Discussions about gas direct injection (GDI) and the cooling effect on the induced charge

[TrackRat]

Please use this thread and NOT the "Current Peak Cylinder Pressures" thread for discussion of GDI and it's impact on allowing higher static compression ratio, lower fuel consumption, etc.

Is best not to go off-topic on a thread so that those reading or desiring to contribute do not need to wade through a lot of discussion unrelated to the thread subject.

140airpower-

Why this "...There is no de-throttling or lean burn mode per se used in the VW VR6 model engines..."?
These expedients work for just about everybody else. It seems VW is leaving something (a lot!) on the table.

I do not know why VW and other auto makers have not changed to induction systems without a T/Body on PFI/GDI engines other than cost. For years BMW has used PFI systems without a T/Body but it is a complicated system and thus more expensive. With VW's sales volume many times that of BMW it apparently is not cost effective or a significant advantage at this stage of the game. There are pros and cons to lean burn mode. Each engine maker has to decide what strategy works best for their particular situation.

 

[BrianPetersen]

Lean burn isn't compatible with complying with NOx emission standards with current technology - a 3-way catalyst will not work. While you can apparently reduce NOx by going very very lean, then ignition becomes unreliable and unburned HC goes up. While you can also reduce NOx by using very high EGR, again ignition becomes unreliable and HC, CO, and particulate matter all go up. The transition between very light engine load (when very lean burn and/or very high EGR is theoretically possible) and full torque output (when neither lean burn nor high EGR are consistent with getting decent torque out of the engine) requires passing through a somewhat-lean and low-EGR regime that produces very high engine-out NOx.

BMW Valvetronic (and Fiat MultiAir) can run without a throttle because of variable valve timing and lift, not because of GDI. They are more-or-less limiting the amount of intake charge by playing with valve timing and lift as opposed to shutting a throttle. Done properly, it reduces pumping losses. But make no mistake, the engine is still running stoichiometric air/fuel ratio (although with some EGR) in order for the 3-way catalyst to function.

I know of no current production spark ignition engines that are successfully using lean burn and complying with current NOx emission standards (US EPA Tier 2 or Euro 6).

As for the cooling effect on the intake charge ... Normal port injection involves squirting fuel against a closed intake valve and around the inside of the intake port, which draws heat mostly out of the cooling system (or the valve).

 

[gruntguru]

"Lean burn isn't compatible with complying with NOx emission standards with current technology - a 3-way catalyst will not work. While you can apparently reduce NOx by going very very lean, then ignition becomes unreliable and unburned HC goes up. While you can also reduce NOx by using very high EGR, again ignition becomes unreliable and HC, CO, and particulate matter all go up."
Which is where technology like Mahle TJI comes in.

"The transition between very light engine load (when very lean burn and/or very high EGR is theoretically possible) and full torque output (when neither lean burn nor high EGR are consistent with getting decent torque out of the engine) requires passing through a somewhat-lean and low-EGR regime that produces very high engine-out NOx."
The future for lean burn tech (if there is to be one) is full-time lean burn - which means reduced peak power output - and must be offset by upsizing, 2-stroke operation or forced induction. Of these, forced induction would be most likely (as in current Formula One power-plants (with 50+% TE compounded)).

je suis charlie

 

[Lou Scannon]

If we look at the example from heavy duty spark-ignited on-highway engines (e.g. Cummins-Westport ISL-G), under current regs, lean burn no longer can cut the NOx-HC trade-off mustard; a stoich + cooled EGR + TWC recipe is needed to simultaneously reach decent BMEP levels with very low emissions. Boosted, of course. Thermal loading is by no means a cakewalk with this approach.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[gruntguru]

Hemi, there are emerging lean-burn technologies (Mahle TJI being only one) which extend lean operation to 2.0 and beyond,with minimal HC (which can be cleaned up with a 2 way cat anyway) and very low NOx.

je suis charlie

 

[Lou Scannon]

The ISL-G was commercialized in 2007. I'll be watching with interest these emerging lean burn technologies.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz