Kindly note that detonation and pre-ignition are two COMPLETELY different issues.

Pre-ignition is when the existing, unburned fuel/air charge is ignited by something OTHER than the spark across the spark plug electrodes. Like something else that's very hot in the combustion chamber area. The flame front started by pre-ignition is often the same as with severely advanced ignition timing, both of which can lead to detonation but the flame front travel initiated by pre-ignition is normal, and slow [according to the fuel being burned].

Detonation occurs AFTER the spark has started the flame front and the resulting heat [from the combustion of a portion of the fuel/air charge] and associated increased pressure(s) heats the remaining unburned fuel/air charge beyond it's instantaneous flash point - where the entire remaining charge explodes.

There is no smooth burning with detonation and it is ALWAYS after the initial ignition point.

Detonation can result from pre-ignition - just like with severely advanced ignition timing - but it occurs for entirely different reasons.

Pre-igntion always occurs before TDC while detonation always occurs after TDC.

 

and you are somewhat incorrect as well.

pre ignition happens when something hot in the chamber pre ignites the fuel far before TDC. and that is why its very destructive compared to detonation. pre ignition usually happens at BDC so there is an expanding charge as piston is heading toward TDC. lots of heat is created very quickly with no exhaust valve open to expel it. usually just a sharp edge in the chamber that glows red and is capable of igniting fuel. but it doesnt happen at or near tdc because the glow will not have enough spark energy to ignite compressed air/fuel charge.

where your wrong is saying detonation always happens after ignition. thats not correct. when you have too much compression and not enough fuel the fuel can pre ignite from the pressure and burnt very quickly at an uncontrolled rate. no spark needs to be present. similar to how a diesel operates only the fuel is being ignited when the piston is not in a position to push piston down the bore. and the fuel burns at an abnormally fast uncontrolled rate. this is considered detonation. detonation as I like to describe it is an explosion of fuel not caused by spark event. that always happens at or near TDC.

 

most DI cars on current market run at ~18/1 if I am not mistaken. the higher tech stuff would allow cars to get over 100 miles per gallon. not yet allowed to happen with 100 trillion dollars of oil still left to be sold..

 

DI has its benefits but there are also some drawbacks.

I work for Audi and we have some big problems with carbon buildup. Since there is no fuel spray to clean the back of the valves, the oil from the PVC system makes large carbon deposits on the back of the intake valves and leads to power loss and drivability issues over time. A few rs4 guys have installed catch cans, but that only slows down the buildup. We need a valve overlap like ford does on their DI engines during cruise to force a cleaning action.

It does allow for a leaner mixture and better fuel control which in turn will decrease spool times and more power/torque throughout the power band.

Funny tho, I do not hear about carbon buildup on Porsche motors, I wonder what their strategy is

 

It looks like some cars like the new RWD Scoobie that's coming out have "normal" injectors on the IM runners and also direct injection. I think this meets environmental standards for cold start and low/mid driving and the direct injection mostly take over during high load. The carbon buildup issue on the valve stems and such is also eliminated by having conventional injectors.

I still don't see too much about radically high idle/cruise AFR's; most that I found on direct injected cars are still 14.7 and I think that's also because of environmental concerns (or as you refer to, the oil lobby prohibiting it).

 

There are direct injected Mitsu motors-

http://en.wikipedia.org/wiki/Mitsubishi_Sirius_engine

DOHC 4G64 even. It was phased out for the 4G69 and they went back to MPI. Read about why here-

http://www.mitsubishi-motors.com/cor...003/15E_08.pdf

Aaron

 

Aww one of the links is broken.

DI is fascinating, but I think we are not gonna see it be integrated to main stream automobiles for some time, if ever.

 

They both work for me and I looked them up last night. Which is broke?

per DI-

One thing i have noticed in both the Speed 3 and the 335 is that they make best power at a 13:1 AFR without knock. The Speed which i have more tuning time with is a 2.3 running a K04 (way small for those that dont audi/VW). At 18-19psi it was knock free and actually lost 10 ft lbs going from the 13:1 to a 12:1. I believe they are a 9.5:1 motor on top of it.

The issue with that setup is there are no upgraded pump setups that actually flow more as it is cam driven and depends on the lobe to an extent. It seems that the high powered ones use the stock DI and also combine port injection as well.

I was of the understanding the 335 was 5,000psi rail pressure whereas the Speed3 is 1780 stock?