How are spark plugs different?

[Harooon]

This is probably a dumb question, but why are spark plugs different? Why can't all engines use the same plugs?

Here is how I see it- since sparkplugs are meant to supply a spark to ignite the fuel, why did my mechanic insist that I had fitted the wrong sparkplugs to my Camry a few days ago? He said I had fitted plugs of the wrong heat grade, but I did not notice a difference in performance or fuel economy, so what was the problem, and what did he mean by "heat grade anyway? Can anyone here please explain that in simple language? 

[salmanahmed]

20 minutes ago, Harooon said:

This is probably a dumb question, but why are spark plugs different? Why can't all engines use the same plugs?

Here is how I see it- since sparkplugs are meant to supply a spark to ignite the fuel, why did my mechanic insist that I had fitted the wrong sparkplugs to my Camry a few days ago? He said I had fitted plugs of the wrong heat grade, but I did not notice a difference in performance or fuel economy, so what was the problem, and what did he mean by "heat grade anyway? Can anyone here please explain that in simple language? 

there are so many ways a spark plug cannot be one-size fits all. 

1. let get oblious out of the way first, 
   1. spark plugs for petrol and diesel are different 
   2. with fuel types, certain cars / SUVs need a large spark to ignite the entire mixture present in the cylinder
2. What does a strong spark do?
   1. a strong and timely spark will increase the efficiency of the engine by burning the complete mixture thus help in 
      1. increasing the pickup or acceleration of the car
      2. increase the overall top speed of the car (at high RPM there is a lot of fuel to ignite in the cylinder, a weak plug will not ensure complete burning of the fuel mixture)
      3. ensures fuel economy as less fuel is required to reach the desired speed.
3. Spark plug "tip"
   1. a titanium based spark plug tip will ensure that there is less erosion and the spark stays strong 
   2. regular plugs tips get carbon deposits and the erosion starts to weaken the spark strength 
4. The Spark Itself
   1. an electric spark is not the best thing there is, its the stock tech which you get from the manufacturer
   2. upgrading to a Laser plug will increase the fuel economy, acceleration and top speed of your car as the ignition provided by laser is far superior than an electric spark

Spark plugs are all about how quickly and strongly can they ignite the fuel mixture at variable RPMs!

Hope this helps.

[Saleem]

Sorry but I have never seen ore hear about spark plugs for diesel engine (except in some multi fuel engines)

it have basically a various thread size, type & length.

Then it you go for head type single or multi spark

then type of internal conductor material which depends on designed operating heat temperature and designed coil voltage.

other than that it's about registered patents and marketing. 

[aatish]

SUPER WOW info Salmanahmed, I have always had this frustrating question in my mind but I was never been so bold to ask in public. Thanks for the great info.

Only thing I can think to add is that all company marketing jargons make things more expensive and they need to justify that additional 5 aed to do something with exploding graphics and crazy color packaging.

[adil]

Only point missing from above is the life. Standard one that comes cheap for 5-10 AED will have limited life of 15-20k Kms as oppose to expensive iridium or platinum plugs that comes for 40-50 AED and last close to 100K Kms. You can use long life plug for cars that has difficult placement to change and it's a blessing.

[Barry]

Diesels don't have spark plugs, they have glow plugs which are a different thing altogether. Glow plugs are used to help start cold engines. They warm up the fuel that is injected into the cylinder to make it easier to ignite by compression. When you try to start a cold Diesel engine, a lot of the heat generated by the compression is absorbed by the cold engine block/liners, therefore the fuel is colder and harder to ignite. Diesels run better when they're hot. 

[gautam]

Hi Harooon,

@salmanahmed is right about the main differences between spark plugs (except for the bit about diesels), but to answer your question about heat grades-

The heat grade of a spark plug has nothing to do with how well the plug delivers a spark,and it only refers to how well a spark plug performs thermally in any given engine. To put it simply, a "hot" plug will heat up easily, while a "cold" plug resists heating up. There are many ways in which manufacturers control the heat grade of a plug, but generally, the heat grade of a plug is determined by;

• The surface area and/or length of the insulator nose
• How well the various spark plug components conduct (or resist) temperature changes
• The material used for the center electrode- copper, for instance
• The position of the insulator tip relative to the end of the ceramic shell  

In practical terms, the heat grade of a plug determines how well it cleans itself, meaning that the plug needs to be able to burn off the carbon deposits that form on the tip of the plug. This happens at temperatures of between 500-, and 800 degrees Celcius. So, if plug takes too long to heat up (a cold plug), the the carbon deposits can build up to the point where the spark might jump across the deposit, and not across the gap between the electrodes. 

If the plug heats up too soon (a hot plug), the plug can overheat, and burn away the electrodes too fast. This is true even for titanium and irridium plugs, but the bottom line is that if a plug is either too hot or too cold for any given application, fuel economy, spark plug life, and engine performance suffer.

The optimum temperature at which carbon deposists burn off spark plugs is around 450 degrees Celcius. Note that this temperature refers to that of the spark plug, and not the combustion process. A spark plug of the correct heat grade will stay at this temperature by transferring heat to the cylinder head by direct contact through its screw threads, as well as through contact with the air fuel mixture when it enters the cylinder. Spark plugs of the incorrect heat grade cannot maintain the optimimum self cleaning temperature, so they fail either through over heating, or carbon fouling.

Generally speaking, the difference from one heat grade to the next is 70-100 degrees Celcius-  enough to reduce spark plug life and engine performance in some engines, which is why it is very important to only use the recommended spark plugs.