the mixture. In fact, in drag racing, having a cylinder fail to fire is very common.
So in Formula One, if two sparkplugs are used in each cylinder, it is because or firing reliability. The engineers want each power stroke to have an ignition sequence. There are many ways to increase the odds of gaining ignition in a combustion chamber under adverse conditions. Raise the spark energy, usually in the form of increase voltage. Make the spark gap wider... if the spark has to jump further, it will in all probability have a better chance of achieving ignition. Or as your topic suggests, add another spark plug.
Additionally, a second spark plug could be designed into the combustion chamber, to ignite a specific area of the combustion chamber. Maybe to burn gasses not reached by the first plug. Maybe for a cleaner burn. There are many good reasons to add a second spark plug.
Are there disadvantages? Definitely, the most obvious is the added mass and complexity. Second is the fact that the combustion chamber has to accomodate a second spark plug. That really complicates things for the engineers, because if you add a second spark plug, you thus have to sacrifice some room, most likely passages for the cooling medium.
On my opinion, enginers hope to design an engine with the needs of just one spark plug. But there has to be a reliable ignition source, it is a must. So if there are ignition issues, maybe adding a second plug could be the simplest, or necessary step.
As far as multiple ignition fronts causing interference? It could happen, but I would believe it's not an issue, because the second plug was in that engine because it had trouble getting ignition, rather than having pre-ignition issues.
I can see from the point of redundancy that two plugs are a good idea, however, would it be a good idea in a petrol engine?
As I say honda use a twin plug setup [in a 1.2 engine] but I think that this must be a bad thing as it produces two flame fronts. Surely you would want to create a linear burn to accelerate the piston cleanly? Any secondary burn would result in 'knocking' wouldn't it?
I agree that the cylinder design is severely compromised which is why I am wondering why it would be such a good idea. It seems a lot of trouble to go to if it doesn't work?
"Knocking" is caused by uncontrolled fuel burn. It usuallly is a result of a localized "hot spot" inside the combustion chamber, a rich fuel mixture,
low octane, the air/fuel charge igniting prematurely, and or any of these combinations. But the key word is ... uncontrolled.
For most situations, when the "knocking" occurs, it is because the air/fuel mixture is igniting BEFORE top dead center. Piston is moving up, fuel ignites, but the piston isn't in position to begin travelling down. So for a short period of time, the piston is still travelling to TDC, against the forces of the premature burn. It is right there when the pressures spike, that knock occurs. Once the piston has passed TDC, it begins it's trip down to the bottom of the cylinder, and of course, lower pressures. The "knock" doesn't happen on the power stroke. It occurse while still in the compression stroke.
I may appear that two distinct flame fronts could cause some form of mutual interference, such as two waves colliding. But from my experience, having multiple sources of fuel ignition would in most likelyhood not cause any "knocking" issues. Remember, the goal inside the combustion chamber is to burn the fuel mixture, as completely as possible.
Take a good look at top fuel dragsters, where they run engines that make totally obscene power. Estimates of over eight thousand horsepower, from five hundred cubic inches. Inside the combustion chamber, it is like something out of a sci fi movie. There is so much fuel, the combustion chamber is almost filled at TDC. And the ignition is like a lightning storm, because it isn't easy to ignite such a crazy mixture. They all run two plugs, and if there was ever any pre ignition issues, that engine would destroy itself. period.
I'm sure all F1 engines are single plug. The modern pent-roof chamber with four valves works quite well with a single, central plug. The plug itself is quite small (usually about 10mm) and it typically requires a very compact, specialized socket for installation and removal. Less room required for the spark plug means more room for ports and valves.
As for detonation, most F1 engines are specifically designed and extensively mapped for operating on a particular blend of race fuel. That fuel is typically supplied by the team's fuel sponsor, and the engine is literally designed and developed to operate on that particular fuel blend only. The engines have a very limited regime of operation, their ECU mapping is very extensive and precise, and there is no need to run at lean A/F ratios for lowering fuel consumption or reducing emissions, so the chance of the engine encountering detonation is very remote.
Twin spark was pretty common in 50s and 60s but since then, meaning in the last 35-40 years, only one engine, the Hart turbo of 1983, adopted it.
As for detonation, the most important thing to know is that it requires time. And when “low end rpm” means 120-130 ignitions per second, time is just too short for it, detonation in F1 simply isn’t an issue, there’s no time for it to happen.
Here's an interesting change to the engine rules for the 2006 F1 season:
"5.8.1 Ignition is only permitted by means of a single ignition
coil and single spark plug per cylinder. The use of
plasma, laser or other high frequency ignition
techniques is forbidden.
5.8.2 Only conventional spark plugs that function by high
tension electrical discharge across an exposed gap are
permitted.
Spark plugs are not subject to the materials restrictions
described in Articles 5.13 and 5.14."
No laser or plasma ignitions??!!!! I guess Ron Dennis can't use the ignition system from his spaceship...............
[quote="DaveKillens"]"Knocking" is caused by uncontrolled fuel burn. It usuallly is a result of a localized "hot spot" inside the combustion chamber, a rich fuel mixture,
low octane, the air/fuel charge igniting prematurely, and or any of these combinations.
A rich fuel mixture results in a cooler burn therefore reducing hot spots and the chance of pre ignition. Lean mixtures do the oppositie.
I would disagree with your definition/cause of ignition "knock" or "detonation". It is most commonly caused, in spark-ignited engines, due to the combustion chamber end gases spontaneously igniting, because of rapid increase in temperature and pressure ahead of the combustion flame front.
To prevent this condition, most engines are designed with a "squish band" in the combustion chamber zones where the end gases are present. The squish band is an area around the periphery of the combustion chamber, where the piston comes very close to the cylinder head at TDC (about 1 mm). The air/fuel mixture that is trapped within the squish band, during the combustion phase, is in very close proximity to the relatively "cool" piston and cylinder head. So it's temperature is maintained below the auto-ignition point, and detonation (or knock) is prevented.
riff_raff wrote:Here's an interesting change to the engine rules for the 2006 F1 season:
"5.8.1 Ignition is only permitted by means of a single ignition
coil and single spark plug per cylinder. The use of
plasma, laser or other high frequency ignition
techniques is forbidden.
5.8.2 Only conventional spark plugs that function by high
tension electrical discharge across an exposed gap are
permitted.
Spark plugs are not subject to the materials restrictions
described in Articles 5.13 and 5.14."
No laser or plasma ignitions??!!!! I guess Ron Dennis can't use the ignition system from his spaceship...............
Plasma and Laser technologies are not yet used for ignition in engines, eventhough these have huge advantages. I suppose that's why they are forbidden.
Plasma-plugs are patented in the US, and allows a very lean mixture. As opposed to igniting with sparkplugs the temperature actually goes down. This phenomena is not yet 100% clear.
I would disagree with your definition/cause of ignition "knock" or "detonation". It is most commonly caused, in spark-ignited engines, due to the combustion chamber end gases spontaneously igniting, because of rapid increase in temperature and pressure ahead of the combustion flame front.
To prevent this condition, most engines are designed with a "squish band" in the combustion chamber zones where the end gases are present. The squish band is an area around the periphery of the combustion chamber, where the piston comes very close to the cylinder head at TDC (about 1 mm). The air/fuel mixture that is trapped within the squish band, during the combustion phase, is in very close proximity to the relatively "cool" piston and cylinder head. So it's temperature is maintained below the auto-ignition point, and detonation (or knock) is prevented.
A rich fuel mixture cools the cylinder charge due to the effect of having to vaporise the fuel as it enters the combustion chamber resulting in lower starting temperatures before compression. This is the main reason that turbo'd production cars tend to run rich as std to give a bit of extra protection.
It seems a lot of trouble to go to if it doesn't work?