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Old 12-05-2013, 12:53 PM   #51 (permalink)
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With cold weather starting, its time to dig this back up.
A major difference that is confusing things is the comparison of very different engine technologies.

A) manual pump ; GM6.5, boats, Cummings
B) computer controlled pumps ; VWs pre 2009, newer trucks
C) CR engines ; VW, BMW, recent trucks

The old manual IPs were fuel + air = go type of engines.cold site was their friend.

The new CRs are more like injected gassers, temp causes the computer to alter all sorts of settings, quantity, start of injection timing, end of injection timing, EGR%, kennuder valve position......

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Old 12-05-2013, 02:17 PM   #52 (permalink)
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All else being equal . . .

. . . hot air is better for combustion for many reasons. The most obvious is the combustion temperature is elevated.

But, as you mentioned, for modern vehicles it is not so simple as the electronic control units are capable of making significant changes.
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Old 12-05-2013, 02:23 PM   #53 (permalink)
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Quote:
Originally Posted by RustyLugNut View Post
. . . hot air is better for combustion for many reasons. The most obvious is the combustion temperature is elevated.

But, as you mentioned, for modern vehicles it is not so simple as the electronic control units are capable of making significant changes.
I have seen plenty of test that show diesels get better fuel economy with cold air intakes until the ambient air starts to get around freezing.

In my diesel the air is heated to 1100'F adding more heat will waste power compressing the air and forcing the heat through the piston and combustion chamber.
Also adding more heat to the combustion process will increase NOx.
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Old 12-05-2013, 02:54 PM   #54 (permalink)
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"all else being equal"

Quote:
Originally Posted by oil pan 4 View Post
I have seen plenty of test that show diesels get better fuel economy with cold air intakes until the ambient air starts to get around freezing.

In my diesel the air is heated to 1100'F adding more heat will waste power compressing the air and forcing the heat through the piston and combustion chamber.
Also adding more heat to the combustion process will increase NOx.
. . . is a term I jot down next to my notes during data gathering. It means exactly that. One variable change on one side of the equation results in a change X on the other side of the equation.

I have seen dyno test after dyno test that shows how cold air in the diesel engine's exhaust produces better fuel economy. But, what are the changes in the SYSTEM due to the introduction of cold air? How does the system react? Also, what is the loading you are testing at? Pin all your variables except for air temperature and test at low cruising loads to test your BSFC (brake specific fuel consumption ). If you run a pressure sensor into your combustion chamber, you can see that the time delay between injection point and heat release is reduced with added heat and it can reach the point that injection timing advance will need to be reduced to take advantage. It is a small but measurable advantage. And yes, NOx is increased as a side reaction, but that is an aside, not the main point at hand.
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Old 12-05-2013, 03:56 PM   #55 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
I have seen plenty of test that show diesels get better fuel economy with cold air intakes until the ambient air starts to get around freezing.

In my diesel the air is heated to 1100'F adding more heat will waste power compressing the air and forcing the heat through the piston and combustion chamber.
Also adding more heat to the combustion process will increase NOx.
Yes, but your/my 6.5L doesn't have an IAT sensor like my wifes CR does.
Things get all wibbly wobbly when the ECU decides to help the engine warm up by messing with the injection timing/duration.

Simply adding a resistor to the IAT doesn't work as the computer sees the change at the O2 sensor (yes there is one) and tries to compensate.

I disconnected the snorkel on the CR...... and the next day the temp outside went from 40 to 65.
We have a 2+ hour trip this weekend. Friday evening will be 60s, Sunday will be 45.
I will let yall know what happens..........
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Old 12-05-2013, 04:18 PM   #56 (permalink)
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I just got off the phone . . .

. . . with an acquaintance who is an engineer with Caterpillar Corp. She pretty much supported what Oil Pan put out in his answer in the above.

Until the air temperature approaches freezing ( 0 deg C ), a diesel engine runs with greater efficiency as the intake temperature drops. However, this is in power generation applications and the specific torque production levels were high.

If the torque needs are low (low mass/drag vehicles ) maybe we can benefit from hot intake air. All the papers I see are in fairly high specific output regimes not the light load regions.

My gut feeling is that, without dynamically controlling the hot air and the associated fueling/timing, there will be no benefits and may even generate a loss of fuel economy.
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Old 12-05-2013, 06:03 PM   #57 (permalink)
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Quote:
Originally Posted by RustyLugNut View Post
. . . with an acquaintance who is an engineer with Caterpillar Corp. She pretty much supported what Oil Pan put out in his answer in the above.

Until the air temperature approaches freezing ( 0 deg C ), a diesel engine runs with greater efficiency as the intake temperature drops. However, this is in power generation applications and the specific torque production levels were high.

If the torque needs are low (low mass/drag vehicles ) maybe we can benefit from hot intake air. All the papers I see are in fairly high specific output regimes not the light load regions.

My gut feeling is that, without dynamically controlling the hot air and the associated fueling/timing, there will be no benefits and may even generate a loss of fuel economy.
Your friend is undoubtedly right.....with regards to manual pump diesels.
The newer ones seem to operate more like an injected gasser.
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Old 12-06-2013, 04:23 AM   #58 (permalink)
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Diesel combustion is the same today as yesterday.

Quote:
Originally Posted by JasonG View Post
Your friend is undoubtedly right.....with regards to manual pump diesels.
The newer ones seem to operate more like an injected gasser.
Even the current Electronically Controlled Piezo Injector engines still must follow the combustion dynamics of compression ignition. The plethora of sensors doesn't change that.

And Caterpillar's power generators are considerably more advanced than you seem to think. They have to meet the Clean Air Standards of the California Air Resource Board. Electronic controls abound.
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Old 12-06-2013, 08:05 AM   #59 (permalink)
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Quote:
Originally Posted by RustyLugNut View Post
Even the current Electronically Controlled Piezo Injector engines still must follow the combustion dynamics of compression ignition. The plethora of sensors doesn't change that.
Where did I ever suggest that the laws of physics changed in my engine?

Please contact your engineer friend and ask if they can clarify for us how the injection computer responds to the IAT input sensor.
That knowledge will provide the conclusive answer that we are all just guessing about.(myself included)
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Old 12-06-2013, 10:36 AM   #60 (permalink)
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Possible answer

This articleAutoSpeed - Common Rail Diesel Engine Management, Part 2 gives some information:

Driving


In normal driving, the injected fuel quantity is determined primarily by the accelerator pedal sensor position, engine speed, fuel and intake air temperatures. However, many other maps of data also have an effect on the fuel injection quantity actually used. These include strategies that limit emissions, smoke production, mechanical overloading and thermal overloading (including measured or modelled temperatures of the exhaust gas, coolant, oil, turbocharger and injectors). Start of injection control is mapped as a function of engine speed, injected fuel quantity, coolant temperature and ambient pressure.

Now we just need confirmation from Mr.Malone

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