Reposting a thread that got buried in the Unicorn "stuff" - D-EGR engine

[RustyLugNut]

Originally Posted by iveyjh

I saw this on the local News this evening.

Car of the future: less pain at the pump - WOAI News 4 San Antonio - Top Stories

More information surfaced on GCC. It is a very interesting solution indeed.

Green Car Congress: SwRI develops D-EGR demonstrator highlighting fuel-efficient, cost-effective engine; 10% and above fuel economy improvements

[P-hack]

meh, very band-aidy. Reminds me of emissions era carbs, where the obvious answer is already available, plus a hydrogen gimmick.

Lots of talk about reducing costs and efficiency and complexity, not seeing it.

[t vago]

I wonder if they tried running this engine without the hydrogen gimmick.

[Daox]

I can't view the videos at work but, the reason for adding hydrogen to the air/fuel mix is that it speeds up the flame propagation. Adding high amounts of EGR to the air/fuel mixture slows down the flame speed. The same thing happens in a lean burn engine. The hydrogen speeds it back up and prevents misfiring as one of the linked articles state.

Green Car Congress: PSA to commercialize SwRI-developed Dedicated-EGR technology in high-efficiency gasoline engines by 2018

Despite the benefits of EGR—e.g., improved cycle efficiencies through knock reduction, charge properties and pumping work; cooler combustion leading to lower emissions—there are challenges. These include misfire and stability; control; boosting; and design and materials.

Dilution reduces laminar burning velocities, decreasing volumetric heat release and slowing reaction rates. In an engine, slower burn rates can lead to unstable operation and full misfire.

High EGR rates (and low pre-turbine temperatures) can lead to low turbine efficiency.

Transient control of EGR is vital.

The design of the EGR system design will be key to control and packaging.

...

The D-EGR concept also combines the high efficiency potential of in-cylinder gasoline reformation. Under D-EGR, excess fuel is sent to the cylinder dedicated to producing the recirculated gases, the hydrogen (H2) content of which then increases. The reformate along with the EGR is distributed to the other cylinders. The resulting H2 levels increases EGR tolerance; increases knock resistance (i.e., higher compression ratios); reduces emissions; and improves fuel consumption.

Just because it is hydrogen doesn't mean its unicorn poo. There is a partial truth that hydrogen is beneficial, you just have to apply it correctly. You also have to produce it efficiently if you're doing so onboard.

[niky]

Wonder how it compares to SkyActiv? SkyActiv already uses cooled EGR, proper exhaust scavenging and direct injection to achieve ultra-high compression and low consumption... though 11.7 is still pretty high, considering they're using this on a turbocharged engine...

[P-hack]

Daox, my point isn't that it is unicornian, but that there proposal (use a dedicated cylinder for reforming gasses and dedicated egr) is enormously more complicated than direct injection compression ignition and has less gain. You gain flame speed and ignition reliability by increasing pressure as well, as opposed to on-the-fly alchemy. I know what hydrogen does, but there are other ways to do that.

It would be akin to saying feedback carbs should be the primary focus of discussion, here, in 2014.

[Daox]

I'm not disagreeing, just explaining to those who don't know.

The problem with adding hydrogen always seems to be finding a good way to generate it.

[Christ]

Atkinson and Miller cycle engines already made this sort of obsolete... in the 80's.

[wickydude]

They're not adding external hydrogen, they're feeding excess fuel into that one cylinder, which then produces H2 and CO, which gets fed back into the intake.

[P-hack]

Yup, more info on rich combustion to make a bit of hydrogen here:
http://www-diva.eng.cam.ac.uk/theses...n-mphil-thesis

But HCCI (speaking of gobs of egr)/DICI solutions still well ahead in efficiency.