LSPI What the Heck Are You Talking About?

[garycrist]

In a recent conversation here about oil catch cans and their value it appears there is a

confusion between Low Speed Pre-Ignition and detonation and or pinging. Sure we have

knock sensors and in conjunction with the ECM, control the timing ot achieve optimal timing

just short of detonation.

 

Pinging we experienced with carbs, port injection or where fuel was present in the intake path,

was caused by hot spots or combustion chamber deposits aside from fuel quality. With the new

Direct Injection DI engines most pinging is eliminated because of prcise fuel injection timing so that

these engines are bordering on a Diesel cycle rather than Otto cycle.

 

DI Engines (DIE) are like a Honda  Stratified system without the extra combustion chamber and

attending valve or some diesels with a per-combustion chamber . Instead, a rich patterned spray surrounds

the spark plug with a rich enough mixture to initiate combustion then spark. Power is achieved by duration

of spray measured in pulse and duration. As one can tell on a DIE this is where the computer can alter timing to alleviate pinging.

 

Now to the meat of this post LSPI or Low Speed Pre-Ignition. This animal is different and the computer

can not control it! Microscopic oil droplets in the intake path from blow-by is one culprit. The other, it

appears is the oil itself and it's additives as well as gasoline dilution of the residual oil film on the cylinder walls.

Some oil and now broken down oil (sludge) is now trapped between the top ring and top of the piston. This gunk

has a lower octane than the fuel and is one of the sources LSPI.

 

LSPI situations arise on cold engines or not up to operating temperature, engines that have been idling for a period

of time like in traffic. So as one may deduce it takes time to burn off the residual oil before applying a bunch of load

aka. boost.

[todd92]

Hence API SN+ then SP and ILSAC GF-6A specs for oil, which greatly reduce the likelihood of LSPI.

[garycrist]

The reason I post about LSPI, was during a conversation with a member,

he thought that the ECM was controlling the timing hence no LSPI. 

Yes I am quite aware of micro-welding of metal and oil particles contributing

to the phenomena too.

 

Thank You very much @todd92!