Diesel Fuel, then and now

Engineering Potpourri Pat's Pub
#1

Feel free to challenge and/or correct me.
I look forward to both comments and opinions and hard data.
Does anyone know if there are specs on the composition of diesel fuel?
As background, I’m working on my bucket list.
To wit, to drive a truck across the country,
I have a job delivering new RVs to dealers.
I have driven in 3 provinces, 4 time zones and 8 states.
I burn a lot of fuel. As much as $8,000 in a month.
I have noticed a marked change in the characteristics of diesel fuel over he last 18 months.
I have always known diesel fuel to be without noticeable vapour pressure.
My filler cap has a two way pressure relief valve that will hold a small amount of positive or negative pressure.
Typically, when I filled my tank and then drove several hundred miles, There would be a negative pressure in my fuel tank.
If I removed the filler cap, I could feel the partial vacuum and hear the air rushing in the fill the space left by the used fuel.
Not any more.
The present blend of diesel fuel has a noticeable positive vapour pressure.
When removing the filler cap, there is now a noticeable pressure and release of vapour.
I have to wonder; If it is taking that much light fraction to balance the heavy fractions, just how heavy are the heavy fractions?
Are the oil companies adding fractions too heavy to properly combust in a high speed diesel engine?
I am seeing other indications that may indicate the addition of heavier fractions to the fuel.

This leads to another related concern:
C versus CO2.
C, soot, elemental carbon,or black carbon, is the result of incomplete combustion of the fuel.
The soot is captured in the Diesel Particulate Filter.
The soot is then burned off periodically to clean the DPF.
The cleaning or regeneration is done by adding fuel to the exhaust stream.
This may not be very efficient;
The soot would not burn in the combustion chamber.
There is not much oxygen in the exhaust to support the combustion of the fuel, and minus that, even less to support the combustion of the soot.
This begs the question; How many hundreds of pounds of CO2 are justified to convert a pound of soot to more CO2?

A comparison;
Carbon pollution. Very bad in cities, but increases soil fertiliy in rural areas.
Persistence; Soot particles typically last until the next precipitation, rain or snow.
CO2, " Carbon dioxide is a different animal, however. Once it’s added to the atmosphere, it hangs around, for a long time: between 300 to 1,000 years." ‘https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/’
Also, the calculations that look good in the office, change on a cold day in Minnesota, North Dakota, Saskatchewan and Alberta.
On a recent trip, my truck was in regeneration about 3/4 of the time when I hit colder weather.
Could the environment be better served by mandating a better grade of fuel?

#2

A note on quantities;
$8000 at $5.00 / gallon = 1600 Gallons.
1600 gallons at 7 lbs / gallon = 11200 lbs.
11200 lbs of fuel at (1 lb fuel = 2.5 lb CO2) = 28000 lbs CO2
28000 lbs = 14 tons. (At four trips per month)

#3

Commercial fuel specs control properties rather than absolute composition. There’s a good summary of the European requirements at EN 590 Diesel Fuel Specifications (ULSD) | Crown Oil.

Why so much freedom to tinker with the composition? The refiner has a limited choice of compositions of feedstocks; they have to provide a range of products from that feedstock in proportions that they have little control over; there’s some, but limited, ability to transform the components of the feedstock to crack or reform them to make more of a more popular product and, crucially, the refiners can’t afford to have anything left over that they can’t sell.

The solution, and the skill, is to pick a range of available/affordable feedstocks that gives a reasonable match to the range of products they have to sell in the sort of proportions that customers want, then adjust the composition of the products so there’s just enough of all of them, they all meet the corresponding spec and all the undesirable fractions are blended into a revenue-earning product without making it non-conforming. The blends change all the time in response to price and availability of the different feedstocks and the forecast demand for the products.

Getting oil products with tighter controls on composition than the standard specifications (especially if you have a peculiar aversion to any of the common additives) is an expensive and enduring nightmare.

1 Like
#4

You probably know this, but need a reminder. Summer and Winter fuel is different.
So you should have seen a change in the fuel, and on mileage.
I have a gas power car, and I have been seeing the mileage dropping from Summer to Winter.

#5

I am familiar with winter diesel. Previous years have not been like this.
Looking at the European requirements at EN 590 Diesel Fuel Specifications, the present blend may have difficulty meeting this spec: % Vol Rec @ 345°C - 85·0 min.

Anecdotally: I typically ran empty at 70 MPH and 20 miles per Imperial gallon.
Now, at 60 mph, my mileage drops to about 19 MPG Imp.
That may be winter fuel, BUT;
If I go above 65 MPH, my mileage drops to about 17 MPG Imp or less.
Why the abrupt drop? Down from 19 MPG Imp to 17 MPG Imp with a small increase in speed.
A typical substance needs a given time at a given temperature to completely combust.
Is it possible that the heavy fractions don’t have time for complete combustion at higher engine speeds?
By the way this ain’t my first (rodeo) winter.
I wasn’t seeing this effect last winter on the same run.
Add to that a further increase in consumption when the DPF goes into regeneration. Loaded, regen. will drop mileage from about 9-10 MPG Imp to 7-8 MPG Imp.
The regen. loaded, has been almost continuous, consistent with incomplete combustion of heavy fractions.
On a related note:
The EPA has been frustrated attempting to control CO2 emissions. Courts have ruled that the EPA does nothave the authority to classify CO2 as an air pollutant.
Recently Congress has passed legislation classifying CO2 as an air pollutant.
Maybe things will change.
A comment on the cost of improving the quality of fuel.
If one refiner is hit with extra cost, they may be in trouble.
If all refiners across the board are faced with a more expensive process, the playing field is level and the extra costs are passed on to the end user.

#6

Hmm…you think the fuel has more heavy fractions (incomplete combustion), but at the same time you see higher vapor pressure - that sounds like there is a higher aromatic content. Have you had any issues with fuel filter plugging? That would indicate olefin content being high as well. Both would suggest the diesel you are burning is coming from the tar sands or similar heavy crude oil?

#7

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Just sharing information from my mileage workbook . . . my 2000 Dodge Diesel Ram 2500 mpg data (1999 to current).

mpg cycles every year depending upon energy value (winter vs summer diesel). In earlier years, I did use Cetane booster, but not any more. for the most part, purchase from same supplier. Some suppliers add additives, others do not.

I did have diesel fuel spec once, but I cannot locate it and I think it was for military purposes.

This link has useful information:ASTM Diesel Fuel Standard Specification - ANSI Blog

#8

Diesel fuel is a blend of different weight fractions.
If he refinery is adding heavier than normal fractions, they must also balance it with lighter than normal fractions.
Hence the high vapour pressure.

My truck has a DP cell across the filter. I get lots of warning to change the filter before it plugs off.
That said, it’s getting colder and I may get a surprise.
That is why I carry a spare filter cartridge.
By the way, thanks for the information and explanations, zeusfaber.
All comments are welcome, friends.

#9

I started today with filled tanks,
Driving was challenging, cold, blowing snow, a few hundred miles of packed snow and ice.
In the worst 80 miles there must have been a dozen cars off the road. I lost count.
The good news:
I got a lot better grade of fuel this time.
At times I was getting close to 25 MPG US. (A strong tail wind was helping a lot.)
The overall average was less but still good.
The last trip the best 30 mile average running empty was about 17 MPG US. The worst, pulling a high trailer into a head wind and the DPF in regen, less than 7 MPG US
Nice mileage on the Ram, pmover.
With full tanks and me behind the wheel, my dually weighs 11,770 lbs. I can’t compete with you for mileage.

#10

Gotta say, I’m impressed with 17 to 25 mpg from a large pickup/SUV. Dad’s old Ford pickups at best would get 12-15 (diesel) and 10-13 gas, and my 6-cyl. pickup would get 17 at best. I think the dump trucks ran 4 mpg when loaded, and maybe 8 at best, empty.

Of course, the wife’s new Rav4 is getting 30 mpg consistently, and my MX-5 gets 32 average, even when I am having fun with it. I know these two rigs have Atkinson cycle capability with their variable valve timing. Technology marches on!

#11

@WaRoss, your mileage comment reminded me that in 2015(?), I replaced the exhaust system, OEM leaked everywhere, with a 4" straight pipe system (manifold to tail pipe). The exhaust gases expanding across the turbo can easily be heard during spooling up/down/idle. the only loads I have are either a 4-wheeler or snow machine. short trips w/ logs; minimal loads. just keep it on the road. Seen plenty of 5" inch exhaust systems around here too, but I honestly believe the difference in pipe size is negligible, unless you have other performance enhancements on the engine.
I also re-installed the “hockey puck” performance chip in 2015. I bought in 2011 and it has 1 fixed setting, no adjustments for my make/model engine. injector pump failed 6-months after install, so I removed it. injector pump failure was due to electronics, not lift pump or otherwise.
So, yes, mileage and power is improved and I’m pleased. No more “deceleration” while heading up inclines like before the changes. now, it is possible for the vehicle to accelerate while heading up inclines.
while living in Fairbanks, I drove to Valdez and back on a tank of diesel, 700+ miles. best ever mileage and this was in 2005 I think. There was a tailwind in both directions.
gotta say, I honestly think the energy content & quality of the diesel being used in your truck is questionable. there are cetane boosters and other additives that I seldom use these days (not in Fairbanks any more). the diesel fuel dispensed should meet all Diesel engine requirements, otherwise there be problems.
Oh, interesting in that replacement of fuel filter is frequent? fyi, in 260,000+ miles, I really do not know how often I replaced mine; maybe on 5-6 occasions. not that many. I do carry a spare, but I never had a water in fuel light illumination at all. I replaced it when I thought about it.

#12

Fuel filters:
On Canadian fuel I ran for a couple of years and almost 100,000 miles without changing a fuel filter.
Since I started burning US fuel, I have to change the fuel filter every 7000 miles, about 4 trips.
The last trip, I got good fuel in Minot, North Dakota. I topped up in Beloit Illinois. I picked up a trailer near Middlebury Indiana and headed back. The engine was doing good and I pushed through to Roberts Wisconsin.
I should have topped up in Beloit.
The fuel in Roberts was horse p-$$$.
Fuel consumption was up 1/3 or more and poor power.
I topped up in Minot a few hours ago.
On the other hand, it’s minus 22F and forecast cold tomorrow and I expect that to affect mileage.
Are you still following this, zeusfaber?
Is this the spec that limits heavy fractions?

#13

It’s all that smog crap that they add to the fuel.

#14

Still following, and yes, that’s the bit you’re looking for.

#15

when you stop to refuel or to stretch, ask the owner or truck driver you see offloading where the get their diesel fuel from. see a truck hauling diesel, ask the truck driver the diesel source. I would think you can then minimize the problem areas.

I recently did that in Sterling and was surprised that the diesel was hauled up to AK and not from the local refinery.

#16

A recent experience reminded me of this posting; hence, a follow-up . . .

Some background information . . . Two winters ago, my in-tank lift pump failed and ended up replacing it.

The fuel filter had dark substance color in it and there was fine debris in bottom of the filter bowl. The filter was replaced. While the fuel tank was laying on the floor, i noticed the diesel fuel inside the tank was really clear and i did not observe anything abnormal inside the tank.

Since this lift pump was replaced and only during cold winter months, when starting the engine, the crank cycle was extended longer than usual. There were occasions of cranking the engine twice to get it started. This extended crank is highly unusual and it has never happend before as engine always started within a second. So, i suspected the debris in fuel filter may have damaged the injection pump. The current injection pump has 153,000 miles and 4500-hrs runtime. I am being told these pumps fail after about 150,000 miles.

In the past month, i spoke at length with an injection specialist and had the fuel system undergo a thorough diagnosis. The fuel filter was dark again and had fine debris in it, so it was replaced again. Additionally, a fungus killer/biocide was added to get rid of any fungus that may be inside the fuel tank. Since ambient temps are now consistently 10-degrees above freezing, no more extended crank. All fuel pressures and flows are very good.

I am being told of the horrible diesel fuel being sold around here and that it has been that way for awhile. I was simply not aware of this situation and apparently, since ULSD has been in production, there are issues with failing injectors and injection pumps. Both fellas highly recommend using a diesel fuel lubricant at each tank refill.

Needless to say, i was surprised to hear of the diesel fuel findings and the lack of finding a cause for the extended crank. After much discussion, we think it could be the injection pump fuel relay freezing up or malfunctioning a bit when exposed to cold temps. I will need to wait unti freezing temps to get another fuel system tests done. We discussed pulling the relay and placing in the freezer overnight, but the time between removing from freezer and engine crank may warm up the relay too much.

I guess diesel engine owners need to add a fuel lubricant at each tank refill.