Study: gasoline GDI engines = lower CO2, but more soot

[t vago]

Originally Posted by MetroMPG

• between model years 2009 to 2015, the percentage of new vehicles sold with GDI engines jumped from 5% to 46%
• GDI engines emit lower levels of CO2, but they emit more black carbon

Your ordinary gasoline engine sucks in an air-fuel mix with fuel droplets that tend to vaporize due to the temperature rise created as each cylinder adiabatically compresses the air-fuel mix.

I suspect that this does not occur with a GDI engine. Rather, the fuel is injected at or near the top of the compression stroke, and the fuel does not have time to vaporize before it is ignited. This will lead to soot formation, since the fuel droplets themselves do not have sufficient surface area to combust completely.

[rmay635703]

Originally Posted by RustyLugNut

It is more about time of injection. If there is not enough evaporation, large enough droplets will be available at combustion and these provide the basis for the carbon soot. Compression and stroke have little to do with this. Look at modern diesels. They always run lean and they produce soot. And they have strokes and compressions far above what a GDI is talking about. But, the soot formation in a GDI is more similar to the diesel than to a PFI spark ignition engine.

Hmm, so we get back to the gasoline running in heated pressurized rails again, so it actually atomizes faster (but oh the NOx)
(heat is something that does not really help diesel atomization)

Originally Posted by RustyLugNut

A source in Korea has told me that some Hyundai models as well as others have the capability of lean burn depending on the target market. Many countries care little about NOx.

And yes, you are correct, you can limit your water injection to only part throttle. Of course there are in cylinder injection schemes that are worth the effort. You will not be able to leverage that with port water injection.

Interesting, if a larger car company had a decent small displacement lean burn engine in foreign markets it might be interesting enough to look for used to import (just saying)

Also I have been told water injection and water wash decrease carbon emissions (washes it out of the air)

At least it does in diesels.

Also I am aware of directly injecting water at some point late during the compression or even expansion stroke, it allows you to extract more power out of the charge, use a longer stroke, reduce NOx and carbon and obviously should create better fuel economy, especially in slow turning engines.

Would be interesting to see on a normal car though.

My original thought was port water injection under certain conditions to keep the ports clean, an added side affect is that it can improve fuel economy modestly under certain conditions,
and that technique could probably be combined with direct injection, now we are getting all kinds of complex!

Sort of like me wishing NA diesels had 2 tanks
1. for diesel
and a 2nd for E85 to inject for power during acceleration, properly tuned you could have massive power out and fuel economy out of a normal simple naturally aspirated block without needing the many headaches associated with timing belts and turbos combined with winter operation.

Oh to dream.