Advanced Engineering Tech - direct injection

View Full Version : direct injection

10-15-2011, 06:07 PM
how much does direct injection help with boosting an engine ?

10-16-2011, 10:33 AM
With direct injection, the fuel can be injected after the compression stroke, immediately before ignition preventing detonation.

10-16-2011, 10:45 AM
I am by far the last person to ask in regards to if direct injection is the best, but I thought I might pass along some info. The turbo Mazda's are having a real problem when modified for higher boost levels with direct injection. It seems that they are finding the intake air stream has a huge effect on if the fuel makes it to the spark gap. When boosting at higher cfm and pressure levels they claim that things change quite a bit.

Typically our injectors are in the intake track and the fuel charge seems to get atomized better and becomes part of the air charge eliminating that issue.

I might be wrong, certainly time will tell if it is superior on a GM engine. From engine to engine I am sure these things can change.

10-27-2011, 10:47 PM
I wonder why it would be a issue. Lots of diesels out there using high pressure common rails systems and direct injection. Of course they dont depend on a spark for ignition but i would think if the issue was with the fuel/air mixture that it would cause hot spotting and high EGT's on modified trucks?

You may be dead on but i was just wondering more of what might be behind it.

10-28-2011, 11:27 AM
I can add this. With direct injection you can have multiple injection events in each firing sequence. A small amount of fuel can be injected to start the burn and and an additional and even third injections after that. Most diesel applications using common rail now uses very high pressures (25,000 psi or more), I doubt at those pressures the air intake streams makes a huge difference in the fuel dispersion. That does change with gasoline however I would also imagine that the timing of the injection event could also improve the performance when airflow changes.

11-12-2011, 08:29 AM
I've no 4 stroke DI experience, I've been around some 2 stroke DI engines.

Some of my observations......heat. Some of the unburnt Air & Fuel cool things considerably. In the case of 2 stroke DI motor's remove fuel from the crankcase, crankshaft & piston temps go ballistic. Then you mount the injectors on the cylinder head & heat those as well.

Then there is the rpm you want to run the injector when trying to compare Diesel's. Blown 2 & 4 strokes would be a bit more comparable that way.

Blown DI 2 strokes add secondary fuel back into the air intake stream.

11-28-2011, 12:47 AM
I can't wait for gen v with di