Modern Diesel Fueling Strategies

[mpgmike]

First, I'm glad you found a nice car that makes you happy. Second, I'm glad you're interested in how it works, and how to make it better.

If I may opine on EGR; ambient air is made up of about 20% oxygen and 79% nitrogen. Exhaust gas is made up of oxygen, nitrogen, water vapor, and carbon dioxide (mostly). To burn a fuel it takes the hydrocarbon (HC) fuel and oxygen. The chemical oxidation process reduces the HC/O2 to H2O and CO2 + heat. Now if you were to pipe bottled oxygen into an engine with a stoichiometric amount of fuel, it would burn, but the engine would have no power, and it would start melting parts almost immediately. Why??

The nitrogen in the air acts as an "Expansion Medium" which absorbs the heat, and in turn expands (creates pressure). Some gasses are "acceptable" expansion mediums, while others are stellar. Water vapor expands at 12X the rate of nitrogen with the same amount of BTU heat input. Carbon dioxide even more so. EGR is actually a superior expansion medium to air.

The trade-off is exhaust gasses contribute very little to the oxidation process. A little EGR and the engine runs a bit better. More and it runs even better. More and it starts getting sluggish, and HC/CO emissions start to spike. The flame propagation process in inhibited by the lack of oxygen.

So how does EGR reduce NOX? The more powerful expansion medium is able to absorb more heat at any given volume. NOX is formed by temperature over time. Reduce either and NOX goes down. Since the more powerful expansion medium (exhaust gasses) are absorbing more of the heat of combustion, peak cylinder temperatures are reduced; thus reducing NOX.

George Arlington Moore took EGR to radical extremes back in the 1920's with impressive results -- both fuel economy and emissions. Here is a good primer on Combustion Efficiency.

As for fuel economy mods on diesels, the largest gains I have been able to squeeze from them is with ozone injection. Whereas ambient oxygen is O2, ozone is O3, O4...O60. It is far less stable than ambient oxygen, which reduces the endothermic losses associated with flame propagation, as less energy is required to split off oxygen atoms.

Ozone can be made with high voltage across 2 stainless steel screens separated by a dielectric. This method is common in air purifiers. Another is with a spark gap. A gasoline engine distributor cap, brushed DC motor, anything that sparks generates ozone. A 3rd method is with 185 nm UV light. (Unfortunately, unlike IR spectrum light, there are no LED lights able to reach the 185 nm range. These lights are all mercury vapor.)

The second best gains was with HHO -- copious amounts of HHO! In my initial testing I used about the same amount of HHO I would for a gasoline engine of the same size. The problem is that at say 2000 RPM moderate load on a gas engine, the throttle plate limits the amount of air in the cylinders to maybe 20% VE. The diesel is gulping 100% VE all the time. So the air-to-fuel-HHO ratio that works on a gas engine simply was nowhere near enough HHO for the same sized diesel. When I cranked up the HHO, things started to look brighter.

OOoooohhhh, look at the time! I think I should stop now. I hope this gives food for thought.

[Isaac Zachary]

Originally Posted by mpgmike

Water vapor expands at 12X the rate of nitrogen with the same amount of BTU heat input. Carbon dioxide even more so. EGR is actually a superior expansion medium to air.

That is incorrect. The specific heat ratio is worse with water and CO2. Water does expand a lot when it vaporizes, but it takes a whole lot more heat.

Nitrogen is around 1.4, water 1.3 and CO2 1.28.

Plug those numbers into thermal expanssion equasion and you get less kinetic energy from heat energy (smaller numbers are worse). You can make up the difference if you increase the compression ratio though.

This is one of the reasons water injection tends to hurt fuel consumption in gasoline engines even though it's anti-knock properties should do the opposite unless you increase the compression along with the water injection.

[mpgmike]

About 20 years ago I played with several different water injection strategies. I found the best was a bubbler that bubbled the PCV gasses up through a stainless steel pot scrubber (actually several). This first removed the oils from the PCV gasses, and added water vapor to the intake charge.

I found an old '70s era Edlebrock electronic water injection system. That was almost as good as the bubbler trick. However, all attempts to spray water mist into the engine seriously hurt fuel economy.

My previous research strongly suggested that water created more pressure than nitrogen at the same BTU input by a factor of 12, and that CO2 created even more pressure. You are stating that I may need to go back and re-research that. I love a challenge! Thank you. I will see where I went wrong.

[Isaac Zachary]

I'm about 90% sure I'm right here. But if you find I'm wrong please let me know.

From what I understand the thermodynamic efficiency (efficiency of heat energy converted to mechanical energy) is:

TE = 1 - 1/CR^k-1

TE = thermodynamic efficiency
CR = compression ratio
k = specific heat ratio

If you do the equation with a CR of 10 to one then:

Nitrogen (k = 1.4) = TE of 60%
Water vapor (k = 1.3) = TE of 50%
CO2 (k = 1.28) = TE of 48%

To get a TE of 60% with water vapor you'd need a CR of 22:1.

And with CO2 you'd need a CR of 27:1.

This is why hellium or argon would be good choices for a closed loop engine like a steriling engine:

Hellium (k = 1.667) at 10:1 CR = TE of 78%!
Argon (k = 1.667) at 10:1 CR = TE of 78%!

[cRiPpLe_rOoStEr]

It's not the same as a performance-oriented water injection setup, but usually when there is a higher amount of moisture in the air I noticed a slightly better performance and also a discrete improvement to the fuel economy on port-injection gassers and direct-injection turbodiesels. Water seems to retain more heat from the compression and releasing it in a more homogeneous way through the combustion chamber, also decreasing the formation of NOx because the heat absorbed by the water won't react with O² and N² so easily.

[mpgmike]

I spent the day digging up lab reports on the subject of "The coefficient of expansion for gasses", "Thermal density for gasses", and several other search phrases. Whereas I would like to say I got an education, It's more like I'm rather confused now.

There is Boyle's and Charles' Laws, molecular density considerations, thermal conductivity, specific heat index at a given temperature, and some constants tossed in for good measure. Some perspectives seem to support some of your conclusions, but then others don't. However, none of them fully support my postulation either. I never did find your "k" factor you listed for the various gasses.

From what I can gather, there are 2 factors at play:
1) Thermal density of the molecule; how much BTU heat does it require to raise 1 mol of the gas 1 degree
2) Expansion factor for 1 degree rise in temperature. This overwhelmingly seems to be constant for all gasses.

The one consistency is that the larger the mass of the molecule, the more heat energy is required to raise the temperature of 1 mol by 1 degree. So, here is what I'm putting forth: First, let's establish the atomic mass for each of the players (rounded to the nearest whole number).

H = 1
C = 12
N = 14
O = 16

From this we can calculate the atomic mass for the molecules being discussed:

H2O = 18
N2 = 28
Air ~ 29 (79% N, 20% O, 1% He)
O2 = 32
CO2 = 38

Using the universal constant expansion rate for BTU input, we can therefore expect H2O to rise in measured temperature with the least thermal energy input. It then should be the most powerful expansion medium of the list. On the other end of the spectrum, CO2 will absorb the most thermal energy without raising in temperature. Thus, CO2 has the lowest coefficient of expansion per unit of energy input.

Avagadro's Law states that there will be the same number of molecules in any given volume at a given temperature and pressure, so that also supports the constant coefficient of expansion rate per temperature rise theory.

So the Report from my day's research can be summed up as:
1) Water vapor injection will enhance the Expansion Medium, delivering more power to the piston crown per unit of thermal energy released from the fuel.
2) Carbon Dioxide has the highest ability to reduce peak combustion temperatures, and thus reduce the formation of NOx

Am I getting closer?? Just so you guys know, once this discussion is concluded, I intend to go back to the Ecoceptor site and update the Combustion Efficiency page to reflect the results.

[Isaac Zachary]

What is a universal expansion rate?

When most fluids are heated, part of that is absorbed and heats up the fluid and part of the energy causes the fluid to expand. How much it assorbs of course depends on the over all mass, but the difference between how much is and how much is turned into expansion depends on the heat ratio. A low heat ratio causes the fluid to expand very little but heat up a lot of atoms for every BTU.

[mpgmike]

It is Avogadro's Law which states:

Avogadro’s law, a statement that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules.

Therefore at any given temperature and pressure, whether the cylinder is filled with nitrogen, water vapor, carbon dioxide, or other, there will be a calculated number of molecules. Furthermore, 1 degree rise in temperature provides for the exact expansion rate regardless of the gas. It then boils down to how much thermal energy is required to raise the temperature of any given gas by 1 degree. This is Thermal Density.

[cRiPpLe_rOoStEr]

Originally Posted by mpgmike

Whereas I would like to say I got an education, It's more like I'm rather confused now.

I can relate to that. Sometimes it is really confusing, even though in theory the basic operating principles are roughly the same, whether a gasser engine has a carburettor, continuous-flow fuel injection, sequential port injection or direct injection, and Diesel engines with so many different injection setups ranging from IDIs to the latest common-rail generations...

[freebeard]

Whereas I would like to say I got an education, It's more like I'm rather confused now.

For me it's more bewilderment.

Melted rock forts of Scotland --- 28,297 views 12 May 2022

It turns out the vitrified 'forts' in Scotland were [allegedly] hilltop smelters using uphill burning trenches full of Gorse.

https://gorseactiongroup.org › gorse
Gorse - Gorse Action Group
Gorse (Ulex europeaus) is an Oregon State Class B Noxious weed found in abundance along the west coast.Gorse was intentionally introduced into the southern Oregon coast in the late 1800s and is now rated as one of the top 100 worst invasive species worldwide (World Conservation Union), and the #1 most invasive species on the south coast of Oregon (Oregon State Parks).

It's an invasive species in Oregon and the State is full of Basalt and Obsidian. There's an opportunity there, I'm just not sure what.