Do these "foreign substances" show up in UOA? I hear that GDI engines produce a lot of soot which ends up in the oil for example.
Conclusions on Ecoboost Engine Oil - Gas Turbo Direct Injection
- Thread starter Navi
- Start date
Soot isn’t going to show up on a standard UOA. It’s composed of carbon and so are the oil molecules.
I'm not disagreeing with you. I'm asking you to explain how it happens. No that it happens.
My two cents. IIRC with TGDI there are instances where these engines must run rich which can introduce excess fuel into the crankcase.
Triple_Se7en
$50 Site Donor 2024
This statement ^^^^^^ has nothing to do with the engine's length of life.
It has more-to-do with the manufacturer's responsibility of that engine coming to a halt, when the warranty period ends.
No manufacturer wants the vehicle they make & we buy, to drop dead a year after the warranty expires.
..... and the assumption that your vehicle lasts a long time, well each of us maintain differently and drive differently. Then there's the quality factor, when the vehicle is put together. Then there's the quality factor of body and engine parts.
All this - plus some I haven't mentioned yet, determine the eventual ages such vehicles last. Even things like climate factor-in.
OVERKILL
$100 Site Donor 2021
From what I recall, one of the issues is that when the engine is cold, because the fuel is blasted at high pressure into the cylinder, some of it inevitably lands upon, and condenses on the cooler walls as droplets, which don't combust as part of the combustion process and/or are basically deposited on top of the compression rings during the compression stroke, forced past the piston during the power stroke. This is exasperated by the fact that fuel of course doesn't lubricate, so the presence of this fuel reduces ring seal, and that startup/warmup enrichment introduces more fuel.
With GDI, more fuel ends up on the cylinder wall. This happens more when cylinder temperatures are cold. It also happens more at high load and rpm, when the injector is still firing while the piston is near BDC, since more of the cylinder wall is exposed, and the lower cylinder wall also runs a lot colder.
Here's a more detailed explanation:
"Fuel condensation typically occurs during the engine warmup phase when the engine is cold and thus some fuel vapor in the cylinder could condense on the cold cylinder wall before the combustion could start. Wall wetting can also be caused by impingement of some liquid fuel drops in the sprays onto the cylinder wall, either directly or indirectly due to interaction of the fuel spray with a strong in cylinder charge motion, more often for side mounted fuel injectors as upward moving tumble flow turns spray towards the cylinder wall [1,3], or due to splashed fuel vapor and / or liquid fuel drops when the sprays impinging the piston top.
In order to meet ever tightening emission regulations, most modern TGDI engines employ homogeneous mixture combustion [3, 4, 5]. For engines under this combustion mode, fuel is injected into the cylinder in the intake stroke or early of the compression stroke, the latter of which is due to long injection duration at high loads or last of the multiple injections. In reality, considerable wall wetting resulted from the piston impingement can also be encountered when the piston is at the bottom dead center (BDC), at which the cylinder wall temperature is close to the coolant temperature [13]. Since the oil film on the cylinder wall near BDC is thick [10], the fuel on the wall can be directly absorbed into the oil film."
It's a simple anecdote that counters the typical dribble here on BITOG that GDI and thinner "CAFE" oils lead to vehicles that don't last..that's all I was after.
Think there are a lot of variables in the fuel dilution department, so I don't think this will always be the case. I could see a vehicle that always got short tripped in cold weather continuing to increase the fuel dilution volume in the sump. There would be no chance to burn any of it off if it's always short tripped.
That's the problem I was having with our Ford Edge. It was only short tripped for the most part and the oil would reek of gasoline. That was not a direct injection vehicle though. The coolant barely ever got to operating temperature so I'm sure oil was barely past lukewarm. I'd take it out and drive it sometimes to alleviate it, but that was just a pain and a time suck.
Re: Figure 8. So they did 3,300 cold starts at 253K (-4F) and then a 5 minute journey? 275 hours with 5 min journeys = 3,300 journeys.Fuel evaporates from the oil when the engine is warm. It can then either get past the piston rings, or go through the PCV system. In either case it will get burned up in the combustion chamber.
Here's what dilution looks like over an OCI. Ignoring the extreme cases with only 5 minute trips, most of the dilution happens in the first 5 hours or so, and it's nearly at equilibrium levels after around 25 hours (1,000 miles at 40 mph).
Here's an example of dilution going up rapidly and reaching near-equilibrium dilution in about 10 hours when the engine is operated cold, then dropping rapidly over the next 10 hours with a warm engine.
IMO, something is wrong with their model, and if verified on a real engine I highly doubt the fuel dilution with time curve would look like that. I don't see how the fuel dilution could become asymptotic at 14-15% after 3,300 cold weather at -4F start-ups with 5 min short trips.
Have you ever compared the exhaust tips on a DI vehicle to a MPI vehicle? The ones I have seen, the exhaust tips are loaded with tons of black combustion soot on the DI vehicles, which means they run way richer at some point in their use cycle. My MPI vehicles exhaust tips are way cleaner over the same use mileage.
Fuel should be able to leave the crankcase even if the engine isn't very warm. The oil at the top piston ring might run 50-100 C hotter than the oil or coolant temperatures, and the higher the fuel concentration, the faster the fuel in this region will vaporize and get past the rings.
The other figure from the actual engine test does show the dilution reaching equilibrium with 50 C oil and coolant temperatures. I don't see why this also wouldn't happen eventually in the case of ~0-30 C oil and coolant temperatures.
- Joined
- Sep 26, 2010
- Messages
- 9,807
While the piston may be that warm, the oil itself may not be (especially on short trips). What temperature does the oil have to be for the gasoline to evaporate from it and how does it have to be at that temperature? I seriously doubt it is 30C (86F).
Again, my first 2 (separate with an oil change for each) UOAs were 100% highway miles at 70MPH or faster FOR HOURS and that should be conditions for the least amount of fuel dilution. Yet, I had 2.5/2.4% which causes me to wonder what it will be this winter.
For this:
Which means what? More fuel dilution?
You may be 100% correct, but some of the examples that you have shown do not make logical sense (at least not to me--which could mean I do not know enough about it either way).
I plan to continue to UOA my oil for a while to understand the trend.
Oil does heat up a lot in certain spots in the engine. A 100C+ increase over the sump temperature is not unrealistic. The oil will first heat up in the rod bearings due to friction, then get flung onto the warmer upper cylinder liner, then make contact with the even hotter ring, and get squeezed into a layer only microns thick, and then get further heated by the high friction in this area. Cold, thick oil will experience more friction heating, and will have a higher temperature rise than hot oil.
Gasoline is a mix of compounds that have different volatilities. Some of it will evaporate at room temperature. Leave a cup of gasoline outside in the sun and it will be mostly evaporated within hours.
I'd expect dilution to be higher in winter, but it might not increase as much as you might think, for a couple of reasons. First, 70+mph highway cruising is not generally the best-case for dilution. Dilution goes up a lot with higher engine load and rpm, so lower speed driving with a warm engine would be better.
Also, GDI engines are often tuned to reduce fuel dilution while the engine is cold, by increasing fuel pressure and advancing fuel injector timing. Once the oil temperature and intake air temperature are both high enough, it will switch over to favour efficiency instead of dilution. This is the way my Subaru is tuned. I'm sure it varies by manufacturer.
I was referring to fuel travelling the other direction past the rings, from the crankcase to the combustion chamber. Some of the fuel vapour will escape this way, while some will escape through the PCV system.
- Joined
- Sep 26, 2010
- Messages
- 9,807
The light parts of gasoline will evaporate at room temperature, but the heavier parts that remain in the oil will not and may require quite a bit of heat over a sustained period to evaporate. Here from member @Shannow gives a good explanation - https://bobistheoilguy.com/forums/threads/evaporation-of-gasoline-in-engine-oil.275801/post-4506942.
I remain highly skeptical that dilution does not increase as the OCI lengthens. Why? Because to do so means that you have to be burning off as much if not more of the gasoline in the oil than is being introduced. Given the dilution rates for most OEMs, the math does not work. If GDI engines are tuned to reduce dilution, then why under optimal conditions am I seeing 2.5%?
It would stand to reason that IF the fuel is being burned from hot oil, THEN on a 7-8 hour run at operating temperatures of 200F+ degrees on the oil would produce less dilution. Maybe it would have been more than 2.5% if the run was shorter or the oil temperature less (not sure)?
I disagree that highway operation would cause more dilution. It has been argued ad nauseum on this site that highway miles are the least stressful on an engine. The boost gauge and 10 speed transmission in my Bronco would agree--if the engine were straining or under load, I would not stay in 10th gear and the boost would not be sitting on 0.0 PSI.
Not sure, but until I see evidence to the contrary for my 2.7L, color me skeptical.
It would have to be a mechanism like that - ie, higher dilution % increases flash off under same exact running conditions - in order for the dilution percentage to roll off and become asymptotic.
Not sure I totally believe that model without an actual real engine test to verify the modeling. I'd really like to see a real engine do 3,300 cold start-ups at -4F and then only run for 5 minutes at a time.
I think it really depends on the engine. My BMW stays very clean despite GDI. The soot is not because they run richer though; I believe GDI creates additional particulate matter through how the mix burns. Most tuners complain about how lean factory GDI turbo tunes are these days.
Here's one from a GM study with a PFI engine that isn't that far off from those conditions (SAE 932838). "Interval 2" had short trips for most of the test, three 3km trips per day for 4 months (1,100 km). The test started in sub-zero winter temperatures and ran through the spring. Fuel hits 11% quickly, then drops to 7.5% as the weather warms up. The last four data points for this interval are were taken after each of four 40 km trips.I'd really like to see a real engine do 3,300 cold start-ups at -4F and then only run for 5 minutes at a time.
3 km/day for 4 months = 360 km, not 1,110 km.Here's one from a GM study with a PFI engine that isn't that far off from those conditions (SAE 932838). "Interval 2" had short trips for most of the test, three 3km trips per day for 4 months (1,100 km). The test started in sub-zero winter temperatures and ran through the spring. Fuel hits 11% quickly, then drops to 7.5% as the weather warms up. The last four data points for this interval are were taken after each of four 40 km trips.
What went on with "Interval 2" around the 16,000 km mark?
Similar threads
