Today's oil filters

[3930dave]

MHarryE, help me out here....

"Carburetors were a huge fuel waster because they had to be tuned so the leanest cylinder was rich enough so on a V-8 most of the cylinders were running super rich which resulted in poor burn and oil contamination."

MPFI engines have only a single, master mass airflow sensor in the engine air intake plenum. They are quite expensive. So how could a MPFI engine have it's A/F ratio tuned per each cylinder? Doesn't it tune the "average" A/F ratio for all cylinders via the O2 sensor in the exhaust pipe?

Curious, thanks.

I'll be interested in Harry's answer, but I'll take a crack at it.... lacking individual control points (todays' injectors), the carb had to be tuned for the worst case - the leanest intake runner.

While it would be nirvana to individually control and meter the air into each cylinder, with the cost of sensors, that ain't gonna happen in mass production MPFI engines. So..... my guess is that when you develop an MPFI intake system/engine head , you build up a mathematical model of how the air flows into each cylinder, relative to RPM - that data would be gathered with extensive airflow lab instrumentation during development.

So, at that stage of development, you know reasonably accurately how much air will be going into each individual cylinder, based on how much total volume the AMM in the plenum reads. Not quite as accurate as one AMM per intake runner, but nobody is going to pay for that, outside of F1 or a Veyron.

So, lets say at 2800 rpm in a 4 banger, you have the air flow split as 22%/26%/25%/27% across 4 cylinders. The development engineer then programs the relevant multi port injector for the correct injector duty-cycle (On Time) for optimum A/F ratio, at that specific engine RPM.

I've never written that particular type of control code, but that's my guess on how it's done.

The main point to MPFI (or DI, for that matter) is that you totally control the exact amount of fuel going into each cylinder. Carbs or TBI in comparison is more of a spray and pray approach - the exact A/F ratio is going to vary (more so) depending on things like how the fuel wets the intake runners walls, on its way to a specific cylinder.

Rgds, D.

 

[3930dave]

The diesel in oil is coming from regens on newer diesels (2008+). During the regen cycle diesel is injected in the exhaust stroke to increase exhaust temperatures. This allows the cleaning of the diesel particulate filter by burning out collected soot. Unfortunately this also allows unburned fuel to wash down the cylinder wall. This process is specific to Diesel engines and is not caused by direct injection itself but rather by emissions controls. Also, this is the main reason you can no longer extend oil change intervals on newer diesels.

I've seen some reports of fuel-in-oil dilution in DI gas motors tracking (elevating) with mileage. Haven't done what I consider research on this yet (as stated, I don't own DI gas stuff), but I'm wondering if as the injector starts to clog up with mileage, then at the higher DI rail pressure you end up with streams of gas as opposed to fine atomization - hence some cylinder wall wash-down with gasoline.

The power output of DI (relative to displacement) is typically pretty impressive. I'm wondering if esp. in turbo and super-charged applications, they have the DI fuel mapping set just slightly rich. AFAIK, running super lean with a turbo is not a great idea.

I have more to learn about DI gas motor characteristics.... I'll get there, before I own one.

Rgds, D.

 

[3930dave]

Borescope video of the head on an Ecoboost DI motor:

bgfueltest.com

PCV/EGR vapour passes over the intake valves, w/o the benefit of incoming fresh fuel vapour for cleaning, ergo deposits form.

One example of why performance demands on motor oil is higher today.

Rgds, D.

 

[Midniteoyl]

DI should be able to do away with at least the EGR system.. I know many non DI engines nowadays do not have it.. I know the Pentastar 6 doesnt, for example. If there is a EGR system on that DI engine, its a bad design.

 

[buickanddeere]

Yes.. But more accurately for changing conditions. A carb properly tuned still makes more peak HP and can get the same MPG.

No the carb can not

 

[buickanddeere]

The GM DI engines vary cam timing to provide EGR.

 

[Peacock]

DI should be able to do away with at least the EGR system.. I know many non DI engines nowadays do not have it.. I know the Pentastar 6 doesnt, for example. If there is a EGR system on that DI engine, its a bad design.

From what I know, NOX emissions tend to be higher with DI engines which is what EGR is used to reduce.

GM hasn't been using EGR much for awhile now. The new Honda DI engines do not have EGR either.

 

[DeereMann]

Good point, and thanks Dave.

It didn't occur to me the ECM folks during engine development would benchmark flow some engine intake manifolds & adjust the A/F ratio code to each cylinder!

Great concept.

Thanks,

 

[Midniteoyl]

No the carb can not

Okie dokie..

 

[jimoq]

I'm an ole geezer. When automotive applications went from oil bath to paper filters, ring jobs went away. Used to be, back in the 50's, 30,000 miles meant a ring job or lots of smoke. Now what? Filters, lubricants, metalurgy and engine controls. All of the above. Same for ag applications.