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Old 04-18-2012, 02:32 AM   #1 (permalink)
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Diesel air intake warm or not

I have read that diesel motors run most efficiently on cold air and I have read that they run most efficiently on warm air.
Most who drive a diesel notice mpg losses threw winter. Could the cold ambient outside air be responsible ? or has it nothing to do with cold air and more to do with winter mixed diesel. Is the winter mix diesel in all gas stations and what months would it be used.
Do people realize poor cold weather mileage even on summer diesel ? If so would warm intake air aid? or is it more to do with a cold block than poor combustion.

A turbo compresses the air in that process the air gets heated just by being compressed it also gets heated by friction and the hot exhaust gases on the turbo. The intercooler, cools that hot air.
When driving efficiently I am not using my turbo or intercooler, the air is not being heated up by the compression of the air in the turbo, meaning it is not as hot as it normally is.
"This would be the time that warm air intake could aid the burn"(my opinion)

Here is some food for thought, if running warmer intake air causes higher combustion chamber temperatures could it mean a more complete (hotter) burn occurred?.

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Old 04-18-2012, 03:56 AM   #2 (permalink)
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Within reason, cooler intake temperatures will increase a diesel's efficiency (assuming you don't get so cold that the ignition delay gets very long and approaches misfire). Just look at the efficiecny of an intercooled vs non-intercooled turbodiesel. The cooler air will make the engine run leaner which generally increases the thermodynamic efficiency, as does the colder air temps themselves (via the specific heat ratio).

That being said, cold ambient temps hurt a diesel in pretty much all the same ways it hurts a gasoline car. I personally have observed about a 1% decrease in FE for every 1 deg C decrease in ambient temperature. About half of this can be attributed to the increase in aero drag via the increased air density. The rest is due to the increased rolling resistance of the tires, and the increased warm up times.

I've heard folks blame the winter fuel, but I don't put too much stock in that myself. Summer diesel is #2 diesel fuel, whereas winterized diesel is a blend of #1 & #2 diesel. Pure #1 diesel contains, on average, about 4% less energy per gallon than pure #2 diesel. That's not completely insignificant, but it's pretty small (especially considering that, in most areas the winterized diesel doesn't go all the eay to pure #1).

I've kept track of all my daily mileage all winter long and I've cleary been able to see the ambient temp effects, but wasn't able to make out any clear tank-to-tank variations.
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Old 04-18-2012, 11:57 AM   #3 (permalink)
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Thanks for that information Diesel Dave.
It would be nice to get to the bottom of this, fuel "may" be getting wasted by as much as 10% in the winter months if people are feeding their diesels cold air on a cold winter day.
Would the oxygen sensor in the exhaust control any over fueling
caused by the warmer and lets face it more combustible air
Could less dense (warmer air) actually use less fuel to burn then the cold dense winter air
I would like to find a study on air temperature and diesel economy not air temperature and max diesel hp.
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Old 04-18-2012, 03:22 PM   #4 (permalink)
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I found a website that deals in commercial diesel engines and its performance intake air temperature is reported to be 25*c which would suggest to me that warm air(not hot air) is better for combustion. It has been a challenge to find info on diesel intake temperatures.

Diesel engines for fast vessels with low load factors

Maximum performance rating

e.g. fast yachts, corvettes and frigates

Power ratings classifiable

Intake air temperature 25C

Sea water temperature 25C

Power reduction at 45C/32C

- Series 8000: none
- Series 1163: 3.0%




Diesel engines for fast vessels with high load factors

Maximum continuous rating

e.g. fast ferries, yachts, corvettes and frigates

Power ratings classifiable

Intake air temperature 25C

Sea water temperature 25C

Power reduction at 45C/32C

- Series 1163: 4.6%
- Series 8000: none


Combined propulsion plants with diesel engines and gas turbines: MTU Online
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Old 04-18-2012, 05:27 PM   #5 (permalink)
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Almost every thing that has a temperature dependent rating uses 25C as a base line temperature because its room temperature. A common reference point makes it easier integrate different components and systems.

Edit: It is part of SAE J1995 test standards for engine tests to be done at 25C
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Old 04-18-2012, 05:30 PM   #6 (permalink)
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Quote:
Originally Posted by ecomodded View Post
Most who drive a diesel notice mpg losses threw winter. Could the cold ambient outside air be responsible ? or has it nothing to do with cold air and more to do with winter mixed diesel.
Diesel engines are more prone to the effects of cold winter temperatures because of they are more efficient than gassers. Greater efficiency -> less waste heat -> longer warm up time. Once the engine is up to temp it is still losing lots of heat to the freezing air flowing through the engine bay. Now, diesels like to run hot for efficiency, but keeping it hot in the freezing wind may be impossible.

My turbodiesel likes to stay around 78C without the upper grille block. With the upper grille blocked, at temperatures slightly above freezing, the warm up process will plateu at 78C, then go to 86-90C after a longer acceleration or hill climb, and stay there. At the higher coolant temp the idle consumption is slightly lower (0.48-0.52 liters per hour vs. 0.50-0.54 lph). This last winter I had a cold start at below -18C, no prewarming, and it took me twenty-something kilometers to get to 60-65C. During the ~400km drive home the coolant temperature hardly ever got above 76-77C, a 3km EOC would instantly cool it by at least 10C. I told my passengers to keep their coats zipped and hats on, because trying to heat the cabin would bring the coolant temperature down to 70-74C. In other words, even though I had both my grilles blocked and heating to the bare minimum (just enough to keep the windshield from icing over), the engine never got to its optimal operating temperature. Other than very low temps, driving conditions were ideal: sunny, dry, no wind, low traffic. Milage sucked on that trip.

Maybe the cold air going into my intake lowered my milage? On many occasions I've noticed that, even though it was cold (-10C), by the time the intake air made its way around my engine bay (my filter box is behind the engine, so I have lots of prewarming before the air enters the turbo), its temperature was between 15-25C before the turbo, where the temp sensor is. I have no idea what the temperature was post-turbo and post-intercooler, but I seriously doubt it was lower than 25-35C.

On the other hand, in the summer my pre-turbo temps can get up to 50C, and the idle consumption doesn't get lower, even though the engine is hot (90-98C).
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Old 04-18-2012, 07:29 PM   #7 (permalink)
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On a tangentially related note, In 1963 Rover entered a turbine powered car in the 24 Hours of Le Mans race, and averaged 6 mpg. A year later they averaged 13 mpg with essentially the same engine, only using the exhaust air to preheat the intake air. With hot intake air the engine was down several horsepower, but since it was able to go twice as many laps between refills, its overall performance didn't suffer much.

I have often wondered if preheating/reheating the fuel and intake air might result in FE gains with diesel engines.

Rover's 1964 turbine car entry at Le Mans...

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Last edited by Stan; 04-18-2012 at 07:31 PM.. Reason: add photo of car
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Old 04-18-2012, 07:50 PM   #8 (permalink)
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Thanks for posting up guys, we will get to the bottom of this,peoples first hand experiences are going to point us in the right direction.
optimal intake temperatures do exist..
I think I found some good info about commercial diesel motors and intake air temperatures.
This report on turbo diesel motors cannot stress enough how important it is to have intake air temperatures as close to the coolant temperature as possible. It may well be that in our diesel motors that great variation in coolant and intake air temperatures is hurting efficiency.

have a look at this informative and interesting
( if your a tech junkie) read on intake temperature of a turbo diesel.
http://www.mandieselturbo.de/files/n.../5510-0005.pdf

And Stan WOW that is encouraging and actually sounds like proof of the benefit.
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Last edited by ecomodded; 04-18-2012 at 08:00 PM.. Reason: say wow stan
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Old 04-18-2012, 08:12 PM   #9 (permalink)
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Quote:
Originally Posted by Stan View Post
On a tangentially related note, In 1963 Rover entered a turbine powered car in the 24 Hours of Le Mans race, and averaged 6 mpg. A year later they averaged 13 mpg with essentially the same engine, only using the exhaust air to preheat the intake air. With hot intake air the engine was down several horsepower, but since it was able to go twice as many laps between refills, its overall performance didn't suffer much.
Stan actually when regeneration is used with a turbine it is used after the compressor and not at the intake. The following should clear up how it works for you.
http://web.me.unr.edu/me372/Spring20...generation.pdf

Unfortunately regeneration is hard to do in a piston engine.
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Old 04-18-2012, 08:31 PM   #10 (permalink)
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Quote:
Originally Posted by ecomodded View Post
This report on turbo diesel motors cannot stress enough how important it is to have intake air temperatures as close to the coolant temperature as possible. It may well be that in our diesel motors that great variation in coolant and intake air temperatures is hurting efficiency.

have a look at this informative and interesting
( if your a tech junkie) read on intake temperature of a turbo diesel.
http://www.mandieselturbo.de/files/n.../5510-0005.pdf
from the article
"The density of the air will be high when
the ship is operating in arctic conditions
with a low turbocharger air intake
temperature. As a result, the scavenge
air pressure, the compression pressure
and the maximum firing pressure will be
high.
In order to prevent excessive pressures
under such ambient air temperature
conditions, the turbocharger air inlet
temperature should be kept somewhat
higher than the ambient air temperature
(by preheating, if possible)."


Nothing to do with efficiency just engine longevity.

Also as noted in the article some ships use exhaust gasses for steam production and a drop in EGT caused by cold air intake could reduce steam production below the minimum required level. This really is applicable to a car.

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