I keep hearing the term used when referring to the leading coil, but cant figure out what it is.

 

A wasted spark, is a spark that is not used to make power or lower emissions.

In the case of a leading coil, it is because coil fires both leading plugs on both rotors at the same time, but since the rotor induction cycle timing is offset, there is no need for the spark on the 2nd rotor, while the first is firing to ignite the mixture, and then when the 2nd rotor is being ignited, no need for the first rotor to spark.

 

Cool, makes perfect sense, thanks.

 

hahaha, thats funny. I was confused on this when i was setting my timing. I was wondering why both rotors would be soarking at the same time when they were a opposate ends of the cycle. so why did mazda to this? thats so freaking weird, its just wearing out the coil for no reason.

 

its cheaper to make one coil fire both plugs at the same time than to have two different coils (and for those obsessed with weight reduction, it's minutely lighter)

 

So, if the wasted spark does no harm, then why do they make that custom race engine with the wasted spark plugs? (RE: Thread with pic of 8 spark plug 2 rotor?) What is the point of that?

 

Mazda didnt decide to do this almost all car manufactures do this, piston or rotary but mostly piston cause everyone knows that rotaries are outnumbered

 

multiple reasons for doing this:

#1 cheaper to use a single coil with two outputs than to use two coils
#2 when advancing or retarding timing both rotors have exactly the same amount of advance or retard
#3 a single coil uses less space (this is very important as coils need to be kept cool- two coils are harder to keep at the same temp in the same location).
#4 easier to troubleshoot in the event of failure
#5 single output from ECU (reducing the number of active transisters in the ECU- reducing cost to manufature trhe ECU)
#6 Less weight - both reduced copper, reduced weight of the coil assemblies.

I could go on for another couple reasons, but what is the point.

 

Waste spark is very, very common in modern ignition systems for all the reasons Mark listed. Some cheaper cars kept using ECI-controlled dizzies for a while and a few manufacturers splashed out on coil-on-plug systems but the bulk use wasted spark. 4-cyl engines have two coils, 6-cyl engines have three coils, etc.

2-rotor engines can use wasted spark on the leading plugs only. If you fired the trailing plugs at the same time one would fire in a partly compressed air/fuel mix. 3-rotors can't used wasted spark at all.

Watch this animation from Rotary Engine Illustrated. It shows 2-rotor wasted spark in action and will instantly clear up any confusion.

http://www.rotaryengineillustrated.c...tions/IGN4.php

 

http://www.rotaryengineillustrated....ations/IGN4.php

That helped alot, thanks, cool site too

 

Actually, the waste spark does fire as a far trailing spark, so each rotor actually sees three sparks per ignition event.
Mazda did this for small emissions reasons.

For piston engines, the waste spark fires on the exhaust cycle, so it doesn't really do anything.


-Ted